Produced by Chris Curnow, Tom Cosmas and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
file was produced from images generously made available
by The Internet Archive)









Transcriber Note

Text emphasis is denoted by _Italics_ and =Bold=. Whole and fractional
parts of numbers are denoted as 3-1/2 and where ranges of numbers
include fractions they are enclosed in parenthesis: (3-1/2).





                                   A

                         TEXT-BOOK OF TANNING.

[Illustration:

  Pl. I.

  _E. & F. N. Spon, London & New York._  "INK-PHOTO." SPRAGUE & CO. LONDON.

LIME PITS AND RINSING TANKS.]




                                   A

                         TEXT-BOOK OF TANNING:

                           A TREATISE ON THE

                   CONVERSION OF SKINS INTO LEATHER,

                    BOTH PRACTICAL AND THEORETICAL.


                                  BY

                       HENRY R. PROCTER, F.C.S.,

                         OF LOWLIGHTS TANNERY;
    EXAMINER IN TANNING TO THE CITY AND GUILDS TECHNICAL INSTITUTE.

               With 8 Plates and numerous Illustrations.

                            [Illustration]

                 E. & F. N. SPON, 125, STRAND, LONDON.
                     NEW YORK: 35, MURRAY STREET.
                                 1885.




PREFACE.


[Illustration]


The aim of the following handbook is two-fold; to give, in a
compendious form, such a summary of our scientific knowledge as may
be useful to the practical tanner; and such a sketch of manufacturing
processes as may enable the chemist to apply his knowledge to their
improvement. Each may, therefore, find some superfluous matter, for
which his indulgence is asked. The book is an expansion of a short
article which appeared in Spons' 'Encyclopædia of the Industrial Arts,'
and to some extent still bears traces of its origin; and, having been
written under stress of limited leisure, and defective eyesight, is
very far from being so perfect as I should desire. For the sake of
completeness it has been necessary to describe many processes which are
outside the range of my own manufacturing experience, and in doing so
I have generally referred to the sources of my information. Chapters
III. and XXIV. are written by Mr. C. G. Warnford Lock, to whose kind
assistance I am much indebted. It may be well to state in conclusion,
that while the work is not intended for a cram-book for technical
students, it is hoped that it may be an assistance to teachers of the
subject.

                                                      HENRY R. PROCTER.

  Tynemouth,
     _August 1885_.




CONTENTS.


[Illustration]


                                                             PAGE

  INTRODUCTORY NOTE                                             1

                             CHAPTER I.

  Anatomical Structure of Hide                                  2


                             CHAPTER II.

  Chemical Composition of Hide                                 17


                             CHAPTER III.

  Commercial Tanning Materials                                 23


                             CHAPTER IV.

  The Chemistry of Tannins                                     57


                             CHAPTER V.

  Water as used in Tanning                                     83


                             CHAPTER VI.

  Methods of Chemical Analysis for the Tannery                 90


                             CHAPTER VII.

  Sole-leather:--Preparing the Hides                          132


                             CHAPTER VIII.

  Sole-leather:--Unhairing Hides                              139


                              CHAPTER IX.

  Sole-leather:--Tanning Materials                            157


                              CHAPTER X.

  Sole-leather:--Treatment in the Tan-house                   169


                              CHAPTER XI.

  Sole-leather:--Treatment in the Shed                        179


                             CHAPTER XII.

  Dressing Leather                                            184


                             CHAPTER XIII.

  Currying                                                    193


                             CHAPTER XIV.

  Enamelled, Patent, or Japanned Leather                      203


                              CHAPTER XV.

  Morocco Leather                                             206


                             CHAPTER XVI.

  Russia Leather                                              208


                             CHAPTER XVII.

  Chamois or Wash-leather                                     210


                             CHAPTER XVIII.

  Crown Leather, or Preller's Leather                         213


                             CHAPTER XIX.

  Mineral-tanned Leather                                      218


                             CHAPTER XX.

  Calf-Kid                                                    223


                             CHAPTER XXI.

  Glove-Kid                                                   225


                             CHAPTER XXII.

  Construction and Maintenance of Tanneries                   231


                             CHAPTER XXIII.

  Drying-sheds for Leather                                    243


                             CHAPTER XXIV.

  Commerce, Statistics, and Bibliography                      255


  Index                                                       275




                                   A

                         TEXT-BOOK OF TANNING

                              ETC., ETC.


                            [Illustration]


                          INTRODUCTORY NOTE.


Leather manufacture may be broadly divided into two stages: "tanning,"
in which the raw hide is converted into the imputrescible and more or
less flexible material known as "leather"; and "currying," in which
this leather is further manipulated, and treated with fatty matters, to
soften and render it more waterproof, and to improve its appearance.
Glove-kid, and certain other leathers, however, are not tanned at all,
but "tawed," or prepared with a mixture in which alum and salt are
the most active ingredients; chamois, "shammy," or "wash" leather, is
produced by fulling with oil alone, and many leathers can scarcely be
said to be curried, although more or less oil is used in the final
processes of "finishing" or "dressing." The first subject to be treated
of in this work will be the operation of tanning, properly so called,
taking for example the tannage of sole- and belting-leather. This
demands thorough explanation, in both its practical and theoretical
aspects, not only because it is one of the most important branches of
the trade, but because the principles involved are those which equally
underlie all other tanning methods. The next to be dealt with will
be the modifications of the process which are necessary in tanning
the more flexible leathers used for boot-uppers, hose-pipes, and
saddlery purposes; then the currying of these leathers; and finally,
the manufacture of moroccos, Russian, and japanned leathers, calf- and
glove-kid, &c.




CHAPTER I.

ANATOMICAL STRUCTURE OF HIDE.


Before speaking of actual processes of manufacture, it is necessary to
devote some attention to the structure and chemical constitution of
hide or skin, which forms the raw material. Although a great variety
of skins are employed in tanning, they are all constituted on the same
general type, and an anatomical description of the hide of the ox will
apply almost equally to those of the calf, sheep, and goat; but from
differences in thickness and closeness of texture, their practical uses
differ widely. Fig. 1 shows a section of ox-hide, cut parallel with the
hair, magnified about 50 diam.: _a_, epithelial layer or _epidermis_,
consisting of horny layer above, and _rete malpighi_ below; _b_, _pars
papillaris_, and _c_, _pars reticularis_ of _corium_, _derma_, or true
skin; _d_, hairs; _e_, sebaceous or fat-glands; _f_, sudoriferous or
sweat-glands; _g_, opening of ducts of sweat-glands; _h_, _erectores
pili_ muscles, for erecting the hair.

The fresh hide consists of 2 layers: an outer, the epidermis; and an
inner, the true skin. The epidermis is very thin as compared with the
true skin which it covers, and is entirely removed preparatory to
tanning; it nevertheless possesses important functions. It is shown in
Fig. 1 at _a_, and more highly magnified in Fig. 2. Its inner mucous
layer _b_, the _rete malpighi_, which rests upon the true skin _c_, is
soft, and composed of living nucleated cells, which are elongated in
the deeper layers, and gradually become flattened as they approach the
surface, where they dry up, and form the horny layer _a_. This last
is being constantly worn away, and thrown off as dead scales of skin;
and as constantly renewed from below, by the continued multiplication
of the cells. It is from this epithelial layer that the hair, as well
as the sweat- and fat-glands, are developed. It will be seen in Fig. 1
that each hair is surrounded by a sheath, which is continuous with the
epidermis. In embryonic development, a small knob of cells forms on the
under side of the epidermis, and this enlarges, and sinks deeper into
the true skin, while the root of the young hair is formed within it;
this is shown in Fig. 3, _a b_. Smaller projections also form on the
stalk of the knob, and in due time produce the sebaceous glands. The
process of development of the sudoriferous glands is very similar to
that of the hairs. There is a great analogy between this process and
that of the ordinary renewal of hair in the adult animal. At _d_^1
Fig. 1, is seen an old and worn-out hair. It is shrunken and elongated,
and is almost ready to fall out. It will be noticed that its sheath or
follicle projects somewhat below the hair to the right. This is the
first production of a young hair, and is quite analogous to the knob of
epithelium which has been described as forming the starting-point of a
hair in embryo. At _d_^2, the same process is seen further advanced,
the young hair being already formed, and growing up into the old
sheath. At _d_^3, it is complete, the old hair having fallen out, and
the young one having taken its place.

[Illustration: Fig. 1.]

[Illustration: Fig. 2.]

[Illustration: Fig. 3.]

The hair itself is covered with a layer of overlapping scales, like
the slates on a roof, but of irregular form. These give it a serrated
outline at the sides, strongly developed in wool. Within these scales,
which are sometimes called the "hair cuticle," is a fibrous substance,
which forms the body of the hair; and sometimes, but not always, there
is also a central and cellular pith, which is mostly transparent,
though under the microscope it frequently appears black and opaque,
from the optical effect of imprisoned air. On boiling or long soaking
in water, alcohol, or turpentine, these air-spaces become saturated
with the liquid, and then appear transparent.

The fibrous part of the hair is made up of long spindle-shaped cells,
and contains the pigment which gives the hair its colour. The hair
of the deer differs from that of most other animals in being almost
wholly formed of polygonal cells, which, in white hairs, are usually
filled with air. At its base, the hair swells into a bulb, which is
hollow, and rests on a sort of projecting knob of the _corium_, called
the hair-papilla. This has blood-vessels and nerves, and supplies
nourishment to the hair. The hair-bulb is composed of round, soft
cells, which multiply rapidly; as they grow, they press upward through
the hair-sheath, become elongated and hardened, and form the hair. In
dark hairs, both the cells of the hair itself and those of its follicle
or sheath are strongly pigmented, but the hair much the more so, and
hence the bulb has usually a distinct dark form. The dark-haired
portions of a hide from which the hair has been removed by liming
still remain coloured, from the pigmented cells of the hair-sheaths,
which can only be got out completely by bating and scudding. The
cells outside the bulb, shown at _f_, in Fig. 4, pass upwards as they
grow, and form a distinct coating around the hair, which is called
the "inner root-sheath." This again consists of 2 separate layers,
of which the inner is "Huxley's," the outer, "Henle's." They arise
from the same cells in the base of the hair; but in the inner layer,
these remain polygonal and nucleated, while in the outer, they become
spindle-shaped and without nuclei. The inner root-sheath does not
extend to the surface of the skin, but dies away below the sebaceous
glands. This figure represents an ox-hair root, mag. 200 diam.: _a_,
fibrous substance of hair; _b_, hair cuticle; _c_, inner root-sheath;
_d_, outer root-sheath; _e_, dermic coat of hair-sheath; _f_, origin of
inner sheath; _g_, bulb; _h_, papilla.

[Illustration: Fig. 4.]

Outside the inner root-sheath is a layer of nucleated cells, continuous
with those of the epidermis, and of the same character. This is the
"outer root-sheath," and is shown at _d_, Fig. 4. This, together with
the whole of the epidermis, is covered next the _corium_ with an
exceedingly fine membrane, called the "hyaline" or glassy layer. It
is possible that this forms the very thin buff-coloured "grain" of
tanned leather, which evidently is of different structure from the rest
of the _corium_, since, if it gets scraped off before tanning, the
exposed portion of the _pars papillaris_ remains nearly white, instead
of colouring. The whole of the hair-sheath is enclosed in a coating of
elastic and connective-tissue fibres, which are supplied with nerves
and blood-vessels, and form part of the _corium_. Near the opening of
the hair-sheaths to the surface of the skin, the ducts of the sebaceous
or fat-glands (_e_, Fig. 1), pass into them, and secrete a sort of
oil to lubricate the hair. The glands themselves are formed of large
nucleated cells, arranged somewhat like a bunch of grapes; one is shown
highly magnified in Fig. 5: _a_, sebaceous gland; _b_, hair-stem; _c_,
part of _erector pili_ muscle. The upper and more central cells are
most highly charged with fat, which is shown by the darker shading.

[Illustration: Fig. 5.]

As already remarked, the sudoriferous or sweat-glands are also derived
from the epidermis layer. They are shown at _f_, Fig. 1, and on a
larger scale (200 diam.) in Fig. 6: _a_, windings laid open in making
section; they consist, in the ox and sheep, of a large wide tube,
sometimes slightly twisted. In this, they differ considerably from
those of man, which form a spherical knot of extremely convoluted
tube. The walls of these glands are formed of longitudinal fibres of
connective tissue of the _corium_, lined with a single layer of large
nucleated cells, which secrete the perspiration. The ducts, which are
exceedingly narrow, and with walls of nucleated cells like those of
the outer hair-sheaths, sometimes open directly through the epidermis,
as shown at _g_, Fig. 1, but more frequently into the orifice of a
hair-sheath, just at the surface of the skin. Each hair is provided
with a slanting muscle (_h_, Fig. 1), called the _arrector_ or _erector
pili_, which is contracted by cold or fear, and causes the hair to
"bristle," or stand on end; by forcing up the attached skin, it
produces the effect known as "goose-skin." The muscle, which is of the
unstriped or involuntary kind, passes from near the hair-bulb to the
epidermis, and just under the sebaceous glands, which it compresses.

[Illustration: Fig. 6.]

The _corium_ or true skin is principally composed of interlacing
bundles of white fibres, of the kind known as "connective tissue";
these are composed of fibrils of extreme fineness, cemented together
by a substance of different composition from the fibres themselves.
This may be demonstrated by steeping a small piece of hide for some
days in a stoppered bottle in lime-, or baryta-water, in which the
inter-fibrillar substance is soluble, and then teasing a small fragment
of the fibre with needles on a glass microscope-slide, and examining
with a power of at least 200-300 diam. In the middle portion of the
skin, these bundles of fibre are closely interwoven; but next the
body, they gradually become looser and more open, forming the _pars
reticularis_ (or netted part); and the innermost layer is a mere
network of loose membrane, generally loaded with masses of fat-cells,
and hence called adipose tissue.

It is this adipose tissue which is removed in the "fleshing" process.
On the other hand, the outermost layer, just beneath the epidermis,
is exceedingly close and compact, the fibre-bundles that run into it
being separated into their elementary fibrils, which are so interlaced
that they can scarcely be recognised. This is the _pars papillaris_,
and forms the lighter-coloured layer, called (together with its very
fine outer coating) the "grain" of leather. It is in this part that the
fat-glands are embedded, while the hair-roots and sweat-glands pass
through it into the looser tissue beneath.

Besides the connective-tissue fibres, the skin contains a small
proportion of fine yellow fibres, called "elastic" fibres. If a thin
section of hide be soaked for a few minutes in strong acetic acid, and
then examined under the microscope, the white connective-tissue fibres
become swollen and transparent, and the yellow fibres may then be seen,
as they are scarcely affected by the acid. The hair-bulbs and sweat-
and fat-glands are also rendered distinctly visible.

The nerves of the skin are very numerous, each hair being supplied
with fibres passing into both the papilla and sheath. They also
pass into the skin papillæ. They cannot readily be seen, without
special preparation, and, so far as is known, exercise no influence
on the tanning process. "Breaking the nerve" is a technical term,
which signifies a thorough stretching and softening of the skin, but
has nothing to do with nerves properly so called. The blood- and
lymph-vessels are, from the present point of view, somewhat more
important. They may often be seen in sections, and are lined with
nucleated cells, similar to those of the glands. These are surrounded
by coatings of unstriped muscular fibre, running both around and
lengthways, and also by connective-tissue fibres. In the arteries, the
muscular coating is much stronger than in the veins.

It may be thought that the space devoted to a discussion of the
anatomical structure of the skin is disproportionately large;
but there can be no doubt that, in order to make improvements,
nothing is of more importance than a clear conception, even to the
smallest details, of the materials and causes to be dealt with. The
illustrations are from actual specimens, and enable the various parts
of the hide to be identified under the microscope.

As this instrument is a most useful means of investigation in the
tanning industry, and one likely to be of increasing importance, it
will be well, before proceeding further, to say a few words, both on
the selection of a suitable instrument, and on its manipulation in
general.

To do useful work, it is not necessary to possess a very elaborate
or expensive instrument, but it is essential that the microscope be
well made and good of its kind. As high powers are often required in
the examination, both of hide sections and of ferments, which are the
principal objects of investigation in a tannery, it is of the first
importance that the fine adjustment should be perfectly steady, without
vibration or backlash. This, in the writer's experience, is never the
case with cheap microscopes, in which the fine adjustment is made by
a screw at the side of the tube moving the nose by means of a lever.
A much more satisfactory arrangement is that in which the whole body
of the microscope is raised or lowered by a screw in a pillar at the
back of the stand on which it slides. A rack for the coarse adjustment
is useful, but not essential. If a sliding tube only is provided, it
must be tight enough not to slip, but must move easily up and down
with a sort of screwing movement. A mechanical stage is not at all
necessary, and for most purposes one of black glass is better as well
as cheaper. The diaphragm for regulating the light should be as near
level with the surface of the stage as possible, and when examined with
a low power should appear in the centre of the field. For research work
on the minuter ferments, an achromatic condenser and the finest oil-
or water-immersion lenses are necessary, but directions for this are
beyond the scope of the present work. It may, however, be mentioned
that Prof. Flügge,[A] a first-class authority on the subject,
especially recommends Abbé's illuminating apparatus as made by Zeiss.

[Footnote A: "Fermente und Mikroparasiten," Leipzig, 1883.]

A frequent defect in cheap English microscopes is that the mirror for
substage illumination does not bring the rays of a lamp to a focus
exactly on the slide, but frequently some inches above it. This may be
to a great extent overcome by the use of a bulls'-eye condenser between
the lamp and the microscope. Another defect is that sometimes the
centre of the mirror is not in a line with that of the microscope body.

The objectives (or lenses at the lower end of the microscope) are the
most important part of the instrument, and however good it may be in
all other respects, if these are defective the whole is useless. The
most useful lenses for our purpose, if only two are to be selected, are
a 1-in., magnifying about 50 diam., and a 1/4-in., magnifying about 200
to 400, according to the eye-piece; a 1/8-in. giving, say, twice this
magnification will be needed to see the smaller bacteria distinctly,
but it is possible just to see even the small putrefaction bacteria
with a really fine 1/4-in. In any case, the highest power should be as
perfect and of as large an angle as attainable. A good 1/4-in. should
resolve _Pleurosigma angulatum_ with direct light, and should show the
movement of the granules of protoplasm in the round corpuscles which
are present in saliva. In using the latter test, it must be remembered
that the motion only lasts a very short time on a cold slide.

About 5_l._ is the very least for which a microscope can be obtained
which is suitable for tanners' use; where it can be afforded, a better
one is advisable.

Without disparaging other makers, it may be mentioned that the writer
has generally used both the eye-pieces and objectives of Dr. Hartnack
of Potsdam; and that they are moderate in price, at least for the dry
combinations, and perfectly satisfactory for all technical purposes.
Numbers 2, 5, and 8 objectives with No. 3 eye-piece, are sufficient
for all ordinary work. If only 2 objectives are to be obtained, Nos.
3 and 7 would be perhaps the best selection. It is always better
to use objectives on the stand, and with the eye-pieces for which
they are intended, but in case Hartnack's objectives are used on an
English stand (which is easily done by means of an adaptor ring), it
is important to remember that they are constructed to work with a
shorter tube than that customary on English microscopes, and that they
will not perform well if its length is much more than 6 in.; these
objectives are not provided with a movable adjustment for thickness
of cover-glasses, which for technical purposes is not required, and
in inexperienced hands is apt to prove troublesome. Extra-thin covers
must therefore always be used. Where this adjustment is provided, the
object must be accurately focused, and then, maintaining this focus
with the fine focusing-screw, the collar must be cautiously turned till
the best definition is obtained. Practically it will be best to make
this adjustment accurately once for all, and to take care to use covers
selected of a uniform thickness.

High-power objectives of wide angle (which condition is essential to
good defining power) necessarily work extremely close to the object,
and it is always best to use the thinnest cover-glasses which can be
got. Even then, with such glasses as Hartnack's No. 8, unless the
sections are very thin, it will be impossible to examine their lower
parts; and one of the greatest difficulties of microscopic research
is to obtain them thin enough. It will be obvious, from what has
been said, that the greatest care is needed to avoid screwing the
objective down on the cover, and so breaking one or both of them. One
way to avoid this is to screw down as close as possible to begin with,
and then focus upwards. Another plan, when the object on the slide
is small, is to keep continuously moving the slide gently with the
fingers, while looking into the tube. It is then easy to notice when
the dust and small particles on the slide come into focus, and if the
point should happen to be overstepped the contact will generally be
felt before serious damage is done.

Illumination is one of the most important points in practical
microscopy. With powers of not less than 1/2-in. focus, objects may
generally be examined by light thrown upon them from above by a
bulls'-eye condenser, or by good daylight. In this case they need not
be transparent; and the plan is often convenient for a mere surface
examination. In examining bodies illuminated in this way, prominences
often appear as hollows and _vice versâ_, by a sort of optical
illusion, which, once established, is very difficult to overcome. By
remembering the direction of the light, and that this appears reversed
in the microscope, it is easy to decide the truth.

For all finer work and higher powers, and most generally with the low
powers also, it is necessary to render the object transparent, and to
examine it by light transmitted from the mirror below the stage.

Good daylight is least trying to the eyes. Where artificial light must
be used, that of a small paraffin lamp is best; and a blue chimney,
or blue glass interposed between the stage and mirror, or lamp and
microscope, spares the sight, and makes it easier to distinguish
colours. The light should be sufficient, but not too dazzling. Work
should never be prolonged after the least strain is felt, nor should
the microscope be used for some little time after a meal. It is well to
accustom oneself to keep both the eyes open while observing.

If it be required to see how far the cellular structures of the hide,
such as hair-sheaths and fat-glands, are affected or destroyed in any
stage of liming or bating, the following ready method may be employed.
If a strip of hide be cut 2/3 through from the grain side, as shown
at _a_ in Fig. 7, and the flap be turned down, and held between the
finger and thumb, the fibrous tissue will be put on the stretch, and
will then allow a moderately thin shaving (including the grain and
parts immediately below it) to be cut by a sharp razor. The hide
should be held in the positions shown, and a steady drawing cut be
made from flesh to grain, the razor being steadied on the tip of
the forefinger, and its hollow surface flooded with water. If the
thin section be now placed on a glass slide, moistened with a drop of
water, and examined on the microscope under a strong light from above,
with a 1-in. objective, the fat-glands will be seen as yellow masses,
embedded in the white fibrous tissue. If a drop of a mixture of equal
vols. of strong acetic acid, glycerin, and water be used to moisten the
section, the fibrous tissue will become quite transparent, and whatever
remains of the cellular tissue will be easily visible, and may even be
studied under tolerably high powers if covered with a thin glass, and
lighted by the mirror from below. (The cover-glass must be carefully
cleaned by rubbing with a linen handkerchief, and placed in position
with a pair of tweezers, one side being supported by a needle, which is
gradually withdrawn, so as to avoid air-bubbles.) Care must be taken
that this mixture does not touch the brass-work of the microscope; even
the vapour is apt to tarnish, so that the preparation must not remain
longer than necessary on the microscope. The same method is applicable
for ascertaining the completeness of the tannage of leather, and to
decide whether the hide fibre is really tanned, or only dyed. Actually
tanned leather is unaffected by the acetic acid, but raw or only
stained hide swells and becomes transparent.

[Illustration: Fig. 7.]

To prepare the very thin sections necessary for detailed study of the
hide, more complicated methods are required. Small slips of hide, not
exceeding 1/4 in. wide, and cut exactly across the lie of the hair,
are placed first in weak alcohol (equal parts methylated spirit and
water), and, after a few hours, are removed into strong methylated
spirit. It is then kept for some days in absolute alcohol, which must
be repeatedly changed, until the hide is hard enough to give fine
shavings, and may be cut either when held as above described, between
cork or pith, or when embedded in paraffin wax. This is accomplished
by placing the piece of hide in a little paper-box and covering it
with melted paraffin (candle), which is just beginning to stiffen. The
piece of hide may be fixed in position with a needle, which must of
course be withdrawn before cutting. When hard, the paraffin is shaved
away till the object is exposed, when it may be cut. The razor must be
wet with alcohol, and the section be made exactly in the plane of the
hair-roots, which may be seen with a hand-lens. (The use of a microtome
for hide-sections is rarely successful, as it is almost impossible to
fix the fragment of hide so that it is cut exactly with the hairs.)
The slices may now be stained by placing them in a watch-glass with
water and a few drops of the logwood or picrocarmine staining-mixtures
sold by opticians, and afterwards either examined in glycerin, or,
after soaking some hours in absolute alcohol, may be transferred to
clove-oil, and afterwards to a slide, and covered with a drop of
dammar varnish or Canada balsam dissolved in chloroform. The sections
moistened with glycerin may also be mounted in Farrant's solution
or glycerin jelly, under a cover-glass for permanent preservation.
If picrocarmine be used, the connective-tissue fibres (gelatinous
fibres) and the nuclei of the cells will be coloured red, and the cells
themselves of both epidermis and glands, together with the muscles and
elastic fibres, will be yellow.

Franz Kathreiner, who has made very elaborate researches on skin, and
the changes which take place in it during the processes of tanning,
employs a mixture of osmic and chromic acids for hardening, and at the
same time staining the tissue. This mixture was first used by a German
histologist with whose name I am not acquainted, in a research on the
internal organs of hearing, and was applied by Kathreiner in 1879 to
the investigation of skin, and communicated by him to the writer in
the autumn of that year. His method is briefly as follows. The pieces
of hide to be examined must, if salted, be well washed, or if dry, be
thoroughly softened. For the study of hide in its unaltered and natural
condition, it is essential that it be quite fresh, and taken from the
animal as soon as possible after death. In any case the _Panniculus
adiposus_ or fatty layer is, as far as possible, removed with scissors,
the hair cut short, and the skin cut up into little pieces of 3-4
millimetres wide by 10-12 millimetres long (about 1/8 in. by 1/2 in.);
the hair must lie exactly across these pieces.

They are then placed for 4-8 days, according to the thickness of the
hide, in about 12 times their volume of a solution consisting of

    0·2 parts osmic acid.[B]
    0·5   "   chromic acid.
  200·0   "   water.

[Footnote B: Solution of osmic acid is best preserved in sealed tubes
in the dark. If obtained in solution it is rarely of full strength,
for which allowance may have to be made. Care must be taken to avoid
inhaling its fumes, which are very irritating to the eyes and to the
respiratory organs, producing severe catarrh.]

This solution must be kept from dust and light, in a glass stoppered
bottle, and in a cool place. On removing the hide-pieces from this
solution, they are placed in about 12 times their volume of absolute
alcohol for 4-8 days, during which time the spirit must be at least 3
times renewed. The sections are cut with a razor flooded with absolute
alcohol, so that the thin shavings float without friction upon it. The
hide-pieces may be held either between soft cork, or, as is generally
preferable, simply between the forefinger and thumb as shown in Fig.
7. The cut must be made exactly parallel with the direction of the
hair roots, and from the grain towards the flesh; and the sections
cannot possibly be too thin. After lying for 1/2-1 hour in absolute
alcohol, the sections are soaked till quite clear in clove oil (which
must be pale and of the purest kind), and may then be mounted in dammar
varnish, or solution of Canada balsam.

In these sections, fat and the oily contents of the fat glands are
stained black, and the limits of the cells both of these glands and of
other elements of the hide (_rete malpighi_, hair-bulb, &c.) are made
very distinct, so as to be capable of the most delicate investigation
under the highest powers; but the beginner will learn most easily to
recognise the different tissues by studying at first some sections
stained with picrocarmine as before described. The method is admirably
adapted for the study of hide as affected by the limes and bates.




CHAPTER II.

CHEMICAL COMPOSITION OF HIDE.


The chemical composition of skin is very imperfectly understood. The
bulk of the skin is, as has long been known, converted by boiling
into gelatin or glue. The yellow fibres and cellular tissue remain
undissolved. Müntz, who made some interesting researches on the
subject, found that completely dried hide contained--3·086 per cent. of
cellular tissue insoluble in hot water, 1·058 of fat, 0·467 of mineral
matter, and 95·395 of matters soluble in hot water. Müntz counts the
whole of the tissue soluble in hot water as converted into glue; but
this is not strictly the case. Gelatin is not identical with the fibre
of the hide, which is only converted into it by boiling. The nature of
the change is not well understood; but it is either simply molecular,
or depends on the addition of one or more molecules of water. The
gelatin of bones seems identical with that of skin and connective
tissue, but that of cartilage differs slightly from it, and is called
chondrin. Raw hide, unhaired and purified, contains, according to
Müntz--carbon, 51·43 per cent.; hydrogen, 6·64; nitrogen, 18·16;
oxygen, 23·06; ash, 0·71; while gelatin has--carbon, 50·1 per cent.;
hydrogen, 6·6; nitrogen, 18·3 (Mulder); carbon, 50 per cent.; hydrogen,
6·5; nitrogen, 17·5 (Fremy). Probably, however, neither substance was
quite pure.

Gelatin is insoluble in alcohol, ether, and cold water, but swells in
the last, absorbing about 40 per cent. It is soluble in hot water,
but is reprecipitated on the addition of a sufficient quantity of
alcohol, resembling in this respect gum, dextrin, and many other
substances. It is soluble in glycerin, with the aid of heat, and in
concentrated sulphuric acid in the cold. Moist gelatin exposed to
the air rapidly putrefies. It first becomes very acid, from formation
of butyric (and perhaps other) acids, but afterwards alkaline, from
evolution of ammonia. Boiled with concentrated potash, it yields leucin
(amidocaproic acid, C_{6}H_{15}NO_{2}), glycocin (sugar of gelatin),
and other substances. The same products are obtained by boiling with
sulphuric acid, and probably also more gradually, and in greater or
less proportions, by the prolonged action of lime or barium hydrate,
by putrefaction, and by any other influence which tends to resolve the
gelatin molecule into its simpler parts. Gelatin is precipitated by all
tannins, even from very dilute solution. A solution containing 2/10000
parts is rendered turbid by infusion of gall-nuts or gallotannic acid.
The precipitate is soluble in excess of gelatin. Solution of gelatin
dissolves considerable quantities of lime phosphate, hence this is
always largely present in common glue. Gelatin is precipitated by
mercuric chloride, in this respect resembling peptones; but not by
potassium ferrocyanide, by which it is distinguished from albuminoids;
and it differs from albumen in not being coagulated by heat. On the
contrary, by prolonged boiling glue loses the property of gelatinising,
and becomes soluble in cold water, being split up into two peptones;
semi-glutin, which is insoluble in alcohol, and precipitated by
platinic chloride; and hemicollin, which is soluble in alcohol, and not
precipitated by platinic chloride. Both are precipitated by mercuric
chloride (see Hofmeister, abst. Chem. Soc. Jour. 1881, p. 294).
Gelatin or glue with about 3 per cent. of potassium dichromate becomes
insoluble when exposed to the light, from the formation of a chromium
compound. This reaction is the base of several modern photographic
processes, and has been used for waterproofing and for cementing glass,
&c.

The connective-tissue fibres are partially converted into gelatin
by the action of strong acids and alkalies, as well as by heat. By
weak acids, they are swollen and gradually dissolved, and Reimer[C]
has found that the material may be reprecipitated by lime-water. It
forms an irregular fibrous mass, which has not the sticky feel of
gelatin, but is at once converted into that body by boiling. Rollet has
demonstrated that when hide and other forms of connective tissue are
soaked in lime- or baryta-water, the fibres become split up into finer
fibrils, and as the action proceeds, these again separate into still
finer, till the ultimate fibrils are as fine as can be distinguished
under a powerful microscope. At the same time, the alkaline solution
dissolves the substance which cemented the fibres together, and this
may be recovered by neutralising the solution with acetic acid, when it
comes down as a flocculent precipitate. This was considered by Rollet
to be an albuminoid substance; but Reimer has shown that it is much
more closely allied to the gelatigenous fibres, if indeed it is not
actually produced from them by the action of the alkaline solution.
Reimer used limed calf-skin for his experiments, and subjected it to
prolonged cleansing with distilled water, so that all soluble parts
must have been pretty thoroughly removed beforehand. He then digested
it in closed glasses with lime-water for 7-8 days, and precipitated the
clear solution with dilute acetic acid. He found that the same portion
of hide might be used again and again, without becoming exhausted,
which strongly supports the supposition that it is merely a product of
the partial decomposition of the hide fibre. The substance, which he
called "coriin," was purified by repeated solution in lime-water, and
reprecipitation by acetic acid. It was readily soluble by alkalies,
but insoluble in dilute acids, though in some cases it became so
swollen and finely divided as to appear almost as if dissolved. It was,
however, very soluble in common salt solution of about 10 per cent.,
though it was precipitated both by the addition of much water, and by
saturating the solution with salt. Reimer found that a 10 per cent.
salt solution was equally effective with lime-water in extracting it
from the hide, and that it was partially precipitated on the addition
of acid, and completely on saturating the acidified solution with
salt. Other salts of the alkalies and alkaline earths acted in a
similar manner, so that Reimer was at first deceived when experimenting
with baryta-water, because, being more concentrated than lime-water,
the coriin remained dissolved in the baryta salt formed on neutralising
with acid, and it was necessary to dilute before a precipitate could
be obtained. The slightly acid solution of coriin gave no precipitate
with potassium ferrocyanide, nor was it precipitated by boiling, being
thus distinguished from albuminoids. The neutral or alkaline solution
was not precipitated by iron or mercuric chloride, copper sulphate, nor
by neutral lead acetate; but was precipitated by basic lead acetate,
basic iron sulphate, and excess of tannin. Its elementary composition
is--carbon, 45·91: hydrogen, 6·57; nitrogen, 17·82; oxygen, 29·60; and
Reimer proposes the following equation as representing its relation to
hide fibre:--

       Hide fibre.                 Water.             Coriin.
  C_{30}H_{46}N_{10}O_{12} + O  +  2H_{2}O  =  C_{30}H_{50}N_{10}O_{15}.

[Footnote C: Dingler's Polyt. Journal, vol. 220, p. 167.]

_Hide Albumen._--The fresh hide, besides this coriin (which, very
possibly, is only evolved by the action of the lime), contains a
portion of actual albumen, viz. that of the blood serum and of the
lymph, which is not only contained in the abundant blood-vessels,
but saturates the fibrous connective tissue, of which it forms
the nourishment. This albumen is mostly removed by the liming and
working on the beam, which is preparatory to tanning. Probably for
sole-leather, the albumen itself would be rather advantageous if left
in the hide, as it combines with tannin, and would assist in giving
firmness and weight to the leather. It is, however, for reasons which
will be seen hereafter, absolutely necessary to get rid of any lime
which may be in combination with it. The blood also must be thoroughly
cleansed from the hide before tanning, as its colouring matter contains
iron, and, in combination with the tannin, would give a bad colour.

The reactions of blood and lymph albumen are very similar to those
of ordinary white of egg. It is precipitated by strong mineral acids,
especially nitric, and also by boiling. The precipitate produced by
strong hydrochloric acid redissolves by the aid of heat to a blue
or purple solution. Tribasic phosphoric, tartaric, acetic, and most
other organic acids, do not precipitate moderately dilute solutions
of albumen, but convert it into a sort of jelly, which, like gelatin,
does not coagulate, but liquefies on heating. It is precipitated by
neutral salts of the alkali metals. Blood-albumen slightly acidified
(with acetic acid) is precipitated by potassium ferrocyanide. It is
not precipitated by dilute infusions of oak bark, but is rendered
uncoagulable by heat, hence it cannot be employed to remove tannins
from their solutions.

_Elastic Fibres._--The elastic or yellow fibres of the hide are of
a very stable character. They are not completely dissolved even by
prolonged boiling, and acetic acid and hot solutions of caustic
alkalies scarcely attack them. Probably they do not combine with
tannin, and are very little changed in the tanning process.

_Hair, Epidermis, and Glands._--These are, as has been seen, all
derived from the epithelial layer, and hence, as might be inferred,
have much in common in their chemical constitution. They are all
classed by chemists under one name, "keratin," or horny tissue, and
their ultimate analysis shows that in elementary composition they
nearly agree. It is evident, however, that the horny tissues are rather
a class than a single compound.

The keratins are gradually loosened by prolonged soaking in water,
and, by continued boiling in a Papin's digester, are dissolved to an
extract which does not gelatinise on cooling. Keratin is dissolved by
caustic alkalies; the epidermis and the softer horny tissues are easily
attacked, while hair and horn require strong solutions and the aid of
heat to effect complete solution. The caustic alkaline earths act in
the same manner as dilute alkaline solutions; hence lime easily attacks
the epidermis, and loosens the hair, but does not readily destroy the
latter. Alkaline sulphides, on the other hand, seem to attack the
harder tissues with at least the same facility as the soft ones, the
hair being often completely disintegrated, while the epidermis is still
almost intact; hence their applicability to unhairing by destruction of
the hair. Keratins are dissolved by fuming hydrochloric acid, with the
production of a blue or violet coloration, like the albuminoids. They
also resemble albumen, in the fact that their solution in sulphuric
acid is precipitated by potassium ferrocyanide. By fusion with potash,
or prolonged boiling with dilute sulphuric acid, keratin is decomposed,
yielding leucin, tyrosin, ammonia, &c. The alkaline solution of keratin
(hair, horns, &c.) is precipitated by acids, and, mixed with oil and
baryta sulphate, is employed under Dr. Putz's patent as a filling
material for leather, for which purpose it acts in the same way as the
egg-yolks and meal used in kid-leather manufacture. Eitner attempted
to use it for the same purpose with bark-tanned leather, but without
much success. Putz has also proposed to precipitate the material after
working its solution into the pores of the leather.




CHAPTER III.

COMMERCIAL TANNING MATERIALS.


=Algarobilla.=--The seed-pods of _Prosopis pallida_ and _P. Algarrobo_
are known as _algarobilla_, the two kinds being distinguished as
_negro_ and _blanco_. The trees are abundant in mountainous parts
of South America, notably Chili and the Argentine Republic. The
pods contain up to 50 per cent. of a bright-yellow tannin, somewhat
resembling that of myrobalans. The friable tannin is readily soluble
in cold water, and is so loosely held in the fibrous network of the
pod, that great loss is sustained by careless handling. The commerce
in algarobilla does not figure in the official trade returns; but J.
Gordon & Co., Liverpool, obligingly state that they imported 50 tons,
at an average value of 18_l._ 10_s._ a ton, in 1880. Widow Duranty &
Son, also of Liverpool, are good enough to add that they received 160
tons in 1881, the first that had reached them for a long time. Havre
imported 50 tons in 1881. The name _algarrobo_ is also applied to
_Balsamocarpon brevifolium_ in Chili, and to _Hymenæa Courbaril_ in
Panama.

=Chestnut-extract.=--The wood of the chestnut (_Castanea vesca_)
contains 14-20 per cent. of a dull-brown tannin. It is quite different
from the bark and bark-extract of the American chestnut-oak (_Quercus
sessiliflora_). Its extract is used largely to modify the colour
produced by hemlock-extract, and for tanning and dyeing. The pulverised
wood is also extensively employed in France. The imports are included
in barks and extracts, p. 39.

=Cork-bark.= See Oak-barks.

=Cutch, Catechu, or Terra Japonica= (Fr., _Cachou_; Ger.,
_Catechu_).--The term _kát_, _kut_, or "cutch," is applied to the
dried extract, containing 45-55 per cent. of dark-coloured mimo-tannic
acid, prepared chiefly from 2 trees:--(1) _Acacia Catechu_ [_Mimosa
Catechu_, _M. sundra_], a tree of 30-40 ft., common in most parts of
India and Burma, growing also in the hotter and drier districts of
Ceylon, and abundant in tropical East Africa--the Soudan, Sennar,
Abyssinia, the Noer country and Mozambique, though the utilisation of
its tannin is restricted to India; (2) _A._ [_M._] _Suma_, a large tree
inhabiting South India (Mysore), Bengal, and Gujerat.

The process for preparing cutch varies slightly in different districts.
The trees are reckoned to be of proper age when their trunks are about
1 ft. diam. They are then cut down, and the whole of the woody part,
with the exception of the smaller branches and the bark, is reduced
to chips: some accounts state that only the darker heart-wood is thus
used. The chips are placed with water in earthen jars, arranged in a
series over a mud fire-place, usually in the open air. Here the water
is made to boil, the liquor as it becomes thick and strong being
decanted into another vessel, in which the evaporation is continued
until the extract is sufficiently inspissated, when it is poured into
moulds made of clay, or of leaves pinned together in the shape of
cups, or in some districts on to a mat covered with the ashes of burnt
cow-dung, the drying in each case being completed by exposure to the
sun and air. The product is a dark-brown extract, which is the usual
form in which cutch is known in Europe.

In Kumaon, North India, a slight modification of the process affords
a drug of very different appearance. Instead of evaporating the
decoction to the condition of an extract, the inspissation is stopped
at a certain point, and the liquor is allowed to cool, coagulate,
and crystallise over twigs and leaves thrown into the pots for the
purpose. By this method is obtained from each pot about 2 lb. of _kath_
or catechu, of an ashy-whitish appearance. In Burma, the manufacture
and export of cutch form one of the most important items of forest
revenue. The quantity of cutch exported from the province in 1869-70
was 10,782 tons, valued at 193,602_l._, of which nearly half was the
produce of manufactories situated in British territory. The article is
imported in mats, bags, and boxes, often enveloped in the large leaf of
_Dipterocarpus tuberculatus_. It is brought down from Berar and Nepal
to Calcutta. That of Pegu has a high reputation.

Our imports of cutch in 1880 were 5155 tons, value 173,040_l._, from
the British East Indies; 539 tons, 15,572_l._, from other countries;
total, 5694 tons, 188,612_l._ Our exports in the same year were:--892
tons, 28,527_l._, to Germany; 676 tons, 24,562_l._, to the United
States; 478 tons, 15,505_l._, to France; 303 tons, 10,537_l._, to
Holland; 177 tons, 5859_l._, to Russia; 141 tons, 4835_l._, to Belgium;
245 tons, 8719_l._, to other countries; total, 2912 tons, 98,544_l._
The approximate London market value of Pegu cutch is 21-42_s._ a cwt.

An astringent extract prepared from the areca nut (_Areca Catechu_) is
said to contribute to commercial cutch; if so, it is a totally distinct
product from those just described.

=Divi-divi, or Libi-dibi.=--These names are applied to the seed-pods of
_Cæsalpinia coriaria_, a tree of 20-30 ft., indigenous to several of
the West Indies, Mexico, Venezuela, and North Brazil, and naturalised
in Madras and Bombay Presidencies, and in the North-West Provinces.
The pod may be known by its drying to the shape of a letter S; it
contains 30-50 per cent. of a peculiar tannin, somewhat similar to that
of valonia. It is cheap, and may be used in admixture with barks; but
it is dangerously liable to undergo fermentation, suddenly staining
the leather a dark-red colour, and is therefore not in extensive
use. The imports of it are mainly from Maracaibo, Paraiba, and St.
Domingo. Maracaibo, in 1880, exported 197,674 lb. of divi-divi, value
3222-1/4 dol. (4_s._ 2_d._), to New York. Our imports of divi-divi into
Liverpool, according to figures kindly furnished by Haw & Co., were
2200 tons in 1877, 1740 in 1878, 2132 in 1879, and 780 in 1880. The
approximate market value is 12-17_l._ a ton.

=Galls.=--The generic term "gall" is applied to those excrescences on
plants which are produced by the punctures of insects, for the purpose
of depositing their eggs. The excrescences are usually considered to be
a diseased condition of vegetable tissue, resulting from the injection
of some secretion of the insects. But this has been combated by A.
S. Wilson, of Aberdeen, who considers that all insect galls are in
reality leaf-buds, or fruit-buds, and not mere amorphous excrescences.
The vascular lines which would form leaves can easily be followed up
in the structure of the oak-leaf galls. And in cases where the egg
has been deposited in the tissue of a young branch, the cap of the
gall is sometimes surmounted by a leaf 2-3 in. long. But in the large
blue Turkish galls, many lacunæ occur where the fleshified leaves have
not filled up the spaces between them. If a dissection be made of one
of the weevil-galls on the bulb of the turnip, the second or third
slice will show the outer foliations, exactly similar to those of the
root-buds. When the centre has been reached, where the maggot will be
found, there will also be a vascular pencil running up from a medullary
ray in the bulb, and bearing on its top a bud of the same description
as that produced by a ray running out from a root. The insertion of the
ovipositor brings a medullary ray into action, producing a tuberculated
bud, and it is only the bud which the larva feeds upon. The growth of a
bud is an intelligible cause of the growth of a gall, but nothing can
be inferred from the injection of a fluid. The analogy to leaves is
further shown by the fact that various microscopic fungi are matured in
the interior of imperforate galls.

The principal commercial kinds of gall are oak-galls and Chinese galls.

_Oak-galls_, _Nut-galls_, _Aleppo_ or _Turkey-galls_ (Fr., _Noix de
Galle_, _Galle d'Alep_; Ger., _Levantische_ or _Aleppische Gallen_,
_Galläpfel_).--These are formed by the punctures of _Cynips_
[_Diplolepis_] _Gallæ tinctoriæ_ on _Quercus lusitanica_ var.
_infectoria_ [_Q. infectoria_], a shrubby tree of Greece, Cyprus, Asia
Minor, and Syria, and probably other varieties and even species of oak.
The female insect is furnished with a delicate ovipositor, by means of
which she pierces the tender shoots of the tree, and lays her eggs
therein. In the centre of the full-grown gall, the larva is hatched
and undergoes its transformations, finally (in 5-6 months) becoming a
winged insect, and boring for itself a cylindrical exit-hole. The best
commercial galls are those which have been gathered while the insect
is still in the larval state. Such have a dark olive-green colour, and
are comparatively heavy; but after the fly has escaped, they become
yellowish-brown in hue, and lighter. Hence they are distinguished in
the London market as "blue" or "green," and "white." In Smyrna, they
are classified as "white," "green," and "black," the first two sorts
generally fetching nearly the same price, while the black obtain
considerably more, the approximate quotations being: white and green,
per Turkish _oke_ (of 2·83 lb.), 8-1/2-9 _piastres_ (of 2_d._);
black, 13-1/2-14 _piastres_. The "nuts" come mostly from Melemen,
Cassaba, and Magnesia, also from the Syrian coasts, being plentiful
on the east of the river Jordan, and are chiefly forwarded to France,
England, and Salonica. The triennial yield is said to be invariably
the best. They begin to reach Smyrna from the interior towards the
end of July. The crop of 1880 was estimated at over 50,000 _okes_.
The province of Aleppo, which used to afford 10,000-12,000 _quintals_
(of 2 cwt.) annually, only exported 3000 in 1871. The galls collected
in the Kurdistan mountains are marketed at Diarbekir, and sent thence
to Trebizonde for shipment. Bussora, Bagdad, and Bushire also export
considerable quantities.

_Knoppern_, a species of gall formed from the immature acorns of
_Quercus pedunculata_ and _Q. sessiliflora_, are largely used for
tanning throughout Austria.

The exports from Aleppo (including yellow berries) in 1880 were:--60
tons, 3600_l._, to Great Britain; 322 tons, 19,320_l._, France; 15
tons, 900_l._, Italy; 44 tons, 2640_l._, Austria; 55 tons, 3300_l._,
Turkey; 30 tons, 1800_l._, Egypt; total, 526 tons, 31,560_l._ In
1878, the figures were 673 tons, 38,400_l._ Alexandretta exported in
1879 (including yellow berries):--41 tons, 2460_l._, to England; 299
tons, 17,940_l._, France; 20 tons, 1200_l._, Italy; 25 tons, 1500_l._,
Austria; 87 tons, 5220_l._, Turkey; 6 tons, 360_l._, Egypt; total
478 tons, 28,680_l._ The shipments from Trebizonde by steamer in 1880
were (from Turkey):--47 sacks (of 2 cwt.), 188_l._, to Turkey; 240
sacks, 960_l._, Great Britain; 264 sacks, 1056_l._, France; 103 sacks,
412_l._, Austria and Germany; 26 sacks, 104_l._, Greece; total, 680
sacks, 2720_l._; (from Persia): 25 sacks, 100_l._, Great Britain; 31
sacks, 124_l._, France; 30 sacks, 120_l._, Austria and Germany; total,
86 sacks, 344_l._ Bushire despatched 5000_r._ worth to India in 1879.
Syra sent 248_l._ worth to Great Britain in 1879. Venice exported 1745
tons of gall and bark, value 34,906_l._, in 1879.

The best oak-galls contain 60-70 per cent. of tannic or gallotannic
acid, and 3 per cent. of gallic acid. "Rove" is a small crushed gall,
containing 24-34 per cent. of gallotannic acid. There are many other
varieties of non-commercial oak-gall.

_Chinese or Japanese Galls._--These are vesicular protuberances
formed on the leaf-stalks and branches of the _Rhus semialata_
[_Bucki-amela_], a tree of 30-40 ft., common in North India, China, and
Japan, ascending the outer Himálaya and the Khasia Hills to 2500-6000
ft., by punctures of the female of _Aphis chinensis_. The galls are
collected when their green colour is changing to yellow, and are then
scalded. They are light and hollow, 1-2-1/2 in. long, and of very
varied and irregular form. The Japanese are the smaller and paler,
and usually more esteemed. The galls contain about 70 per cent. of
tannic or gallotannic acid, and 4 per cent. of another tannin. They are
consumed mainly in Germany, for the manufacture of tannic acid.

Hankow exported 30,949 _piculs_ (of 133-1/3 lb.) in 1872; and 21,611
_piculs_, value 136,214 _taels_ (of about 6_s._), in 1874. In 1877, the
total Chinese export did not exceed 17,515 _piculs_. Hankow exported
24,742-1/2 _piculs_ in 1878, and 28,392 _piculs_, 59,614_l._, in 1879;
Pakhoi, 62_l._ worth in 1879; Canton, 3155-1/3 _piculs_ in 1877, 1939
in 1878, 3163-1/2 in 1879; Ichang, 100-1/2 _piculs_, 132_l._, in 1878,
402-1/2 _piculs_, 586_l._, in 1879; Shanghai, 27,659-1/2 _piculs_ in
1879.

In China trade returns, they are always miscalled "nut-galls" or
"gall-nuts": correctly, they are _wu-pei-tze_. Oak-galls are exported
from China resembling those of Western Asia. Japanese galls, _kifushi_,
are sent in increasing quantities from Hiogo.

Our imports of galls in 1880 were:--24,590 cwt., 68,697_l._, from
China; 17,311 cwt., 60,648_l._, from Turkey; 9182 cwt., 9013_l._,
from other countries: total, 51,083 cwt., 138,358_l._ Our re-exports
in the same year were:--6260 cwt., 18,479_l._, to Holland; 6022
cwt., 18,147_l._, to Germany; 3214 cwt., 11,002_l._, to France; 3045
cwt., 8598_l._, to Belgium; 2651 cwt., 11,004_l._, to the United
States; 1625 cwt., 5205_l._, to other countries; total, 22,817 cwt.,
72,435_l._ The approximate London market values of galls are:--Bussora,
blue, 82-102_s._ a cwt.; do., white and in sorts, 50-90_s._; China,
50-70_s._; Japan, 55-56_s._

=Gambier, Pale Catechu, or Terra Japonica= (Fr., _Gambir_, _Cachou
jaune_; Ger., _Gambir_).--These names are conferred upon an extract
from the leaves of _Uncaria Gambier_ [_Nauclea Gambir_] and _U. acida_,
containing 36-40 per cent. of a brown tannin, which rapidly penetrates
leather, and tends to swell it, but alone gives a soft porous tannage;
it is largely used in conjunction with other materials for tanning
both dressing- and sole-leather. The plants are stout climbing shrubs,
the first-named being a native of the countries bordering the Straits
of Malacca, and especially the islands at the eastern end, though
apparently not indigenous to any of the islands of the volcanic band,
growing also in Ceylon, where no use is made of it; while the second,
probably a mere variety, flourishes in the Malay islands.

The shrubs are cultivated in plantations, often formed in jungle
clearings; the soil is very rapidly exhausted, and further injured
by excessive growth of the ineradicable _lalang_-grass (_Andropogon
caricosus_). It is found advantageous to combine pepper-culture with
that of gambier, the boiled leaves of the latter forming excellent
manure for the former. The gambier-plants are allowed to grow 8-10
ft. high, and as their foliage is always in season, each plant is
stripped 3 or 4 times in the year. The tools and apparatus for the
manufacture of the extract are of the most primitive description. A
shallow cast-iron pan about 3 ft. across is built into an earthen
fire-place. Water is poured into the pan, a fire is kindled, and the
leaves and young shoots, freshly plucked, are scattered in, and boiled
for about an hour. At the end of this time, they are thrown on to a
capacious sloping trough, the lower end of which projects into the pan,
and are squeezed with the hand so that the absorbed liquor may run back
into the boiler. The decoction is then evaporated to the consistence
of a thin syrup, and baled out into buckets. When sufficiently cool,
it is subjected to curious treatment: instead of simply stirring it
round, the workman pushes a stick of soft wood in a sloping direction
into each bucket; and, placing two such buckets before him, he works a
stick up and down in each. The liquid thickens round the stick, and,
the thickened portion being constantly rubbed off, while at the same
time the whole is in motion, it gradually sets into a mass, a result
which, it is said, would never be produced by simple stirring: it is
reasonable to suppose that this manner of treating the liquor favours
the crystallisation of the catechin in a more concrete form than it
might otherwise assume. The thickened mass, resembling soft yellowish
clay, is now placed in shallow square boxes; when somewhat hardened,
it is cut into cubes, and dried in the shade. The leaves are boiled a
second time, and finally washed in water, which is saved for another
operation.

A second plan is as follows:--The leaves are boiled, and bruised in a
wooden mortar (_lesong_), from which they are put into a kind of basket
of rattan open-work, which is pressed by a long piece of wood acting
as a lever; the liquid is received into a trough, and there allowed to
settle. When the sediment has acquired sufficient substance, it is put
into a _kulit-kayo_, formed like a tub without a bottom, which lets
the superfluous water drain off; when that is done, it is taken out,
made into small cakes, and dried for use. A plantation employing 5
labourers contains 70,000-80,000 shrubs, and yields 40-50 _catties_ (of
1-1/3 lb.) of gambier daily.

Plantations were commenced in Singapore in 1829, and once numbered 800;
but owing to scarcity of fuel, abundance of which is essential to the
manufacture, and dearness of labour, the culture was fast declining
in 1866. In 1872, it had much recovered. It is largely pursued on
the mainland (Johore), and in the Rhio-Lingga Archipelago, S.-E. of
Singapore; on Bintang, the most northerly of the group, there were 1250
plantations of it in 1854. None is cultivated in Sarawak, though found
wild in many parts; the foreign export from Sarawak in 1879 had a total
value of 88,148 dol. The best kind is brought largely from Sumatra,
but is often adulterated with sago. The Rhio product is also thus
sophisticated, and rendered heavier by the Chinese purposely packing
it in baskets lined with wet _cajangs_, occasioning a loss to the
purchaser of about 30 per cent.

Singapore is the great emporium for gambier, and exported 34,248 tons
in 1871, 19,550 tons having been imported, chiefly from Rhio and the
Malay Peninsula. In 1876, the export increased to over 50,000 tons of
pressed block, and 2700 tons of cubes. In 1877, it fell to 39,117 tons,
owing to differences with the Chinese dealers concerning adulteration;
of this quantity, 21,607 tons were for London, 7572 for Liverpool, and
2345 for Marseilles. The United Kingdom imports in 1872 were 21,155
tons, 451,737_l._, almost all from the Straits Settlements; in 1880,
they were 26,061 tons, 461,781_l._, from the Straits, and 352 tons,
6468_l._, from other countries; total, 26,413 tons, 468,249_l._ Our
re-exports in 1880 were:--2487 tons, 48,507_l._, to Holland; 1591 tons,
31,542_l._ to Germany; 1137 tons, 23,694_l._, to Russia; 594 tons,
12,026_l._, to other countries; total, 5809 tons, 115,769_l._ The
approximate London market values are 15_s._ 6_d._-21_s._ 6_d._ a cwt.
for block, 18-24_s._ for pressed cubes, and 23-27_s._ for free cubes.

=Hemlock.=--The bark of the hemlock or hemlock spruce (_Abies
canadensis_), of Canada and the United States, contains nearly 14 per
cent. of tannin. The stripping of the bark commences in the southern
parts of the United States in spring, and lasts during April-May;
in New York, Michigan, and Wisconsin, the season is June-July; and
farther north, it is still later. It is said that the best product is
obtained farthest south. The destruction of the hemlock forests is fast
approaching. Within the last 25 years, the preparation of an extract
from the bark, containing 18-25 per cent. of a deep-red tannin, giving
considerable weight and firmness to leather, has superseded the export
of crude bark. One mode of preparing the extract is as follows:--The
bark in pieces 1/2-1 in. thick, and several inches long, is soaked for
about 15 minutes in water at 200° F. (93° C.); it is then fed into
a hopper, which conducts it to a 3-roller machine, something like a
sugar-cane mill, through which it passes, coming out lacerated and
compressed; it next falls into a vat of hot water, where it is agitated
by a wheel, that the tannin from the crushed cells may be dissolved
in the water; hence it is raised by a series of buckets on an endless
chain, somewhat in the manner of a grain-elevator, to another hopper,
whence it is fed to another 3-roller mill; here it receives its final
compression, and comes out in flakes or sheets, like coarse paper, and
almost free from tannin. The buckets are made of coarse wire, that the
water may drip through during the elevation. In order to avoid the
blackening action of iron, wherever this metal will come into contact
with the solutions it is thickly coated with zinc. The solution is
evaporated to a solid consistency, generally by vacuum-pans. About
2 tons of bark are represented by 1 bar. (of less than 500 lb.) of
extract. The chief makers are A. S. Thomas, Elmira, N.Y.; S. Brown &
Co., New York; Canada Tanning Extract Co., St. Leonard and Bulstrode;
J. Miller & Co., Millerton, New Brunswick. The total production is
probably over 10,000 tons annually, ranging in value between 14_l._ and
20_l._ a ton. Our imports are included in barks and extracts.

=Kino= (Fr., _Kino_; Ger., _Kino_).--The term "gum kino" is applied
to a class of astringent extracts of varied origin, none of which can
accurately be called either resins or gums.

[Illustration:

  Pl. II.

  _E. & F. N. Spon, London & New York._  "INK-PHOTO" SPRAGUE & CO. LONDON.

REMOVING THE HAIR; SCRAPING AND CLEANING THE SKINS.]

(1) _East Indian or Amboyna Kino._--This is obtained from _Pterocarpus
Marsupium_, a common tree in the central and southern parts of the
Indian peninsula, and in Ceylon; and a liquid kind from _P. indicus_,
of South India, Burma, Malacca, Penang, the Andamans, and Malaysia.
The collection of the juice is effected in the following manner. A
perpendicular incision, with lateral offshoots, is made in the stem of
the tree when blossoming has set in, and a receptacle is placed at the
foot of the incision. The exuding juice appears like red-currant jelly,
but it soon thickens by exposure to the air, and when sufficiently
dried, is packed into wooden boxes for exportation. It is one of the
reserved timber-trees of the Government forests in Madras, and its
juice is collected by natives, who pay a small fee for the permission.
The hardened juice consists of blackish-red, angular, pea-like grains,
partially soluble in water, almost entirely in spirit of wine of sp.
gr. 0·838, readily in caustic alkaline solutions, and largely in a
saturated solution of sugar. The liquid kino produces a very inferior
article on drying. The annual collection of kino in Madras probably
does not exceed 1-2 tons. Its approximate London market value is
60-150_s._ a cwt. It is employed medicinally, and in the manufacture
of wines, and might be employed as a source of tannin in dyeing and
tanning, if sufficiently cheap.

(2) _Butea, Bengal, Palas or Dhak Kino._--This variety is afforded by
the _palas_ or _dhak_ tree (_Butea frondosa_), common throughout India
and Burma, and affording a dyestuff, and a fibre, as well as by _B.
superba_ and _B. parviflora_. During the hot season, there issues from
natural fissures and from wounds made in the bark of the stem, a red
juice, which quickly hardens to a ruby-coloured, brittle, astringent
mass. It occurs in small drops or tears, and in flat pieces which have
been dried on leaves, and is almost always mixed with bark-fragments.
It is transparent, freely soluble in cold water, and does not soften in
the mouth. It is unknown in European commerce, but is employed in India
as a substitute for the kind first described.

(3) _African or Gambia Kino._--This is derived from _Pterocarpus
erinaceus_, a native of Tropical West Africa, from Senegambia to
Angola. The juice exudes naturally from fissures in the bark, but more
abundantly from incisions, and soon coagulates to a blood-red and
very brittle mass, known to the Portuguese of Angola as _sangue del
drago_ ("dragon's-blood"). It is practically undistinguishable from
the officinal kind first described, but is not a regular article of
commerce.

(4) _Australian, Botany Bay, or Eucalyptus Kino._--Several species of
_Eucalyptus_ afford astringent extracts, those from the "red," "white,"
or "flooded" gum (_E. rostrata_), the "blood-wood" (_E. corymbosa_),
and _E. citriodora_, being quite suitable for replacing the officinal
kind. It is chiefly obtained by woodcutters, being found in a viscid
state in flattened cavities in the wood, and soon becoming inspissated,
hard, and brittle. Minor quantities are procured in a liquid state by
incising the bark of living trees, forming a treacly fluid yielding 35
per cent. of solid kino on evaporation. It is imported from Australia,
but there are no statistics to show in what quantity.

=Mimosa- or Wattle-bark.=--The bark of numerous species of _Acacia_,
natives of Australia, contains considerable percentages of deep-red
mimo-tannic acid, which forms a hard and heavy tannage if used strong,
though soft upper-leathers may be tanned with it in weak liquors. The
chief kinds are as follows:--The common wattle (_Acacia decurrens_),
including its variety _A. mollissima_, is known also under the names of
green, black, and feathery, but must not be confounded with the silver
wattle (_A. dealbata_), though but doubtfully a distinct species. The
bark is obtainable in vast abundance, and is much used by tanners. The
trees are stripped in September and the 2 or 3 months following, and
the bark, being allowed to dry, is then in a marketable condition. This
tree, which grows in the uplands, affords a larger percentage of tannin
than the silver wattle.

Blackwood or lightwood (_A. melanoxylon_) yields tanners' bark, which,
is inferior, however, to that from _A. decurrens_. The bark of _A.
penninervis_ yields of tannic acid 17·9 per cent., and of gallic acid
3·8 per cent. The bark of the native hickory (_A. suppurosa_) yields of
tannic acid 6·6 per cent., and of gallic acid 1·2 per cent.

The bark of _A. saligna_, of South-Western Australia, is much used
by tanners, as it contains nearly 30 per cent. of mimo-tannin. _A.
harpophylla_, of South Queensland, furnishes a considerable share
of the mercantile wattle-bark for tanning purposes. The bark of _A.
lophantha_ contains only about 8 per cent. of tannin.

The broad-leaved or golden wattle (_A. pycnantha_), of Victoria and
South Australia, deserves extensive cultivation. It is of rapid growth,
will succeed even in sandy tracts, and yields seed copiously, which
germinates with the greatest ease. The perfectly-dried bark contains
about 25 per cent. of tannin. The aqueous infusion of the bark can
be reduced by boiling to a dry extract, which in medicinal and other
respects is equal to the best Indian cutch. It yields approximately
30 per cent. of tannin, about half of which, or more, is mimo-tannic
acid. Probably no other tanning plants give so quick a return in
cultivation as the _A. pycnantha_ and _A. decurrens_ of Australia. The
latter varies in its proportions of tannin from 8 to 33 per cent. In
the mercantile bark, the percentage is somewhat less, according to the
state of its dryness, it retaining about 10 per cent. of moisture. The
bark of the silver wattle (_A. dealbata_) is of less value, often even
fetching only half the price of that of the black wattle. The bark
improves by age and desiccation, and yields 40 per cent. of tannin,
rather more than half of which is tannic acid.

Amongst all the kinds, the bark of the broad-leaved wattle is
considered the most valuable, containing the greatest quantity of
tannin; that of the silver wattle is not so valuable, being deficient
in tannin; the black wattle is considered the most productive species;
it can be barked at 8 years of age, and will produce 40-60 lb. dried
bark, and full-grown trees will yield 100-150 lb. per tree.

The cultivation of wattles for commercial purposes has till now
remained undeveloped; but no doubt, as soon as it is understood, the
utilisation of many acres of land lying waste, or which have already
been exhausted and rendered unfit for the growth of cereals, will
be effected by the cultivation of the wattle. It requires so little
attention as to make it very profitable, and wattle-growing and grazing
can be combined satisfactorily. After the first year, when the young
trees in the plantation have reached the height of 3-4 ft., sheep can
be turned in.

Wattles grow in almost any soil, even the poorest, but their growth
is most rapid on loose sandy patches, or where the surface has been
broken for agricultural purposes. When the soil is hard and firm,
plough furrows should be made at a regular distance of 6-8 ft. apart,
into which the seeds are dropped. The seed should be sown in May,
having been previously soaked in hot water, a little below boiling
temperature, in which they may be allowed to remain for a few hours.
The seed should be dropped at an average distance of 1 ft. apart along
the furrow, in which case, about 7200 seeds would suffice for one acre
of land. The seed should not be covered with more than about 1/4 in. of
soil.

On loose sandy soil, it might even be unnecessary to break up the
soil in any way; the furrows may be dispensed with, and the seed sown
broadcast after the land is harrowed. After the plants have come up,
they should be thinned so that they stand 6-8 ft. apart. When the
young trees have attained the height of 3-4 ft., the lower branches
should be pruned off, and every effort afterwards made to keep the
stem straight and clear, in order to facilitate the stripping, and
induce an increased yield of bark. It is advisable that the black and
broad-leaved should be grown separately, as the black wattle, being
of much larger and quicker growth, would oppress the slower-growing
broad-leaved one. Care should be taken to replace every tree stripped
by re-sowing, in order that there should be as little variation in the
yield as possible. The months of September-December, in Victoria, are
those in which the sap rises without intermission, and the bark is
charged with tannin. Analysis proves that the bark from trees growing
on limestone is greatly inferior in tannin to that obtained from other
formations, differing 10-25 per cent.

The estimated expenditure on a wattle-bark plantation of 100 acres
during 8 years is:--

                                                              £   _s._ _d._

  Rent of 100 acres for 8 years at 6_s._ per acre per annum   240   0    0
  Ploughing 100 acres in drills 10 ft. apart                   25   0    0
  Sowing wattles and actual cultivation, including cost
    of seed                                                    37  10    0
  Supervision for 8 years (nominal), say 10_l._ per annum      80   0    0
  Pruning the trees, taking off useless wood (necessary
    for 2 years), 10_s._ per annum                             50   0    0
  Incidental and unforeseen expenses                           27  10    0
  Interest on the whole amount expended during 8 years        240   0    0
                                                             ─────────────
                                                              700   0    0
  Actual cost of stripping and carting, as shown below       1515   0    0
                                                             ─────────────
                                                            £2215   0    0
                                                             ─────────────

The receipts derivable from a wattle plantation of 100 acres,
planted in the manner proposed, would be:--

                                                              £   _s._ _d._

  Each acre planted with wattles, 10 ft. apart, would
    carry 400 trees, and at end of 5th year trees would
    yield say 56 lb. matured bark: stripping only
    every 3rd tree, 332 trees would be obtained off
    100 acres: this, at 4_l._ per ton, would give for
    1st stripping                                            1332   0    0

  In the 6th or following year, a similar number of
    trees would be stripped: the bark having increased
    in weight (say 14 lb.), the increased yield of 2nd
    stripping would be 400 tons at 4_l._ per ton             1600   0    0

  In the 7th year, the remaining trees would be
    stripped, from which a still greater increase would
    be obtained, say 480 tons at 4_l._ per ton               1920   0    0

  Total yield of bark                                        4852   0    0

  The cost of stripping would not exceed 15_s._ per ton,
    on account of the facilities presented by the
    regularity of the trees, while carting would represent
    another 10_s._ per ton: these combined
    charges would be 25_s._ per ton, and on 1215 tons,
    would be                                                 1515   0    0
                                                             ─────────────
  Leaving a clear profit on the 100 acres of                £2637   0    0
                                                             ─────────────

The exports of mimosa-bark in 1876 were 11,899 tons from Victoria,
4758 from South Australia, and 1735 from Tasmania. Later returns are
included in barks, p. 39. Shanghai imported 7038 _piculs_ (of 133-1/3
lb.) in 1879. The approximate London market values of mimosa-bark
are:--Ground, 6-13_l._ a ton; chopped, 5-12_l._; long, 5_l._-9_l._
10_s._ A very superior extract has been made from this bark.

=Myrobalans or Myrabolams.=--The fruits of several species of
_Terminalia_ constitute the myrobalans of commerce; they are chiefly
_T. Chebula_ and _T. Bellerica_, natives of India, the former being
a tree 40-50 ft. high, and esteemed for its timber also. The fruits
contain 30-35 per cent. of gallotannic and ellagitannic acids,
producing a soft and porous tannage, and good samples giving a
bright-yellow colour. The tannin exists in the pulp, and is absent from
the very hard "stone." The dried fruits are known locally as _har_,
_harra_, or _bahera_, and are used commonly for dyeing, but not for
tanning.

Our imports of myrobalans in 1880 were:--238,151 cwt., 121,465_l._,
from Bombay and Sind; 115,670 cwt., 51,339_l._, from Madras; 11,020
cwt., 4717_l._, from Bengal and Burma; 3520 cwt., 1402_l._, from other
countries; total, 368,361 cwt., 178,923_l._ Our re-exports in 1880
were 8015 cwt., 4328_l._, to Germany; 16,127 cwt., 8515_l._, to other
countries; total, 24,142 cwt., 12,843_l._ The approximate London market
values of myrobalans are 7-14_s._ a cwt. for good, and 5-10_s._ for
common. Shanghai imported 4403 _piculs_ (of 133-1/3 lb.) in 1879.

=Oak-barks= (Fr., _Écorces de Chêne_; Ger., _Eichenrinden_).--The barks
of several species of oak have valuable tanning properties. They are
chiefly:--The common oak (_Quercus Robur_, varieties: _sessiliflora_,
Ger. _Traubeneiche_; _pedunculata_, Ger. _Stieleiche_), which is of
even greater importance as a timber-tree; the cork-oak (_Q. Suber_);
the evergreen oak (_Q. Ilex_); and the American chestnut-oak (_Q.
Castanea_). These barks are among the most esteemed tannins as regards
quality of leather, but are incapable of giving much weight, and from
their bulk are costly to handle, containing only 10-12 per cent. of
tannin (quercitannic acid). They give a reddish fawn-coloured leather,
and deposit a good deal of bloom, but yield little or no gallic acid.
The barks of the cork-oak and evergreen oak from Southern Europe,
are stronger and darker-coloured than English bark. The American
chestnut-oak contains a peculiar fluorescent principle like æsculin.

Our imports of unspecified barks for tanners' and dyers' use in 1880
were:--189,399 cwt., 101,108_l._, from Australia; 123,302 cwt.,
32,974_l._, Belgium; 57,232 cwt., 20,988_l._, United States; 22,100
cwt., 6030_l._, Holland; 18,648 cwt., 3676_l._, Italy; 16,151 cwt.,
6972_l._, Algeria; 22,669 cwt., 8838_l._, other countries; total,
449,501 cwt., 180,586_l._ Our imports of unenumerated bark-extracts in
the same year were valued at:--516,578_l._ from Holland, 92,654_l._
France, 30,187_l._ United States, 16,315_l._ British North America,
12,796_l._ Belgium, 13,769_l._ other countries; total, 682,299_l._ Our
re-exports of barks in 1880 were:--19,548 cwt., 10,348_l._, to Germany;
14,627 cwt., 7425_l._, France; 4555 cwt., 3041_l._, Holland; 10,304
cwt., 6080_l._, other countries; total, 49,034 cwt., 26,894_l._

With regard to cork-tree bark, James Gordon & Co., Liverpool,
obligingly write that very little comes to England, the great bulk
going direct to Ireland, where the consumption is large. The imports
at Liverpool in 1880 were 186 tons, average value 8_l._ per ton. Of
oak-bark, Hungary, in 1877, produced 25,000 tons, of which, 20,000
were exported to Germany for tanning purposes. The approximate London
market values of oak-bark are:--English, 12-16_l._ per load of 45 cwt.;
Foreign, tree, 5-8_l._ a ton; ditto, coppice, 6-8_l._ In 1879, Algiers
exported 12,660,047 _kilo._ (of 2·2 lb.) of tanning bark.

=Quebracho.=--The local name _quebracho_, contracted from
_quebra-hacho_ ("axe-breaker"), is applied to several South American
trees possessing hard wood, belonging to distinct genera. They are
chiefly as follows:--(1) _Aspidosperma Quebracho_, the _quebracho
blanco_, a tree growing in the province of Catamarca, Argentine
Republic; (2) _Loxopterygium_ [_Quebrachia_] _Lorentzii_, the
_quebracho colorado_, most prevalent in the province of Corrientes, the
wood and bark of which come largely into commerce as tanning materials;
(3) _Iodina rhombifolia_, the _quebracho flojo_, whose wood and bark
are mixed with those of No. 2; (4) _Machærium fertile_ [_Tipuana
speciosa_], the _tipa_, which affords both wood and bark of less
tanning value than No. 2. It would seem that the wood and bark of No.
2 are by far the most largely employed, containing 15-23 per cent. of
a bright-red tannin. The wood and an extract from it are imported into
Europe.

From information kindly furnished by James Gordon & Co., and Haw &
Co., of Liverpool, it appears that the imports of quebracho-wood into
Liverpool in 1880 were 200 tons, value about 4_l._ 10_s._ a ton; and of
quebracho-bark, about 20 tons, none of which had been sold.

=Sumach or Shumac= (Fr., _Sumac_; Ger., _Gerbersumach_,
_Schmack_).--The commercial term "sumach" is applied to the dried
leaves of a number of South European and American tannin-yielding
plants. These are chiefly as follows:--In Sicily, the European or
tanning-sumach (_Rhus Coriaria_); in Tuscany, _R. Coriaria_, often
adulterated with leaves of _Pistacia lentiscus_; in Spain, several
_Rhus spp._, the products being divided into 3 kinds--Malaga or Priego,
Malina, and Valladolid; in the Tyrol, the smoke-tree or fragrant or
Venetian sumach (_R. Cotinus_); in France, _Coriaria myrtifolia_,
divided into 4 sorts--_fauvis_, _douzère_, _redoul_ or _redon_, and
_pudis_; in Algeria, Tezera sumach (_R. pentaphylla_), used by the
Arabs for making morocco-leather; in North America, the smooth or
white sumach (_R. glabra_), the Canadian sumach (_R. canadensis_), the
staghorn sumach (_R. typhina_), and the dwarf or black sumach (_R.
copallina_). These are found growing wild in the countries indicated,
and are further subjected to cultivation in some districts, notably
in Sicily. _R. glabra_ and _R. copallina_ are recommended chiefly for
extended cultivation in the United States.

The soil usually chosen for cultivation of the plants is poor and
light; but a much larger crop of leaves can be secured from strong,
rich, deep soils, and it is generally admitted that the product in the
latter case is also better. In Italy, limestone soils are considered
to be especially suited to this culture, but the American varieties
appear to be well adapted to sandy and clay soils as well. The primary
requisite in a soil is that it shall be well drained, the presence
of stagnant water about the roots being exceedingly prejudicial. To
prepare the soil for planting, it is ploughed as deeply as possible,
and laid out in rows about 2 ft. apart. In Italy, small holes are made
about 2 ft. long, 7 in. wide, and 5 in. deep, and a plant is inserted
at each end. A more convenient method would consist in marking the
field in shallow furrows in one direction 2 ft. apart, and then, with
a heavy plough, tolerably deep furrows the same distance apart as, and
at right angles to, the first. A plant may then be placed in the deep
furrows at each intersection, the furrow again filled with the plough,
and the earth pressed about the plant with the foot. If this were done
in early spring-time, as soon as the earth is sufficiently dry to be
conveniently worked, there can be no doubt that it would be successful,
while it would certainly involve little cost. Plants are generally
propagated from the young shoots which form each year about the base of
an older plant, but may also be produced from cuttings made from young
well-ripened wood, rooted by setting in a nursery or in frames, as in
the propagation of grape-vines from cuttings. This latter method is
scarcely ever required, however, when the cultivation has been started.
Plants are also raised from seed, and seedlings are always found to
be strong, vigorous, and thoroughly hardy; but on account of the
greater time and labour involved in their production, this method of
propagation has not received extended application. The first-mentioned
generally gives the quickest, and probably most satisfactory results.

In selecting plants from any source, there are certain points to be
observed:--(1) The shoots should come from young vigorous plants; (2)
they should be over 1 ft. long; (3) those with large roots and few
rootlets should be rejected; (4) those having white roots, covered with
a fibrous, white, silky down, are also to be rejected, this being an
indication of the presence of a very injurious subterranean parasitic
fungus, capable of destroying the entire crop; (5) a good shoot is
straight, at least 1/2 in. diam., 18 in. long, furnished with numerous
buds close to each other, root short, but covered with rootlets. Shoots
for planting may be collected in autumn, after the leaves have fallen,
and be preserved in a nursery until spring; or this may be done in
early spring, when the ground is very moist and soft. In either case,
care should be observed that the rootlets are not injured by drying, or
from any other cause.

The culture to be given the plant is somewhat similar to that required
by Indian corn: the earth about it should be kept tolerably mellow
and free from weeds, and such conditions can probably be maintained
to a degree sufficient for sumach, by working several times during
the growing season with a cultivator, and passing through the rows
occasionally with a plough. All this work is not absolutely necessary
to the life of the plant, but its vigour, and consequently its yield in
leaves, may be considerably increased and strengthened thereby. After
the first year, the number of operations may be diminished, but they
should always be sufficient to keep the ground free from weeds and
grass.

Shortly after planting, and when the plant is well set, the stock is
pruned to a length of 6-8 in., when the plant is left to assume any
form, and is no further pruned except by the process of collecting the
leaves, unless hand-picking is resorted to; in such case, after the 2nd
year, pruning takes place each year in the fall or winter, the plant
being reduced to a height of 6-10 in. After the 3rd year, the plant
begins to produce the shoots from about its base, already mentioned;
these, if not needed for new plantations, should be removed each year,
for if left to develop, they weaken the plant. If not removed during
the summer, the operation should without fail be effected during the
fall or winter.

The 1st crop of leaves may be secured during the year following that
of planting. This develops and matures somewhat later than that from
older plants, and in Italy it is not collected until the end of August
or the 1st of September; but there are reasons for believing that in
the United States, especially in the Northern States, the collection of
leaves from native varieties should be made much earlier, because the
summer is much shorter, and the habits of the varieties grown differ
from the Sicilian. Macagno has shown (Chem. Soc. Journ., xxxviii., p.
733) that the leaves from the upper side of the branches contain much
more tannin than those below, and that especially in the lower leaves
the percentage of tannin is much higher in June than in August. All
the leaves, except the young and tender ones of the extremities of the
branches, are stripped off and placed in baskets, in which they are
carried to a threshing-floor, where they are spread out in thin layers
to dry. Here they must be frequently stirred and turned over, for which
purpose a fork with wooden prongs is employed. In the fall, when growth
is finished, and before the leaves have had time to become red, those
remaining on the extremities are collected. To this end, the branches
are broken just below the tuft of leaves, and the latter are allowed
to remain suspended from the branch by a piece of bark not detached,
and left in this condition until nearly or quite dry. They are then
collected and treated in the same manner as other leaves, but the
product obtained in this way is always of inferior quality.

After the 2nd year, crops of larger quantity and superior quality are
obtained, and the collection is made in a different way, and much
more frequently. The two methods followed in Sicily are (1) pruning,
and (2) defoliation. The first, which is the more ancient, but much
less costly, requires less care, and is simple and rapid; but it is
injurious to the future condition of the plant, and the quantity of
subsequent crops. The second, though slower, serves to better maintain
the vigour of the plant, and the uniform quantity of the crop from
year to year; in consequence, it reduces the necessity for frequent
renewal of stocks.

Harvest by pruning is carried on in Italy as follows. During May,
the lower leaves, which, from greater age, appear to have attained
full maturity, and may be in danger of loss from falling, are removed
in the same manner as described for collecting the leaves from
yearling plants. Toward the end of June, and during the course of
July, all branches bearing leaves are cut away, reducing the plant
to the principal stock: by this means, the crop is harvested and the
plant is pruned at the same time. But even in Sicily, the time for
this operation is limited to no absolute period, and varies with
the development of the leaf, as indicated by cessation of growth
and increase in size. In this condition, also, the leaves will have
acquired their deepest green colour, and attained their maximum weight
and best quality. It is further stated that while this time varies
according to locality, about Palermo it is never earlier than June nor
later than July. The harvest by pruning must always be made by men
accustomed to the work, and equal to the exertion required. Provided
with a pruning-bill, they cut off all leaf-bearing branches, collecting
them an the left arm, until each has cut as much as he can conveniently
carry, when he places the armful on the ground with the butts in the
direction of the prevailing wind, which, if tolerably strong, might
carry away some of the leaves if turned in the opposite direction;
finally, he presses down the branches with his foot, to make the heap
more compact, and leave less surface exposed to the wind and sun.
Another labourer deposits a second armful in the same place, presses it
with his foot in like manner, and the two deposits constitute a bundle.
At the close of the operation, there remain the young shoots which are
formed about the base of the plant, the leaves of which are not fully
developed, and consequently not fit for collection until at least 20
days later. After this time, they are removed by hand, care being
observed not to injure the buds, especially if the shoots are to be
used for stocks in the formation of plantations in the following year.

Defoliation, or collection by hand, is carried on whenever the leaf
may be fully developed and ripe, beginning at first with the lower
leaves, and continuing eventually to the ends of the branches. It takes
place at 3 different times during the season: the 1st in May, the 2nd
late in July or early August, and the 3rd in September. At the last
collection, the extremities of the branches are broken down, and the
leaves are allowed to dry before removal from the plant, as described
under collections of the 2nd year. In the application of this method,
the regular pruning is effected during the fall or winter, when the
plant is dormant, and under such conditions the operation becomes a
regenerative one, giving in this particular an advantage over the other
method, in which the pruning is effected in the summer when the plant
is in full vegetative activity, and so has a strongly deteriorating
influence. In both methods of pruning, care should be observed to leave
a long slanting section, upon which water will be less likely to settle
and promote decay.

The leaves collected by either method are dried in the open field where
they have grown, and when dried, are carried to a threshing-floor to
be beaten, or at once to the threshing-floor and dried there. In the
former, the operation is rather more rapid, but there is greater danger
of injury by rain, the effect of which is very deleterious, especially
if it fall upon the leaves when they are partially dried. The damage
resulting from this cause is less if the leaves are not lying upon the
ground, and are so arranged that the air may circulate freely about
and under them. In the pruning method, the leaves are dried upon the
branches and in the heaps where they are first deposited. Sometimes
they are turned, but generally it is considered better not to disturb
them until completely dried, and ready for transportation to the
threshing-floor. In this way, they are protected to a greater extent
from the action of direct sunlight, which is said to be injurious to
the quality of the product. When the leaves are collected by hand,
they are dried upon the threshing-floor, where they are spread in
thin layers, and stirred 3-4 times a day. They are then beaten with a
flail to separate the leaves from the branches and stems. If this be
done during the middle of the day, when the leaves are most thoroughly
dry and consequently brittle, they are reduced to small particles,
producing what is called "sumach for grinding." But if it be done in
the morning, or on damp days, when the air is charged with moisture and
the leaves are tough, they are separated from the stems more nearly
entire and less broken, and the product obtained is called "sumach for
baling." The stems remaining after the separation of sumach for baling
still retain small particles of leaves attached to them, and they are
therefore again beaten when perfectly dry for the production of a
low-grade sumach, called by the Italians _gammuzza_. The products are
classed as follows:--

                                 Relative Market
                                      Value.

  Sumach for baling                    2·5
    "     "  grinding                  2·3
    "    from yearling plants          1·5
    "     "   ends of branches      }
                collected in autumn }  1·0

To prepare these different grades for ultimate consumption, they are
ground in mills similar to those employed for crushing olives, that
is, in which two large stone wheels follow each other, revolving upon
a circular bed, the whole construction being about the same as the
Spanish or Mexican _arrastre_. The sumach thus pulverised is passed
through bolting-screens, to separate the finer from the coarser
particles.

In Virginia, the leaves are collected and cured by the country
people, and sold and delivered to owners of mills for grinding. Their
particular object being to secure the largest possible quantity of
product at the lowest cost, little attention is given to the quality
obtained, or the manner of collecting. The most intelligent dealers
in the raw material urge upon collectors to observe the following
particulars:--The leaf should be taken when full of sap, before it
has turned red, has begun to wither, or has been affected by frost, to
ensure a maximum value for tanning purposes. Either the leaf-bearing
stems may be stripped off, or the entire stalk may be cut away, and
the leaves upon it allowed to wither before being carried to the
drying-shed; but care must be observed that they are neither scorched
nor bleached by the sun. When wilted, they are carried to a covered
place, and spread upon open shelving or racks to dry, avoiding the
deposit in any one place of a quantity so great as to endanger the
quality of the product by overheating and fermentation. Sumach should
be allowed to remain within the drying-house at least one month before
sending to the market; in case of bad weather, a longer period may be
required. When ready for packing for shipment, it should be perfectly
dry and very brittle, otherwise it is likely to suffer injury in
warehouses from heating and fermentation.

Buyers of sumach leaves for grinding depend largely upon colour for
the determination of the value; the leaves should, therefore, when
ready for market, present a bright-green colour, which is evidence that
they have suffered neither from rain after being gathered, nor from
heating during the process of drying. Leaves having a mouldy odour or
appearance are rejected. The Virginian crop reaches 7000-8000 tons, and
is collected at any time between July 1 and the appearance of frost.

There is an important difference in the value of the European and
American products. The proportion of tannic acid in the latter
exceeds that found in the former by 6-8 per cent., yet the former is
much preferred by tanners and dyers. By using Sicilian sumach it is
possible to make the finer white leathers, in great demand for gloves
and fancy shoes; while by the employment of the American product, the
leather has a disagreeable yellow or dark colour, apparently due to a
colouring matter, which, according to Loewe, consists of quercitrin and
quercetin, and exists in larger quantity in the American than in the
Sicilian.

The experimental results obtained by collecting sumach at different
seasons were:--

                                               Per Cent. of
                                               Tannic Acid.

  Virginia, mixed,   collected in June, gave      22·75
     "        "           "       July,           27·38
     "      _R. glabra_    "      August, "       23·56
     "      _B. copallina_ "        "     "       16·99
  Sicilian, _B. Coriaria_  "        "     "       24·27

It is evident, therefore, that in order to secure the maximum amount of
tannic acid, the sumach should be collected in July, but the colouring
matter of the leaves has an important influence upon the value of the
product. The leaves of the upper extremities of the stalks are always
richer in tannic acid than those of the base; and the increase of age
of the plant is accompanied by a general diminution of this acid. Yet
the collection of the crop should be delayed as long as possible,
because the diminution of tannin in the leaves will be abundantly
compensated for by the quality of the product.

Experiments upon the presence of colouring matters were made by
treating gelatine solutions, and gave the following results:--

  Virginia, mixed,   collected in June, gave   A nearly white precipitate.
     "        "             "     July,  "     A decidedly yellowish-white
                                                 precipitate.
     "      _R. copallina_, "     August "     A dirty-yellow precipitate.
     "      _B. glabra_,    "       "    "     A very dirty-white
                                                 precipitate.
  Fredericksburg mixed,     "       "    "     A dirty-yellow precipitate.
  Sicilian                  "       "    "     A slightly yellowish-white
                                                 precipitate.

It is therefore advised that for the purpose of tanning white and
delicately-coloured leathers, the collection should be made in
June; while for tanning dark-coloured leathers, and for dyeing and
calico-printing in dark colours, where the slightly yellow colour will
have no injurious effect, the collection be made in July. It appears
that for all purposes, the sumach collected after the 1st of August is
inferior in quality.

[Illustration: Fig. 8.]

Fig. 8 shows a mill for grinding sumach-leaves; it consists of a heavy
solid circular wooden bed _a_, 15 ft. diam., with a depression around
the edge _b_, a few inches deep and 1 ft. wide, for the reception
of the ground sumach from the bed, and 2 edge-rollers _c_, weighing
about 2500 lb. each, 5-6 ft. diam., and provided with numerous teeth
of iron or wood, thickly inserted. Most mills have to be stopped to
allow the unloading of the bed, but this delay is obviated by an
apparatus consisting of an angular arm _d_, attached to a scraper _e_,
and worked by a lever _f_, which passes through the hollow shaft _g_
and extends to the room above, where it terminates in a handle _h_.
The scraper carries the ground sumach to the opening _i_, whence it is
taken by an elevator to a revolving sieve or screen in a room above.
After screening, the sumach is packed in bags, 15 to the ton, being
always sold by that weight. The chasers and beds are inclosed in a
case or drum, and the grinding is done by the application of power to
the upright shaft _g_. The mills are fed from above. The packing is
sometimes done by machinery alone. The best mills cost about 600_l._
In Europe, and in some parts of the Southern States, sumach is still
ground by stones revolving on a stone bed, and the sifting is often
done by hand.

E. Coez & Co., St. Denis, near Paris, make a sumach extract. It is
concentrated to a syrupy consistence in a vacuum-pan, and keeps
well, exhibiting none of the acidity which is manifested by a simple
decoction of sumach leaves. Sumach contains 16-24 per cent. of
gallotannic acid, and is somewhat similar in tanning properties to
myrobalans, but paler in colour. It is principally used for tanning
morocco and other fancy leathers.

The district of Ancona yields 200 tons per annum of sumach, said to be
equal to and cheaper than the Sicilian, but mostly consumed locally.
Palermo exported of "ventilated" sumach to the United States 120,043
bags (14 = 1 ton) in 1877, and 50,085 in 1878, the average value being
14_l._ a ton. Trieste exported 7800 cwt. by land in 1877; in 1878,
the shipments to England were 16,600 _kilo._ (of 2·2 lb.), value 1328
fl. (of 2_s._), and in 1880, 91,800 _kilo._ 7344 fl. Rustchuk in 1880
exported 1400 tons, chiefly to Roumania and Austria. Our imports
in 1880 were 10,573 tons, 133,249_l._ from Italy, and 1047 tons,
12,416_l._, from other countries; total, 11,620 tons, 145,665_l._ The
approximate London market value is 15_s._-16_s._ 6_d._ a cwt. for
Sicilian, 10-11_s._ for Spanish.

=Valonia= (Fr., _Vélanèdes_; Ger., _Valonia_). This is the commercial
name for the large pericarps or acorn-cups of several species or
varieties of oak, chiefly _Quercus Ægilops_ and _Q. macrolepis_. The
former is found growing in the highlands of the Morea, Roumelia,
the Greek Archipelago, Asia Minor, and Palestine; the latter
constitutes vast forests in many parts of Greece, and especially on
the lower slopes of Taygetos, towards Ætylon and Mani (Laconia). Prof.
Orphanides, of Athens, alludes to a third species or variety called
_porto galussa_, which yields a superior kind of valonia, and named
by him _Q. stenophylla_. The chief localities of production in Asia
Minor are Ushak, Borlo, Demirdji, Ghiördes, Adala, Nazlü, Buldur,
Sokia, Balat, Troja, Aivalik, and Mytilene. The annual exports,
mainly from Smyrna, reach 600,000 _quintals_ (of 2 cwt.), value about
400,000_l._ In Greece, the production is chiefly centred in the
following districts: (1) The province of Lacedemonia, which afforded
10,000 cwt. in 1872; (2) the province of Gythium, in the lower part of
Mount Taygetos, which gave 60,000 cwt. in 1872; (3) the island of Zea,
which formerly yielded 30,000-40,000 cwt., lately reduced to 15,000
cwt. yearly; (4) Attica, especially the neighbourhood of Cacossalessi,
grows 3000-5000 cwt., shipped from Oropos, in the Strait of Chalcis;
(5) the island of Eubœa, whence about 1000 cwt. are shipped annually
at Bouffalo; (6) the province of Triphyllia raises 3000 cwt., which go
to Trieste, viâ Cyparissie; (7) the province of Pulos, especially the
commune of Ligudista, grows over 2000 cwt., despatched from Navarino to
Trieste; (8) the province of Achaia has a yearly crop of 30,000-40,000
cwt., shipped to Trieste from Courupeli and Caravostassi, between
Patras and Cape Papa; (9) the small towns of Anatolico and Astakos
(Dragomestre) collect the valonia of the eastern parts of Ætylon,
Acarnania, and Cravassaras (a port in the Gulf of Arta), and of all
the other western parts, to be sent to Trieste for shipment to England
and Italy. Ætolia and Acarnania furnish abundant crops, that of 1872
exceeding 100,000 cwt. The total area of the Greek valonia-yielding
forests is said to be about 13,000 _stremme_ (of 119-1/2 sq. yd.). The
total production in 1877 was estimated at 2,601,000 _quintals_ (of
2 cwt.); the greater part is exported, about 2/3 going to Austria,
and the rest to Italy and England. The proportions of tannic acid in
the valonia from different districts of Greece are said to vary as
follows: Patras, 19-28-1/2 per cent.; Gythium, 27-1/4-35-1/2; Zea,
12-1/4-25-1/4; Vonitza, 18-20.

In Turkey, the fruit ripens in July-August, when the trees are beaten,
and the fallen acorns left on the ground to dry. The natives afterwards
gather them, and transport them on camel-back to stores in the towns,
whence they go by camel and train to Smyrna, and are there placed in
heaps 5-6 ft. deep in large airy stores for some weeks, during which
the mass heats, and the acorn itself, which contains but little tannin,
and is used for feeding pigs, contracts and falls from the cup. This
incipient fermentation is attended with considerable risk; if carried
too far, a large proportion of the valonia becomes dark-coloured and
otherwise damaged. When ready for shipment, the heaps are hand-picked,
the best being reserved for the Austrian market (Trieste), and the rest
going to England. In some cases, the rubbish having been removed, the
remainder is known as "natural," and is thus exported to England.

In Greek commerce, three qualities are distinguished, _chamada_,
_rhabdisto_, and _charcala_. The _chamada_ (_camata_ and _camatina_
of Asia Minor) is the best; it is collected in April, before the
acorn is matured, hence the cup which encloses the acorn is small and
incompletely developed. The _rhabdisto_ is the second quality; it is
collected in September-October, and is distinguished by the fruit being
larger and riper; the name means "beaten," the fruits being beaten
down from the trees with sticks. After mid-October the collection
ceases, because the first rains cause the fallen fruit to ferment
or turn black, and they then take the name of _charchala_. They are
distinguished by the cups being completely open, and containing no
acorns. They are considered much inferior, possessing little tannin.

[Illustration: Pl. IV.

_E & F. N. Spon, London &. New York._

"INK PHOTO". SPRAGUE & CO LONDON

REVOLVING, WASHING AND PRESSING MACHINES.]

Sometimes the acorn cup is attacked by a kind of honey-dew, which
deposits on the cup, and makes it very liable to heat when gathered,
the cup becoming very dark and deficient in tannin. The Turkish crop of
1875 was much damaged from this cause, many parcels reaching England in
an unsaleable condition. The cause of the disease is yet unknown; it
seems specially prevalent when the crop is large and the acorn fully
developed. A good sample of valonia should be composed of medium-sized
cups, with the rim or wall very thick, and the exterior spines small
and uniform. The cut or broken cup should show a bright-drab fractured
surface. Valonia contains 25-35 per cent. of a tannin somewhat
resembling that of oak-bark, but giving a browner colour and heavier
bloom. It makes a hard and heavy leather, and is generally used in
admixture with oak-bark, myrobalans, or mimosa-bark.

The Greek crop in 1880 was much damaged by the cold spring: It gave
600 tons in Acarnania and Ætolia, 650 in Cape Papa, and 1400 in Mania;
total, 2650 tons. Calamata and Messenia produced 115 tons, 1700_l._
Syra exported in 1879, 1174_l._ worth to Great Britain, 348_l._
Austria, 259_l._ Russia, 250_l._ Turkey, 178_l._ Egypt. Hungary
exported 942 tons in 1880. Adana shipped 9450_l._ worth in 1878; and
Dedeagatch, in the same year, 1,500,000 lb., 9000_l._ Musyna [Mersineh]
sent 670 tons, 3350_l._, to Italy, and 450 tons, 2250_l._ to Austria,
in 1879; and 480 tons, 2240_l._, to Italy, and 128 tons, 640_l._, to
Greece, in 1880. Our imports in 1880 were:--From Turkey, 30,391 tons,
471,637_l._; Greece, 2916 tons, 41,312_l._; other countries, 466 tons,
7105_l._; total, 33,773 tons, 520,054_l._ The approximate London
market values are:--Smyrna, 12_s._ 6_d._-20_s._ 6_d._ a cwt.; Camata,
15_s._-19_s._; Morea, 10_s._ 6_d._-18_s._

=Miscellaneous.=--Besides the foregoing tannins, which already occupy
prominent places in European and American commerce, there are many
others as yet of minor importance, but possessing qualities which may
bring them into note in the near future. They are as follows:--

_Abies Larix_ bark, the larch, contains 6-8 per cent. of a red tannin.

_Acacia albicans_ fruits, the _hiusache_ of Mexico, are used as
substitutes for gall-nuts, costing locally about 5_d._ a lb. _A.
arabica_, the _babul_ of India, yields a tannin which gives a nearly
pure-white precipitate with gelatine: the proportions are 12·55 per
cent, in trunk-bark, 18·95 in branch-bark, 15·45 in twig-bark. The
supply is unlimited. It works well with myrobalans. _A. Cebil_, the red
cebil of the Argentine Republic, contains 10-15 per cent. of tannin in
the bark, and 6-7 per cent. in the leaves; another variety, the white
cebil, contains 8-12 per cent. in the bark, and 7-8 per cent. in the
leaves. _A. Cavenia_, the _espinillo_ of the Argentine Republic, has
33-34 per cent. of tannin in the fruit-husks. _A. penninervis_ bark,
the "hardy" acacia of Australia, contains 18 per cent. of tannic acid
and 3-4 of gallic.

_Alnus glutinosa_ bark, the common alder, contains about 16 per cent.
of tannin.

_Cœsalpinia Cacalaco_ fruits, the _cascalote_ of Mexico, are very rich
in tannic and gallic acids, and are locally used for tanning.

_Comptonia asplenifolia_ leaves, the sweet-fern of the United States,
contain 9-10 per cent. of tannin.

_Coriaria ruscifolia_ bark, the _tutu_ of New Zealand, contains 16-17
per cent. of tannin.

_Elæocarpus dentatus_ bark, the _kiri-hinau_ of New Zealand, contains
21-22 per cent. of tannin. _E. Hookerianus_ bark, the _pokako_ of New
Zealand, contains 9-10 per cent. of tannin.

_Ephedra antisyphilitica_, on the tablelands of Arizona and Utah, gives
11-12 per cent. of tannin.

_Eucalyptus longifolia_ bark, the "woolly-butt" of Australia, contains
8·3 per cent. of tannic acid, and 2·8 of gallic. The "peppermint"-tree
contains 20 per cent. of tannic acid in its bark. The "stringy-bark"
(_E. obliqua_) gives 13-1/2 per cent. of kinotannic acid. The Victorian
"iron-bark" (_E. leucoxylon_) contains 22 per cent. of kinotannic acid,
but is available only for inferior leather.

_Eugenia Maire_ bark, the _whawhako_ of New Zealand, contains 16-17 per
cent. of tannin. _E. Smithii_ bark, the "myrtle"-tree of Australia,
contains 17 per cent. of tannic acid and 3-4 of gallic.

_Fuchsia macrostemma_ root-bark is thin, brittle, and easily exhausted;
it contains about 25 per cent. of a bright-red tannin, which has been
successfully tried. It is the _churco_ bark of Chili, which, however,
is attributed by the Kew authorities to _Oxalis gigantea_.

_Inga Feuillei_ pods, the _pay-pay_ of Peru, contain 24 per cent. of an
almost colourless tannin.

_Laurus Peumo_ rind is used in Chili for tanning uppers.

_Malpighia punicifolia_ bark, the _naucite_, or _manquitta_ bark of
Nicaragua, contains 20-30 per cent. of a very light-coloured tannin.

_Persea Lingue_ bark is red-brown, soft, and easily exhausted by
water; it contains 20-24 per cent. of tannin, and much slimy matter
which promotes the swelling of the hides. It serves in South America,
especially in the Chilian province of Valdivia, for tanning Valdivia
leather. In Southern Chili are enormous forests of the tree. The
imported bark has given good results with heavy leathers.

_Phyllocladus tricomanoides_ bark, the _kiri-toa-toa_ of New Zealand,
contains 23 per cent. of tannin.

_Polygonum amphibium_ leaves, an annual plant abundant in the Missouri
Valley, contain 18 per cent. of tannin, and can be mown and stacked
like hay. It is largely used in Chicago tanneries, and said to give a
leather which is tougher, more durable, of finer texture, and capable
of higher polish, than that tanned with oak-bark.

_Punica Granatum_ fruit-rind, the pomegranate, contains about 13·6
per cent. of a tannin like myrobalans, and a considerable quantity of
starch; the tannin is greatest in the bitter kind, which is used for
preparing morocco leather; the root-bark also is rich in tannin.

_Rhizophora Mangle_ bark, the mangrove, of Venezuela, contains 24-30
per cent. of deep-red tannin, if obtained from young stems; samples
from the West Indies have given 11·94 per cent., probably by the
gelatine process; two samples from Shanghai, by Löwenthal's improved
method, gave respectively 9·8 and 9·5 per cent. calculated as oak
tannin, and 71·96 and 78·52 of woody fibre. Guayaquil exported 9328
cwt. of the bark to Peru in 1879.

_Tecoma pentaphylla_ bark, the _roble colorado_ of Venezuela, contains
27 per cent. of tannin, accompanied by a soluble orange-red colouring
matter.

_Wagatea spicata_ pods contain 15 per cent. of tannic acid. The plant,
a scrambling shrub, is a native of the Concans.

_Weinmannia racemosa_ bark, the _tawhero towai_, or _kamai_ of New
Zealand, contains 12-13 per cent. of tannin.




CHAPTER IV.

THE CHEMISTRY OF TANNINS.


The essential constituents of tanning materials are various members of
a large group of organic compounds called tannins or tannic acids.[D]

[Footnote D: Ger. _gerbsäure_; in German the word _tannin_ denotes
usually gallotannic acid only.]

These bodies often differ widely both in chemical constitution and
reaction, but have the common property of precipitating gelatin from
solution, and forming insoluble compounds with gelatin-yielding
tissues. By virtue of this power, they convert animal hide into the
insoluble and imputrescible material called "leather." They are
mostly uncrystallisable; and all form blackish-blue or blackish-green
compounds with ferric salts, and in common with many other organic
substances are precipitated by lead and copper acetates, stannous
chloride, and many other metallic salts, and those of organic bases,
such as quinine. In some cases, the tannin combines with the base
only, liberating the acid; but frequently the salt as a whole enters
into combination. This is the case with the precipitates formed with
lead and copper acetates. With alkalies, the tannins and many of their
derivatives give solutions which oxidise and darken rapidly, usually
becoming successively orange, brown, and black. A. H. Allen has shown
that these bodies also give instantaneously a deep-red coloration with
a solution of potassium ferricyanide and ammonia. The reaction is one
of considerable delicacy.

Tannins are more or less soluble in water; and freely so in alcohol,
mixtures of alcohol and ether, and ethyl acetate, but scarcely in dry
ether alone, nor in dilute sulphuric acid; and insoluble in carbon
disulphide, petroleum spirit, benzene, and chloroform.

From their amorphous character, tannins are extremely difficult to
purify; and when, as is frequently the case, two or more tannins occur
in the same plant, it is often quite impossible completely to separate
them. Owing to their considerable differences in character, no general
method of purification can be given, but the following processes will
be found in many cases to give good results. For the special methods
adopted by different investigators, the original memoirs must be
consulted, references to many of which will be found in the following
pages.


Preparation and Purification of Tannins.

The oldest method of separating tannins from other constituents is
that applied by Pelouze to the preparation of commercial gallotannic
acid from gall-nuts. The finely pulverised material is placed in a
percolator and exhausted with commercial ether containing water and
alcohol. The liquid separates, on standing, into 2 layers of which the
lower contains most of the tannin in a tolerably pure form, dissolved
in water and alcohol with a little ether, while the upper mainly
ethereous layer contains the gallic acid. Gall-nuts thus treated yield
35-40 per cent. of tannin. If equal parts of ether and 90 per cent.
alcohol are used, a larger yield is obtained, but the liquid does not
separate into 2 layers, and it is questionable if the product is so
pure. For Chinese galls, washed ether acts better than ether alcohol.
The tannin may be still further purified by dissolving in a mixture of
1 part water with 2 of ether, when 3 layers are formed, of which the
lowest contains nearly pure tannin.

These methods are applicable to the dried or highly concentrated
extracts of many tanning materials. Many tannins may be separated from
their strong aqueous solution in a state of considerable purity by
first agitating with ether to remove gallic acid, and then saturating
with common salt, and shaking well with acetic ether, which takes
up the tannin. Another method is to extract with alcohol, evaporate
to a small bulk at as low a temperature as possible, and treat at
once with a considerable quantity of cold water. The infusion is
then precipitated with successive small quantities of lead acetate;
the first and last portions of the precipitate are filtered off and
rejected as contaminated with colouring matters and other impurities,
while the remainder, after rapid washing, is suspended in water and
decomposed with sulphuretted hydrogen. The filtrate is shaken with
ether to remove gallic acid, and the aqueous portion is evaporated at
a low temperature in a partial vacuum to a thin syrup, and the drying
completed over sulphuric acid in vacuo.


General Chemistry.

The natural tannins are all compounds of carbon, hydrogen and oxygen
only. They all contain the benzene group of carbon atoms, but their
ultimate structure is, except in the case of gallotannic acid, very
imperfectly understood, and probably differs considerably in type in
different members of the family.

In order to make clear to those readers who have not studied modern
organic chemistry, what we do know on the subject, a few words of
introduction will be necessary. All organic compounds contain carbon,
in combination with hydrogen, and very frequently also with oxygen,
nitrogen, and other elements. A single atom of carbon is able to
combine with 4 atoms of hydrogen, as it does to form marsh gas, or
methyl hydride, CH_{4}. Other elements may be substituted for the
hydrogen; for instance, if we replace 3 of the hydrogen atoms with
chlorine, we obtain chloroform, CHCl_{3}. Again an atom of oxygen may
be inserted between the carbon atom and one of the hydrogen atoms,
producing methyl hydroxide or wood spirit. The group CH_{3} is called
methyl, and we may substitute in wood spirit this entire methyl group
for one of the atoms of hydrogen, when we shall have ordinary alcohol,
C_{2}H_{5}OH. This building-up process may be repeated almost _ad
infinitum_, producing a whole series of alcohols of higher and higher
boiling point as the atoms of carbon become more numerous. Again, if
in wood spirit we substitute an atom of oxygen for 2 of the remaining
atoms of hydrogen we obtain formic acid, CHO.OH, the first of a long
series of acids, of which the second, corresponding to ordinary
alcohol, is acetic acid, and the highest members, such as stearic acid,
C_{18}H_{35}O.OH, are solid fats. Hence the whole series are commonly
called the fatty acids. A few structural formulæ will serve to make
these points clearer, but it may be well to say that such formulæ must
be taken simply as indicating the order in which the different atoms
are united, and in no sense their actual position in space. The atoms
in a molecule are held together by attractions and are in continual
motion, so that they are more comparable to the planets of the solar
system than to a rigid shape.

  _Methyl Hydride._  _Methyl Alcohol._  _Common Alcohol._

        H                H                  H  H
        │                │                  │  │
     H──C──H          H──C──O──H         H──C──C──O──H
        │                │                  │  │
        H                H                  H  H

  _Chloroform._      _Formic Acid._      _Acetic Acid._

        Cl               O                  H  O
        │                ║                  │  ║
     H──C──Cl         H──C──O──H         H──C──C──O──H
        │                │
        Cl               H

In benzene, C_{6}H_{6} we have a compound of another type.
There is reason to think that the carbon atoms in this case
are united in a ring, as shown,

  H  H  H
  │  │  │
  C──C══C
  ║     │
  C──C══C
  │  │  │
  H  H  H

This benzene group forms the foundation of an immense number of bodies
known as the aromatic series, to which belong aniline, carbolic acid,
picric acid, gallic acid, and a host of other compounds important alike
in a scientific and commercial sense, and among which we may pretty
safely group the whole of the tannins. Commencing with benzene, we may,
by inserting atoms of oxygen, produce a series of alcohols or phenols,
of which common phenol (usually but incorrectly called carbolic acid)
is the first.

The following table gives a general view of some of these, so far as
they are known, with their corresponding acids:--

  ──────────────┬─────────────────┬────────────────────┬───────────────────
    C_{6}H_{6}  │  C_{6}H_{5}OH   │ C_{6}H_{4}(OH)_{2} │ C_{6}H_{3}(OH)_{3}
    Benzene.    │     Phenol.     │    Pyrocatechol    │    Pyrogallol,
                │                 │   (or catechol),   │   Phloroglucol.
                │                 │    Hydroquinol,    │
                │                 │    Resorcinol.     │
  ──────────────┼─────────────────┼────────────────────┼───────────────────
        {H_{5}  │      {H_{4}     │      {H_{3}        │      {H_{2}
   C_{6}{CO.OH  │ C_{6}{OH        │ C_{6}{(OH)_{2}     │ C_{6}{(OH)_{2}
                │      {CO.OH     │      {CO.OH        │      {CO.OH
   Benzoic acid.│ Salycylic acid, │ Protocatechuic acid│ Gallic acid,
                │ Oxybenzoic acid.│   (and 5 other     │     &c.
                │                 │  isomeric acids).  │
  ──────────────┴─────────────────┴────────────────────┴───────────────────

It will be noticed that a large proportion of the formulæ given above
represent several compounds identical in composition, but frequently
very distinct in their properties. The explanation of these differences
lies in the different relative position of the OH and CO.OH groups
round the benzene ring. Thus the following diagram represents the
relative positions of the pyrocatechol series. It may be noted that
each phenol yields two isomeric[E] acids. Miller (C. S. Jour., xli.
398), who has investigated these acids, remarks, "Of the 3 phenols
C_{6}H_{4}OH_{2}, catechol alone gives a precipitate with lead acetate,
and of the 6 acids, C_{6}N_{5}OH_{2}, CO.OH, none yields precipitates
with lead acetate, except the 2 which are obtained from catechol."

[Footnote E: _Isomeric_, of similar composition but different structure
and properties.]

  Pyrocatechol 1-2.   Resorcinol 1-3.  Hydroquinol 1-4.

   H──C══C──O──H      H──C══C──O──H     H──C══C──O──H
      │  │               │  │              │  │
   H──C  C──O──H      H──C  C──O──H     H──C  C-H
      ║  ║               ║  ║              ║  ║
   H──C──C──H         H──C──C──O──H     H──O──C──C-H

All the natural tannins with which we are acquainted, are derived
from, and yield on decomposition either catechol, phloroglucol, or
pyrogallol, and sometimes more than one of these. Artificial products,
however, with many of the reactions of tannins have been obtained from
other members of the group, and most phenols and their derived acids
give either purplish or greenish black with ferric salts.

Several classifications of the tannins have been suggested. The
division most obvious to the tanner is into those tannins which yield
the whitish deposit in the surface of the leather, called "bloom," and
those which do not. Stenhouse, some years since, divided tannins into
2 classes, one of which gives a bluish, and the other a greenish-black
with ferric salts. In the main these 2 classes correspond to the 2
former, as most tannins which yield a blue-black with iron acetate
also give bloom to the leather. In some cases, however, the difference
of tint is due to accidental impurities, and even gallotannic acid
will give a decided green with strongly acid ferric chloride. These
classifications both correspond to well-defined differences of
constitution, and it is obviously more scientific to arrange tannins
according to the products which they yield on decomposition, and which
indicate their ultimate structure, rather than on any less essential
point.

If those tannins which give bloom to leather are cautiously heated
to about 392° F. (200° C.), they are decomposed, and a substance
is volatilised which condenses in feathery crystals, and which on
examination turns out to be pyrogallol. Those tannins, on the other
hand, which yield no bloom, but red deposits, produce a somewhat
similar sublimate of catechol. From oak-bark and valonia, which yield
both bloom and red colouring matters, both catechol and pyrogallol
have been obtained. We may, therefore, divide tannins broadly into
derivatives of catechol, which yield no bloom, and usually give
greenish-blacks with iron acetate, and which include hemlock, mimosa,
cutch, gambier, quebracho, &c; derivatives of pyrogallol, which give
bluish-blacks with iron, deposit bloom in leather, and embrace galls,
sumach, divi-divi, myrobalans, pomegranate rind, &c., and tannins which
contain both pyrogallol and catechol, such as oak-bark and valonia, and
which, as is well known, yield bloom, and give blue-blacks with iron.

If tannins are boiled with dilute sulphuric or hydrochloric acids, and
allowed to ferment under the influence of pectose and other natural
ferments, which are always present in vegetable tanning materials, a
different series of decompositions takes place. Many tannins yield
glucose, or starch sugar, as one of their products, or as that of
closely associated impurities. Of this more must be said later. In
addition it will be found that the catechol tannins invariably yield
insoluble reddish-brown bodies which have been called phlobaphenes,
and which differ from the original tannins in containing one or more
molecules less water, and which, in chemical language, are anhydrides
of their respective tannic acids. The pyrogallol tannins, on the other
hand, yield gallic acid, or ellagic acid (the deposit forming bloom)
either alone or in mixture. Oak-bark and valonia give both bloom and
insoluble reds, and by digestion with acids in sealed tubes also gallic
acid.

If the red anhydrides, which are produced from the catechol tannins, be
fused with caustic potash, or in many cases, if they be simply boiled
with concentrated potash solution, they are broken up still further,
and from the fused mass, protocatechuic acid (which bears the same
relation to catechol that gallic acid does to pyrogallol) may always
be obtained. This is in many cases accompanied by phloroglucol, a
phenol isomeric with pyrogallol, as may be seen by the table on p. 61,
but which tastes sweet like a sugar. Cutch, gambier, mimosa, quebracho,
and probably many others, are phloroglucide tannins. The tannins which
do not yield phloroglucol frequently give acetic acid, and other acids
of the "fatty" group, along with protocatechuic acid. We may summarise
this classification in the following table:--

  Tannins boiled with dilute sulphuric acid
     yield (frequently glucose, and)
  /─────────────────────^───────────────────────\
  _Insoluble Reds_, which fused with potash
      yield _protocatechuic acid_, and,----
         /────────────────────────^───────────────────────────────────\
         _Phloroglucol_, as chestnut, gambier, kino, cutch, quebracho,
             rhatany, fustic, horse-chestnut, tormentil.
            _Acetic acid_, coffee, Peruvian bark, male-fern.

  _Reds and gallic     }
    and ellagic acids; } Oak-bark and valonia tannins.
    no glucose_        }

  _No reds, but gallic { Galls, myrobalans, sumach, divi-divi, pomegranate
    and ellagic acids_ {   rind.
                       { _These are probably mixtures of two tannins
                            which yield_

  _Gallic acid only_     Digallic, or pure gallotannic acid.

  _Ellagic acid only_    Pure ellagitannic acid.

This classification is as yet very incomplete, and there are many
tannins of which the decomposition products have not been examined,
while our knowledge of the differences between the tannins which are
classed together is extremely limited. In order to make the information
which has been given practically available for further research, the
characteristics and mode of recognition of the different products
will be given, and as simple a scheme as possible of treatment of the
tannin to be examined will be described; but the recognition of such
products in a state of mixture presents great practical difficulties,
and the tanner will usually be compelled to confine his attention to
simpler, though less conclusive tests, based on the work of chemical
specialists. Such tests will be described later (p. 111).

[Illustration:

  Pl. III.

  _E & F N. Spon, London & New York_  "MARS PHOTO" SPRAGUE & CO. LONDON

ARTIFICIAL FERMENTATION.]


General Methods of Examination of Tannins.

_Decomposition by Heat._--The ordinary method is to distil the tannin
or dried extract in a small retort, and examine the distillate for
catechol and pyrogallol. Unless the heat be very carefully regulated,
much loss is caused by the destruction of the catechol and pyrogallol
with formation of metagallic acid, &c., and their detection is greatly
complicated by the presence of secondary products. This difficulty is
somewhat lessened by passing a stream of carbon dioxide through the
retort, which carries the products quickly out of the heated portion.
A better method is to heat the tannin in glycerin (Thorpe, Chem. Soc.
Abstr., 1881, 663; Allen, 'Commercial Organic Analysis,' 2nd ed.).
About 1 _grm._ of the sample is heated with 5 _c.c._ of pure glycerin
to 392°-410° F. (200°-210° C.) for 20 minutes. After cooling, about 20
_c.c._ of water is added, and the liquid is shaken with an equal volume
of ether, without previous filtration. The ethereous layer, which
contains the pyrogallol and catechol, is separated from the aqueous
portion, evaporated to dryness, and dissolved in 50 _c.c._ of water.
The filtered solution is divided into several portions and tested with
lime-water, ferric chloride, and ferric acetate (see pp. 66-7); by
these means it is easy to distinguish between catechol and pyrogallol;
and either may be detected in presence of a small portion of the other;
but if in nearly equal quantities, their recognition is difficult.
Catechol may be derived from catechin, &c., and pyrogallol from gallic
acid, and it is therefore necessary in some cases to remove these
bodies from the tannin before treatment. As a general rule, however,
catechins and catechol derivatives are only present in any quantity
with catechol-tannins, and the same is true of gallic acid with regard
to pyrogallol. (For methods of separation see pp. 69, 71, 80). Catechol
has been formed by long continued heating of cellulose, starch, and
other carbohydrates with water under pressure (see p. 67).

_Products of the Decomposition of Tannins by Heat._--Pyrogallol,
_pyrogallic acid_, C_{6}H_{6}O_{3}, has a bitter, but not sour taste,
and feebly reddens litmus, but the addition of the smallest trace of
alkali gives it an alkaline reaction. It is poisonous, 2 gr. having
killed a dog. It is soluble in less than 3 parts of cold water, and
still more freely in hot. It is also soluble in alcohol, ether,
acetone, ethyl acetate, and glycerin, but not in absolute chloroform,
or petroleum spirit. It fuses at 268° F. (131° C.) (_Etti_), and
sublimes at about 410° F. (210° C.).

With pure ferrous sulphate it gives a white precipitate, which
redissolves to a fine blue liquid in presence of the least trace of
ferric salt. Mineral acids change this to red, and the blue tint
is restored by cautious neutralisation with ammonia, and is not
destroyed, but sometimes rendered greenish by excess of acetic, and
other organic acids. Any excess of ammonia produces an amethyst-red,
and acetic acid restores the blue. Its solution is turned brown by
traces of nitrous acid. With lime-water it produces a beautiful but
evanescent purple, rapidly turning brown. In presence of alkalies it
absorbs oxygen from the air with great avidity, turning orange, brown,
and black. Pyrogallol does not precipitate gelatin. Its solution
rapidly reduces permanganate, Fehling's solution, and salts of gold,
silver,[F] mercury, and platinum. It precipitates copper and lead
acetates, and with ammoniacal cupric sulphate it gives an intense
purple-brown coloration. Gum arabic, saliva, and various other organic
matters cause solutions of pyrogallol exposed to the air to absorb
oxygen, by which purpurogallin is formed and separates in small yellow
capillary crystals. If 0·2 per cent. of pyrogallol be added to a 1
per cent. solution of gum arabic, it becomes yellow in a few hours,
and purpurogallin separates in hairlike crystals, which continue to
increase for some months. It these crystals are freed from pyrogallol
by washing with water, and a trace of alkali is added, they dissolve
with an intense blue colour. Purpurogallol is also formed by oxidation
with silver nitrate, potash permanganate, and many other reagents.
Pyrogallol forms compounds with aldehydes; with formaldehyde, a body
which reacts like a tannin and precipitates gelatin is produced.
If pyrogallol be heated with hydrochloric acid, and aldehyde,
chloral, or acetone, a red substance is produced. The less volatile
portions of crude beech-tar creasote contains ethers of pyrogallol,
methyl-pyrogallol, and propyl-pyrogallol, from which these bodies
may be obtained by the action of hydrochloric acid under pressure.
Methyl- and propyl-pyrogallols differ from ordinary pyrogallol in
having an atom of hydrogen replaced by the groups CH_{3} or C_{3}H_{7}
respectively; and it is very probable that some tannins are derivatives
of such modified pyrogallols.

[Footnote F: Hence its use as a "developer" in photography.]

If pyrogallol be heated rapidly to 482° F. (250° C.) it parts with
the elements of water, and is converted into metagallic acid,
C_{6}H_{4}O_{2}, a black amorphous body, insoluble in water, soluble in
alkalies. When pyrogallol is made in the ordinary way by heating gallic
or tannic acids to 410° F. (210° C.), much of this body is formed, even
if the process be conducted in a stream of carbonic acid, and the yield
of pyrogallol usually amounts to only about 5 per cent. of the gallic
acid employed (see p. 65).

Catechol.--_Pyrocatechol_, _pyrocatechin_, _oxyphenic acid_,
C_{6}H_{4}(OH)_{2}.

Sources.--Beside that of the decomposition of certain tannins by heat
(see p. 63), catechol is produced by the dry distillation of catechin
and some allied bodies which frequently accompany the tannins. It is
also formed together with pyrogallol and its homologues (see above) by
the dry distillation of wood, wood tar creasote consisting largely of
ethers of pyrocatechol and its homologues, methyl and pyrocatechol,
&c., and hence it is also found in crude pyroligneous acid. It has also
been produced by heating carbohydrates with water under pressure, and
is found ready formed in Virginia-creeper (_Ampelopsis hæderacea_), and
probably in other plants. It has also been formed synthetically.

Reactions.--Catechol melts at 232° F. (111° C.) and sublimes at about
the same temperature, condensing in brilliant laminæ like benzoic acid.
It is readily soluble in water, alcohol, and ether, and is extracted
from its aqueous solution when shaken with the latter. Its aqueous
solution precipitates lead acetate but not gelatin or alkaloids. With
lime-water or caustic soda solution it becomes reddish, but remains
clear for some time. It does not colour ferrous salts, but gives a
dark green with ferric (avoiding excess); and after some time a black
precipitate. The green is changed to a fine violet-red by alkalies and
hydric sodic carbonate, and restored by acids. To fir-wood moistened
with hydrochloric acid it gives, like phloroglucol, a violet coloration
by combination with the trace of vanillin which this wood contains.
This reaction does not seem to be given by pyrogallol or by common
phenol. Catechol gives a red coloration with citric acid, and after
standing, ceases to react with iron.

_Decomposition of Tannins by Dilute Acids._--It has been stated that
tannins when heated with dilute sulphuric or hydrochloric acids are
decomposed, yielding frequently glucose, and either gallic or ellagic
acids, or red anhydrides. To determine whether glucose is produced, the
tannin must first be carefully purified from glucose, gums, or other
bodies likely to interfere, by the methods mentioned on p. 58. Either
the tannin itself or its washed lead-salt may be used, and must be
heated to 212° F. (100° C.) for some hours in a sealed tube, or tightly
closed bottle with dilute hydrochloric acid. After cooling, the mixture
must be allowed to stand for some time to separate any sparingly
soluble products, which must be filtered off. The filtrate must be
shaken with ether and acetic ether to remove gallic acid (p. 59), the
aqueous solution must be boiled, neutralised with soda, precipitated
with basic lead acetate to remove any traces of tannin or colouring
matters, the liquid again filtered, and excess of lead removed with
dilute sulphuric acid, the mixture again neutralised with soda, and
heated to boiling with Fehling's copper-solution, when a yellow or red
precipitate of cuprous oxide will prove the formation of glucose. The
precipitate produced by cooling may consist (of lead chloride, if the
lead salt has been used,) of ellagic acid, or of red anhydrides or
phlobaphenes of the tannin. The lead chloride may be removed by washing
with boiling water. If the remaining precipitate has a pale yellow or
fawn colour it probably consists of ellagic acid (see p. 71), soluble
in ammonia and hot alcohol and dissolving freely in strong nitric acid,
forming an intense crimson liquid.

The ethereous layer will contain the gallic acid, if any has been
formed, and must be evaporated to dryness, and the residue taken up
with cold water, and filtered. Addition of a few drops of solution of
potassium cyanide will produce a fine red coloration if gallic acid be
present, which rapidly fades, but is restored by shaking. A solution
of picric acid, to which excess of ammonia has been added, gives a
red coloration rapidly changing to a fine green, even in very dilute
solutions of gallic acid.

It is not, however, generally necessary to resort to so elaborate a
process merely to distinguish the class to which tannins belong. The
tannin, or its infusion, may be simply boiled with dilute hydrochloric
acid for some time, replacing the acid lost by evaporation. The
solution is diluted to 50 _c.c._ and allowed to cool. Ellagic acid and
phlobaphenes may separate, and must be filtered off. If the precipitate
is pale, it is probably ellagic acid, and maybe recognised by the
nitric acid test. If red, it probably consists of phlobaphenes, and may
be treated with cold alcohol, in which phlobaphenes are freely soluble,
but ellagic acid very little. The ellagic acid will therefore be left
on the filter if present in any quantity, while the alcoholic solution
may be precipitated by the addition of water, and the phlobaphenes
further examined by treatment with potash.

Gallic Acid.--_Dioxysalicylic acid_, C_{6}H_{2}(OH)_{3}CO.OH, exists
ready formed in some plants, and is a product of the fermentation
of gallotannic acid under the influence of the nitrogenous ferment,
pectase, or of its decomposition by boiling with acids or alkalies.
It crystallises in white, or yellowish white needles, containing 1
mol. (9·5 per cent.) of water, which it loses at 212° F. (100° C.).
It is soluble in 100 parts of cold or 3 of boiling water, in alcohol
or glycerin, and slightly so in ether, by agitation with which it may
however be removed from its aqueous solution. Gallic acid fuses at a
temperature of about 449° F. (232° C.) (Etti, Chem. Soc. Jour., xxxvi.
160), but at about 410° F. (210° C.) begins to lose carbonic dioxide,
and yields a crystalline sublimate of pyrogallol (see p. 66). If the
heat be raised suddenly to 482° F. (250° C.) a considerable quantity of
black shining metagallic acid is formed.

Aqueous solution of gallic acid gives the following
reactions:--Solution of ferric chloride gives a deep blue coloration
which is destroyed by boiling. Ferrous sulphate, if free from ferric
salt, gives no reaction in dilute solutions, but a white precipitate
in strong ones. The mixture rapidly darkens by oxidation. In alkaline
solution gallic acid absorbs oxygen from the air and darkens from the
formation of tannomelanic acid. Lime-water produces a white precipitate
which rapidly becomes blue from oxidation. The same reaction is
produced by baryta-water, or by the chlorides of barium or calcium on
addition of ammonia (distinction from pyrogallol). It is distinguished
from gallotannic acid by the following:--It does not precipitate
gelatin, except in the presence of gum. It does not precipitate tartar
emetic in presence of ammonic chloride, though both tannin and gallic
acid are precipitated by tartar emetic alone. It precipitates lead
acetate but not lead nitrate, while tannin precipitates both. A dilute
solution of potassium cyanide gives a red coloration which disappears
on standing, but is restored by shaking with air. If to even a very
dilute solution of gallic acid, sodic arsenate, or some other faintly
alkaline salts be added, the mixture absorbs oxygen and becomes a deep
green. Aqueous solution of picric acid to which excess of ammonia
has previously been added gives a red coloration, changing to green.
Tannic and pyrogallic acid produce no reaction with cyanide, and
with ammonic picrate a reddish coloration only. Gallic acid reduces
silver nitrate and gold chloride rapidly when hot, but not Fehling's
solution, and decolorises acidified potassic permanganate. If tannin
and other oxidisable bodies be removed from its solution it may be
estimated quantitatively by titration with permanganate in presence
of indigo (see p. 118). It may be separated from tannin by gelatin
or hide raspings (see pp. 121, 124). Gallotannic and quercitannic
acids may also be removed by precipitation with ammoniacal solution
of cupric sulphate, or by cupric acetate, in presence of excess of
ammonic carbonate (see also p. 125). Many other tannins, however,
give precipitates with cupric salts which are soluble in ammonia and
ammonic carbonate. In absence of such tannins it may be estimated
gravimetrically by precipitation with cupric acetate. The precipitate
is rapidly washed with water and digested with a solution of ammonic
carbonate, in which it dissolves; any insoluble cupric tannate is
filtered off, the solution is evaporated to dryness and the residue
moistened with nitric acid and ignited. The weight of the remaining
cupric oxide multiplied by 0·9 gives the weight of the gallic acid plus
a little tannin dissolved by the ammonic solution.

Gallic acid may also be separated from tannin by lead acetate strongly
acidified with acetic acid, by which tannic acid is precipitated, while
lead gallate is dissolved.

Ellagic acid C_{14}H_{8}O_{9}, when pure, is a sulphur-yellow
crystalline body almost insoluble even in boiling water, and only
slightly so in alcohol and ether, though by agitation with the latter,
small quantities may be completely removed from aqueous solution. In
hot alcohol it dissolves with a yellow colour, and crystallises on
cooling. Solid ellagic acid gives with ferric chloride at first a
greenish, and then a black coloration. In strong nitric acid it is
soluble with a deep crimson coloration: that from divi-divi gives a
crimson liquid on dilution with water, but from other sources it is
rather orange.

Ellagic acid may be obtained in considerable quantity by pouring
a concentrated alcoholic extract of divi-divi into water, when it
separates and may be filtered off and recrystallised from hot alcohol.
It may also be obtained by boiling the aqueous extracts of divi,
myrabolans, pomegranate rind, &c., with dilute hydrochloric acid, and
purified by the same means. It may be prepared from gallic acid by
heating the latter with dry arsenic acid to 320° F. (160° C.), but is
difficult to purify from traces of arsenic. Ellagic acid has not been
reconverted into gallic acid. Its constitutional formula is, according
to Schiff,

            {CO.OH
            {OH
  C_{6}H_{2}{
            {O────┐
            {O }  │
               }  │
            {CO}  │
            {O────┘
  C_{6}H_{2}{
            {OH
            {OH

differing from gallotannic acid only by the loss of two atoms of
hydrogen.

Air-dried ellagic acid, C_{14}H_{8}O_{9} + OH_{2}, contains 1 mol.
of water, which it loses at 212° F. (100° C.) but reabsorbs in moist
air. When heated to 392°-410° F. (200°-210° C.) it forms an anhydride,
C_{14}H_{6}O_{8}, losing another molecule of water, which it does not
recover from moist air, but is slowly reconverted to ellagic acid by
boiling with water.

The phlobaphenes or reds are chemically the anhydrides of the different
tannic acids from which they are derived, or in other words they
are formed from the tannins by the loss of one or more molecules of
water. It is in this way that they are produced by the action of
acids, and similarly they are often formed when alcoholic or highly
concentrated aqueous extracts are poured into cold water, under which
circumstances a part of the tannin seems unable to take up water
again, and separates as a red precipitate. They exist ready formed in
most tanning materials capable of producing them. They are soluble in
alcohol, by which they may be extracted from tanning materials or dried
residues containing them. They are also dissolved by dilute alkalies
and alkaline carbonates, and by borax, which is said to be used in the
preparation of some extracts, and was suggested by Sadlon as a means of
making phlobaphenes available for tanning. Many of them are scarcely
soluble in water even at a boiling temperature, though they become
more so in presence of sugar, tannic acid, and some other substances.
Their solubility in water depends on their degree of hydration, many
tannins giving a series of anhydrides of which those containing only
one molecule of water less than the original tannin are quite soluble
in water, while the higher members of the series become less and less
soluble as they lose water. Those which are soluble form the colouring
matters of tanning materials, and generally are practically tannins,
precipitating gelatin and combining with hide to form leather. Hemlock
bark yields a series of such bodies, of which the lower members are
deep red soluble tannins, while the higher form the red sediment, so
well known to extract-tanners. Thus it is chemically impossible to
decolorise hemlock extract without at the same time greatly lessening
its tanning power, though by careful manufacturing and concentration
at low temperature, the proportion of the higher anhydrides formed may
be kept at a minimum. In many cases it is known, as in gambier, and
in others it is probable that the tannin itself is merely the first
anhydride of the series, and derived from a catechin which itself is a
white crystalline body destitute of tanning properties (see p. 79).

_Decomposition of the Phlobaphenes by Fusion with Caustic
Alkalies._--It has been mentioned (p. 64) that the reds of different
tannins yielded, in addition to protocatechuic acid, either
phloroglucol, or acetic acid, or some other member of the fatty acid
series. Some tannins, as those of alder and hop, give both phloroglucol
and acetic acid, but it is very possible that this arises from the
presence of two distinct tannins in these materials. It is stated that
all those tannins which yield acetic acid on fusion with potash, also
yield considerable quantities of glucose to dilute acids, while the
phloroglucide tannins do not do so. Gallic acid fused with caustic
soda has been found by Barth and Schroeder to produce a small quantity
of phloroglucol, and it is similarly formed by resorcinol and common
phenol (Chem. Soc. Jour., xliv. 60). It is therefore possible that in
some cases where phloroglucol is detected, it may have been formed by
the action of the alkali, and not have been originally a constituent of
the tannin.

The following is the best method in which to proceed to investigate
the products of the action of potash. 20 _grm._ of the red, or of the
tannin from which it is derived, or its lead salt, is boiled with 150
_c.c._ of solution of caustic potash of 1·20 sp. gr. for 3 hours, and
the liquid is then concentrated with constant stirring till it becomes
pasty. It is then cooled and treated with a volume of dilute sulphuric
acid slightly more than enough to neutralise the alkali employed. After
cooling it is filtered from potassium sulphate and other solid matters,
and the filtrate treated with sodium bicarbonate till its wine-red
reaction with litmus shows that the sulphuric acid is neutralised. The
liquid is then shaken with an equal measure of ether, the ethereous
layer drawn off and the treatment repeated several times. On distilling
off the ether, phloroglucol is left and may be purified by solution in
water, when protocatechuic acid and other products may be precipitated
by neutral lead acetate, and filtered off, and the phloroglucol again
extracted with ether, and recognised by its reaction with ferric
chloride and bromine water, and by its sweet taste.

Phloroglucol.--_Phloroglucin_ C_{6}H_{6}O_{3} is a phenol isomeric
with pyrogallol. It crystallises with 2 molecules of water, which
it loses at 212° F. (100° C.). It melts at about 428° F. (220° C.),
sublimes without odour, and solidifies again on cooling. It is soluble
in water, alcohol, and ether, and by agitation with the latter it
may be removed from its aqueous solution. It is not precipitated by
any metallic salt but basic lead acetate. It is coloured deep violet
red by ferric chloride. If bromine be added to its concentrated
solution in water, it absorbs 3 atoms, forming tribromophloroglucol,
C_{6}H_{6}Br_{3}O_{3}, which separates in crystalline needles, with
evolution of heat and a very irritating odour. If a deal shaving
be moistened with solution of phloroglucol, and then with strong
hydrochloric acid, it soon takes a deep violet colour, from the
formation of phloroglucol-vanillin with the trace of vanillin contained
in all coniferous woods. Pyrocatechol gives a similar reaction, and it
is stated by Etti (Chem. Soc. Jour., xliv. 60) that pyrogallol forms
a similar compound; it does not, however, give the colour reaction on
deal. It is extremely probable that this reaction may be used to detect
phloroglucide tannins without the troublesome fusion with potash, in
cases where pyrocatechol is absent. The reaction is strongly given
by gambier, which is known to contain phloroglucol, but not by oak
bark and valonia, though these contain protocatechuic acid. If to a
dilute solution of phloroglucol a solution of aniline or toluidine
nitrate be added, and then a trace of potassic nitrite, the liquid
gradually becomes yellow or orange, then turbid, and finally deposits
a cinnabar-red precipitate. This reaction is given by gambier, but is
also produced by oak bark infusion, which is not supposed to contain
phloroglucol; and gall tannin, pyrogallol, and other substances give
similar but browner precipitates.

Protocatechuic Acid.--C_{6}H_{3}(OH)_{2}CO.OH, one of the six isomeric
dihydroxybenzoic acids of this formula (see Miller, Chem. Soc. Jour.,
xli. 198), crystallises in needles and plates with 1 mol. water, which
it loses at 212° F. (100° C.). It melts at 228° F. (109° C.) and on
further heating is decomposed into pyrocatechol and carbonic acid.
It is somewhat soluble in cold water, and readily so in hot water,
alcohol, and ether. It is coloured bluish green by ferric chloride,
which is changed to red by alkalies. Solutions of protocatechuates
give a violet coloration with ferric salts. It is precipitated by lead
acetate, and reduces silver ammonio-nitrate, but not Fehling's solution
(see also p. 107).


Constitution of Tannins.

Having described the products of decomposition, something must be
said of the way in which these constituents are combined to form the
unaltered tannins. The only tannin of which we have as yet anything
approaching complete knowledge is that obtained from galls, sumach, and
myrabolans, and which is thence called gallotannic acid.

_Gallotannic, or digallic acid_ exists as the principal tannic acid
of the galls of oak, tamarisk, &c.; and, in mixture with more or less
ellagitannic acid, in myrabolans, divi-divi, sumach, pomegranate rind,
and many other plant-products. It has also been formed by Schiff from
gallic acid, by mixing it, after drying at 230° F. (110° C.), with
phosphorus oxychloride to a thin paste, and heating, first to 212° F.
(100° C.) and then to 248° F. (120° C ). Much hydrochloric acid was
evolved, and the gallic acid was converted into a yellow powder, which
after purification by washing with ether, dissolving in water, allowing
the gallic acid to crystallise out, saturating with salt, washing the
precipitated tannin in salt solution, and redissolving in alcohol and
ether, had all the reactions of purified gall tannin, but was perfectly
reconverted into gallic acid on boiling with hydrochloric acid, without
the formation of any trace of ellagic acid, or glucose. By analysis of
the tannin and its acetyl compounds it was shown to be digallic acid,
and its constitutional formula is almost certainly as follows:--

            {CO.OH
            {OH
  C_{6}H_{2}{
            {OH
            {O }
               }
            {CO}
            {OH
  C_{6}H_{2}{OH
            {OH

By boiling gallic acid with solution of arsenic acid, Schiff obtained a
product which precipitated gelatin, and otherwise reacted like tannin,
and he regards this as digallic acid, but other experimenters have
failed to obtain digallic acid by this means, and have found that on
complete removal of arsenic, the compound was reconverted to gallic
acid. It therefore remains a moot point whether digallic acid is really
formed, and reconverted into gallic acid by the prolonged action of
hydric sulphide, which is necessary to remove the arsenic, or whether,
as seems more probable, the supposed tannin is merely an arsenical
compound of gallic acid.

Gallotannic acid as obtained from plants invariably yields traces of
glucose, as well as of ellagic acid, when boiled with dilute acids. It
is still an open question whether the glucose exists in the plant as a
glucoside of tannic acid or is always the product of some impurity (as
is shown by Etti to be the case with oak bark, where lævulin is always
present). It seems most probable however that natural gallotannic acid
is really a glucoside of digallic acid, or possibly, according to the
theory of Hlasiwetz, a gummide, or compound of dextrin, which, by the
action of acids, is easily converted into glucose. What has been said
of gallotannic acid in this respect, applies to many other tannins,
which like it give glucose by treatment with acids.

Gallotannic acid is met with, in commerce, in the form of light
buff-coloured scales, with a faint peculiar odour and a powerfully
astringent taste. It is soluble in 6 parts of cold water or glycerin,
and very readily in hot. It is also very soluble in alcohol containing
water, but much less so in absolute. It is moderately soluble in
washed, but scarcely at all in anhydrous ether, chloroform, benzene, or
petroleum spirit.

The commercial acid usually contains more or less of gallic acid, which
may be detected by dissolving in water, shaking with ether, and after
decanting and evaporating the ether, applying the tests described under
gallic acid (p. 70). It may also be frequently distinguished in the
simple aqueous solution of the tannic acid by the tests given. Its
quantity may be determined (in the absence of other impurities) by the
Löwenthal method (p. 121), the gallic acid forming the "not-tannin,"
by comparison with a solution of pure gallic acid.

Commercial tannic acid is sometimes adulterated with starch, which is
left undissolved on treating the sample with ordinary alcohol.

For the estimation of gallotannic acid see pp. 118 _et seq._ For its
principal reactions, Table, p. 113.

_Ellagitannic acid_, C_{14}H_{10}O_{10}, is contained in divi-divi,
myrabolans, and as a glucoside in pomegranate rind. When boiled
with dilute acids, or treated with water at 230° F. (110° C.) in
a sealed tube, it yields its anhydride, ellagic acid (see p. 71),
C_{14}H_{8}O_{9}. In its reactions ellagitannic acid closely resembles
gallotannic acid.

_Quercitannic acid._ Oak-bark tannin.--This tannin may be prepared
from oak bark by agitating an alcoholic extract with ethyl acetate,
and separating and evaporating the ethereous layer. It is still
contaminated with a brownish-green terpene resin, and with some of the
higher anhydrides of the tannin. The resin may be removed by treating
the dried extract with ether or benzene, in which it is readily
soluble; and the phlobaphenes, or higher anhydrides, by dissolving
the tannin in ether-alcohol, or probably to a great extent, by simple
solution in cold water in which the phlobaphenes are scarcely soluble.

It may also be prepared by evaporating the alcoholic extract, and
extracting with water, which leaves the phlobaphenes, or higher
anhydrides undissolved. The first anhydride, which is partially
soluble, may be precipitated by the addition of salt, and the
quercitannic acid extracted by shaking the filtered solution with
acetic ether. In very dilute alcohol it yields a pure yellow
precipitate with lead acetate. In aqueous solution the precipitate
is light-brown. It gives a blue-black with ferric salts. When pure,
quercitannic acid yields nothing to pure ether or to benzene.

If quercitannic acid be heated to 266°-284° F. (130°-140° C.) it loses
water, and yields a red anhydride slightly soluble in water, which
constitutes the red colouring matter of oak bark, and which has also
been called "difficultly soluble tannin." It precipitates gelatin and
is one of the class which Eitner well designates "tanning colouring
matters." It gives a brownish red with lead acetate, and a blue-black
with ferric salts; it is difficultly soluble in water and ether, but
readily so in alcohol of all strengths. Together with other anhydrides,
it exists naturally formed in the bark. At higher temperatures, or by
boiling with acids, a series of higher anhydrides may be obtained which
are quite insoluble in water, but are soluble in alcohol and caustic
alkalies. No glucose is produced by treatment of pure quercitannic
acid with acids, that formed by so treating oak-bark extract being due
to the alteration of the lævulose present. If oak-reds are fused with
potash they yield, according to Johansen (Chem. Soc. Jour., xxxii.
721), protocatechuic and butyric acids. If heated in sealed tubes with
dilute hydrochloric acid, gallic acid only is formed, with evolution
of methyl chloride. The constitutional formula of quercitannic acid is
as yet very uncertain: it is probably a methyl derivative of digallic
acid. Its formula is variously given as C_{17}H_{16}O_{9} (Etti, Chem.
Soc. Jour., xliv. 994), C_{28}H_{26}O_{15} (Ibid. xl. 901, Löwe),
C_{19}H_{16}O_{10} (Böttinger, Berichte, xvi. 2710). For further
details the original memoirs must be consulted.

For the reactions of oak-bark and valonia infusions the Table, p. 113,
may be consulted.

Before describing the catechol-tannins it will be necessary to speak
of a group of compounds of which it is probable that these tannins are
decomposition products. These are the catechins. It is as yet by no
means certain how far they should be considered a group, some chemists
holding the opinion that there is only one catechin, of which the rest
are merely impure preparations.

Catechin is a white crystalline substance, contained to the extent
of some 30 per cent. in cube gambier, and in smaller proportion in
block gambier and cutch, and very probably in all tanning materials
yielding catechol-tannins. It melts at 422-1/2° F. (217° C.) and
yields a sublimate of catechol on further heating. It is readily
soluble in alcohol and in boiling water, but requires 1133 parts of
cold water for its solution. Hence it separates on cooling from a hot
solution of gambier, and may be purified by redissolving in hot water
and treatment with animal charcoal, and subsequent crystallisation.
It may also be extracted from its aqueous solution by agitation with
ether. It possesses no acid properties, though some writers have
incorrectly called it catechuic acid. The aqueous solution gives
precipitates with lead acetate and mercuric chloride, and reduces
ammonia-nitrate of silver; but, unlike tannins, it does not precipitate
gelatin, alkaloids, or tartar emetic. It is oxidised by permanganate
in presence of free acid, and hence, when in solution, is estimated
by the Löwenthal method as "not tannin." It dissolves in concentrated
sulphuric acid with a deep purple coloration. By fusion with caustic
alkalies it yields protocatechuic acid and phloroglucol together with
hydrogen. Its constitution is very uncertain, but it is probable
that the phloroglucol stands in a somewhat similar relation to the
protocatechuic acid that glycerin does to the fatty acids in natural
fats; and that its decomposition by fused alkalies is a process much
akin to saponification. This constitution is represented by the
following formula:--

                                      {O.C_{6}H_{3}(OH)_{2}
  C_{19}H_{18}O_{8} or C_{7}H_{8}O_{2}{
                                      {O.C_{6}H_{3}(OH)_{2}

When acted on by heat and dilute acids the following anhydrides are
produced--the formulæ given must be taken as to some extent provisional.

  Catechin 2C_{19}H_{18}O_{8} = C_{38}H_{36}O_{16}  Not acid; does not
                                                      precipitate gelatin.

  Catechutannic acid            C_{38}H_{34}O_{15}}
                                                  } Acid, precipitate
  Dianydride                    C_{38}H_{32}O_{14}}   gelatin.

  Trianydride                   C_{38}H_{30}O_{13}} Insoluble in water.

  Catechuretin                  C_{38}H_{30}O_{12}} Soluble in alcohol and
                                                      alkalies.

The white deposit which occurs on pit sides and in the interior of
leather where gambier is largely used, and which is sometimes called
"the whites," consists of catechin. It may be decomposed by warm
sulphuric acid. This deposit is favoured by the use of _hot_ gambier
liquors. It is probable that by exposure to the air and by boiling,
catechin is gradually converted into catechutannic acid during the
tanning process, and hence the practical tanning value of cube gambier
is probably greater than analysis indicates. Hunt has, however, shown
(Jour. Soc. Chem. Ind., iv. 266) that, as estimated by the Löwenthal
process, the tannin is to some extent lessened by boiling.

_Kinoin_, C_{14}H_{12}O_{6} (Etti, Berl. Ber., xi. 1879), obtained from
green or malabar kino, a product very similar to cutch, by boiling
with dilute hydrochloric acid and extraction by agitation with ether,
is very similar in its properties to catechin. It does not itself
precipitate gelatin, but like catechin, yields a series of anhydrides
or reds, which do so. On dry distillation it yields catechol and
common phenol; and when heated with hydrochloric acid at 248°-266° F.
(120°-130° C.) methyl chloride, catechol and gallic acid. Hence its
constitution is probably that of methyl-catechol gallate.

_Quebracho-catechin_ was found by P. N. Arata (Chem. Soc. Jour., xl.
1152) in the wood of quebracho colorado (p. 40), but in too small
quantity for detailed investigation. It probably bears a similar
relation to quebrachitannic acid that ordinary catechin does to
catechutannic acid. It is insoluble in cold and only slightly soluble
in hot water, but very soluble in alcohol and ether. Its solution is
clouded by normal lead acetate, and gives rose-coloured precipitates
with basic lead acetate and mercurous nitrate, and blackish with ferric
acetate; it reduces silver-nitrate and gold chloride, and is coloured
yellow by nitric acid, red by sulphuric acid, yellowish by sodium
hypochlorite, and green by Fehling's solution. It does not precipitate
gelatin, or alkaloids.

_Catechutannic_ acid has been pretty fully described under catechin,
of which it is the first anhydride (p. 80). It is possibly identical
with mimo-tannic acid, the tannin of cutch and mimosa bark, which is
chemically very similar, but greatly differs in its practical effect
in tanning. For some further reactions of cutch and gambier infusions
see p. 113. It gives a greyish-green precipitate with ferric salts, and
(distinction from gallotannic acid) precipitates cupric sulphate but
not tartar emetic.

_Quebrachitannic_ acid is got from the wood of the quebracho colorado,
_Quebrachia lorentzii_ (formerly _Loxopterygium_) which must not be
confounded with the bark of the _Aspidospermum quebrachia_, which is
valuable, not for its tannin, but for an alkaloid, aspidospermin,
which is used for medical purposes. It has been pretty thoroughly
investigated by P. N. Arata (Chem. Soc. Jour., xxxiv. 986 and xl.
1152). It seems, however, a little doubtful to the writer whether the
substance investigated by Arata was not the anhydride of the tannin,
rather than the tannin itself, as it presents many points of analogy to
catechu-red and was less soluble in water than quebracho tannin appears
in practice to be.

According to Arata, quebrachitannic acid is a pale red amorphous mass,
having an astringent taste and yielding a light cinnamon coloured
powder. It is insoluble in carbon-bisulphide, turpentine oil, and
benzene. Its aqueous solution gives a white precipitate with both
normal and basic lead acetate, which when heated, acquires first a
rose, and then a chocolate colour; with ferric chloride a green liquid
is produced, which changes after a time to red and becomes black on
addition of sodium acetate. It forms white precipitates with gelatin,
albumen, and alkaloids. By dry distillation it yields catechol. By
fusion with potash or the action of sulphuric acid, phloroglucol and
protocatechuic acid, while nitric acid converts it into oxalic and
picric acids. While it shows great similarity in its reactions to
catechutannic acid, it differs materially in percentage composition,
containing only 52·5 as compared with 62·0 per cent. of carbon.




CHAPTER V.

WATER AS USED IN TANNING.


Water, as obtained from rivers, wells, or water companies, contains a
variety of impurities which affect its use in tanning, but of which
in most cases the precise influence is very imperfectly known. These
may be classified into (1) merely suspended matters, such as clay and
mud, and sometimes animal or vegetable organisms such as infusoria;
(2) dissolved mineral matters, which consist mostly of lime and
magnesia salts and which make the water hard; (3) and organic dissolved
impurities, such as the brown colour of peat water and the putrefying
animal matters of sewage contamination.

_Mud_ is always objectionable. It frequently contains organic slime
and organisms which encourage the putrefaction of hides put in it to
wash or soften. It also almost invariably contains iron as one of its
constituents, and hence stains leather, and gives bad coloured liquors.
It is not easily got rid of by filtration, as large filter-beds are
expensive and difficult to keep in order, and much space is required
to clear water by subsidence. Some filter easily cleaned offers the
best chance of success. The Pulsometer Company supply such a filter,
consisting of sponge tightly packed below a perforated piston. To
cleanse the filter a stream of water is passed the reverse way, and the
piston raised, and worked up and down, either by hand or power, so as
to loosen and knead the sponge. The Atkins "water scrubber," in which
sand may be used as a filtering medium, seems also well adapted for
the purpose. If lime be precipitated by Clark's, or other process, it
usually carries down the mud with it.

Rain water and the water of streams in mountain districts of hard
igneous rock are generally nearly free from mineral constituents. This
is the case with the Glasgow water from Loch Katrine, and the Thirlmere
water which is to supply Manchester. Such water, if cold enough, and
free from mud and organic impurity, is the best for almost every
purpose in tanning. Most river water, however, and all spring water, is
contaminated with mineral matter which it has dissolved out of the soil
and rocks through which it has flowed. The principal of these mineral
constituents are lime and magnesia. These occur both as sulphates and
chlorides, and as hydric carbonates, or "bicarbonates." The sulphates
and chlorides constitute "permanent" hardness, while that due to
bicarbonates is called "temporary," from the fact that on boiling, half
the carbonic acid is driven off, and the lime or magnesia is deposited
as an insoluble neutral carbonate, thus softening the water. Any water
which can be softened in this way by boiling may also be softened by
the addition of a suitable quantity of lime, thus:--

      Calcic hydric
       carbonate.          Lime.       Chalk.     Water.

  (CO_{3})_{2}CaH_{2} + Ca.(OH)_{2} = 2CaCO_{3} + 2OH_{2}

This is Clark's process, and the chalk may either be separated
by subsidence, which quickly takes place, or by a special filter
(Porter-Clark). Thus the Bristol water, which from determinations by
Mr. W. N. Evans, contains considerable temporary hardness and but
little of permanent, may be almost completely softened by Clark's
method. (For method of determining hardness and quantity of lime
required, see p. 97).

The lime and magnesia constituting permanent hardness may be removed
by the addition of sodic carbonate (soda ash or crystals); but this
is expensive on a large scale, and as an equivalent quantity of sodic
sulphate or chloride is left in the water, it is for most purposes
of questionable advantage, though in some cases useful for the feed
water of boilers. When employed for this purpose, the water should if
possible be softened and settled before using, instead of adding the
soda in the boiler itself, as is generally done. Soda is the active
ingredient of many boiler compositions. For preventing furring, most
tanning materials or even waste tan-liquors are very effective, and the
danger of any corrosive action is lessened by the addition of a portion
of soda ash. So far as is yet known, from the tanning point of view, it
is hardly necessary to make any distinction between lime and magnesia,
which may be considered simply as "hardness." A hard water probably
softens dried hides more slowly, though it is possible that the
observed difference may be due in many cases to the lower temperature
of wells from which hard water is generally derived. In the actual
limes, the hardness of the water can have no appreciable influence,
though if sodium sulphide be used alone, a certain waste occurs from
temporary hardness, which may render it advisable to add a little lime.
It is in the washing of the hides from lime that the influence is first
distinctly felt. If limey goods, after unhairing, are placed in a water
with much temporary hardness, the same action occurs as in Clark's
water softening process, and chalk is deposited in the surface of the
hides, making them harsh and apt to "frize" or roughen the grain in
scudding, and causing bad colour by combining with the organic acids
of the liquors. The common, but not wholly satisfactory, expedient is
to add a little lime, or better, a few pailfuls of lime liquor to the
water before putting in the hides. The best plan is to use a properly
softened water. Permanent hardness is not injurious in this way.

The hardness of water, and the dissolved carbonic acid which it
contains, are, together with its temperature, the principal factors
which determine whether a hide will plump or fall in it. Almost
the only accurate investigation of this point has been made by W.
Eitner ('Der Gerber,' iii. 183). He placed pieces of hide, unhaired
by sweating, and quite flat and fallen, in water for 4 days at a
temperature of 46° F. (8° C.), with the following results:--

  1. In distilled water                           Scarcely at all plumped.

  2. "  water saturated with CO_{2}                Well plumped.

  3. "    "   with lime bicarbonate, 20° German }
                     scale of hardness          } Tolerably plump.

  4. "    "    "   magnesia bicarbonate, 20° do.     do.     do.

  5. "    "    "   lime sulphate, 20° do.         Well plumped.

  6. "    "    "   magnesia sulphate, 20° do.     Best plumped.

  7. "    "    "   magnesium chloride, 20° do.    Not at all plumped.

  8. "    "    "   common salt, 20° do.               do.      do.

     (1 German degree of hardness corresponds to 1 of lime in 100,000.)

The peculiarities which were shown by the hide pieces on removal
from the water were maintained throughout the tanning, which was
conducted in imitation of the German method, the hide being swollen
and coloured through in weak birch-bark liquors, made with distilled
water and acidified in each case with equal quantities of lactic
acid, and finally laid away till tanned in a mixture of oak bark and
valonia. No. 6, from magnesia sulphate, was the best; then No. 2; No.
3 was less good, but all the pieces from 1 to 6 were firm, close,
and of good substance and texture, No. 1 having swelled well in the
sour liquor. On the other hand, 7 and 8 scarcely swelled in liquor,
but remained flat throughout, and were looser, thinner, and of finer
fibre. From this experiment it is clear that while sulphates and
carbonates exert a favourable influence on plumping, chlorides do the
reverse, not only not plumping themselves, but placing the hides in an
unfavourable condition for the plumping action of acids in the liquors.
These experiments are quite borne out by the writer's experience in
practice. The water at the Lowlights Tannery, which in dry weather
is mostly obtained from beds of what was originally sea-sand, and
which consequently contains a very abnormal proportion of chlorides
(up to 68 pts. NaCl per 100,000), requires special and very careful
management to make thick leather, notwithstanding its containing a
considerable quantity of calcium and magnesium sulphates. These facts
also indicate the importance of the thorough removal of salt from hides
intended for sole-leather. Plumping is not a desirable thing in leather
intended for dressing purposes, and it is possible that the use of a
small percentage of salt in the liquors or wash waters might enable
bating to be dispensed with. Like a bate, salt would dissolve a small
proportion of hide substance (see p. 19). There is no practicable means
of removing chlorides from water, but Eitner suggests the addition of
a small quantity of sulphuric acid to water containing much temporary
hardness (bicarbonates), by which it is converted into permanent
(sulphates), which, as we have seen, plumps better. For this purpose
about 2·8 oz. of ordinary English vitriol (sp. gr. 1·490) per 100 cub.
ft. of water is required for each part of lime Ca(OH)_{2} per 100,000
(see p. 97 for testing of water). A simpler guide is to add enough to
purple, but not to redden litmus paper, even after moving it about in
the water for some minutes. The acid must of course be well mixed by
plunging. It must be borne in mind that Eitner's experiment was on
sweated hides, and that with limed hide, which is kept plump by the
dissolved lime retained in the hide, the conditions are different,
and different results as regards carbonic acid and bicarbonates would
probably be obtained. Both these would convert the lime in the hide
into chalk, which is both insoluble and inert, and the hide would
probably fall, at any rate till the lime was completely carbonated,
while hides would remain plumpest in waters most free from substances
capable of neutralising lime. One of the waters most effective in
plumping limed hides is that of the river at Lincoln. Its hardness
and contents in chlorine is, as compared with Lowlights water in dry
weather,

                                                           Per 100,000.

  _Lincoln_, permanent hardness 8·43, temporary 8·32, chlorine 2·60 pt.
  _Lowlights_,    "       "    60·5,      "    45·0      "    41·7  "

Both waters have a considerable quantity of organic matter, and both
owe their hardness in part to magnesia. From this we might conclude,
what may be _à priori_ expected, that the softer the water, the plumper
limed hides remain in it. I am informed, however, by Mr. S. L. Evans,
that in the Dartmoor water, which is very soft, but peaty, hides fall
rapidly. In this case the colouring matters of the peat, which are
of the nature of very weak acids, probably neutralise the lime. It
may also be remarked, that wherever the conditions of putrefaction or
decaying organic matter is present, hides rapidly fall, for the same
reasons as they do in a bate.

While the injurious effect of bicarbonates on limed hide is matter of
common experience, their influence on liquors and tanning is not so
well understood. It is certain that they neutralise and combine with
the organic acids of the liquors, and probably with some species of
tannin, and as 1 part per 100,000 amounts to 1 oz. per 100 cub. ft.,
the acid required to neutralise a very hard water amounts to something
considerable. It is well known that hard waters make bad tea, and the
influence of hardness on the extraction of tannin is a subject well
worthy of investigation, and which the writer hopes to examine.

On dyeing, at least as regards dye-woods, the influence of bicarbonates
is distinctly favourable, and this is also stated to be true of woad,
cochineal, and indigo-carmine.

Beside lime and magnesia salts, water may contain sulphates and
chlorides of soda and potash; but not carbonates of these bases in
presence of permanent hardness. In soft waters carbonates are sometimes
present, and form carbonate of lime in limed hides. Hides are said
to soften rapidly in such water. Alkaline sulphates are not known to
have any injurious action, and chlorides have already been spoken of.
Iron may be present in solution as bicarbonate, but not in any other
form in presence of bicarbonate of lime. It is removed completely with
the temporary hardness by Clark's process, or boiling. Iron is much
more common merely in suspension, as mud, but is always objectionable.
Most waters contain a little silicic acid and alumina, and some few
considerable quantities. Such waters are said to harden leather, but
the writer knows of no case where they are in use in England; and their
occurrence is comparatively rare.

For comparison, analyses of a few spring and river waters are given on
p. 89.

Analyses of various Waters.

  ────────────┬───────┬─────────┬───────┬───────────┬─────────┬──────────┐
              │Thames,│ Thames, │Severn,│ Thirlmere.│ Rhine,  │ Spring,  │
              │at Kew.│ at      │Wales. │           │ Basle.  │ Witley,  │
              │       │ London  │       │           │         │ Surrey.  │
              │       │ Bridge. │       │           │         │          │
  ────────────┼───────┼─────────┼───────┼───────────┼─────────┼──────────┤
  Total solids│ 31·0  │  40·8   │  3·87 │    5·15   │  16·9   │   7·6    │
  Ca          │  7·6  │}  8·21  │{  ·3  │     ·43   │   5·55  │    ·81   │
  Mg          │   ·47 │}        │{  ·2  │     ·12   │    ·48  │    ·18   │
  Na          │   ·87 │   1·43  │   ·6  │     ·49   │    ·06  │    ·64   │
  K           │   ·39 │    ·17  │   ·1  │      ..   │    ..   │    ·23   │
  CO_{3}      │ 10·53 │   6·94  │   ·2  │    1·09   │   8·62  │   trace  │
  SO_{4}      │  3·95 │   3·22  │  1·3  │     ·75   │   1·54  │   1·33   │
  Cl          │  1·21 │   6·36  │   ·8  │    1·1    │    ·15  │   1·28   │
  SiO_{2}     │   ·63 │    ·18  │   ·2  │     ·07   │    ·21  │   1·23   │
  Temporary   │}      │         │       │           │         │          │
   Hardness   │}20·0  │    ..   │   ·9  │     ·7    │     ..  │   2·8    │
  Permanent   │}      │         │       │           │         │          │
  hardness    │       │         │       │           │         │          │
  ────────────┴───────┴─────────┴───────┴───────────┴─────────┴──────────┘

  ────────────┬────────┬─────────┬─────────┬────────┬────────┬───────────┐
              │Spring, │Artesian,│Ripley's,│ Well,  │River   │Beamhouse  │
              │Watford,│Well     │Well     │ Council│Witham, │ well,     │
              │Herts.  │Trafalgar│Holbeck, │ Acad., │Lincoln.│ Lowlights.│
              │        │Square.  │Yorks.   │ Vienna.│        │           │
  ────────────┼────────┼─────────┼─────────┼────────┼────────┼───────────┤
  Total solids│ 33·8   │  84·9   │ 150·4   │  212·2 │  33·0  │    ..     │
  Ca          │ 11·0   │   1·56  │   1·22  │   19·6 │   6·08 │    ..     │
  Mg          │  ..    │    ·84  │    ·42  │   10·4 │   ..   │    ..     │
  Na          │  1·1   │  29·4   │  58·1   │   41·1 │   ..   │    ..     │
  K           │  ..    │    ·85  │    ·83  │   10·5 │   ..   │    ..     │
  CO_{3}      │ 15·6   │  11·3   │  39·8   │   97·6 │   ..   │    ..     │
  SO_{4}      │   ·68  │  20·6   │   1·03  │   26·7 │   7·59 │    ..     │
  Cl          │  1·21  │  16·5   │  45·2   │    3·5 │   2·60 │   21·8    │
  SiO_{2}     │  1·16  │    ·57  │   2·63  │     ·3 │   ..   │    ..     │
  Temporary   │        │         │         │        │        │           │
   hardness   │   ..   │    ..   │    ..   │    ..  │{ 8·0   │   39·7    │
  Permanent   │        │         │         │        │        │           │
   hardness   │   ..   │    ..   │    ..   │    ..  │{ 8·4   │   48·0    │
  ────────────┴────────┴─────────┴─────────┴────────┴────────┴───────────┘




CHAPTER VI.

METHODS OF CHEMICAL ANALYSIS FOR THE TANNERY.


It is assumed that the reader has an elementary knowledge of chemistry,
and of the common manipulations of the laboratory; but at the risk of
giving information which to many is already familiar, the principles
that underlie those methods of testing which are most applicable to
technical purposes must be briefly explained.

_Standard Solutions._--If 40 _grm._ of pure caustic soda (NaHO) be
dissolved in water, and a little tincture of litmus added, it will be
coloured a bright blue. If hydrochloric acid be now added, drop by
drop, the litmus will at last become purple, and a single drop more
would turn it a bright red. At this point the liquid is neither acid
nor alkaline, and if it be evaporated to dryness, nothing will be left
but 58·5 _grm._ of common salt (NaCl), while 18 _grm._ of water will
be formed and have escaped. We have therefore used exactly 36·5 _grm._
of pure HCl, and if we dissolve 40 _grm._ of caustic soda in 1 _litre_
of water, and 36·5 _grm._ of pure HCl in another, equal parts of these
liquids will always exactly neutralise each other, forming nothing
but common salt and water. It will be obvious that if we have a soda
solution of the strength named, we can find the amount of hydrochloric
acid in any solution of unknown strength, by seeing how much of it
is required to neutralise, say, 10 _c.c._ (= 0·4 _grm._ soda) of the
known solution. Instead of 40 _grm._ of caustic soda, we may take 56
_grm._ of potash to the _litre_, and it will exactly neutralise an
equal volume of the hydrochloric solution containing 36·5 _grm._ If,
again, we make a solution containing 49 _grm._ of pure sulphuric
acid (SO_{4}H_{2}) per _litre_, it will neutralise an exactly equal
volume of either the soda or the potash solution, thus being precisely
equivalent to the HCl solution. Such solutions are called normal, and
any normal acid solution will neutralise an equal volume of any normal
alkali, and _vice versâ_. For many purposes normal solutions are too
strong, and solutions containing 1/10 of the quantities required for
normal solution are preferable; such solutions are called decinormal.
All solutions containing known quantities of chemicals, and intended
for use in volumetric analysis, are called Standard solutions.

_Indicators._--The tincture of litmus used to show when the solution
is exactly neutral is called an indicator, and many materials are
used in a similar way in different analytical processes. Thus the
indigo solution in Löwenthal's process is an indicator. A more useful
indicator than litmus for tannery purposes is Dr. Lunge's "methyl
orange," which is indifferent to carbonic acid, and may therefore be
used in the cold with solutions of alkaline carbonates; which are much
more easily made and preserved than those of the caustic alkalies
necessary with litmus. It is very sensitive to mineral acids, but not
equally so to organic. It may be obtained of Messrs. Mawson and Swan,
of Newcastle; and as a minute quantity only must be used for each
test, it is really cheaper than litmus, and a few _grm._ will last a
lifetime. It must be dissolved in water, and not more than 2 or 3 drops
taken for each titration. (Titration signifies an estimation by means
of a standard solution.) Other indicators will be named in connection
with the analytical methods in which they are used.

[Illustration: Fig. 9.]

_Instruments._--To practically carry out analysis by standard
solutions, measuring glasses are required. One or more flasks marked
in the neck to hold exact quantities (Fig. 9), one at least, holding
1 _litre_, are indispensable. One or two graduated cylinders (Fig.
10), holding 100 _c.c._, and divided into tenths of _c.c._, are very
useful, and it is well also to have one holding a _litre_, and provided
with a stopper (Fig. 11). This is called a "test mixer," but is not
absolutely essential.

[Illustration: Fig. 10.]

[Illustration: Fig. 11.]

[Illustration: Fig. 12.]

[Illustration: Fig. 13.]

[Illustration: Fig. 14.]

Pipettes (Fig. 12) are tubes with a mark on the stem by which exact
quantities of liquid can be taken. Several holding 5, 10, 20, and 25
_c.c._ are necessary, and one holding 10 _c.c._ and divided into tenths
is advisable. Most important of all is the burette (Fig. 13). If only
one is to be had, it must be a Mohr's burette with a glass tap, but as
alkaline solutions are apt to set glass taps fast, it is well to have
one with a tap, and another with a pinchcock (Fig. 14). They should
hold 50 or 25 _c.c._ and be divided into tenths. The burette in use is
fixed in a stand (Fig. 15) and filled up to the top of the graduation,
and the quantity of solution delivered is then shown by the scale. It
is usual to read by the under side of the hollow of the liquid, keeping
the eye carefully level with it.

[Illustration: Fig. 15.]

A chemical balance suitable for the preparation of standard solutions
and general analytical use, is shown in Fig. 16. The beam is provided
with steel or rock-crystal knife-edges at the centre, which are
supported on agate planes, and similar edges _a_ support the pans.
Except at the moment of weighing, the beam, and in good balances the
pans also (at _b_), are steadied by supports raised by turning the
milled head _c_. The long pointer _d_ moving over a scale, shows when
the beam is horizontal; but the weighing is performed, not by waiting
till the balance comes to rest, but by noting when the oscillations
are equal on each side of the zero point. The _weights_, which should
run from 50 _grm._ downwards, are usually of brass (preferably gilded)
down to 1 _grm._, while the fractions to 0·01 _grm._ are of platinum
foil. Milligrammes and fractions are weighed by a "rider" of wire
weighing 0·01 _grm._, and moved along the beam (which is graduated for
the purpose like a steelyard) by the arms _e_. A fair balance should
turn distinctly with 0·001 _grm._, and a good one with 0·0001 _grm._
If equal weights are placed on each pan, they should of course balance,
and if changed side for side the balance should be maintained. If not,
the arms of the beam are unequal. Weights always have trifling errors,
but if by a really good maker, these are generally so small that they
may be disregarded except in very delicate researches. The weights
should always be placed on the scale in regular order, beginning with
the heaviest, and it is well to accustom oneself to reading the weight
by the vacant places in the box as well as by the weights on the scale.

[Illustration: Fig. 16.]

While of course it is most important, and for accurate work essential,
to have as good a balance as possible, much may be done in technical
work, even with a good pair of druggists' scales; and most standard
solutions may be bought ready made; while from two or three accurately
adjusted solutions many others may be made volumetrically.

_Preparation of Standard Acid and Alkaline Solutions._--In practice
it is very difficult to obtain perfectly pure caustic soda, free from
water and carbonic acid, both of which are greedily absorbed by it from
the air, so that a standard solution cannot practically be made by
directly weighing out the substance as suggested in the introductory
paragraph. In sodic carbonate, however, we have a substance which is
easily obtained pure and dry, and which may be used for almost all the
purposes to which a caustic solution could be applied. A decinormal
solution is strong enough for most of the work in a tannery, though it
is a convenience to have both normal and decinormal, and a stock of the
stronger solution will last a longer time and is readily diluted to
decinormal strength by adding 1 part to 9 parts of distilled water. To
make a normal solution, about 60 _grm._ of the purest sodic carbonate
are placed in a porcelain basin or platinum crucible and heated over
a Bunsen gas-burner or spirit-lamp, nearly to redness, and allowed
to cool closely covered up. Of the salt thus dried 53 _grm._ are
accurately weighed into a beaker and dissolved in distilled water. The
solution is then poured into a gauged _litre_ flask, and carefully
filled up with water at a temperature of 59° F. (15° C.) to the mark on
the neck. The whole is then poured into a good-sized stoppered bottle
(40 oz.) and vigorously shaken for 5-10 minutes. This thorough shaking
is important with all standard solutions, and without experience no
one would believe how much shaking is required uniformly to mix a
solution. Probably more difficulty to beginners in analysis arises from
neglect of this matter than from any other cause. To make a decinormal
solution, proceed in precisely the same way, using 5·3 _grm._ instead
of 53; or dilute as above.

_Standard Acid Solution._--For this purpose any one of several acids
may be used, each of which has its special advantages.

Oxalic acid is the easiest to make of any. A sufficient quantity of
pure crystallised oxalic acid is powdered and pressed between filter
paper, so as to absorb the moisture which occasionally is retained
in cavities of the crystals. 6·3 _grm._ is then weighed out and
dissolved in water, exactly as was done with sodic carbonate, forming
a decinormal solution. It is used in Löwenthal's tannin estimation
process and may also be employed to determine alkalies, but forms
insoluble calcium oxalate with lime salts, and does not give a sharp
reaction with methyl orange indicator. Hence litmus must be used, or a
few drops of a neutral solution of calcium chloride added to the methyl
orange, when hydrochloric acid will be liberated as soon as there
is excess of the acid, and the indicator will be promptly reddened.
Sulphuric acid is the most permanent of any acid solution, and may be
generally employed. It forms insoluble sulphates with lime, baryta, and
strontia. To make a normal solution, 35 _c.c._ of the pure concentrated
acid are poured into at least 3 or 4 times as much distilled water,
and allowed to cool, and are then made up to about 1 _litre_ and well
shaken. The burette is filled with the mixture, 10 _c.c._ of the
standard sodic carbonate are measured into a beaker, 2 or 3 drops of
methyl orange solution are added, and the acid is run in with constant
stirring till the indicator is just beginning to redden. This must be
repeated, and the two titrations should exactly agree. Suppose that
9.5 _c.c._ are required, then 950 _c.c._ of the trial acid are equal
to 1 _litre_ of the soda. If therefore 950 _c.c._ be measured into a
test mixer, and made up to 1 _litre_, the solution should be accurately
decinormal. Of course great care must be used in the whole process.
If a gauged flask only is at hand it will be easier to measure into
it the water required to make up the _litre_, and then fill to the
mark with the trial acid. Normal hydrochloric acid may be made exactly
as described for sulphuric acid, but using about 100 _c.c._ of the
strongest acid. Decinormal solutions of both these acids may be made by
the same methods; using 1 tenth the quantities, or by dilution of the
normal solution.

Beside comparison with sodic carbonate solution, hydrochloric acid
may also be checked by determining the amount of chlorine present,
with silver nitrate (see p. 98) 10 _c.c._ of decinormal acid should of
course be equal to 10 _c.c._ of decinormal silver nitrate.


Table giving the Quantity of the Following Substances contained in or
equivalent to 1 _litre_ of Normal or 10 _litres_ of Decinormal Standard
Solution.

     Sulphuric acid             49 _grm._ SO_{4}H_{2} = 40 _grm._ SO_{3}
     Hydrochloric acid          36·5  "   ClH = 35·5 _grm._ Cl.
  [G]Oxalic acid                63·0  "   C_{2}O_{4}H_{2} + 2 Aq.
     Acetic  "                  60·0  "   C_{2}H_{3}O_{2}H.
     Soda                       40·0  "   NaHO.
     Sodic carbonate            53·0  "   Na_{2}CO_{3}.
  [G]Lime                       28·0  "   CaO = 37·0 _grm._ CaH_{2}O_{2}.
  [G]Calcic carbonate           50·0  "   CaCO_{3}.
     Ammonia                    17·0  "   NH_{3}.
  [G]Barium hydrate             76·5  "   BaO = 85·5 _grm._ BaH_{2}O_{2}.
     Barium chloride           104·0  "   BaCl_{2}.
     Zinc chloride or sulphate  32·6  "   Zn = 16·0 _grm._ S. as sulphide.
     Silver nitrate            170·0  "   AgNO_{3} = 35·5 _grm._ Cl.
     Potassic permanganate      31·6  "   K_{2}MnO_{4}.

[Footnote G: Insufficiently soluble in water to form a normal solution.]


EXAMINATION OF WATER.

_Hardness_ (Hehner's process). (_a_) Temporary Hardness.--As has
been stated (p. 84), this consists of lime and magnesia carbonates.
As methyl orange is not affected by carbonic acid, bicarbonates of
alkaline earths have an alkaline reaction, and may be estimated in
solution by standard acid like the alkalies themselves. 100 _c.c._,
or in soft waters 200 _c.c._, of the water is measured into a beaker,
a drop or two of solution of methyl orange added, and decinormal
hydrochloric or sulphuric acid run in from the burette with constant
stirring till the colour just changes to pink. This is repeated, and
the average taken. The two determinations should not at the most differ
more than 1/10 _c.c._ Each _c.c._ represents 5 parts per 100,000 of
CaCO_{3} or 2·8 parts of CaO; or corresponding quantities of magnesia
(4·2 parts of MgCO_{3} or 2 parts MgO), when 100 _c.c._ of water are
used.

(_b_) Permanent Hardness.--200 _c.c._ are measured into a beaker and
boiled for 15 minutes with 40 _c.c._ decinormal sodic carbonate. The
mixture is then allowed to cool and made up to 250 _c.c._; or the flask
and its contents may be weighed before boiling and made up again to the
same weight. It is then filtered, and 60 _c.c._ representing 50 _c.c._
of the original water, is twice titrated with decinormal acid and the
result added. If the water were pure, exactly 10 _c.c._ should be
required to neutralise the 10 _c.c._ of sodic carbonate, but if there
be permanent hardness a part of the sodic carbonate will be already
neutralised with the acids of the lime and magnesia salts, which have
been precipitated as carbonates together with the carbonates of these
bases originally present in the water. The hardness will therefore be
represented by the loss, i. e. the number of _c.c._ of acid used for
100 _c.c._ of the original water must be subtracted from 20 and the
remainder calculated as before, or if calculated as sulphates, each
_c.c._ represents 6·8 parts of CaSO_{4} or 6 parts of MgSO_{4} per
100,000. If, as is sometimes the case, more acid is required than is
needed for the sodic carbonate used, the excess corresponds to sodic
carbonate originally present in the water. In this case there can be no
permanent hardness.

_Chlorine in Water._--If silver nitrate be added to a solution of any
chloride, the silver is precipitated as white curdy insoluble silver
chloride. As indicator, a few drops of neutral potassic chromate are
used. So long as any chloride is present the red silver chromate
which forms is at once decomposed, and the silver converted into
white chloride. But as soon as all the chloride is exhausted, the
red chromate becomes permanent. To prepare a standard decinormal
solution of silver, 17 _grm._ of pure recrystallised silver nitrate are
dissolved in 1 _litre_ of distilled water. To perform the estimation
50 _c.c._ of water are measured into a beaker, 2 or 3 drops of strong
solution of pure yellow potassic chromate are added, and then silver
nitrate from the burette till a permanent red is formed. This is
repeated, and the results are added together, representing 100 _c.c._
of water. Each _c.c._ of silver nitrate used represents 3·55 parts of
chlorine, or 5·85 parts of sodic chloride per 100,000. If more than 10
_c.c._ of silver solution are required to 50 _c.c._, it is advisable
to use a smaller quantity of water. If the process be applied to
other liquids than natural water, it must be borne in mind that the
solution must not contain free acids or alkalies except carbonic acid.
If this is not the case the liquid may be rendered faintly alkaline,
with lime-water free from chlorides, and the excess of lime removed by
passing carbonic acid through it; or it may be slightly acidified with
sulphuric acid, and shaken with a little pure precipitated calcic or
baric carbonate.

_Detection of other Impurities._--Sulphuric acid (as sulphates) is
seldom wholly absent, but its presence may be proved, by adding excess
of barium chloride to the water slightly acidified with hydrochloric
acid (2-3 _c.c._ of saturated solution of BaCl_{2} are sufficient for
any ordinary water); if the mixture be allowed to stand overnight in a
100 _c.c._ cylinder beside a solution containing a known, and not very
different quantity of decinormal sulphuric acid, the quantity present
may be roughly compared by measuring the bulk of the precipitates.

Lime may be similarly detected and roughly measured by precipitation
with excess of ammonic oxalate in presence of ammonium chloride, to
hinder precipitation of magnesia. Lime-water, which may be used as a
standard, contains about 128 parts of lime per 100,000.

Magnesia is detected by adding ammonium phosphate to the filtrate from
the precipitated oxalate of lime. If the mixture be allowed to stand
in a warm place for 24 hours all the magnesia will be precipitated as
ammonio-magnesic phosphate.

Silica, &c.--100 _c.c._ of the water is acidified with a little HCl
evaporated to dryness, moistened with HCl, and treated with a little
hot water. The silica or silicic acid is left undissolved. The solution
from which the silicic acid has been filtered off is evaporated to
small bulk and ammonia added, when iron will be precipitated as brown
ferric oxide, which is coloured black by tannin or tanning liquor.
If copper be present it will give a blue solution with the ammonia.
Iron may also be recognised by evaporating the water to small bulk
with a trace of HCl, and adding a little sodium acetate, when if
iron be present it will be coloured black by tannin, red by ammonium
sulphocyanide, and blue by potassium ferrocyanide (prussiate of
potash). Its quantity may be estimated (Thomson, Chem. Soc. Abstracts,
May 1885) by measuring 100 _c.c._ of the water to be tested and 100
_c.c._ distilled water into two similar cylinders, adding to each 5
_c.c._ of dilute hydrochloric acid (1:5) and 15 _c.c._ of a solution
of potassium sulphocyanide (40 _grm._ per _litre_), and then adding to
the distilled water cylinder a very dilute standard solution of ferric
salt, till its colour matches the other. If the iron contained in the
water is in the ferrous condition, it must be oxidised with potassic
permanganate before testing.

A suitable ferric standard solution may be made by dissolving 0·1
_grm._ of clean, bright, soft iron wire in a little hydrochloric acid
in a long-necked flask, adding nitric acid so long as red fumes are
produced, evaporating nearly to dryness, and making up to 1 _litre_
(more accurately 996 _c.c._). Each _c.c._ will then equal 0·0001 _grm._
Fe.

Lead (and copper) may be detected by passing sulphuretted hydrogen
through the water acidified with HCl, or by adding a drop of fresh
ammonium or sodium sulphide to the slightly acidified water, when a
brownish coloration clearly visible in a deep beaker set on a sheet of
white paper will be produced. Iron also gives a black with sulphides in
alkaline solution. Copper may be distinguished from lead by the blue
given with ammonia, and by a reddish-brown precipitate with potassium
ferrocyanide.

For accurate quantitative estimation of these impurities, the regular
works on the subject, such as Thorpe's 'Quantitative Analysis,'
Sutton's 'Volumetric Analysis,' or Fresenius' 'Quantitative Analysis,'
must be consulted.


EXAMINATION OF COMMERCIAL ACIDS.

_Sulphuric acid_ 10 _grm._ may be made up to 100 _c.c._ and well
mixed, and of this 10 _c.c._ may be tested with normal sodic carbonate
in presence of methyl orange. Each 1 _c.c._ of soda solution used
corresponds to 0·049 _grm._ or 4·9 per cent. of H_{2}SO_{4}. For most
purposes, the strength may be ascertained from the specific gravity, as
measured by a hydrometer or weighed in a specific gravity bottle. The
following table gives the strength at 59° F. (15° C.):--

  ─────────┬───────────────┬────────────
  Specific │  Degrees      │  Per cent.
  Gravity. │ Twaddell.[H]  │ H_{2}SO_{4}
  ─────────┼───────────────┼────────────
           │     °         │
  1·8426   │   168·5       │    100
  1·8376   │   167·5       │     95
  1·822    │   164         │     90
  1·786    │   157         │     85
  1·734    │   147         │     80
  1·675    │   135         │     75
  1·615    │   123         │     70
  1·557    │   111         │     65
  1·501    │   100         │     60
  1·448    │    90         │     55
  1·398    │    80         │     50
  1·351    │    70         │     45
  1·306    │    61         │     40
  1·264    │    53         │     35
  1·223    │    45         │     30
  1·182    │    36         │     25
  1·144    │    29         │     20
  1·106    │    21         │     15
  1·068    │    14         │     10
  1·032    │     6         │      5
  ─────────┴───────────────┴────────────

[Footnote H: Degrees of Twaddell's hydrometer may be reduced to
specific gravity by multiplying by ·005 and adding 1·, thus 10° Tw. =
1·050 sp. gr.]

The impurities of sulphuric acid most common and injurious for tanning
purposes are iron and nitrous acid. Iron is detected on neutralising
with soda or ammonia, when it falls as a yellowish precipitate, which
may be recognised by the ordinary tests (p. 100). Nitric and nitrous
acids are detected by pouring a strong solution of ferrous sulphate
cautiously on to the top of the strong cold acid, when a dark ring is
formed at the junction of the two liquids.

_Hydrochloric acid_ may be tested with soda solution like sulphuric. 1
_c.c._ of normal soda = 0·0365 _grm._ or 3·65 per cent. HCl. It may
also be calculated from specific gravity.

  ──────────────────┬───────────────
  Specific Gravity, │ Per cent. HCl.
      15° C.        │
  ──────────────────┼───────────────
      1·200         │     40
      1·177         │     35
      1·151         │     30
      1·126         │     25
      1·100         │     20
      1·075         │     15
      1·050         │     10
      1·025         │      5
  ──────────────────┴───────────────

The presence of iron is indicated by a yellow colour, and may be
confirmed by the usual tests as in sulphuric acid.

_Oxalic acid_ should be pure white and soluble in distilled or
rain-water. 6·3 _grm._ may be weighed out, and made up to 200 _c.c._
If 20 _c.c._ of the solution for a test be used, each _c.c._ of
normal soda solution equals 10 per cent. of pure crystallised acid,
C_{2}O_{4}H_{2} + 2 Aq. The end-reaction with methyl orange is rendered
sharper by the addition of a few drops of neutral calcic chloride
towards the end of the titration.

_Acetic acid_ may be similarly determined, each _c.c._ of normal alkali
being equivalent to 0·06 _grm._ of C_{2}H_{4}O_{2}. Caustic soda, or
lime-water and litmus, give sharper results than sodic carbonate and
methyl orange. Brown pyroligneous acid is difficult to test from the
dark compounds formed with soda, but may be indirectly determined
by the quantity of marble, baric carbonate, or magnesia which it
will dissolve (compare p. 100), or very possibly by lime-water like
tan-liquors with a little tannin as indicator.


EXAMINATION OF LIME AND LIME-LIQUORS.

The quantity of caustic lime in either quicklime or lime-bottoms may
be determined by weighing a quantity of the finely powdered material
containing not more than 1 _grm._ of caustic lime, and shaking it
thoroughly with 1 _litre_ of distilled water and filtering. 100 _c.c._
should be taken, and decinormal acid, sulphuric or hydrochloric (or
if oxalic, with addition of neutral calcic chloride, or with litmus
instead of methyl orange as indicator). Each _c.c._ of decinormal
acid corresponds to 0·0028 _grm._ of CaO. If the filter and residue
be treated with sufficient normal acid to dissolve the whole of the
carbonates, and then titrated back with normal sodic carbonate and
methyl orange, the loss (less soda solution required than acid was
originally employed) is equal to the carbonate of lime and carbonate
and hydrate of magnesia present. 1 _c.c._ of normal acid = 0·05 _grm._
of CaCO_{3}.

[Illustration: Fig. 17.]

[Illustration: Fig. 18.]

Lime-water and lime-liquors may be titrated as above, with sulphuric
or hydrochloric acid and methyl orange; but in the latter case ammonia
(and if soda ash or "Inoffensive" is used, soda and potash also),
and the lime salts of weak organic acids will be estimated with it.
It is difficult to get a sharp end-reaction in old liquors from the
organic acids (caproic, amidocaproic, &c.) present. To determine the
ammonia, 50-100 _c.c._ of the liquor may be distilled in a small
retort or flask, and the escaping NH_{3} collected in a =U=-tube or
"nitrogen bulb" (Fig. 17), containing 20-50 _c.c._ of normal acid,
which is afterwards titrated back with sodic carbonate and methyl
orange. Kathreiner employs the arrangement shown in Fig. 18. 30 _c.c._
of the liquor to be examined is placed in a shallow vessel on a piece
of ground-glass, and 10 _c.c._ of normal acid in a second cup, which
is supported over the other by a glass or wire triangle. The whole
is covered with a small bell-glass, of which the edges are smeared
with, vaseline. At the end of 24 hours, all the ammonia will have been
absorbed by the acid, which is titrated back. The lime-liquor sample
should be drawn after well plunging the lime, and rapidly filtered into
a flask from a funnel covered with a clock-glass.

_Determination of Gelatin and Coriin in Lime-liquors._--This cannot
be done directly, though considerable quantities of dissolved
hide-substance are precipitated on acidification of the liquor with
hydrochloric acid and saturation with common salt. If the liquor be
neutralised with hydrochloric acid, and evaporated to dryness on the
water-bath, nitrogen may be determined in the residue by combustion,
and the hide-substance calculated from it (compare p. 108). This method
is serviceable in determining the amount of hide dissolved by different
solutions, or under different conditions.

The total solids of lime-liquors are estimated by evaporating 20-30
_c.c._ in a porcelain crucible at 212° F. (100° C.). The organic matter
is then found by igniting and determining loss (using ammonia nitrate
if necessary to complete the combustion of the carbon). The ash is
mostly lime carbonate. Soda, potash, and other bases may be determined
in it by the usual methods, if required.


ESTIMATION OF SULPHUR AS SULPHIDE IN SODIUM SULPHIDE, &c.

32·6 _grm._ of chemically pure zinc is dissolved in dilute sulphuric or
hydrochloric acid. This is readily accomplished in a flask, if a piece
of platinum foil, or a few drops of platinic chloride are added to form
a galvanic couple with the zinc. After solution, sufficient ammonia is
added to redissolve the precipitate at first formed,[I] and the whole
is made up to 1 _litre_. Each _c.c._ = 0·016 _grm._ sulphur or 0·242
_grm._ of sodic sulphide. This solution is added drop by drop from a
burette to the solution of sulphide, and forms a white precipitate of
zincic sulphide. The end of the reaction is known by placing a drop
(with a glass rod) side by side on a piece of white filter paper,
with a drop of solution of lead acetate. So long as sulphide remains
in solution, it will form a black margin of lead sulphide where the
drops touch. The drops must not be placed too close, as the solid zinc
sulphide is _always_ darkened if it comes in contact with lead acetate.
It must be noted that tank-waste liquors, and many other sulphur
solutions, contain polysulphides which are estimated by zinc, but which
do not unhair, at any rate in an unaltered state.

[Footnote I: If any brown residue remains, the zinc is contaminated
with iron.]


CHEMICAL EXAMINATION OF LEATHER.

[Illustration: Fig. 19.]

_Estimation of Grease._--To determine oil and grease, a weighed
quantity (5-10 _grm._) of the leather in fine shavings or raspings
is exhausted with petroleum-ether (gasoline) in a fat-extraction
apparatus, of which a convenient form is represented in Fig. 19. The
leather is placed in the upper vessel, of which the lower opening is
loosely plugged with cotton-wool, and the petroleum-ether in the flask,
which is gently heated in a water-bath. The petroleum-ether boils and
condenses in the inclined condenser through the casing of which a
stream of cold water is passed, whence it drops back into the flask
through the material to be exhausted. When the exhaustion is complete
(when a drop of petroleum-ether from the leather leaves no grease when
allowed to evaporate on a clean glass), the upper part of the apparatus
is removed, and the ether is distilled off. If the flask has been
previously weighed, it is maintained in an air-bath at 212°-248° F.
(100°-120° C.) for some hours, allowed to cool, and weighed, when the
gain of weight is the grease and oil. Paraffin would also be extracted
and reckoned, and probably traces of resin if present. Ordinary ethylic
ether cannot be used, since tannins and many of their products are
soluble in it. Probably carbon disulphide might be substituted. Care
must be taken to avoid explosion, as the vapours of petroleum are very
combustible. The residue left in the percolator may be examined for
matters soluble in water, by extracting again with hot distilled water,
or for resins (and phlobaphenes) by extraction with alcohol.

_Estimation of matters soluble in water._--This is important both to
detect weighting, and to draw conclusions as to the materials used in
tanning. Fine raspings or shavings may be exhausted with warm water
in a percolator, or roughly a weighed piece (20 _grm._) of leather,
air-dry, may be well kneaded and worked in 100 _c.c._ of warm water
in a basin. 50 _c.c._ of this may be evaporated to dryness in a light
basin over the water-bath (or under a paper hood on a steam boiler),
and the gain of weight will give the amount dissolved from 10 _grm._
This is more accurate and quicker than redrying the leather and
weighing loss. The residue will contain tannins and their products,
often in considerable quantities, and may be examined by the table of
reactions, p. 112, though these are as yet very imperfect. It will
also contain glucose, dextrin, and soluble salts, if these have been
used to give weight and firmness. The absolute proof of weighting with
glucose or dextrin is difficult, since tanning materials naturally
contain these and analogous principles. The residue may be powdered
and exhausted with cold water, and the tannins and colouring matter
removed by shaking with magnesia (p. 108) or lead carbonate. Fehling's
solution[J] is then added and the mixture is heated nearly to boiling.
A rapidly formed and considerable precipitate of red cuprous oxide
indicates weighting with glucose or dextrin. Leather extracts, however,
invariably reduce Fehling's solution more or less, and a conclusion can
only be drawn after some experience and comparative tests. Gallotannic
acid and pyrogallol reduce it when heated, but not cane sugar or gum
arabic. If a solution of cane sugar be heated to 68° C. for 1/4 hour
with 10 per cent. of fuming hydrochloric acid, it is "inverted," and
then after neutralising the acid with potash or soda, will reduce
Fehling's solution when heated.

[Footnote J: 4 _grm._ cryst. cupric sulphate are dissolved in 20 _c.c._
of water; and 16 _grm._ of neutral potassic tartrate and 13 _grm._ of
fused sodic hydrate are dissolved in 60 _c.c._ The two are mixed, made
up to 100 _c.c._, and boiled for some minutes. It should always be
tested before use by boiling a portion, which should remain perfectly
clear.]

The soluble mineral salts are detected by igniting the residue left
after evaporation of a separate portion in a porcelain crucible.[K]
From unweighted leather, the quantity is very small. The ash is
exhausted with a few _c.c._ of distilled water, which will dissolve
most sulphates and chlorides, which may be detected in small portions
of the solution by baric chloride and silver nitrate respectively.
Baric chloride and lead acetate are precipitated by a drop of sulphuric
acid, and the latter is blackened with ammonic or sodic sulphide.
Lime is precipitated by addition of ammonic chloride, ammonia, and
ammonic oxalate; magnesia by the subsequent addition of sodic phosphate
(see p. 109). The carbonates in the insoluble part (mostly derived
from salts of organic acids) may be taken up by dilute hydrochloric
acid and tested separately, or the acid may be used at first. Any
residue undissolved by the acid is probably lead chloride, and will be
dissolved by hot water.

[Footnote K: A platinum crucible must not be used for fear of its
destruction by lead, unless this metal has been proved absent.]

_Estimation of ash._--The leather in small pieces (either after or
before extraction with water) is incinerated in a porcelain crucible.
The ash is extracted with hydrochloric acid. The insoluble portion may
contain barium sulphate (barytes), lead sulphate, sand, clay, &c. For
further examination, ordinary chemical text-books must be consulted.
Any large amount of ash indicates weighting. Müntz found only about 0·5
per cent. of ash from bark-tanned leather.

_Determination of hide substance._--It is sometimes of interest to
determine the proportion of dry hide-substance in a sample of leather,
but there is no known means of doing this directly. If, however,
the leather be dried, finely powdered by rasping, and the nitrogen
determined by combustion, either with soda-lime (Will and Varrentrapp's
method), or with copper oxide (Dumas), the hide-substance may be
calculated, since tannin contains no nitrogen. Müntz found unhaired
skin dried at 230° F. (110° C.) to contain 51·43 per cent. of nitrogen
(compare also p. 20).


DETERMINATION OF FREE ACIDS IN TAN-LIQUOR.

The lime-water method mentioned on p. 172 is, from its simplicity, well
suited for daily use in the tannery as a control method for ordinary
working; but where it is necessary to make very exact estimations, or
to determine the various acids separately, it is not so satisfactory as
one recently published by Kohnstein and Simand (Dingl. Polyt. Jour.,
1885, cclvi. 38).

The acids usually present in liquor consist of several members of the
fatty or acetic group, which distil over with boiling water, of other
non-volatile organic acids, and sometimes sulphuric acid, which is
added to assist the swelling of the leather.

To determine the acids of the acetic group, Kohnstein and Simand
proceed as follows:--100 _c.c._ of the liquor are distilled, in a flask
or retort with a good condenser, to about 30 _c.c._, allowed to cool
a little, made up again to 100 _c.c._, and again distilled; and this
is repeated till about 300 _c.c._ have passed over. The distillate
is then made up to 300 _c.c._, well mixed by shaking, and the acid
is determined with standard soda. Methyl orange and sodic carbonate
is not so suitable for this titration, as caustic soda and litmus,
since methyl orange is not very sensitive to vegetable acids. If it be
desired to ascertain what quantity of acids of the acetic group exist
in combination with lime and other bases in the liquor, small excess
of sulphuric acid may be added to the residue in the retort, and the
distillation repeated, when the organic salts will be decomposed and
the volatile acids come over.

To determine the total free organic acids, Kohnstein and Simand shake
about 80 _c.c._ of the liquor with 3-4 _grm._ of freshly ignited
magnesia, quite free from carbonate and from lime, and allow to stand
for some hours with frequent vigorous shaking, till the liquor, which
at first is brown or dirty green, becomes almost colourless and gives
no reaction of either acid or tannin. The mixture is then filtered,
and the tannin and colouring matter are retained on the filter in
combination with magnesia, while the organic salts of magnesia, which
are mostly soluble, pass through with the filtrate. 10-30 _c.c._ of
the filtrate, according to the amount of acid present, is evaporated
to dryness, and gently ignited so as not to decompose any magnesic
sulphate present. The residue is moistened with water saturated with
carbonic acid, to convert any magnesic oxide into carbonate, and then
dried, in order to make the mass powdery, and easier to wash, It is
next taken up with hot distilled water, filtered and well washed.
Any sulphate which is present passes into the filtrate, while the
carbonate, which corresponds to the organic salts present before
ignition, remains on the filter, and after solution in hydrochloric
acid, is estimated as magnesic pyrophosphate. To the hydrochloric
solution is added excess of ammonia and sufficient ammonic chloride
to redissolve the precipitate formed, and prevent the precipitation
of the magnesia; the solution is heated and then ammonic oxalate
solution, first dilute, and then concentrated, is added to precipitate
any lime which may be derived from lime salts present in the liquor.
After filtering out and washing the precipitate, 10-15 _c.c._ of 10
per cent. sodic phosphate solution is added, and the liquid is stirred
with a glass rod without touching the sides of the beaker, and allowed
to stand 12 hours. The crystalline precipitate is then rinsed on to
a filter, and washed with a mixture of 1 of ammonia and 3 of water,
till the washings no longer give any milkiness with silver nitrate.
The filter is then dried and the precipitate is placed in a platinum
crucible and first gently, and then strongly ignited with the cover on;
the filter paper, freed as much as possible from the precipitate, is
burnt in the usual way on the crucible lid, the ashes are added to the
precipitate in the crucible, and the whole is again ignited and allowed
to cool in the desiccator, and finally weighed. 111 parts of magnesia
pyrophosphate correspond to 120 parts of acetic, or 180 parts of lactic
acid. Kohnstein and Simand calculate the pyrophosphate corresponding to
the acetic acid already found by distillation, and after deducting it
reckon out the remainder as lactic acid. Of course the volatile acids
are really a mixture consisting of acetic, propionic, butyric and other
members of the fatty group; but it would be difficult if not impossible
to separate them. Similarly other fixed acids exist in mixture beside
the lactic acid, but as their action is similar and lactic acid is
always the most abundant, these acids are to be reckoned as lactic.

It has been mentioned that when sulphuric acid is present in the liquor
it is found in the filtrate from the magnesia carbonate as sulphate.
After removal of the lime as oxalate, as previously described, the
magnesia may be similarly determined as pyrophosphate, and reckoned
out as sulphuric acid (111 parts of pyrophosphate being equal to 98
parts sulphuric acid, H_{2}SO_{4}). It may also be estimated with
barium chloride, but in this case regard must be had to the sulphates
originally present in the liquor.

Since waters invariably contain both lime and magnesia salts, a
portion (50 or 100 _c.c._) must be evaporated, ignited, and after
precipitation of the lime, the magnesia must be estimated as already
described, and deducted from the amount found in a similar amount of
liquor after saturating with magnesia. If, together with the organic
acids, the liquor contains sulphuric acid, the correction may be
divided equally between the two.

The method is not applicable in presence of phosphoric, tartaric, or
oxalic acids. To overcome this difficulty, Messrs. Kohnstein and Simand
are at present investigating a method dependent on decolorisation of
the liquor with bone charcoal, completely free from mineral salts, and
subsequent titration with soda.

It may be interesting to add the determinations of a complete set of
handlers in a Continental upper-leather tannery, in which larch bark is
used. 100 _c.c._ of liquor contained as follows, in _grm._:--

  ─────────┬────────────┬───────────────┬──────────────────────
  No. of   │Total Acids │ Volatile Acids│  Fixed Organic Acids
  Handler. │ reckoned   │  reckoned     │   reckoned as Lactic.
           │ as Acetic. │  as Acetic.   │
  ─────────┼────────────┼───────────────┼──────────────────────
    1      │  0·205     │    0·050      │       0·232
    2      │  0·628     │    0·237      │       0·586
    3      │   ..       │    0·372      │        ..
    4      │  0·688     │    0·426      │       0·393
    5      │  0·569     │    0·432      │       0·206
    6      │  0·509     │    0·453      │       0·084
    7      │  0·487     │    0·456      │       0·047
  ─────────┴────────────┴───────────────┴──────────────────────


QUALITATIVE DETECTION OF TANNINS.

It is often desirable to determine from what tanning materials an
extract or liquor is made, or with what a sample of leather is tanned.
The following table gives reactions of the principal tanning materials,
which will enable any one of them to be recognised with certainty,
and in many cases will determine the constituents in a mixture of
several, though this is naturally far more difficult. In such cases,
colour reactions are apt to mislead, that of one tannin being modified
by another, and it is safest to rely on the categorical test of
precipitate or no precipitate, coloration or no coloration, without
regard to the tint. The infusions must be very weak, not exceeding
1-2° Bktr., or precipitates will be formed where mere coloration or
clouding is noted. In some cases only negative peculiarities can be
given, and the material cannot be positively determined in mixture
with materials where these peculiarities are present. Thus myrobalans
could not be distinguished from divi with certainty, where any other
material, such as gambier, was present, which gave a deep coloration
with concentrated sulphuric acid. The writer will feel greatly obliged
by the communication of more distinctive reactions.


CHEMICAL ANALYSIS FOR THE TANNERY

  ────────────┬────────────┬────────────┬─────────┬───────────┬─────────────┐
  Reagent.    │Myrabolanes.│ Divi-divi. │ Valonia.│ Oak Bark. │Chestnut wood│
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Boiled with │Pale deposit│Pale deposit│ Slight  │Slight pale│ Slight red  │
  equal volume│ (eliagic   │ (eliagic   │ pale    │ deposit or│ deposit on  │
  of sulphuric│ acid) on   │ acid) on   │ deposit.│ turbidity │ cooling.    │
  acid (1 vol.│ cooling.   │ cooling.   │         │on cooling.│             │
  to 9 vol.   │            │            │         │           │             │
  water).     │            │            │         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Bromine     │  No pp.    │  No pp.    │  No pp. │  Pale pp. │  No pp.     │
  water.      │            │            │         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Dilute      │Blue-black  │Dark blue   │Blue-    │Bluish     │Blue-        │
   ferric     │pp.         │ pp.        │black pp.│ black pp. │ black pp.   │
   chloride.  │            │            │         │           │             │
  Add         │Brown pp.   │Dark red pp.│Red brown│ Red brown │Dull red pp. │
   ammonia.   │            │            │ pp.     │ pp.       │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Sol.        │ No pp.     │Faint       │ No pp.  │ No pp.    │Slight       │
    tartar    │            │  clouding. │         │           │  clouding.  │
    emetic.   │            │            │         │           │             │
  Add ammonic │Light pp.   │Dense pp.   │Pale pp. │Whitish    │ Pale pp.    │
    chloride. │            │            │         │  pp.      │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Copper      │Faint       │Slight      │ No pp.  │Slight pp. │ No pp.      │
    sulphate. │  clouding. │  green pp. │         │           │             │
  Add         │Dense dark  │Dense dark  │Dark     │Brown pp.  │Dark         │
    ammonia.  │  pp.       │  pp.       │  reddish│           │  brown pp.  │
              │            │            │  pp.    │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Lime-water. │Yellow pp.  │Yellow pp.  │Yellow   │Brown pp.  │Purplish     │
              │  turning   │ turning    │  pp.    │           │  brown pp.  │
              │  greenish. │  purple.   │  turning│           │             │
              │            │            │  red-   │           │             │
              │            │            │  purple.│           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Ammon.      │Dirty       │Dark        │Dark     │Greenish   │Dirty        │
    molybdate │  yellow    │  greenish  │ greenish│  pp.      │  green pp.  │
    in nitric │  pp.       │  pp.       │  pp.    │           │             │
    acid.     │            │            │         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  With sodic  │Yellow      │ Yellow     │Turns    │Turns      │Reddish pp.  │
    sulphide  │  colour.   │  colour.   │purpulish│  red.     │             │
    exposed to│            │            │ red.    │           │             │
    air on a  │            │            │         │           │             │
    tile.     │            │            │         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Add         │Yellow      │Intense     │Deep     │Deep red   │Dark brown.  │
  concentrated│  colour.   │  crimson.  │  yellow.│  pp. on   │             │
    sulphuric │            │            │         │  dilution │             │
    acid to   │            │            │         │           │             │
    1 drop    │            │            │         │           │             │
    infusion. │            │            │         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Lead        │Light       │Dark        │Pale pp. │Brown pp.  │ Brown pp.   │
    Nitrate   │  yellow pp.│  yellow pp.│         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Cobalt      │Buff pp.    │Buff        │Dirty    │  Ditto.   │Dirty        │
    Acetate   │            │  pink pp.  │ pink pp.│           │  yellow pp. │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Manganese   │ Yellow pp. │ Yellow pp. │ Dirty   │ Ditto.    │ Grey pp.    │
    acetate.  │            │            │  yellow │           │             │
              │            │            │  pp.    │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Uranium     │Dark red    │Dark red    │Dark red │Dark brown │ Dark red    │
    acetate.  │  colour.   │  colour.   │  colour.│  pp.      │  colour.    │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Ammoniacal  │  No pp.    │   No pp.   │Brown pp.│ No pp.    │  No pp.     │
    picric    │            │            │         │           │             │
    acid sol. │            │            │         │           │             │
  ────────────┼────────────┼────────────┼─────────┼───────────┼─────────────┤
  Potassic    │ Brown pp.  │ Brown pp.  │Brown pp.│ Brown pp. │ Brown pp.   │
   dichromate.│            │            │         │           │             │
  ────────────┴────────────┴────────────┴─────────┴───────────┴─────────────┘

CHEMICAL ANALYSIS FOR THE TANNERY -- Continued.

  ┬───────────┬───────────┬───────────┬────────────┬────────────┬───────────┐
  │Hungarian  │ Hemlock   │Mimosa     │Cutch       │ Gambier    │Gallotannic│
  │Larch      │ (Extract).│     bark. │ (Pegu).    │ (Cuba).    │ Acid, 1   │
  │(Extract). │           │           │            │            │ per cent. │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼──────────-│
  │Yellow     │Abundant   │Heavy red  │Light red   │ Reddish    │ Usually   │
  │Flocculent │  red      │  deposit  │ deposit    │ deposit    │ some pale │
  │deposit    │ flocculent│  on       │ on cooling.│ on cooling.│ deposit.  │
  │separates  │ deposit.  │  cooling. │            │            │           │
  │quickly.   │           │           │            │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Yellow pp. │Yellow pp. │Yellow pp. │ Yellow pp. │ Yellow pp. │ No pp.    │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Dull brown │Dirty green│Full brown │Green-black │Intense     │ Blue      │
  │  pp.      │  pp.      │ pp.       │  pp.       │ green      │  -black   │
  │           │           │           │            │ colour.    │  pp.      │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Dull red   │Reddened   │Purple     │ Dark red   │ Reddened   │ Reddened  │
  │  pp.      │ pp.       │ colour.   │   pp.      │  pp.       │  pp.      │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │No pp.     │No pp.     │White pp.  │ No pp.     │ No pp.     │ No pp.    │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Pale pp.   │Slight pale│Dense white│ Pale pp.   │ Faint      │ White pp. │
  │           │ pp.       │ pp.       │            │ clouding.  │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Slight     │Pale pp.   │Slight pp. │ Dense pp.  │ No pp.     │ No pp.    │
  │  cloud.   │           │           │            │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Deep blue  │Dark green │Deep red   │Deep violet │Dark green  │ Brown pp. │
  │coloration.│coloration.│  pp.      │ coloration.│ coloration.│           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Dirty      │ Brown pp. │ Slight    │Slight cloud│  No pp.    │ Pale pp.  │
  │brown pp.  │           │reddish pp.│ soluble in │            │turns blue.│
  │           │           │           │  excess.   │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Slight     │ Slight pp.│ Brown pp. │ Ditto.     │ Ditto.     │ Yellow    │
  │ clouding. │           │           │            │            │  colour.  │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │No change. │ No change.│ Turns red.│ Slight     │ No change. │ No change.│
  │           │           │           │ reddening. │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Dark brown │ Intense   │ Intense   │ Deep red no│ Dark brown │ Yellow.   │
  │or crimson.│ crimson.  │purple-red.│ pp. on     │ or crimson.│           │
  │           │           │           │dilution.   │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Pale pp.   │ Pale pp.  │ Clouding. │ No pp.     │ Faint      │ White pp. │
  │           │           │           │            │ clouding.  │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │ Purplish  │ Purple pp.│ Brown pp. │ Brown pp.  │ No pp.     │ Purple pp.│
  │  pp.      │           │           │            │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Slight     │ Slight pp.│ No pp.    │ No pp.     │ Ditto.     │ White pp. │
  │ clouding. │           │           │            │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │Slight     │Light brown│ Dark red  │ Dark red   │ Dark red   │ Crimson   │
  │ darkening.│  pp.      │ colour.   │  colour.   │  colour.   │  colour.  │
  │           │           │           │            │            │ Brown pp. │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │ No pp.    │ Clouding. │ No pp.    │ No pp.     │ No pp.     │ No pp.    │
  │           │           │           │            │            │           │
  ┼───────────┼───────────┼───────────┼────────────┼────────────┼───────────┤
  │   Ditto.  │ Brown pp. │ Brown pp. │Brown       │ Brown pp.  │ Brown pp. │
  │           │ slowly    │           │  colour.   │  slowly    │           │
  │           │ formed.   │           │            │  formed.   │           │
  ┴───────────┴───────────┴───────────┴────────────┴────────────┴───────────┘


QUANTITATIVE DETERMINATION.

Many processes have been proposed for the quantitative estimation of
tannins, but it cannot be said that any method yet known is wholly
satisfactory. The oldest, that of Sir H. Davy, recently improved by
Stoddart and others, consists in precipitating with gelatin, and drying
and weighing the precipitate. This is almost impossible to filter off
as directed by Davy; but by the use of a little alum, and by pouring
hot water on the precipitate, it becomes curdled into a mass which
may be washed by decantation. As the precipitate contains varying
quantities of tannin, according to the strength of solution employed;
as it is soluble in excess of gelatin solution, and as it is almost
if not quite impossible to wash it free from gelatin and alum, the
method can hardly lay claim to much accuracy. A somewhat better one
consists in the employment of a standard solution of gelatin with a
little alum, determining the end of the reaction by filtering off a
portion and ascertaining if another drop of the reagent produces a
further precipitate. This method is very tedious, the end reaction
is difficult to hit, the standard solution is very unstable, it is
inapplicable to gambier and cutch because the mixture will not
filter clear, and its results are irregular, probably from the power
of tannin to combine with various proportions of gelatin. A plan,
which has a seductive appearance of simplicity, is that of Hammer;
he takes the sp. gr. of the infusion, then absorbs the tannin with
slightly moistened hide-raspings, again takes the sp. gr., and from
the difference calculates the percentage of tannin, a difference of
5 per cent. of tannin corresponding to one of 1·020 sp. gr. (20°
barkometer). Unfortunately the hide is more or less soluble in the
liquor, and absorbs acids other than tannic with considerable energy;
the moistening of the raspings introduces an error, and the smallness
of the quantity to be measured makes a slight error completely vitiate
the results. With extreme care, due corrections for temperature, for
the water introduced with the raspings, and for their solubility,
and by substituting evaporation of the infusions to dryness for mere
calculation from their sp. gr., the method is useful as giving almost
the only information obtainable as to the actual weight of tannin in
any material capable of being absorbed by hide. It is, however, only
suitable for use as a check on easier and more rapid methods, such as
Löwenthal's, which give accurate relative results, but no information
as to absolute weight of unknown tannins. A modification of Hammer's
method has been introduced by Müntz and Ramspacher, in which the liquor
whence the tannin is to be removed is forced through a piece of raw
hide by pressure. This method, except that it is more rapid, has all
the evils of Hammer's in an intensified form, and gives such variable
results as to be quite useless in practice. A set of very careful
determinations of one sample of sumach gave results ranging from 18 to
28 per cent., and similar variations occurred when the experiment was
repeated with valonia. Wagner's method by precipitation with a standard
solution of cinchonine and magenta has proved wholly unreliable.

Gerland's method with a volumetric solution of tartar emetic, used in
presence of ammonic chloride, gives constant results with sumachs,
2/3 of those given by permanganate and Neubauer's equivalent.
Tartar emetic does not precipitate the tannins of cutch and gambier.
Fleck's, by precipitation with copper acetate, and subsequent washing
with ammonic carbonate and gravimetric estimation, either of the
tannate dried at 212° F. (100° C.), or of the copper oxide left
on ignition; and Carpene's, by precipitation with ammoniacal zinc
acetate, and subsequent estimation with permanganate and indigo,
though giving fairly accurate results on some tannins, are only of
limited application. They may therefore be passed over, as well as
Jean's method with a volumetric solution of iodine in presence of sodic
carbonate, and Allen's method with lead acetate, which are tedious and
difficult, and present no advantage over Löwenthal's improved process.
This last is easy of execution, constant in results, and universally
applicable. Before proceeding to describe it in detail, it may be well
to give some hints as to the best modes of sampling and preparing
tanning materials for analysis, since this is often more difficult and
tedious than the actual analysis.

Sampling.--Samples should always be drawn from at least 10 sacks or
separate parts of the bulk, and, in the case of valonia, special
care should be taken to have a fair average quantity of "beard."
No attention is usually paid to this point by merchants, and the
proportion varies greatly in different parts of the same cargo. If
several sacks are spread in layers on a level floor, and then portions
going quite to the ground are taken from several parts of the floor,
this will be accomplished. Where samples must be dealt with which have
not been specially drawn, it might be safest to weigh out from each the
same proportion of beard and whole cups, bearing in mind that the beard
is always the richest part of the valonia. In sampling myrobalans, it
should be remembered that the poor and light nuts will rise to the
top, and hence the hand should be plunged well into the sack. Grinding
of valonia and myrobalans when practicable is probably best done in a
small disintegrator, fitted with gratings. The material, of which some
pounds must be used, is screened over a sieve of say 15 wires per in.,
and all coarser parts are returned to the mill till they will pass. The
mill must grind into a close box, that no dust may be lost. Bark may
be reduced to fine saw-dust by cutting a portion of each piece in the
sample with a circular saw or rasp driven by a lathe. The advantage of
these methods is that samples can be ground without previous drying,
and thus in many cases time may be saved and separate determination
of moisture avoided. When this is not practicable, the sample of some
lbs. at least is ground in an ordinary bark-mill, well mixed, spread
out flat on a floor or table, and several portions are taken as already
described, say 50-100 _grm._ in all, and dried in a water- or air-oven
at 212° F. (100° C.). The moisture is best determined, to save time,
in a small separate portion of 10 _grm._, which must be dried till
it ceases to lose weight, and the loss taken as moisture. It must be
weighed in a covered capsule, as it is very hygroscopic. When the
larger portion of the sample has been dried some hours, it is passed
twice through a good coffee-mill, and then returned to the oven till
thoroughly dried, for which, 12-24 hours is generally sufficient.
Another method sometimes convenient is to take each acorn, or each
piece of bark of the sample to be tested, and snip a piece from it with
a pair of tinners' shears, taking care that in the case of valonia the
section runs right to the centre of the cup; and in bark, that fair
shares of the outer and inner layers are taken. The reason for drying
before grinding is, that unless hard dried, tanning materials cannot be
passed through a small mill. Bark and valonia usually contain 12-16 per
cent. of moisture.

Exhaustion.--10 _grm._ of valonia, 20-30 _grm._ of bark, or
corresponding quantities of other material, are boiled briskly for
half an hour with 1 _litre_ of distilled water, a funnel being placed
in the neck of the flask, and great care being taken at first to avoid
frothing and boiling over. The flasks used should have a capacity of
at least 1-1/2 _litre_. The whole contents are finally rinsed into
a gauged flask, allowed to cool to 59° F. (15° C.), and made up to
1 _litre_. In the case of sumach, a little more boiling even than
this is desirable. This method has been found by the writer to give
better results than boiling with successive portions of water. Another
method is to boil for 1/2 hour with 250 _c.c._ of water, then pour the
whole on a filter, wash with boiling water so long as a drop of the
filtrate blackens paper moistened with a dilute solution of ferric
acetate, and finally make up to 1 _litre_. Many materials, however,
clog the filter to such an extent that washing is almost impossible.
Kathreiner has used 15 _litres_ of water, and corresponding quantities
of material, in a large steam-jacketed copper pan, for each exhaustion,
making the weight up finally to 15 _kilos._, with very uniform and
excellent results. (See also p. 130.) With all materials which deposit
ellagic acid or other insoluble derivatives, on cooling and standing,
considerably higher results will be obtained if the titration be made
as soon as the liquor is cold, than if it be allowed to stand 24 hours;
in this respect, a uniform practice should be adhered to. Addition of
1/2 _c.c._ of glacial acetic acid renders the infusions less liable to
change.

Analysis.--Of all the methods which have been proposed for the
estimation of tannins, the only one which has met with any general
acceptance is that of Löwenthal, and indeed it is the only one which in
rapidity of execution and constancy of results is fitted for general
use. The method, as originally proposed, depends on the oxidation of
the astringent solution by permanganate in presence of indigo, which
not only serves as an indicator, but controls the oxidation, limiting
it to those bodies which are more oxidisable than indigo. As, however,
these include gallic acid and other substances which are useless to
either tanner or dyer, it is necessary to remove the tannin, and by
a second titration to obtain its value by difference. This Löwenthal
(Zeitschrift f. Anal. Chemie, 1877, p. 33) accomplished by a solution
of gelatin and common salt, to which, after mixture with the tannin
infusion, a small quantity of sulphuric or hydrochloric acid was added.
It was necessary to let this stand at least some hours before a clear
filtrate could be obtained, and the gelatin remaining in solution had
a slight though generally negligible effect on the permanganate. In
some cases, even after long standing, perfect filtration was extremely
difficult and tedious, and it was also clearly proved by Simand
(Ding. Polyt. Jour., ccxliv. 400) that a certain proportion of the
tanno-gelatin precipitate, varying with the acid present, and with
the species of tannin, remained in solution, and thus gave too low a
result. He therefore proposed to revert to the old method of separating
tannin with hide raspings, or, as an improved substitute, with the
gelatinous tissue of bones, and this is probably the most accurate
method, but has the disadvantage of requiring considerable time for
its execution. (See also p. 130.) The writer has therefore tried, and
he thinks successfully, so to modify Löwenthal's original method as to
increase its accuracy, and at the same time to make it more rapid and
easy of execution. It was found that by saturating the clear filtrate
with salt, a further precipitate containing tannin was formed, but
unfortunately, it was so finely divided that no amount of standing,
or even of warming, and repeated passing through the paper, would
obtain a clear filtrate. Finally, he hit on the device of mixing with
the liquid, before filtration, a portion of the pure kaolin used by
photographers. The effect was instantaneous and complete. A perfectly
clear filtrate was obtained without any of the tedious waiting which
before was necessary, and it was not only free from tannin, but also
nearly so from gelatin, so that it only gave the faintest cloudiness
with tannin solution. Gelatin gives a more considerable precipitate,
but this is simply due to its insolubility in the saturated salt
solution, and it is redissolved on dilution with water.[L]

[Footnote L: Hunt (Jour. Soc. Chem. Industry, April 1885) states, that
saturation with salt causes partial precipitation of gallic acid when
present, and that results agreeing more closely with those obtained by
absorption with hide are obtained by employing a mixture of 50 _c.c._
liquor, 25 _c.c._ 2 per cent. gelatin solution, and 25 _c.c._ saturated
solution of salt containing 50 _c.c._ of concentrated sulphuric acid
per _litre_ and a teaspoonful of kaolin. This approaches very nearly to
Löwenthal's original method, but with the addition of the kaolin, and
as in it, it is to be feared that a portion of the tannate of gelatin
will remain in solution. For accurate work, therefore, absorption by
hide-raspings is preferable, though even that has been shown by the
writer to remove gallic acid and other matters beside tannin. Hunt
states that raw hide also absorbs catechin.]

A slight error is introduced by the presence of a trace of oxidisable
matter in the gelatin, and when very great accuracy is required, it
is well to make a blank estimation of "not-tannin" without tannin
infusion, and deduct 1/2 of the permanganate consumed as a correction
from the not-tannin; but this may usually be disregarded. Each
titration should be made twice, and successive tests should not differ
by more than 0·1 _c.c._ of permanganate.

Reagents.--Solutions are required of (1) Pure potash permanganate, 1
_grm._ per _litre_. (2) Pure soda or potash sulphindigotate, 5 _grm._,
and concentrated sulphuric acid, 50 _grm._ per _litre_. (3) Pure
oxalic acid, 6·3 _grm._ per _litre_ (decinormal). The sulphindigotate
(indigo carmine), must be filtered, and when oxidised by permanganate,
should give a pure clear yellow, free from any trace of brown or
orange. Any contamination with indigo-purple, which gives brown
oxidation-products, is quite fatal to the accuracy of the analysis.
The permanganate solution is standardised by measuring 10 _c.c._ of
the (decinormal) oxalic acid solution, adding a little pure sulphuric
acid and distilled water, warming to 136° F. (58° C.), and running in
the permanganate till a faint permanent pink is produced, for which
about 32-33 _c.c._ should be required. The indigo-carmine solution
should be of such strength that 14-16 _c.c._ of permanganate are
required to bleach the quantity employed, which may be 20-25 _c.c._, as
convenient. (4) Gelatin solution: 2 _grm._ of Nelson's or other good
gelatin are allowed to swell in distilled water for two hours, melted
by setting the glass in a pan of boiling water, and made up to 100
_c.c._ This will not keep. (5) Dilute sulphuric acid: 10 _c.c._ of pure
concentrated acid are added to 90 _c.c._ of distilled water. (6) Good
table salt. (7) Purified kaolin.

The analysis is performed in the following manner:--20 _c.c._ of indigo
solution, and 5 _c.c._ of the infusion of tanning material is added,
in a white basin as recommended by Kathreiner, to about 3/4 _litre_
good water, which it is best to measure approximately, so that if it
contains any impurity which affects the permanganate it should be
constant, and thus be eliminated with the indigo. Permanganate solution
is then allowed to drop in, with constant stirring till the pure yellow
liquid shows a faint pinkish rim, most clearly seen on the shaded
side. This end-reaction, which is of extraordinary delicacy, is due
to Kathreiner, and is quite different to the pink caused by excess of
permanganate, being an effect common to all pure yellow liquids. It is
not needful to make the titration so slowly as has been advised--the
permanganate may be dropped in steadily with vigorous stirring, so
long as there is large excess of indigo, but as soon as the bottom
of the basin can be seen through the solution, it must be added very
cautiously, one or two drops at a time, and with occasional pauses, to
allow time for its complete mixture through so large a mass of fluid.
The titration is repeated twice, and the results added together and
denoted by _a_. Then take 50 _c.c._ of the infusion, and add 28·6
_c.c._ of the gelatin solution of Nelson's gelatin of 2 _grm._ to 100
_c.c._ After shaking, the mixture is saturated with salt, which brings
the volume up to 90 _c.c._, and 10 _c.c._ of the dilute sulphuric acid
(containing 1 vol. of concentrated acid in 10) and a teaspoonful of
pure kaolin are added. It is best to do this in a flask in which it
can be well shaken, after which, filtration may be at once proceeded
with, although it is safer to let it stand an hour or two: (the flask
may be cleansed with caustic soda solution). 10 _c.c._ of this filtrate
(= 5 _c.c._ of the original infusion) are employed for a second pair
of titrations, which are added as before, and the result denoted _b_.
If, further, _c_ be the quantity of permanganate required to oxidise
10 _c.c._ of decinormal oxalic acid, and 10 _grm._ of the tanning
material have been employed to make 1 _litre_ of infusion, _c_ : (_a_ -
_b_) :: 6·3 : _x_, where _x_ is the percentage of tannin expressed in
terms of crystallised oxalic acid. If it be desired to calculate the
gallic acid and non-tannin substances contained in the infusion, the
value in permanganate of the indigo alone must be determined. Calling
this _d_, as _c_ is to (_b_ - _d_), so is 6·3 to the percentage of
non-tannins in terms of oxalic acid, and for the present it is best
invariably to calculate results in this way, since we do not actually
know the relation of any single tannin to permanganate, even Neubauer's
number for gallotannic acid being probably too high, according to the
recent investigations of Councler and Schroeder,[M] and Oser's for
quercitannic being at most only approximate. It happens, moreover, that
this last equivalent (62·36 _grm._ of quercitannic acid = 63 _grm._
of crystallised oxalic acid) does not differ from that of oxalic acid
more than the ordinary limits of error of such estimation, and the
substitution is therefore of no commercial importance, while it is
surely better to employ a standard which is easily and exactly verified
than one which is certain to be modified by further research, and so
to run the risk either of having our results made useless for future
comparison, or of establishing a false or arbitrary equivalent. What
is wanted for practical purposes is not the absolute weight of tannins
in the various materials, but only a means for the relative comparison
of two samples of the same material; cross comparisons of different
tannins being simply delusive. If, however, it is necessary at any time
to give actual percentages of gallotannic acid, it is probably best
to stick to Neubauer's number for the present, as it is in general
use. Neubauer states that 63 _grm._ of oxalic acid consume as much
permanganate as 41·37 _grm._ of gallotannic acid. Tshekawa found 41·688
as the equivalent for tannin from Japanese gall nuts (Chem. News,
xlii. 274). Councler and Schroeder on the other hand give only 34·3
_grm._ Simand gives 61·1 _grm._ as the equivalent of quercitannic acid.
Commercial "pure tannin" always gives results higher than the truth, as
the gallic acid which it contains consumes more permanganate than an
equal weight of tannin, or even than the tannin which would yield it
if boiled with acid. When this is done the equivalent used should be
definitely stated, or it will certainly lead to confusion. Neubauer's
equivalent is only properly applicable to gall nuts, and possibly to
sumach and myrabolans. For oak bark Oser's number or that of oxalic
acid is most likely nearly correct; and this may also be approximately
true of oak wood and valonia, but as respects all other materials we
have no information whatever, and the oxalic equivalent is as likely to
be right as any other. (Compare note, p. 128.)

[Footnote M: From researches by von Schroeder, published since the
above was penned, it seems that the permanganate consumed by tannin is
largely influenced by the way in which the titration is conducted, see
p. 128.]

A few results are given below, not as showing the relative values of
the materials, which, of course, cannot be directly compared by any
analytical process, but for comparison with those obtained by other
methods and modes of calculation:--

  ─────────────────────────────────┬──────────────────┬──────────────────┐
                                   │                  │   Other Bodies   │
                                   │       Tannin     │     Oxidised     │
                                   │ (as Oxalic Acid).│ (as Oxalic Acid).│
  ─────────────────────────────────┼──────────────────┼──────────────────│
  Spent Liquor                     │     O·12         │    11·0          │
  Valonia (good Smyrna). Sample 1  │    29·1          │     2·3          │
    "            "       Sample 2  │    30·7          │     2·1          │
    "            "       Sample 3  │    30·5          │     1·9          │
  Hungarian Larch Extract. Sample 1│    14·78         │     1·95         │
      "         "          Sample 2│    18·08         │     2·33         │
  Chestnut-wood Extract, 25° B.    │    25·53         │     3·68         │
  Pegu Cutch                       │    63·59         │     2·45         │
  ─────────────────────────────────┴──────────────────┴──────────────────┘

It is proved by experiment that kaolin removes nothing which is
oxidised by permanganate, but simply facilitates the precipitation
and filtration; and it is often found useful to clarify the original
infusions and liquors before the first titration. On the other hand,
there is no doubt that the salt and acid of Löwenthal's method
precipitate of themselves a large proportion of certain tannins. In
the case of cutch this amounted, in the analysis given, to 67 per cent.
of the whole. There is, however, good reason to believe that this would
also have been absorbed, or at least removed from solution by hide in
the process of tanning. This is shown by the analysis of the spent
liquor above given, which originally contained the tannins of oak bark,
valonia, myrabolans, gambier, hemlock, and oak wood extracts, &c., to
the extent of 10 to 15 per cent., but which was reduced by contact
with hide to 0·12 per cent. That a portion had not been absorbed but
decomposed is proved by the large accumulation of oxidisable impurities
(equal to 11 per cent. of oxalic acid); at the same time this example
shows that the method is capable of estimating a very small portion of
tannin in presence of much gallic acid and other analogous substances.
It is worth remark that such spent liquors become very pale in colour,
and also that the filtrates, freed from tannin by precipitation, are
nearly colourless, thus proving that the colouring matters present in
tanning materials are of the nature of tannins, at least as regards
their precipitability by hide and gelatin.

Simand (Dingl. Polyt. Jour., ccxlvi. 133) has recommended instead of
precipitation with gelatin, the use of the gelatinous tissue of bones
to remove the tannin. For this purpose porous bones, such as horn
piths, are coarsely powdered, and after treatment with dilute soda
solution to remove the fat, are steeped in weak hydrochloric acid
till all the calcareous matter is dissolved. They are then thoroughly
washed, ground wet through a steel mill, washed again and dried at
a low temperature; the tannin is removed more quickly than by raw
hide, and the amount of gelatinous matter dissolved by cold water is
a very trifling one. This method, or that with purified hide-powder,
is to be recommended for scientific research, since no element capable
of precipitating substances other than those absorbed by the hide
is introduced, while it is not certain in all cases that saturation
with salt and acidification may not remove other constituents of the
liquor besides tannins. It has, however, for technical purposes the
great disadvantage of requiring a much longer time for absorption of
the tannin than is the case with gelatin solution, and of the process
being much more difficult of execution. If hide-powder be employed, it
must be moistened with a small quantity of water before adding to the
infusion, and this water must be taken into account in the quantity
of the filtrate employed for the titration of the "non-tannin." The
digestion with the hide- or bone-powder must be continued till the
filtered liquid does not give the faintest clouding with a drop of
clear gelatin solution, and it is always very difficult to be sure that
the tannin is so completely removed as with gelatin and salt. Hide-
or bone-powder may be employed to determine the actual weight of any
unknown tannin absorbable by hide, by evaporating equal quantities of
the original infusion and of that freed from tannin by digestion with
the powder; the difference giving the tannin absorbed. The evaporation
must be conducted as far as possible in absence of air, for instance
in _vacuo_, or in a current of carbonic dioxide, and the residues both
dried at 212° F. (100° C.) so long as they lose weight. The amount of
matter dissolved from an equal quantity of the hide- or bone-powder by
water must also be ascertained and taken into the calculation.

Ammoniacal solution of cupric acetate or sulphate has been employed by
several chemists to remove tannin from solutions. N. H. Darton of New
York, who has a large practice in tannin analysis, employs cuprammonic
sulphate in the following manner.

The infusion, for which 20 _grm._ of hemlock bark or a corresponding
quantity of other material must be used, is made by exhausting with
2 or 3 quantities of water successively, first cold, and then with
heat (by placing the flask in a pan of boiling water), each portion of
water being poured off into a _litre_ flask. The last should be almost
colourless. The liquor is thus made up to nearly 1 _litre_, 25 _c.c._
of dilute sulphuric acid (about 1 vol. concentrated in 10) is added,
and the liquor is filtered through a small filter, which is finally
rinsed with a small quantity of water. Liquid ammonia is now added till
the liquor slightly smells of it, and, if any precipitate is formed, it
is filtered off as before; 25 _c.c._ of dilute sulphuric acid is again
added (which should give the liquid an acid reaction), and it is made
up to 1 _litre_. The titration is done as described under Löwenthal's
method, but instead of precipitating with gelatin, 100 _c.c._ is mixed
with 100 _c.c._ of a solution of copper sulphate to which sufficient
ammonia has been added to redissolve the precipitate first formed, and
containing 1-1/4 per cent. of copper sulphate. This is well shaken and
filtered, and the "not-tannin" is determined in the filtrate just as
with gelatin; a little dilute sulphuric acid being added in the basin
to neutralise the ammonia. The writer has examined this method with
regard to a few tanning materials. With valonia (and therefore probably
with oak bark) the preliminary treatment is unnecessary, and copper
precipitation gives results practically identical with the improved
gelatin, while it is less troublesome. On the other hand, a sample of
Miller's Hungarian Larch Extract which gave tannin equal to 18·08 per
cent. (by the gelatin method) gave no precipitate with cuprammonic
sulphate, and hence a result in tannin of _nil_ by Darton's method. It
is worth remark that by the copper method it is therefore possible to
estimate the valonia tannin alone in a mixture of larch and valonia
tannin. Probably this mode of analysis may also be utilised to separate
other tannins. With chestnut extract the results seem satisfactory, as
regards the precipitation of the tannin by copper, the figures agreeing
very closely with those by gelatin, but the preliminary treatment with
sulphuric acid and ammonia precipitates about 75 per cent. of what
is usually reckoned as tannin, leaving 7·53 per cent. of tannin only
instead of 25·53 per cent. as reckoned by the gelatin method; which,
judging by practical results in tanning, can hardly be accepted as
correct. The results of the gelatin method are found to agree fairly
with those of direct absorption by hide-powder, which is strong
confirmation that what is estimated as tannin is what is absorbed
by the hide. It is well known that sulphuric acid precipitates many
tannins, and in an experiment with cutch it was found by the writer
that saturation with salt and the addition of dilute sulphuric acid as
for Löwenthal's process, but without the gelatin, precipitated 67 per
cent. of the total tannin as usually reckoned.

It is obvious that it is impossible by analysis to compare the relative
value of different tannins, such as those of myrobalans and gambier,
or hemlock and valonia. All that analysis can reasonably be expected
to do is to give the relative values of different samples of the
same substance, or at the most, of materials of the same class. All
other comparisons are misleading; and would be so, even if the exact
percentage of each tannin could be calculated; since the commercial and
practical value of different materials does not depend on the quantity
of tannin only, but on the character of the leather it produces, hard
or soft, dark- or light-coloured and heavy- or light-weighing.

A Commission of German technical chemists, under the presidency of
Dr. Councler of Eberswalde, and including Messrs. Eberz, Kathreiner,
Schaun, von Schroeder, and Simand, have recently reported on methods
of tannin estimation ('Bericht über die Verhandlungen der Commission
zur Feststellung einer einheitlichen Methode der Gerbstoffbestimmung,'
Cassel, 1885). After reviewing earlier methods, they recommend the
following modifications of the Löwenthal method, for general adoption.


Chemicals employed.

(1) _Permanganate solution._ 10 _grm._ of the purest potash
permanganate are dissolved in 6 _litres_ of distilled water.

(2) _Indigo solution._ 30 _grm._ dry sulphindigotate of soda (Carminum
cærul. opt., "pure Indigotin I" of Gehe & Co., Dresden), air-dry, are
dissolved in 3 _litres_ of dilute sulphuric acid (1 vol. H_{2}SO_{4}
to 3 vols, water), 3 _litres_ of distilled water are added, the whole
is shaken till dissolved, and filtered. In each titration, 20 _c.c._
are used in 3/4 _litre_ of water, and reduce about 10·7 _c.c._ of
permanganate.

(3) _Hide-powder_ must be white and in a fine woolly state of division,
and should yield to cold water no substance capable of reducing
permanganate. Such a powder is prepared by Dr. Both of Berlin,[N] and
by the Vienna Research Station.

[Footnote N: Messrs. Mawson and Swan, of Newcastle, have kindly
undertaken to keep these, and the other reagents mentioned in this
book, in stock for the convenience of English tanners and chemists.]


Mode of Titration.

Instead of adding the permanganate solution drop by drop, to the
mixture of indigo, water, and liquor (as described, p. 121), it is
recommended to add it 1 _c.c._ at a time,[O] vigorously stirring 5-10
seconds after each addition. When the liquid has become bright green,
2-3 drops at a time are cautiously added with stirring, till the liquid
is pure yellow. Either a beaker on a white tile or a white basin may be
used (compare p. 121). It is advantageous in strong sunlight to shade
the window with white tissue-paper.

[Footnote O: It has been noted by several chemists, and especially by
Kathreiner, and later by Prof. von Schroeder, that the quantity of
permanganate reduced by a given amount of tannin varies within rather
wide limits, according to the rate at which the permanganate is added;
and the "1 _c.c._ method" was suggested by Prof. von Schroeder, to
secure uniformity in this particular. It has, however, been found by
the writer, in the course of experiments not yet completed, that the
quantity of permanganate required, was a function not simply of time,
but of the rapidity of diffusion through so large a bulk of liquid;
and by the alternate use of a simple glass rod, and of a specially
constructed perforated stirrer, he was able, while adhering strictly
to Prof. von Schroeder's directions, to obtain results even more
divergent by the "1 _c.c._ method" than could be obtained by the drop
method previously recommended, when properly carried out. Employed in
conjunction with the use of tannin for standardising, as recommended by
the Commission, either method gives perfectly dependable results.

The explanation of the variation is a simple one. The oxidation in
the Löwenthal process should be limited to indigo, and bodies more
oxidisable than indigo, but there exist both ready formed in liquor,
and among these oxidation products many substances which in the absence
of indigo will readily reduce permanganate. When the latter is added
rapidly, and with insufficient stirring, it destroys the indigo and
tannin in contact with it, and proceeds also to oxidise the other
matters present, although in other parts of the beaker indigo and
tannin still exist. Thus more permanganate is reduced than corresponds
to the indigo and tannin, and this is especially so towards the end
of the process, when very little of either remains. The more slowly
the permanganate is added, and the more vigorously it is stirred, the
more closely it will approximate to the theoretical quantity required
merely to oxidise the indigo and tannin. It seems to the writer more
scientific to approach this as nearly as possible, than to attempt to
establish a purely arbitrary standard such as the "1 _c.c._ method;"
but he would rather refrain from committing himself to a definite
opinion till his experiments are complete.]

[Illustration: PL. V.

_E. & F. N. Spon, London & New York._

"INK-PHOTO." SPRAGUE & CO. LONDON.

SOFTENING THE SKINS.]


Standardisation of the permanganate.

To avoid the uncertainty involved in comparing tannin (which reduces
different quantities of permanganate according to the method of
titration) with so dissimilar a reducing agent as oxalic acid, it
is recommended to employ tannin, titrated under precisely the same
conditions as the tanning material, so that whatever method be
employed, the differences will be common to both, and will so be
eliminated. Prof. von Schroeder has shown (Report, p. 45) by careful
experiment, that with the purest samples of tannin the permanganate
value estimated on the total dry substance of the tannin varied by
very little from that of the part of the tannin absorbed by hide as
determined by Hammer's process, but on the average bore the proportion
of 1 : 1·05. The percentage of water in an air-dried tannin must
be estimated by drying a portion at 201°-212° F. (94°-100° C.) and
determining the loss, and a quantity equivalent to 2 _grm._ must be
dissolved in 1 _litre_ of water and 10 _c.c._ titrated with indigo in
the usual way. If the permanganate value thus obtained be multiplied
by 1·05, it will be equivalent to that of 2 _grm._ of chemically pure
tannin. It is only necessary to determine the moisture occasionally, if
the tannin be kept in a well-closed box or bottle.

To ascertain if a tannin is pure enough for this, use a solution made
as above described (it is not necessary to determine the moisture) and
10 _c.c._ are titrated with permanganate in the usual way. 50 _c.c._
are then digested in the cold with 3 _grm._ hide-powder (previously
moistened with distilled water and well squeezed in linen) for 18-20
hours, with frequent shaking, filtered, and 10 _c.c._ again titrated.
If the second titration ("not-tannin") does not exceed 5 per cent.
of the total, it is _good_, but it may be _used_ so long as the
"not-tannin" does not exceed 10 per cent.[P] The purest tannin examined
by Prof. von Schroeder was Schering's Phar. Ger., which may be obtained
of Messrs. Mawson and Swan.

[Footnote P: Gallic acid suggests itself to the writer as being a good
standard, since it behaves with permanganate like tannin, and being
crystalline is easily purified and of definite composition.]

[Illustration: Fig. 20.]

The course of analysis is as follows:--

_Preparation of the infusions._--Extracts are dissolved in hot
water, and if necessary, filtered. Barks and other solid materials
are treated in Prof. von Schroeder's extraction-apparatus (Fig. 20)
(which seems very well adapted for its purpose). This consists of a
perfectly cylindrical vessel of cast-tin, about 12·5 _c.m._ deep and
7 _c.m._ diameter. A strainer covered with fine muslin fits it like a
piston.[Q] The powdered material is placed in the cylinder, and stirred
up with 200 _c.c._ of cold water. At the end of an hour, the piston is
inserted and pressed down gently, the clear liquor is poured off, and
the process is 4 times repeated with hot water, at intervals of 1/2
hour, placing the cylinder in a water-bath. The liquid is made up to 1
_litre_, and, if necessary, filtered (Report, p. 66). The quantity of
material used should be such as to give an infusion of which 10 _c.c._
do not reduce more than 8 _c.c._ permanganate. If it is desired to
determine separately the "easily soluble tannin" (viz. that extracted
by cold water), Real's Press (Fig. 21) is employed, which consists of
a cylinder _a_, through which water may be forced by the pressure of a
column of liquid. The small sieve _d_, covered with a disc of linen,
is placed in _a_, next the tanning material previously thoroughly
moistened with water, and the tap is closed. The press is then filled
with water and left 15 hours under a pressure of 1-1/2 _metres_. The
tap is then opened and 1 _litre_ is allowed to run through in the
course of about 2 hours, and mixed by shaking. The material is finally
exhausted like a new material in von Schroeder's apparatus to extract
the difficultly soluble tannin.

[Footnote Q: Both this apparatus, and the Real's press, may be obtained
from C. Focke, Zinngiesser, Grosse Kirchgasse 3, Dresden.]

[Illustration: Fig. 21.]

The titration is carried out as before described; in each infusion
separately to determine the "not-tannin" 50 _c.c._ are treated with 3
_grm._ hide-powder, and 10 _c.c._ are titrated.

It may be well in conclusion for the writer to state for the
information of the non-chemical reader, that though for purposes of
comparison of the results of different chemists, it is most desirable
to have a standard method of the highest possible perfection; any of
the accepted modifications of the Löwenthal method will give excellent
practical results in careful hands.




CHAPTER VII.

SOLE-LEATHER:--Preparing the Hides.


The principal sources of hides for sole-leather are:--

(I.) Market hides, from the cattle slaughtered for food in the United
Kingdom. These are received by the tanner, fresh, or slightly salted,
and are either bought directly from the butcher, or, now more commonly,
through the auction markets established in all large towns. The latter
system, while it perhaps slightly enhances the price of the hides to
the tanner, ensures him a better classification according to weight,
and, in some cases, as notably in that of Glasgow, a better flaying,
through an organised system of inspection and sorting. The Scotch
hides, being mostly from Highland cattle, are many of them small and
very plump, for, as a rule, the hides are thickest on those animals
which are exposed to cold and the hardships of out-door life. On the
other hand, the hides of highly-bred cattle are apt to be thin and
spreading; and, if they have been kept much indoors, and negligently
managed, the grain of the hide is injured by the dung which adheres to
it. The Irish hides are usually somewhat roughly flayed.

(II.) South American hides are from the River Plate, Uruguay, and Rio
Grande. Those from the River Plate are considered the best, as being
stoutest and finest in texture. They are usually cured by salting,
and are known as "saladeros," "estancias," and "mataderos," according
to the slaughter and cure. The saladeros are the best, and are from
cattle killed at large slaughtering establishments on the coast. The
estancias are from cattle killed in the interior, and are worse in
flaying than the saladeros, but free from the objectionable dark cure
of the mataderos, which are killed by the city butchers. Many hides
are brought from Brazil, and are generally both salted and sun-dried,
or simply stretched out and dried. Hides are also imported from
Valparaiso, both dry and wet-salted.

Chinese and West Indian hides are mostly dried. Chinese hides are
occasionally infected with _Bacillus anthracis_, which produces the
dangerous "malignant-pustule," or "wool-sorters' disease." Hence any
pimple appearing after working with such hides should have immediate
medical attention. French market hides have been of recent years
largely imported; they are mostly well flayed, and some of them
very heavy, but are sold at original butchers' weight, and, in the
experience of some tanners, the result in leather is 5-6 per cent. less
than from English market hides. They usually lose about 25 per cent.
in skulling and salting. Lisbon hides are often well flayed, but are
frequently branded, and the grain is injured by insects. They yield
considerably more leather than market hides in proportion to weight.
Hambro' hides are salted, but mostly wet and ill-flayed. Very heavy
hides are produced in the Rhine district and in Switzerland.

For further information about hides, see the Commercial Section.

_Preparation for Tanning._--Market hides should be well washed in
fresh water, to remove blood and dirt, before unhairing; but prolonged
soaking dissolves a portion of hide-substance, and probably reduces
weight, though it facilitates the action of the lime. It is very
advantageous if grease and flesh, and also dung can be removed before
liming, and if hand-labour is too costly machinery might be employed.
Salted hides should be soaked somewhat longer, and in clean water, so
as to remove the salt before liming. This water should be frequently
changed, since 10 per cent. brine dissolves coriin freely (see p.
19). Dried hides require more lengthened treatment. Before they are
prepared for tanning, they must be brought back as far as possible
to the condition of fresh hides, and, for this purpose, must be
thoroughly soaked and softened in water. There are many ways of doing
this: sometimes hides are suspended in running water; sometimes laid in
soaks, which may be either renewed, or allowed to putrefy; sometimes in
water to which salt, borax, or carbolic acid has been added, to prevent
putrefaction.

The first of these methods, were it desirable, is rarely possible in
these days of River Pollution Acts; of the others, it is difficult to
say which is better, since the treatment desirable varies with the
hardness of the hide and the temperature at which it has been dried.
The great object is to thoroughly soften the hide, without allowing
putrefaction to injure it. As dried hides are often damaged already
from this cause, either before drying, or from becoming moist and
heated on ship-board, it is frequently no easy matter to accomplish
this. The fresh hide, as has been seen, contains considerable portions
of albumen, and if the hide is dried at a high temperature, this
becomes wholly or partially coagulated and insoluble. The gelatinous
fibre and the coriin (if indeed the latter exists ready formed in the
fresh hide) do not coagulate by heat, but also become less readily
soluble. Gelatin dried at 266° F. (130° C.) can only be redissolved by
acids, or water at 248° F. (120° C.). Eitner experimented with pieces
of green calf-skin of equal thickness, which were dried at different
temperatures, with results given in the following table:--

  ───────┬────────────┬───────────┬──────────┬────────────┬─────────────────┐
         │Temperature │           │ Time of  │            │ Coriin Dissolved│
  Sample.│  of Drying.│ Remarks.  │ Softening│ Remarks.   │   by Salt       │
         │            │           │ in Water.│            │   Solution.     │
  ───────┼────────────┼───────────┼──────────┼────────────┼─────────────────┤
     I.  │ 59° F.     │ In vacuo  │  24 hours│{Without   }│ 1·68 per cent.  │
         │  (15° C.)  │           │          │{mechanical}│                 │
    II.  │ 71-1/2° F. │  In sun   │   2 days │{ work     }│ 1·62    "       │
         │  (22° C.)  │           │          │            │                 │
         │            │           │          │            │                 │
   III.  │ 95° F.     │{In drying-│}   5  "  │twice worked│ 0·15    "       │
         │  (35° C.)  │{closet    │}         │            │                 │
         │            │           │          │            │                 │
    IV.  │ 140° F.    │      "    │ {Refused to soften   }│  Traces.        │
         │  (60° C.)  │           │ { sufficiently for   }│                 │
         │            │           │ { tanning            }│                 │
  ───────┴────────────┴───────────┴──────────┴────────────┴─────────────────┘

Hence it is evident that, for hides dried at low temperatures, short
soaking in fresh and cold water is sufficient, and, except in warm
weather, there would be little danger of putrefaction. With harder
drying, longer time is required, and it may be necessary to use brine
instead of water. A well-known tanner recommends a solution of 30°-35°
barkometer (sp. gr. 1·035, or about 5 per cent. of NaCl). This will
have a double action, not only preserving from putrefaction, but
dissolving a portion of the hide-substance in the form of coriin.
Although this is undoubtedly a loss to the tanner, it is questionable
if there is any process which will soften overdried hides without loss
of weight: since even prolonged soaking in cold water at too low a
temperature to allow of putrefaction will dissolve a serious amount
of hide-substance. Water containing a small quantity of carbolic acid
has been recommended for the purpose, and will prevent putrefaction,
while it has no solvent power on the hide, but, on the contrary,
will coagulate and render insoluble albuminous matters. Concentrated
carbolic acid, however, tans the grain and renders it incapable of
colouring in the liquors. Borax has been proposed for the same purpose,
and, in strong solution, certainly prevents putrefaction, but is
probably too costly. Sodium sulphide and other sulphides seem to have
considerable effect in softening dried hides, from their property of
attacking hard albuminous matters, without injuring the true hide-fibre.

For some descriptions of hides, however, and notably for India kips,
putrid soaks seem actually to be an advantage, the putrefactive action
softening and rendering soluble the hardened tissue. In India the
native tanners soften their hides in very few hours by plunging them in
putrid pools, into which every description of tannery refuse is allowed
to run. Putrefactive processes are always dangerous, as the action,
through changes of temperature, or variation in the previous state of
the liquor, is apt to be irregular, and either to attack one portion of
the hide before another, or to proceed faster than was expected. Hence
hides in the soaks require constant and careful watching, and the goods
must be withdrawn as soon as they are thoroughly softened, for the
putrefaction is constantly destroying as well as softening the hides.
It is possible that putrefactive softening is less injurious to kips,
and such goods as are intended for upper-leather, than to those for
sole purposes, as it is generally considered necessary in the former
case that the albumen and interfibrillary matter be removed, and that
the fibre be well divided into its constituent fibrils for the sake of
softness and pliability; so that the putrid soak, if acting rightly,
only accomplishes a part of the work which would afterwards have to be
done by the lime and the bate. The actual fibre of the hide seems less
readily putrescible than the albuminoid parts; hence the putrefaction
may soften the latter better, and even at less expense of valuable
hide-substance, because more rapidly, than fresh water. On this point,
there is room for investigation. Putrefaction is a general name for a
class of decompositions which are caused by a great variety of living
organisms, each of which has its own special products and modes of
action. It is quite possible that, if we knew what precise form of
putrefaction was most advantageous, we might by appropriate conditions
be able to encourage it to the exclusion of others, and obtain better
results than at present. It will be necessary to revert to this subject
when speaking of the bates used in preparing dressing-leather, which
also owe their activity to putrid fermentation.

Beside merely soaking the hides, it is necessary to work them
mechanically, to promote their softening, which was formerly
accomplished by "breaking over" the hides on the beam with a blunt
knife. This process is now usually superseded or supplemented by the
use of the "stocks"; these consist of a wooden or metallic box, of
peculiar shape, wherein work 2 very heavy hammers, raised alternately
by pins in a wheel, and let fall upon the hides, which they force
up against the side of the box with a sort of kneading action. The
ordinary form of this machine is shown in Fig. 22. A more modern form,
which seems to possess some advantages, is the American double-shover,
seen in Fig. 23.

[Illustration: Fig. 22.]

[Illustration: Fig. 23.]

The number of hides which can be stocked at once naturally varies with
the size of both hides and stocks, but should be such that the hides
work regularly and steadily over and over. The whole number should not
be put in at once, but should be added one after another, as they get
into regular work. The duration of stocking is 10-30 min., according
to the condition and character of the hides. Hides should not be
stocked till they are so far softened that they can be doubled sharply,
without breaking or straining the fibre. After stocking, they must be
soaked again for a short time, and then be brought into an old lime. A
small quantity of sodium sulphide added to the soaks or in the stocks
has been recommended as of great value in softening obstinate hides,
and probably with justice, from its well-known softening action upon
cellular and horny tissues.

In Continental yards, another machine is in use for softening hides,
and which seems to present some advantages over stocks, as being less
severe on the thinner portions of the hide. It consists of a pair
of rollers, arranged like those of a wringing machine, and pressed
together by springs, but not allowed to come into actual contact. One
of them is studded with rounded pegs, which correspond in position to
grooves round the other, and the hide when passed between them is thus
subjected to a very thorough kneading and stretching. Tumbler drums of
various forms may also be used with good effect for softening purposes,
especially for skins.




CHAPTER VIII.

SOLE-LEATHER:--Unhairing Hides.


In England, lime is the agent almost universally employed for
loosening the hair, though every tanner admits its deficiencies and
disadvantages. It is hard, however, to recommend a substitute which is
free from the same or greater evils, and lime has one or two valuable
qualities which will make it very difficult to supersede. One of these
is that, though it inevitably causes loss of substance and weight,
it is also impossible, with any reasonable care, totally to destroy
a pack of hides by its use; which is by no means the case with some
of its rivals. Another advantage is that, owing to its very limited
solubility in water, it is a matter of comparatively small consequence
whether much or little is used; and even if the hides are left in a
few days longer than necessary, the mischief, though certain, is only
to be detected by careful and accurate observation. With all other
methods, exact time and quantity are of primary importance, and it is
not easy to get ordinary workmen to pay the necessary attention to
such details. Again, the qualities of lime, its virtues and failings,
have been matter of experience for hundreds of years, and so far as
such experience can teach, we know exactly how to deal with it. A new
method, on the other hand, brings new and unlooked-for difficulties,
and often requires changes in other parts of the process, as well as
in the mere unhairing, to make it successful. As our knowledge of the
chemical and physical changes involved becomes greater, we may look
to overcoming these obstacles more readily; for the power of dealing
successfully with new difficulties constitutes one of the main
advantages of a really scientific knowledge over an empirical one.

Slaked lime is soluble in water at 60° F. (15° C.), to the extent of
1 part in 778. Unlike most substances, it decreases in solubility at
higher temperatures, requiring 972 parts of water at 130° F. (54° C.),
and 1270 parts at 212° F. (100° C.). Its action upon animal tissues
increases rapidly, however, with temperature, though no doubt it is
moderated to some extent by the lessened solubility. Calculating
from Dalton's numbers, pure lime-water at 60° F. (15° C.) contains
1·285 _grm._[R] of CaO per _litre_, and should require 459 _c.c._
of decinormal acid to neutralise it. This estimate in some cases
appears to be slightly too high; e. g. a saturated lime-water from
Carboniferous limestone at 56.5° F. (13° C.) required only 433 _c.c._
of decinormal acid, which equals 1·211 _grm._ of CaO per _litre_, and
this lime-water, kept with excess of lime, gave nearly constant results
for many months together. A magnesian limestone lime-water tested at
the same time required 472 _c.c._ of decinormal acid, confirming the
old observation of tanners, that such lime is stronger than that made
either from chalk or carboniferous limestone. This increased strength
must arise from the presence of some soluble base other than lime, and
may be due to the magnesia, which, however, is very slightly soluble.
Magnesian limestone contains a very large amount of magnesia, and
hence would not go so far as a purer limestone; but as a very large
proportion of the lime ordinarily used is thrown away undissolved, this
is perhaps of little practical moment. (For the chemical examination of
limes, see p. 102).

[Footnote R: 1 _grm._ per _litre_ is very approximately equal to 1 oz.
per cub. ft.]

The action of lime on the hide has already been spoken of to some
extent. It is throughout a solvent one. The hardened cells of the
epidermis swell up and soften, the _rete malpighi_ and the hair-sheaths
are loosened and dissolved, so that, on scraping with a blunt knife,
both come away more or less completely with the hair (constituting
"scud," as some English tanners name it, Ger. _gneist_ or _grund_).
The hair itself is very slightly altered, except at its soft and
growing root-bulb, but the true skin is vigorously acted on. The fibres
swell and absorb water, so that the hides become plump and swollen,
and, at the same time, the "cement-substance" (coriin) is dissolved,
the fibres become differentiated into finer fibrils, and the fibrils
themselves become first swollen and transparent, and finally corroded,
and even dissolved. This swelling of the fibres is produced both by
alkalies and acids, and is probably due to weak combinations formed
with the fibre-substance, which have greater affinities for water than
the unaltered hide. It is useful to the tanner, since it renders the
hide easier to "flesh" (i. e. to free from the adhering flesh), on
account of the greater firmness which it gives to the true skin. It
also assists the tanning, by opening up the fibre, and so exposing a
greater surface. This is advantageous in dressing leather which is
afterwards tanned in sweet liquors, and must have the cement-substance
dissolved and removed for the sake of flexibility; and, in the case of
sole-leather, it is necessary for the sake of weight and firmness that
the hide be plumped; but it is probable that the effect is produced
with less loss of substance and solidity by suitable acidity of the
liquors. A more certain advantage of lime is that it acts on the fat of
the hide, converting it more or less completely into an insoluble soap,
and so hindering its injurious effects on the after tanning process,
and on the finished leather. If strong acids are used later on, this
lime soap is decomposed, and the grease is again set free. In sweated
or very low-limed hides this grease is a formidable evil.

The customary method of liming is simply to lay the hides flat in milk
of lime in large pits. Every day, or even twice a day, the hides are
drawn out ("hauled"), and the pit is well plunged up, to distribute
the undissolved lime through the liquor. The hides are then drawn in
again ("set"), care being taken that they are fully spread out. How
much lime is required is doubtful, but owing to its limited solubility,
an excess, if well slaked, is rather wasteful than injurious. Great
differences exist in the quantity of the lime used, the time given,
and the method of working. Lime, as we have seen (p. 140), is only
soluble to the extent of about 1·25 _grm._ per _litre_, or (as 1 cub.
ft. of water weighs about 1000 oz.) say 1-1/4 oz. per cub. ft., or,
in an ordinary lime-pit, not more than 1/4 lb. per hide. Only the
lime in solution acts on the hide, but it is necessary to provide
a surplus of solid lime which dissolves as that in the liquor is
consumed. Jackson Schultz prescribes 1 bush. (56 lb.) of fresh lime to
60-70 hides, and 3-4 days as sufficient time to unhair and plump them;
while a well-known English tanner states that, after working for 6-10
days through a series of old limes, the hides (presumably wet-salted
South Americans) should have 4 days in a fresh lime, made with 3-12
lb. of lime per hide. It is obvious that if the American authority
is right, the English process is wasteful in the extreme, both in
hide-substance and lime. Much depends on the amount of hauling which
the hides receive, and the more frequently they are moved the better.
It is probable, however, that it would be found impossible to unhair
and flesh hides, to suit the English market, in cold limes with the
quantity and time mentioned, and if the limes are steamed, it is quite
likely that the destructive action on the pelt may be even greater than
by the longer and slower process in the cold. Most likely a compromise
between the two is the most desirable, but about 2-4 lb. of lime per
hide, according to weight, should be amply sufficient; while a week
for market hides, and 14 days for heavy salted, will loosen the hair
and plump the pelt as much as is requisite. This is on the supposition
that the limes are kept at a uniform average temperature of about
60° F. (15° C.) in winter and summer. If they are heated to 80°-90°
F. (27°-32° C.), of course much less time is required; but there are
no published experiments showing the relative weights made by the
two processes, and, from the fact that warmed limes are principally
used for descriptions of leather where weight and solidity are not of
primary importance, it may be concluded that, in this direction, the
results are unsatisfactory. Hides do not plump in warm limes.

Another undecided point is whether the best results are obtained by
making fresh limes for every pack, or by strengthening up the old ones.
An old lime becomes charged with decomposing animal matter and with
ammonia, and, within limits, loosens the hair more effectually than a
new one. An experienced tanner states that, by using old limes, better
weights are obtained, but that the leather is thinner than when a fresh
portion of lime is used; and this is quite possible. If, however, the
old lime-liquor be retained too long, it ceases to swell the hides as
it should, and, in warm weather, the liming proper is complicated by a
putrefactive process allied in principle to sweating.

Beside considerable quantities of ammonia, old limes contain tyrosin,
leucin or amidocaproic acid, and some caproic acid, the disagreeable
goaty odour of which is very obvious on acidifying an old lime-liquor
with sulphuric acid, by which considerable quantities of a partially
altered gelatin are at the same time precipitated. Very old limes,
especially in hot weather, often contain active bacteria, which may be
seen in the microscope under a good 1/4-in. objective. Their presence
is always an indication that putrefaction is going forward, and leather
out of such limes will generally prove loose and hollow-grained.
Spherical concretions of calcium carbonate may also be seen under
the microscope, resembling on a smaller scale those found in Permian
limestone, and caused perhaps in both cases by crystallisation from
a liquid containing much organic matter. It is probable that in many
tanneries the ammonia would pay for recovery from the lime-liquors,
which would be easily done by steaming the old limes in suitable
vessels, and condensing the ammoniacal vapours in dilute sulphuric
acid. (Some appliances suitable for this purpose are described in
the Journal of the Soc. of Chem. Industry, iii. 630.) For methods of
estimation of ammonia, see p. 103.

Several variations in the above-described method of liming have been
proposed. The hides may be suspended on laths, or by strings attached
to pegs or notches, and the liquor agitated by plunging in place of
hauling. Probably this is an actual improvement, especially if some
mechanical agitating contrivance be substituted for hand plunging. It
has, however, the drawback that much room is required, though this may
be, to some extent, compensated by the hides liming more quickly. The
method has been long in use in America, and had been tried in several
places in England before the patent of Messrs. Conyers and Pullein was
obtained. Two other American labour-saving methods in connection with
liming may be mentioned here. One is to have the liming-vat double
the ordinary size, and, instead of hauling the hides, to simply draw
them from one side to the other by two strings, which are attached to
the fore and hind shank of each hide, either by sharp iron hooks or
by loops. The strings are looped over iron rods at the four corners
of the pit, or have simple knots, which are placed in notches sawn in
wood. Of course, while the hides are at one side of the pit, the other
side may be plunged or warmed. The other method (Fig. 24) is to have
a spindle sunk below the surface of the liquor, and with discs A, at
each end, to which the hides or sides are attached by hooks set round
the edges. The hides are turned over by revolving the spindle with a
handspike inserted in the holes C, at the ends of the cross-arms B, and
the whole spindle is also capable of being raised and lowered in the
liquor, in the slot D. In Germany, hides are frequently suspended on
laths radiating from a central upright revolving spindle in a round vat
(_Drehkalk_).

An American plan, sometimes known as the "Buffalo method," is described
by Jackson Schultz. The hide is prepared in the usual way, and is then
thrown into a strong lime for 8-10 hours, when it is taken out and
immersed in water heated up to 110° F. (43° C.), in which it remains
24-48 hours. The warm water soaks, softens, and swells the roots of
the hair, and much the same result is obtained as in "scalding" pigs.
So little lime really permeates the inner fibre that, after a slight
wheeling, the hides may be thrown into cold water, and allowed to cool
and plump, preparatory to taking their places in the handlers. The
process is strongly recommended for sole-leather, particularly where
great firmness of fibre is desired. The tanner who tries it must be
satisfied if he gets 20-30 sides a man unhaired and fully ready for the
liquor per diem. Of course this process may be varied to any extent by
giving more liming, and less hot water, and this is frequently done in
America. About 3-4 days' cold liming in good limes, and with hauling
if possible twice daily, followed by 12-24 hours in water at 86°-95°
F. (30°-35° C.), which should be changed at least once, will give good
results. The hides are of course less plump than usual, but if properly
managed in the handlers will swell well in the tan-house. Grease is
obviously less thoroughly "killed" than in the ordinary method, and
especial care must be used that the hides are well worked on the beam,
both on grain and flesh. In this method, and indeed in all liming
processes, much is gained if the fat can be fleshed off green.

[Illustration: Fig. 24.]

On the Continent and in America, the prevalent mode of loosening the
hair, at least for sole-leather purposes, is called "sweating," and
consists in inducing an incipient putrefaction, which attacks the soft
parts of the epidermis and root-sheaths, before materially injuring
the hide-substance proper. The old European method of "warm-sweating"
consisted simply in laying the hides in pile, and, if necessary, in
supplying heat by covering them with fermenting tan; but as this crude
and dangerous process is everywhere being supplanted by the American
plan, where sweating at all is adhered to, it is not necessary to
do more than describe the latter. This is called "cold sweating,"
but really consists in hanging the hides in a moist chamber, kept at
a uniform temperature of 60°-70° F. (15°-21° C.); or in some cases
slightly warmer.

The "sweating-pit" now in use is sometimes of wood, but usually
consists of a building of brick or stone, protected from changes of
temperature, both above, and at the sides, by thick banks of soil or
spent tan. If soil be used, it will form an excellent bed for vines,
&c., which are fertilised by the ammonia penetrating from below,
which is evolved in large quantities and which assists the unhairing
process by its action on the epidermis.[S] Though called a "pit,"
it is undesirable that it should be actually below the level of the
ground, but should be arranged so that the hides can be wheeled in
and out in barrows. It is lighted and ventilated by a lantern roof
above a central passage, and should be divided into chambers, each
capable of suspending a pack of hides. By means of sprinklers above and
steam-pipes below, the chambers may be cooled or warmed, as required,
and the air kept so moist that globules of condensed water collect on
all parts of the hides, which are suspended from tenterhooks.

[Footnote S: Hides have been unhaired by the action of gaseous ammonia
alone, but the method does not seem suited for technical use.]

The process is principally used in America for dried hides, but may
be employed either for wet or dry salted, after complete removal of
the salt. It is imperatively necessary that dried hides should be
completely softened before sweating. As the sweating process advances
more rapidly in the upper than in the lower part of the pit, and as
the thick portions are more resistant than the thin ones, the hides,
after about 3 days' sweating, require constant attention in changing
their positions, and in checking the forward ones by taking down and
laying in piles on the bottom of the pit.

The usual treatment for sweated hides, when the hair is sufficiently
loosened, is to throw them into the stocks, and work out in this way
the slime and most of the hair. This has the disadvantage of working
out too much of the dissolved gelatin, and of fulling the hair so
firmly into the flesh, that it is difficult again to remove it. To
overcome these evils, some American tanners now pass the hides, after
sweating, through a weak lime. This, to a great extent, prevents
the hair fixing itself in the flesh, and tends to counteract the
injurious effect of the vitriol (which is almost invariably used in
plumping sweat stock) on the colour of the leather. By this process,
10,000 Texas and New Orleans wet-salted hides gave an average yield
of leather of 73 per cent. on their green weight, and the leather was
excellent in quality (Schultz). If sweated or very lightly limed hides
are imperfectly worked on the grain, greasy spots are apt to remain,
which will not colour in the liquors ("white spots"). These may be made
to colour by scraping and working the grain with a knife, or by the
application of a solution of soda or soda ash, and would probably be
avoided by the use of soda ash in the soaks on greasy parcels of hides.

It must be clearly understood that all sweating depends on partial
putrefaction. This is proved both by the plentiful production of
ammonia in the pits, and by the fact that antiseptics, such as salt
or carbolic acid, entirely prevent sweating till they are removed.
Although the process undoubtedly has advantages, and especially so in
the treatment of dried hides, it is an open question whether it gives
the extreme gains over liming in weight and firmness, which are claimed
by some of its advocates.

An unhairing process, largely coming into use on the Continent, depends
on the action of alkaline sulphides, and particularly sodium sulphide,
upon the hair. While all the methods already spoken of involve the
softening and destruction of the hair-sheaths, either by lime or
by putrefaction, the sulphides are peculiar in attacking the hair
itself; when strong, they disintegrate it rapidly and completely into
a sort of paste. From very early times to the present day, arsenic
sulphide ("rusma") mixed with lime has been used in unhairing skins for
glove-leather and similar purposes. About 1840, Böttger concluded that
the efficacy of arsenic sulphide was due simply to the sulphydrate of
lime formed by combination of the sulphur with the lime, and proposed
lime sulphydrate, formed by passing sulphuretted hydrogen into milk of
lime, as a substitute for the poisonous and expensive arsenic compound.
It proved a most effective depilatory, but has never obtained much hold
in practice. This is probably due to the fact that it will not keep,
oxidising rapidly on exposure to the air; hence it must be prepared
as it is required, which is both troublesome and expensive. A minor
objection is the unpleasant smell of sulphuretted hydrogen, which is
inseparable from its use.

It was proposed to replace it by sodium sulphide, which, though at
first said to be only effective when mixed with lime, so as to produce
calcic sulphide, has since proved a powerful depilatory alone. Its use
has been greatly extended on the one hand by its production on a large
scale, and in the crystallised form (at first by reduction of sulphate
by heating with small coal), and on the other, by the great interest
which Wilhelm Eitner, the able director of the Austrian Imperial
Research Station for the Leather Trades, has taken in its introduction.
The substance, as manufactured by De Haen, of List, Hanover, is in
small crystals, coloured deep greenish-black, by iron sulphide, which
must have been held in suspension at the time of crystallisation.
If the salt be dissolved in water, and the solution be allowed to
stand, this is gradually deposited as a black sediment, leaving the
supernatant liquor perfectly clear and colourless. Sodium sulphide is
now manufactured from tank waste in a much purer form by Schaffner
and Helbig's process, of which Messrs. Gamble of St. Helens are sole
licencees. The crystallised salt is SNa_{2}10Aq, and therefore contains
69·8 per cent. of water.

For sole-leather, the method recommended by Eitner is to dissolve 4-5
lb. of sulphide per gal. of water, making the solution into a thin
paste (of soupy consistence) with lime or pipe-clay. This is spread
liberally on the hair side of the hides, one man pouring it down the
middle of the hide from a pail, while another, with a mop or cane
broom, rubs it into every part. The hide is then folded into a cushion,
and in 15-20 hours will be ready for unhairing, the hair being reduced
to a paste. In the writer's experience, the concentrated solution here
prescribed will completely destroy all hair wetted with it in 2-3
hours, and if left on longer, will produce bluish patches, and render
the grain very tender. The hides should be thrown into water before
unhairing, to enable them to plump, and to wash off the sulphide,
which is very caustic, attacking the skin and nails of the workmen.
There is no doubt that this process gives good weight, and tough and
solid leather; but there are several difficulties attending its use.
Unless the mopping is done with great care, it will fail to completely
destroy the hair, and the patches of short hair left are very difficult
to remove. The expense of the material and the loss of hair are also
important considerations. The hides are rather difficult to flesh,
unless previously plumped by a light liming, and it is necessary to
swell them with acid or sour liquor in the tanhouse, as the sulphide
has but little plumping effect.

Another method, which is much cheaper in labour and easier in
execution, is to suspend in a solution of sodium sulphide, containing
3/4 lb. a hide or upwards; the hide should unhair in 24 hours. Very
weak solutions loosen the hair, without destroying it; but it is
always weakened, as the specific action of the sulphides is on the
hair itself. After or before unhairing, the hides may receive a
light liming, to plump them, or lime may be added to the solution of
sulphide, which by forming calcium sulphide, and liberating caustic
soda, considerably increases the unhairing and plumping effect. The
pit may be several times strengthened for successive packs, but
the loosened hair must be fished out, or it will quickly spoil the
solution. When hides have been suspended in sodium sulphide solution,
the hair is very quickly loosened by a short liming. Squire, Claus,
and J. Palmer have all taken out patents for the use of tank-waste
as a depilatory. It consists of impure calcium sulphides, and when
brought into the form of soluble sulphydrate, either by boiling in
water, or by the oxidising action of the air, it will unhair hides. The
conversion is, however, very imperfect in either case, and its action
is uncertain and slow; while the iron present is apt to cause unsightly
stains. It is probable that the weights obtained may somewhat exceed
those by liming. Palmer employs sulphuric acid to plump the hide and
remove stains, and then reduces it by a bate of whiting and water. He
claims that this prepares the hide for rapid and heavy tanning, but
the swelling and subsequent reduction almost certainly entail loss of
weight and quality, and to get good results the bate should at most
only be allowed to have a superficial effect. Professor Lufkin proposed
the use of a mixture of various sulphides of lime and soda, formed by
mixing 10 lb. each of soda ash and sulphur, kneading to a paste with a
little moist slaked and then mixing _warm_ in a cask with 80 lb. stone
lime slaked to a paste. This quantity will unhair 50 hides in the same
way and in about the same time as an ordinary lime. The pelt is not
much plumped and is easily reduced by a few minutes' wheeling in warm
water. (J. S. Schultz.)

Various other depilatories have been proposed, but as they have not
come into general use, brief mention of the most important will
suffice. Anderson, in 1871, patented the use of wood-charcoal, applied
in a similar manner to lime in the ordinary process. The hair is
probably loosened simply by putrefaction, as in sweating, while the
charcoal acts as a deodoriser, very little smell being produced, and
the action proceeding with considerable uniformity. John Palmer has
patented a process for unhairing, in which the hides are alternately
steeped in water and exposed to the air till the hair loosens. In this,
very similar principles to those of the charcoal method are involved.
Caustic potash and soda will loosen hair, but seem to have no decided
advantage over lime, though it is quite possible that in skilful
hands good results might be obtained. They are more costly, and their
corroding action on the hide-substance is more powerful, but they form
soluble soaps with the grease of the hide. Unless used in very dilute
solution, the pelt is so swollen as to fix the hair, and the leather is
dark-coloured and spongy. Soda-ash or crystals (sodic carbonate) may be
used to strengthen ordinary limes, in which caustic soda is formed. The
time of liming is shortened, the hides are more swollen, and the grease
is better "killed" than when lime alone is used. The patent for Moret's
"Inoffensive" claimed the use of the carbonate or caustic potash formed
from calcined wool-washings, for unhairing. This is more costly than,
and has no advantage over soda. I am not aware whether "Inoffensive,"
as now sold, has other constituents.

Whatever method of loosening the hair may be adopted, the next step
is to remove it by mechanical means. This is usually accomplished by
throwing the hide over a sloping beam, and scraping it with a blunt
two-handled knife (Fig. 25), the workman pushing the hair downwards
and away from him. The beam is now usually made of metal. The knife
employed is also shown at C, Fig. 26.

When a hide is lightly limed, it is often easy to remove the long
hair, but excessively difficult to get rid of the short under-coat
of young hairs, which are found in spring, and which can sometimes
only be removed by the dangerous expedient of shaving with a sharp
knife. The reason of this difficulty is obvious: not only do the short
hairs offer very little hold to the unhairing knife, but, as has been
explained in describing the anatomical structure of the skin, their
roots are actually deeper seated than those of the old hairs they
replace. Several attempts have been made to unhair by machinery, but
so far without such success as to lead to their general adoption. The
fleshing-machine invented by Garric and Terson, and manufactured in
this country by T. Haley and Co., of Bramley (Fig. 27), is furnished
with a special wheel for unhairing. An American machine for the
purpose, invented by J. W. Macdonald, and said to be capable of
unhairing 800 sides a day, is shown in Fig. 28.

[Illustration: Fig. 25.]

[Illustration: Fig. 26.]

[Illustration: Fig. 27.]

[Illustration: Fig. 28.]

When the hair is very thoroughly loosened, as by sweating, or
destroyed, as by sodium sulphide, it is not uncommon to work it off by
friction in the stocks; but it is very doubtful whether the saving of
labour is not more than compensated by the loss of weight, consequent
upon submitting the hide while its gelatin is in a partially dissolved
condition, to such rough usage.

[Illustration: Fig. 29.]

After unhairing, the loose flesh and fat are removed from the inner
side of the hide by a sharp-edged knife E (Fig. 26), partly by brushing
or scraping, partly by paring. It is necessary not only to cut off the
visible adhering fat, but to work the hide well, so as to force out
that contained in the loose areolar tissue, which would not only impede
tanning, but is liable to soak completely through the hide, producing
most unsightly blotches. Several machines have been introduced to
supersede hand-fleshing, but with only partial success. One of the
best is Garric and Terson's machine (Fig. 27), which gives a very
level flesh, free from galls, and without so much loss of weight, but
scarcely so clean as desirable, while the saving in labour is not
great. Molinier's machine (Fig. 29), and that of Jones and Rocke, are
well adapted for skins, but hardly capable of fleshing an entire hide.
All these machines are very similar in principle, the working parts
consisting of drums with oblique or spiral knives.

When unhaired and fleshed, the hides intended for sole-leather are, in
England, almost invariably "rounded," or separated into (1) "butts,"
which are the best and thickest parts, and receive the most solid
tannage, and (2) "offal," which is thinner, and for which a cheaper and
more rapid tannage is sufficient. Fig. 30 shows the customary division.
Frequently the butt is divided down the centre, and the halves are then
called "bends." A piece called a "middle" is sometimes taken between
the butt and the shoulder.

[Illustration: Fig. 30.]

After rounding, it is necessary to get rid of the lime, as completely
as possible, before taking into the tan-house. For this purpose,
the butts are usually suspended in fresh water for 12-24 hours, and
frequently shaken up in it to remove adhering lime and dirt. If
the water is hard, it is best to add to it, before putting in the
butts, a few pailfuls of clear lime-water, to precipitate the lime
bicarbonate,[T] which would otherwise cause a deposit of chalk on the
surface of the butts; this would not only make the grain harsh, but
afterwards, by combining with the tannin of the liquors, would cause
bad colour. For the same reasons, it is important that limey hides
should be as little exposed to the air as possible, as the latter
always contains a small amount of carbonic acid, which renders the lime
insoluble.

[Footnote T: Lime softens water containing lime bicarbonate in
solution by combining with half the carbonic acid, when the whole is
precipitated as normal carbonate or chalk. CaO + CaCO_{3} . H_{2}CO_{3}
= 2CaCO_{3} + OH_{2}. This is Clark's process. See also p. 84.]

This suspension in water is frequently considered sufficient for
sole-leather, but it removes the lime very imperfectly. In olden days,
it was customary not only to wash the hides much more thoroughly in
water, but to "scud" them (i.e. work them over with a blunt knife),
to remove lime, and the detritus of hair-roots and fat-glands, and
this should never be omitted from sole-leather treatment where bright
colour and clean buff are desired. Some tanners go so far as to bate
best butts slightly with hen-dung, but with such treatment firmness
and weight are lost. Washing in weak solution of sugar, or ammonic
chloride or sulphate, or of sulphuric, or hydrochloric acid, may be
adopted. It is essential to use acids nearly free from iron, as it may
be precipitated on the butts and give a bluish colour in the liquors,
and the acid must be of such a strength as neither to allow the iron
to be precipitated, nor, on the other hand, perceptibly to plump the
butts, which in this stage would endanger buff and colour. 100 _cc._
may neutralise 15-20 _cc._ of lime-water for this purpose. Hydrochloric
acid and chlorides have a tendency to prevent plumping, and are
therefore better adapted for dressing than for sole leather. Great
care must also be taken to prevent putrefaction, or the use of putrid
solutions, if firmness and plumpness are desired.




CHAPTER IX.

SOLE-LEATHER.--Tanning Materials.


Before describing the management of the hides in the tan-house, it
is necessary to say a few words about one or two of the principal
materials used, and the methods of preparing them for use. Further
details of their nature and origin have been given in the section on
Tannins, p. 23.

Oak-bark is one of the oldest of tanning materials, and the leather
produced by its aid is still considered for many purposes the best. For
sole-leather, its weakness in tannin (8-12 per cent.), the slowness
of its action, and the light weight of the leather produced, render
it unavailable alone except for the very finest class of work. It
is, however, generally used in admixture with stronger and cheaper
materials, such as valonia.

Valonia, the acorn-cup of an evergreen oak growing in Greece and the
Levant, is perhaps the most important of materials to the English
sole-leather tanner. It contains 25-35 per cent. of a tannin somewhat
similar to oak-bark, and, like it, communicating a light-coloured bloom
to the leather, but giving much greater firmness and weight, and a
browner colour.

Myrabolanes or myrobalans, the fruit of an Indian shrub, contains about
as large a percentage of tannin as valonia, and gives a similar bloom,
and excellent colour; but it can only be used very sparingly on butts,
since it produces a soft and porous leather.

Divi-divi is a South American bean, which contains much of a brown
tannin in the pod, being considerably stronger than valonia. It makes
a heavy and solid, but somewhat horny leather. Its great danger arises
from a tendency to sudden fermentation in thundery weather, which,
produces brown or red stains on the leather. At all times it is liable
to give a bluish or violet colour, which is most obvious in the
interior of the leather, and which resists both acids and alkalies.

Mimosa-bark is the product of several Australian acacias, and is
probably nearly as strong as valonia. It gives a hard and heavy
leather, but of a dark-red colour.

Hemlock-extract is a deep-red syrupy extract of the bark of the hemlock
pine of America.

Chestnut-extract is a similar product from the rasped wood of the
Spanish chestnut. Its colour is paler and yellower than that of the
hemlock, and hence it is often employed to correct the red tone
produced by the latter.

Oakwood extract is an analogous preparation from oak saw-dust.


Grinding and Exhaustion of Tanning Materials.

Before tanning materials can be exhausted, it is almost invariably
necessary to crush or grind them, so as to enable the water to get
freely at the tannin, which, in most cases, is enclosed in the cellular
tissue of the plant. It may be thought that for this purpose it would
scarcely be possible to crush too finely, but in practice, a very
fine powder is extremely difficult to spend, as it cakes into compact
and clay-like masses, through which liquor will not percolate. The
object, therefore, is to grind finely enough to allow the liquor
ready access to the interior, but not so finely as to prevent liquids
running through the mass. The mill most usually employed for this
purpose consists of a toothed cone, working inside another cone, also
toothed on its interior, precisely like those of a coffee-mill. As
bark is frequently delivered "unhatched," or in long pieces, it is
necessary to crush it preparatory to grinding, and this is usually
accomplished by rollers composed of toothed discs, called breakers. In
Fig. 31 is illustrated such a mill, as made by Newall and Barker, of
Warrington, combining both utensils. Fig. 32 shows a section of the
well-known American "keystone" mill, in which the preliminary breaking
is accomplished by the arms A; the bark is then finely ground by the
toothed cones N, and discharged at the spout R by the revolving shover
M. Fig. 33 shows a somewhat similar mill, made by Gläser of Vienna,
in which the axis is horizontal, and driven directly by a belt. It is
better to drive bark-mills by a belt than by toothed gearing, as in
event of iron getting into them there is less danger of breakage. In
America, a cheap cast-iron coupling is frequently used, weak enough to
give way before serious damage is done. Safety "friction" clutches are
generally ineffective. American bark-mills are run faster than English,
up to about 80 rev. per minute, and where the bark is to be used
immediately it is frequently damped by a small jet of steam below the
mill, which lays dust, and prevents danger of fire. Bark which is damp
before grinding can scarcely be ground in these toothed mills, but must
be dried, or a disintegrator used.

[Illustration: Fig. 31.]

[Illustration: Fig. 32.]

[Illustration: Fig. 33.]

Now that a large variety of other materials besides bark are required
by tanners, the mills just described are not always sufficient for the
purpose. Myrobalans and mimosa-bark have proved specially troublesome,
the former from its very hard stones and clogging character, and the
latter from its combined hardness and toughness. "Disintegrators" of
various makes have proved admirably adapted for grinding both of these
materials, their advantage being the universality of their reducing
powers, ranging from oak-bark to bones or brick-dust, and their
disadvantages, the somewhat considerable power they consume, and the
rather large portion of fine dust they make. Their principle is that
of knocking the material to powder by rapidly revolving beaters,
which, in the smaller mills, are driven at so high a speed as 2500-3000
rev. a minute. Wilson's is shown in Fig. 34, as an example. It is one
of the oldest tanners' disintegrators, and probably still one of the
best. In the figure, it is opened, showing the disc with its steel
beaters attached. When myrobalans are only required roughly crushed,
a machine with fluted or toothed rollers (Fig. 35) acts better than
a disintegrator, making less dust, and requiring less power. Such a
machine also crushes valonia very satisfactorily.

[Illustration: Fig. 34.]

[Illustration: Fig. 35.]

In England, the tanning material is generally carried from the mill, to
the pits where it is exhausted, in baskets or barrows; in America, this
is frequently accomplished by a "conductor," or horizontal spout, in
which a double belt, or malleable iron "drive chain,"[U] with wooden
cross-pieces, carries the bark forward, on the same principle as the
elevators of corn-mills. Fig. 36 shows the conveyors used in a Chicago
tannery. Another American plan is to use circular tubs for extraction.
These are mounted on wheels, and are worked on a railway, coming up to
the mill to be filled, and thence under a series of sprinklers like
those used by brewers, and finally "dumping" their contents before
the boilers, which are heated solely by wet bark, burnt in a peculiar
furnace with brick chambers. This furnace for burning wet bark seems
worthy of extended adoption in Europe, as spent tan is frequently
not only valueless, but costly to get rid of. Full details and scale
drawings may be found in Jackson S. Schultz's book on 'Leather
Manufacture' and in Fig. 37 is shown a modification of it, patented by
Huxham and Brown, which has been very successfully used in burning wet
tan, either alone or with a portion of coal. In American sole-leather
tanneries, where the bark is resinous and almost unlimited in quantity,
sufficient steam may be raised with tan wet from the leaches; but
in England, where material is more sparingly used, it is advisable
partially to dry it before burning. This is accomplished by powerful
roller-presses, as shown in Fig. 38. Gläser, of Vienna, constructs
tan-burning furnaces on a different principle from the American, the
essential point being the use of a "ladder-grate" (_Treppenrost_), on
which the burning tan is exposed to a draught of air playing over its
surface. Fig. 39 shows a portable stove of this construction. Gläser
also makes furnaces of larger size for heating air for drying-rooms,
and for boiler purposes. The essentials of successful tan-burning
are good draught, a large grate-surface, and a high temperature of
the combustion-chamber, and hence the ordinary Cornish or Lancashire
boiler, with its limited grate-area, surrounded by the comparatively
cool boiler-tube, is peculiarly ill-adapted for the purpose. The writer
has profitably burnt a mixture of wet tan and very small coal in such a
boiler by the aid of a steam-jet under-grate blower, but such a method
can only be regarded as a makeshift in default of better appliances.

[Footnote U: Such chains with attachments for elevators and conveyers,
are manufactured in this country by Ley's Malleable Casting Company, in
Derby.]

[Illustration: Fig. 36.]

[Illustration: Fig. 37]

In England, the tanning material is usually exhausted in pits called
"leaches," "latches," or "taps." These, in large yards, are made
capable of holding about 50 cwt. of material. The new material is first
flooded with a pretty strong liquor. When this has gained as much
strength as possible, it is pumped off, and is followed by a weaker
one, and so on till the material is exhausted. Much of the economy of
a tan-yard depends on the way, systematic or otherwise, in which this
is done. It is customary to complete the exhaustion with hot liquors,
or water, but opinions differ on the expediency of the practice. By
the use of heat, however, stronger liquors and more rapid spending are
attained; and with some materials, such as mimosa, complete exhaustion
is impossible in the cold.

[Illustration: Fig. 38.]

[Illustration: Fig. 39.]

The worst tap is frequently boiled by inserting a steam-pipe; but if
heat is used at all, it would probably be better to heat a strong
liquor by a steam-coil, and run it on the new material, which would
be softened and swollen, and yield a much larger proportion of its
strength to the first liquor; while it is stated by Eitner that the
colouring matters of tanning materials are much less soluble in strong
than in weak infusions. Boiling weak old liquors containing lime is
specially prejudicial, causing great darkening and discoloration.

Careful tanners also cast their material over from one pit into
another, before throwing away, so as to lighten it up, and allow
the liquor to penetrate to every part. In bark-yards, latches are
frequently worked in series, which are connected by pipes, so that the
liquor flows from the bottom of one upon the top of the next stronger.
This is an excellent plan for bark, which is open and porous, but is
scarcely adapted to such materials as valonia or myrabolans, which
have a tendency to form compact masses, through which the liquor does
not circulate. The same objection, in an almost higher degree, must be
urged against the Allen and Warren, or sprinkler leach, in which the
liquor, distributed on the surface by a rotary sprinkler, is allowed
to percolate downwards, and run freely away at the bottom. In this
case, it is almost sure to form channels, instead of flowing uniformly,
and, in addition, the material is constantly exposed to the action of
the air, which causes oxidation, with its attendant discoloration and
loss of tannin. Various attempts have been made to exhaust tanning
materials in closed vessels. Dr. Kohlrausch applied the _diffuseur_
used in extracting beet-root sugar, and which consists of a series of
closed copper vessels in which the coarsely ground material is placed,
of which the bottom of one is connected with the top of the next by
a pipe, through which the liquor is forced by steam pressure. This
apparatus is in use at the large tannery of Gerhardus, Flesch, and Co.,
of Vienna, and is said to give satisfaction, though it is very costly,
and the liquors produced are not of great strength. Gläser, of Vienna,
has patented an apparatus of which a model is illustrated in Fig. 40,
in which the materials are used finely powdered, and very rapidly
exhausted by the combined action of heat and mechanical agitation. Of
its mechanism I have not been able to obtain any detailed description,
but it is said to be capable of exhausting 9 tons of valonia _per
diem_, to 2 per cent., giving only 70° liquors, clear and of good
colour, while good bark is exhausted to 0·5 per cent. giving 30°
liquors. The cost of the apparatus is very heavy, but if the results
claimed are realised in practice it would pay well for an extensive
tannery. I have not been able to ascertain where it is to be seen in
use.

[Illustration: Fig. 40.]

It is one of the great attractions of extracts that they avoid almost
all the expense and labour inseparable from the exhaustion of other
tanning materials. It is usually necessary to dissolve the fluid
extracts in water or liquor of as high a temperature as has been
employed in their preparation, as otherwise, from some unexplained
chemical change, a large portion of the tannin is precipitated,
probably as an anhydride of the tannin. Gambier is usually dissolved by
boiling or steaming, but is said to give a better colour when dissolved
cold. This may be accomplished in a rotating latticed drum, sunk in a
pit of liquor.

Where circumstances permit, it is a great advantage to place the taps
either on a higher or a lower level than the layers and handlers, so
that liquors may be run one way without pumping.




CHAPTER X.

SOLE-LEATHER.--Treatment in the Tan-house.


On first coming into the yard, the butts are usually suspended by
the shoulder or butt ends from sticks placed across the pits. They
should be kept in almost constant movement, either by raising and
shaking them by hand, or by supporting them on frames, which are
rocked, or otherwise worked. Perhaps the best device for this purpose
is the "travelling handler" of W. N. Evans, which consists of a frame
supported on wheels, and worked slowly backwards and forwards by power.
This frame should extend the length of a range of pits sufficient to
take in at least a 3 days' stock of butts, which should be tied to
sticks resting crossways upon it. It should have a stroke of 1-2 ft.,
repeated, say 6 times a minute. The power required is very small.

The American rocker consists of a wooden frame balanced on its centre,
and made to oscillate by power. It is a cheap and efficient machine,
its defects being that the butts at the ends are much more moved than
those in the centre, and that their upper parts, being lifted out of
the liquor, are liable to become blackened.

The suspender pits should be supplied with old handler liquors, which,
if the tannage is a mixed one, may range from 12° to 20° barkometer,
as a large proportion of the weight consists only of lime-salts,
gallic acid, and other worthless products. It must here be explained
that the barkometer (also called "barkrometer" or "barktrometer") is a
hydrometer, graduated to show the sp. gr. thus--20° Bark. = 1·020 sp.
gr. In using it the temperature of the liquor must be at or near 60° F.
(15° C.). It is, of course, affected by any other matters in solution,
precisely the same as by tannins. In the Lowlights Tannery the waste
liquors are constantly about 12° Bark., and contain tannin equal to
less than 0·2 per cent. (expressed as crystal oxalic acid), and gallic
acid and similar matters equal to O·6 to 0·7 per cent. If the tannage
is pure bark, it may perhaps be advisable to let the strength be
somewhat less, but something depends on whether the exhausted liquors
are returned with all their impurities to the "taps" or liquor-brewing
pits, or whether the liquors are made with water, and hence purer. In
any case, the free acid in the suspenders should always be sufficient
in quantity to neutralise the lime brought in by the butts, or bad
colour will certainly result, making itself visible in the shed, or as
the tanning proceeds. If the butts, when first brought into liquor,
take a lemon-yellow colour, especially in places that have been
imperfectly exposed to it, this is an indication of danger which must
not be disregarded. It may be met either by cleansing the butts more
thoroughly before bringing into the yard, or by adding acid (acetic,
hydrochloric, or sulphuric) to the liquor. If this be done, great care
must be taken not to over-do it, and an acid free from iron must be
used. The use of sulphurous acid for the purpose has been patented, and
presents some advantages. Sulphites have been observed by the writer
to give a pink or purple reaction even with very dilute infusions of
valonia (see p. 112); but any coloration from this cause would probably
disappear as the tannage proceeds. The difficulty can, however, often
be remedied, either by altering the way of working the liquors, so
as to bring more sour liquor down to the suspenders, or by using a
larger proportion of materials capable of yielding acetic acid by
fermentation, such as myrobalans. It is a common error to call all the
free acid of sour liquors "gallic," as this is scarcely present in pure
bark-yards, and at the best is a very feeble acid. The most abundant
acid is usually acetic, though butyric, lactic, and other acids are
frequently present in varying proportions, according to the tanning
materials employed. In the English process, with its comparatively
short layers, in which the butts almost float in strong liquors, but
little souring takes place, and we have nothing comparable to the
German "sour bark" and "sour liquor" from long layers with weak liquor,
and much dusty material. These contain large quantities of acetic
and lactic acids, and plump almost like vitriol. Though the American
tanners generally use the latter, their hemlock liquors sour much
more intensely than those of English yards. It must always be borne
in mind, in comparing English with American and Continental tanning,
that, in the first, the opening up of the fibre is effected by lime,
and the swelling is maintained in the liquors, not so much by acids,
which are only present in very small proportion, as by the careful and
gradual working forward into infusions stronger and stronger in tannin;
while in the two latter, lime, if used at all, is simply employed to
loosen the hair, and the swelling and differentiation of the fibre
is first accomplished in the liquors either by vegetable or mineral
acids. Hence good results cannot be expected in English yards from such
processes as sweating or painting with sodium sulphide, which does not
plump, without a radical modification of the whole tanning process.
This point has been ably treated by Eitner in a series of papers
on _Extract-gerberei_, published during the last few years in 'Der
Gerber,' which will well repay attentive perusal by English as well as
German tanners.

The butts should at first be brought into the weakest liquor; a
circulation system, by which the liquors are all pumped in at one end
of a set of suspenders, and run out at the other, the butts being moved
forward in the opposite direction, seems to have much to recommend it.
In this case, the top of one pit should be connected by a wooden box
with the bottom of the next.

It is usually advisable to run away the first liquor into which butts
are brought from the lime-yard, as it is very completely spent, and
highly charged with lime salts and impurities. Whether other exhausted
liquors are to be retained or rejected is largely a question of
climate, and mode of working. In hot weather, such liquors, charged
with organised ferments (moulds, _bacilli_, and _bacteria_), are apt
to cause ropiness, and other fermentive diseases of the liquors. This
danger may be lessened by boiling all spent liquors, so as to kill the
ferments, before running on the taps, or prevented by the free use
of antiseptics, such as carbolic acid. Small doses of carbolic acid,
however, are useless; at least 1/10 per cent. must be employed; and it
must be borne in mind that antiseptics prevent souring as well as other
fermentations, and hence, where they are employed, other means must be
adopted to maintain the necessary acidity. Such liquors are very liable
to darken if boiled.

The suspender liquors should be acid enough freely to redden
litmus-paper. The present author has published a simple volumetric
method for the determination of the free acid; 10 _cc._ of the
carefully filtered liquor is placed in a beaker, and clear lime-water
is run in from a burette till permanent cloudiness is produced. The
quantity of lime-water employed is that which the acid is capable of
neutralising, without producing discoloration of the leather, and care
must be taken that the lime introduced with the butts does not exceed
this proportion. The explanation of the reaction is that dark-coloured
tannates of lime are formed, which are dissolved by the free acid so
long as it remains in excess. It must be remembered that this process
estimates all acids capable of retaining tannates of lime in solution,
including some so feeble as to have practically no plumping effect.
A liquor may have acidity equal to several _cc._ of lime-water, and
yet react absolutely alkaline to methyl-orange (see p. 9), a colour
which is distinctly reddened by small excess of acids, even so weak
as gallic, which is barely acid to the taste. Hence, the acidity of
a liquor available for plumping may be taken as represented by the
lime-water required to change the red of methyl-orange to yellow,
and if the liquor does not redden methyl-orange it is incapable
of plumping. If 5 or 10 drops of orange solution be added to the
pale filtered liquor from suspenders, there is no difficulty in
approximately hitting the point of change, but great accuracy is
not to be expected. If the liquor will not filter clear, kaolin (see
p. 119) may be used to clear it. It is well to test the lime-water
occasionally on 10 _cc._ of decinormal sulphuric or oxalic acid (p.
96), to make certain of its constancy. Lime-water should be kept in a
bottle with excess of lime, shaken occasionally, and a small quantity
filtered off as required. Liquors are frequently miscalled "sour" which
are not acid, but putrid. Such liquors will not plump, but reduce and
soften hides placed in them. (Compare also p. 185). Suspender liquors
usually consist mainly of liquors from the handler shift. If liquors be
used direct from the leaches, they generally produce harsh grain and
bad colour.

From the suspenders, the butts are transferred to the "handlers,"
where they are laid flat in the liquor. They are usually pulled over
by hooks, which are very apt to scratch the grain. Sometimes strings
are used, attached to the corners and held in notches or on pegs at the
edge of the pit. Other tanners place a frame below the pack, with ropes
at the four corners, by which it is raised sufficiently for the men to
grasp the top butts with their hands. This is only practicable in pits
of ample size. In American yards, the handling is almost universally
performed by tying the sides with strings or fastening them in a long
band by drawing the slit tail of one side through a hole in the nose
of the next, and inserting a wooden "key." The string of the sides is
then wound from one pit to another over a skeleton reel (Fig. 41).
This method is also used in the lime-yard, and is frequently employed
in England to handle offal, but it is not well adapted for butts. Fig.
42 shows the application of mechanical power in a Chicago yard for the
same purpose, by means of Ewart's drive-chain, which is manufactured in
this country by Ley's Malleable Castings Co., at Derby, to whom I am
indebted for the block.

[Illustration: Fig. 41.]

The handlers are generally worked in sets, to each of which a fresh
liquor is daily run, and the most forward pack is pulled over into it,
and is often also dusted down with a little fine bark or myrabolans.
The second pack follows into the liquor out of which the first has
been taken; the third into that of the second, and so on. Frequently
the greenest packs are handled up a second time in the course of the
day, and put down again in the same liquor. The strength of liquors,
and the length of time for which butts are retained in the handlers,
are varied; but a time of 1-2 months, and liquors of 20°-35° Bark.
are usual. It is well to divide the handlers into at least two sets.
Gambier is very useful, especially to the greener goods, and if
hemlock and other extracts are employed, their appropriate place is
in the forward handlers or earlier layers. New valonia liquors must
be avoided, but old layer liquors of considerable strength (up to 40°
Bark. where the handling is long continued) may be employed.

[Illustration: Fig. 42.]

At the end of this period, the butts are taken to the "layers" or
"bloomers," in which they are laid down with stronger liquors and much
larger quantities of "dust"; the latter is usually bark or valonia,
though mimosa is occasionally used. The liquors vary from 40° to 60°
or 70° Bark. in strength in mixed tannage, and the duration of each
layer from 10 days in the earlier stages to a month in the later ones.
For the best heavy tannages, 6-8 layers are required. Each time the
butts are raised, they should be mopped on the grain, to remove dirt
and loose bloom. Strong valonia liquors, or heavy valonia dusting,
causes a brown sandy crust to form on the freely exposed parts of the
butts. This is removed in striking, but is sometimes very troublesome
on rough dried dressing leather. In pure bark tannage, which, however,
is gradually becoming extinct, the liquors used are of necessity much
weaker, as it is extremely difficult to obtain liquors of more than
25°-30° Bark. from this material. The last layer, however, should
always have liquors of the greatest strength which can possibly be
obtained, or the leather will be deficient in firmness.

After receiving their last layer, the butts are well mopped or brushed
and washed up in a clear liquor, and thrown over a horse to drain
before going into the shed. In America, the Howard scrubber (Fig. 43)
is generally employed instead of hand labour at this stage. It consists
of 2 rotating wooden frames at the top of a pit, provided with brushes
or birch-brooms, and, when in use, enclosed by a cover A, through a
slit G in which the sides are inserted and drawn back, while water is
supplied by the pump B. Sometimes the brush-drums are placed one above
another, and the leather is passed in at the side.

[Illustration: PL. VI.

_E & F. N. Spon, London & New York._

"INK PHOTO" SPRAGUE & CO. LONDON

OPENING, STRETCHING AND STORING WHITE SKINS.]

[Illustration: Fig. 43.]

In mixed tannages, where the colour is dark, the leather is frequently
handled or suspended in a warm sumach or myrobalanes liquor, and
occasionally in dilute sulphuric or oxalic acids. If these acids are
not effectually removed before drying, the toughness of the leather
will be destroyed, and in extreme cases the leather will become brittle
and refuse to take black. In any case, strong acids are prejudicial to
the durability of the leather. In America, alternate baths of vitriol
and sugar of lead are frequently used for bleaching and weighting the
leather, but the colour given is not durable.

The great point to aim at, in arranging the mode of work of a tannery,
is to contrive that butts should always receive the strongest liquors
they can bear with safety, and that the strength should constantly
increase in a regular and systematic way. To attain this end, very
frequent handling and change of liquor are requisite in the early
stages, when the butts rapidly absorb the tannin presented to them. As
the process advances, the exterior part of the butt becomes thoroughly
tanned, and the liquor only slowly reaches the interior, which is yet
susceptible of its action, and hence longer layers in stronger liquors
are permissible.

The varied requirements of the trade render it difficult to give any
practical information as to the selection of tanning materials. As
a general rule, it is important at the outset to give the required
colour; and if materials undesirable in this respect are to be used for
the sake of cheapness, they should be introduced in the form of liquors
in the middle stages of the process, i. e. in the later handlers or
earlier layers. Materials used as dust generally have more effect in
producing bloom and colouring the leather, than those used in liquors
at this stage. Some information as to the respective qualities of the
different tanning materials will be found in the chapter on Tannins;
but even practical men are very deficient in accurate information on
these points, since many materials are never used alone, but invariably
in connection with others which mask their effects.

The use of extracts, and the demand for low-priced leathers, to
compete with the American tannages, has introduced still more rapid
methods than those described, and very fair-looking heavy leather has
been tanned in 5-10 weeks. These tannages are very various, but their
main feature is the free use of hot liquors, composed principally of
extracts and gambier. This treatment imparts great firmness, or more
properly speaking, hardness; but the leather is deficient in toughness,
and the grain usually cracks on bending sharply. Extract properly used
is, however, capable of making excellent leather; it is employed in at
least one of the highest priced tannages in the country.

It may be noted here, that when Continental writers speak of extracts
and extract tannage, what we should call liquor tannage only is meant,
and not specially the use of the concentrated extracts, to which alone
in England the term is applied.




CHAPTER XI.

SOLE-LEATHER.--Treatment in the Shed.


[Illustration: Fig. 44.]

The butts, after being treated as above described, are frequently oiled
lightly on the grain, and are taken into the drying-lofts, where they
are hung on poles till about half dry. They are then laid on the floor
in piles, and covered up till they heat or "sweat" a little, which
facilitates the succeeding operation of "striking." This is performed
by laying the butt over a horizontal "beam" or "horse," and scraping
its surface with a triangular pin, shown at D in Fig. 25. This pin has
an even, though tolerably sharp, edge, and is so used that it stretches
and smooths out the grain, without breaking it; and at the same time
it removes a portion of the white deposit called "bloom," which has
been mentioned. Common goods are frequently struck by the machine
introduced by Priestman, of Preston Brook, shown in Fig. 44; but the
work is not very uniform, and the leather is much compressed and
stretched. For offal, the machine is a very useful one, and perfectly
satisfactory.

[Illustration: Fig. 45.]

[Illustration: Fig. 46.]

Butts are now generally struck by the very ingenious machine of
Wilson, whose name has also been mentioned in connection with the
disintegrator, and which is shown in Fig. 45. The arms carry blunt
brass or steel knives or sleekers, and work outwards from the centre,
while the butt is carried backwards and forwards over the drum. Stones
may be substituted for the sleekers, when it is required to remove the
bloom. The machine requires a firm foundation, as its reciprocating
motion causes considerable vibration.

[Illustration: Fig. 47.]

After a light oiling and a little further drying, the butt is laid on
a flat "bed" of wood or zinc, and is rolled with a brass roller loaded
with heavy weights. Various machines are also in use for this purpose.
In Fig. 46, is shown Wilson's spring butt-roller, in which the pressure
is produced by springs immediately above the roller, which works
backward and forward over a flat table, beneath a fixed girder. In the
later patterns of this machine the roller is automatically reversed
by a mechanical finger before coming to the edge of the butt. Fig. 47
shows an adaptation of the American pendulum roller, which is specially
suited for refinishing Singapore kip sides and the commoner class of
goods, giving great firmness and a high gloss. Fig. 48 represents a
machine in which the roller is fixed, and works over a brass drum; it
is specially adapted for offal, and, when used for butts, is apt to
make them "baggy." In this machine, the reversing motion is obtained by
using two belts, one being crossed.

[Illustration: Fig. 48.]

The leather is now frequently coloured on the grain with a mixture,
for which each tanner has a recipe of his own, but usually consisting
mainly of yellow ochre with size or liquor and oil in order to give
a gloss, and to hide uneven or dull colour, and, when sufficiently
dry, is well brushed by hand or power, rolled a second time, and
dried-off in a room gently heated by steam. This is the Bristol method
of finishing. In the Lancashire district, butts are generally struck
out much wetter, and "stoned," so as to remove the whole of the bloom,
and show the natural brown "bottom" of the grain. When sufficiently
dry, they are struck a second time, to set the grain, and rolled as
described, the painting being omitted. This method has the disadvantage
of requiring more labour, and causing a loss of weight; but leather so
got up brings a higher price, as the finish is only applicable to such
tannages as make a fair colour. The usual London plan is a compromise
between the Bristol and Lancashire methods; the leather is sammed, or
tempered by partial drying and piling before striking; stoning is not
resorted to, but the bloom is thoroughly removed from the surface with
the pin and scrubbing-brush. Colour is not generally used.

It is very important, and especially so with heavy mixed tannages,
that the drying should be conducted in the dark, and not too rapidly.
No artificial heat should be used, except in frosty weather, to wet
leather; and it should be carefully protected from harsh drying
winds. After the leather is finished, it should be dried off in a
well-ventilated drying-shed, heated to about 70° F. (21° C.). The same
observations apply to the drying of rough dressing-leather, except that
artificial heat should be avoided. Frost makes dressing-leather porous,
and prevents it carrying a proper quantity of grease in currying. On
the construction of drying-sheds, see pp. 243-54.




CHAPTER XII.

DRESSING LEATHER.


Hides which are intended for purposes where softness and flexibility
are required, as for instance, for the upper-leathers of boots, and
for saddlery purposes, are called "dressing" or "common" hides, or, if
they are shaved down to reduce their thickness before tanning, they are
denominated "shaved" hides. Hides for this purpose are limed much in
the same way as has been described for butts; but if they are required
very soft and flexible, a somewhat longer liming is permissible. After
unhairing, fleshing, and washing in water, they are usually transferred
to a "bate," composed of pigeon- or hen-dung, in the proportion of
about 1 peck to 25-30 hides.

In this they are retained for some days, being handled frequently.
They completely lose their plumpness, and become soft and slippery;
the caustic lime is entirely removed; and the remaining portions of
hair-sheaths and fat-glands are so loosened that they are easily worked
out by a blunt knife on the beam. This final cleansing process is
called "scudding." The theory of the action of the "bate," or "pure,"
as it is sometimes called, is somewhat imperfect. It is frequently
attributed to the action of ammonia salts, and phosphates, contained
in the fermenting dung. Ammonia salts certainly will remove caustic
lime, free ammonia being liberated in its place, and weak solutions
of ammonia sulphate or chloride will rapidly reduce hides, and remove
or neutralise the lime. The phosphates in dung are mostly, if not
entirely, in the form of lime phosphate, which is quite inert. In
point of fact, the process seems to be a fermentive one, the active
bate swarming with _bacteria_; to this, rather than to its chemical
constituents, its action must be attributed. The _bacteria_ act not
only on the organic constituents of the dung, but on those of the hide,
producing sulphuretted hydrogen, together with tyrosin and leucin,
and other weak organic acids, which neutralise and remove the lime,
and, at the same time, soften the hide by dissolving out the coriin,
and probably also portions of the gelatinous fibre. The truth of this
theory is supported by the fact that, in warm weather, the activity
of the bate is greatly increased, and that, if one pack of hides is
over-bated, the next following is much more severely affected, the
hides having in fact themselves furnished food for the multiplication
of the bacterian ferment from the destruction of their own tissues.
It also explains the effective use (as a substitute) of warm water
with a very small portion of glucose, which, in itself, would be
insufficient to dissolve the lime, but with a small quantity of
nitrogenous matter, forms an excellent _nidus_ for the multiplication
of these organisms. An American invention for bating is the use of old
lime-liquor neutralised with sulphuric acid, an idea which is much more
scientific than would at first sight appear. Old lime-liquors, as we
have seen (p. 143) contain much ammonia and weak organic acids, such as
caproic, amidocaproic (leucin), and tyrosin. On adding sulphuric acid,
the lime forms an inert sulphate, and the sulphate of ammonia and the
weak organic acids which remain dissolved are just what are required
in a chemical bate. The lime-liquor should of course be filtered or
settled clear before using, and enough acid added barely to neutralise
the lime, and the liquor again settled or filtered. By this means both
the dissolved gelatin and the iron of the acid will be got rid of. The
liquor might then be slightly acidified before use. The writer has no
experience of the method, but imagines that used as described it might
be worth trying, although it would have a very unpleasant smell. In
this connection may be mentioned the fact that, when bran drenches
are used, in which lactic acid is developed, the butyric fermentation
is liable, in hot weather, to take its place, and as butyric acid is
a powerful solvent of gelatinous tissue, and the dissolved tissue
itself feeds the fermentation, rapid destruction of the skins is the
result. Cleanliness, scalding out of the drench vats, and washing the
bran before using with cold water to remove adhering flour, are useful
precautions.

If the removal of the lime be the only object aimed at in bating, the
ordinary process is most wasteful, as well as disgusting, from the loss
of pelt it entails. It is easy to find chemical reagents which will
remove the lime; but the resultant leather has been found wanting in
softness, and it is probable that the solution of the inter-fibrillar
matter is in many cases advantageous. Probably one reason for the
non-use of such chemicals is their expense. Maynard has patented the
use of sulphurous acid for the purpose. If sugar, glucose, or ammonia
salts be used, and the alkalinity of the solution nearly neutralised
after each lot of hides by common vitriol, the same liquor may be used
again and again. In this case, if iron is contained in the acid it will
be precipitated by the ammonia and must be settled out. The writer is
convinced, from his own experience, that with suitable tannage such
bating would yield better weights and quite as satisfactory leather for
many purposes as the ordinary mode. French tanners, by the free use of
water, and careful working at the beam, and the employment of very weak
liquors at the commencement of tanning, make excellent dressing leather
without bating and this is also true of the celebrated French calf.

The bating required may be shortened, and probably with advantage, by
washing the hides with warm water in a "tumbler," or rotating drum,
Fig. 49, prior to putting them into the bate, or the whole bating may
be done in the tumbler. After a short bating, also, the hides may be
softened and cleansed by stocking for 15-20 minutes. Warm bates act
much more rapidly than cold ones.

[Illustration: Fig. 49.]

Various machines have been proposed to take the place of hand-labour
in the beam work, and, at least as regards the smaller skins, with
considerable success. As a type of these, may be mentioned Molinier's
hide-working machine, Fig. 29, which consists of a drum covered with
helical knives, rotating at a speed of about 500 rev. a minute, over a
cylinder coated with india-rubber. The skin is allowed to be drawn in
between these drums, and the two being pressed together by a treadle,
it is drawn out by a mechanical arrangement in a direction contrary to
the rotation of the knives, which scrape off the flesh, or work off the
hair.

After bating, "shaved" hides are reduced in thickness in the stronger
parts by a shaving-knife, on an almost perpendicular beam. The workman
stands behind the beam, and works downwards. The knife is represented
at A, Fig. 26, and is a somewhat peculiar instrument. The blade is of
softish steel, and after sharpening, the edge is turned completely over
by pressure with a blunt tool, so as to cut at right angles to the
blade. There is an obvious economy in shaving before tanning, since the
raw shavings are valuable for glue-making, while, if taken off by the
currier, they are useless for this purpose. The hide also tans faster.

Instead of shaving, the untanned hide is frequently split, by drawing
it against a rapidly vibrating knife. The piece removed is tanned for
some inferior purpose, if sufficiently perfect. In sheep-skins, which
are split by a special machine, the grain-side is tanned for French
morocco or basil, while the flesh-side is dressed with oil, and forms
the ordinary chamois or wash-leather (see p. 210). Such a machine is
shown in Fig. 50.

[Illustration: Fig. 50.]

Tanned leather is frequently split by forcing it against a fixed knife,
as in the American "Union" machine, Fig. 51. This is however being
gradually superseded by the band-knife splitting machine, Fig. 52, in
which an endless steel blade travels over two pulleys like a belt, and
is kept constantly sharpened by a pair of emery-wheels seen below the
machine. I am indebted for the block to Messrs. Haley and Co., who have
made great numbers of these machines.

[Illustration: Fig. 51.]

After bating, scudding, and shaving, the hides are taken into the
tan-house, where they are grained, either by frequent handling, or by
working in a paddle-tumbler (a vat agitated with a paddle-wheel, and
known in America as an "England wheel"), with a liquor of suitable
strength. What this strength should be depends on whether a well-marked
grain is required or not. The stronger the liquor, the more it
contracts the hide, wrinkling the surface into a network of numberless
crossing furrows, which form the well-known marking of "grain-leather."
In bark tannage, the after management is much like that described with
sole-leather, except that weaker infusions are employed, and acid
liquors, which would swell the hide and produce a harsh leather, are
avoided. In old-fashioned country yards, which produce some of the best
bark-tanned shaved hides, the liquors rarely range above 10°-15° of
the barkometer, and the time employed is 3-6 months. The hides, after
passing through a set of handlers, of gradually increasing strength, in
which they are at first moved every day, are laid away with bark liquor
and a good dusting of bark, receiving perhaps 4-5 layers of 2-4 weeks
each. Unfortunately, these tannages are so unprofitable that they are
rapidly being supplanted by quicker and cheaper methods.

[Illustration: Fig. 52.]

These more rapid and cheap tannages mostly depend on the use of "terra"
(block or cube gambier) in combination with bark, valonia, mimosa,
and myrobalanes. Liquors warmed to 110° or even 140° F. (43°-60° C.)
are frequently employed, and a bright colour is finally imparted by
handling in a warm sumach or myrobalanes liquor, which dissolves out
much of the colour imparted by terra or extracts. The tannage is helped
forward by frequent handling, by working in tumblers, or sometimes by
suspension on rocking or travelling frames, after the American fashion.

To this class of tannage belongs that of East India kips, which is
largely carried on in the neighbourhood of Leeds. These kips are
the hides of the small cattle of India, and are imported in a dried
condition, and with their flesh-side protected (and loaded) with a coat
of salt and whitewash or plaster. They are usually softened in putrid
soaks, and unhaired with lime, and are used in England for many of the
purposes for which calf-skins were formerly employed. A variety of East
India kips, called "arsenic kips," are treated (instead of plastering)
with a small quantity of arsenic before drying, to prevent the ravages
of insects, which are often very destructive to these goods. Many kips
tanned in India have also been imported of late years, and have greatly
interfered with the profits of English tanners.

In yards where the leather is intended to be sold uncurried, it is
taken up into the drying-sheds, well oiled on the grain with cod-liver
oil, and either simply hung on the poles to dry, or stretched with a
"righter," a tool shaped somewhat like a spade-handle, and finally
set out with it to a smooth and rounded form. As in the case of
sole-leather, too much light or wind must be avoided, and it is very
difficult to use artificial heat successfully in the early stages
of the process. It is, however, now very common for the tanner who
produces such leather also to curry it, and, as this effects a
considerable economy, both in labour and material, it is likely to
become universal. When leather is to be sold rough, it is necessary
to tan it in such a way as to give it a white appearance, from the
deposit of "bloom" already mentioned; this being regarded by curriers
as an essential mark of a good tannage, although the first step in
the currying process is to completely scour it out. When the tanner
curries his own leather, he of course aims at putting in as little
bloom as possible, thus economising both tanning material and labour.
In addition, the leather goes direct from the tan-house to the
currying-shops, thus saving both drying and soaking again, and, it is
said, giving better weight and quality. The tanner, too, is enabled to
shave his hides or skins more completely, utilising the material for
glue-stuff, which, had the leather been for sale in the rough, must
have been left on to obtain a profitable weight.




CHAPTER XIII.

CURRYING.


In general terms, the process of currying consists in softening,
levelling, and stretching the hides and skins which are required for
the upper-leathers of boots, and other purposes demanding flexibility
and softness, and in saturating or "stuffing" them with fatty matters,
not only in order to soften them, but to make them watertight, and to
give them an attractive appearance.

It is obvious that great differences must be made in the currying
process, according to the character of the skin and the purpose for
which it is intended, since the preparation of French calf for a light
boot, and of the heaviest leather for machine belting, equally lie
within the domain of currying. In this case, however, as in that of
tanning, the clearest idea of the general principles involved will
be gained by taking a typical case, and afterwards pointing out the
different modifications needed for other varieties. The French method
of currying waxed calf is selected as an example, since the well-known
excellence of this leather makes it interesting to compare the details
with the methods ordinarily in use in this country.

After raising the skins from the pits, and beating off the loose tan,
they are hung in the sheds till partially dry (_essorage_), great
care being taken that the drying is uniform over the whole skin. In
modern shops, this drying is usually accomplished at once, and in a
very satisfactory manner, by means of a hydraulic press. If dried in
the air, they must be laid in pile for a short time to equalise the
moisture, and then brushed over on flesh and grain. The next process
consists in paring off loose flesh and inequalities (_dérayage_).
This is done on a beam, and with a knife similar to that used in
bate-shaving, and shown in A, Fig. 26. This knife has the edge turned
by rubbing with a strong steel, and is called _couteau à revers_.

Next follows the _mise au vent_. The skins are first placed in a tub
with water or weak tan-liquor for 24 hours; they are then folded and
placed in a tub with enough water to cover them, and beaten with wooden
pestles for 1/4 hour. At the present day, stocks (_foulon vertical_),
or a "drum-tumbler" (_tonneau à fouler_), a machine on the principle
of the barrel-churn, usually take the place of this hand-labour. The
skin is next placed on a marble table, flesh upwards, and with one
flank hanging somewhat over the edge, and is worked with a "sleeker" or
stretching-iron (_étire_), B, Fig. 26. The first 2 strokes are given
down and up the back, to make the skin adhere to the table, and it is
then worked out regularly all round the side on the table, so as to
stretch and level it. The flesh is then washed over with a grass-brush
(_brosse à chien-dent_), the skin is turned, and the other flank is
treated in the same way. It is lastly folded in 4, and steeped again
in water. The next process is the cleansing of the grain. The skin is
spread again on the table, as before, but grain upwards, and is worked
over with a stone (_cœurse_), set in handles, and ground to a very
obtuse edge. This scours out the bloom; after washing the grain with
the grass-brush, it is followed by the sleeking-iron, as on the flesh.

The next step is resetting (_retenage_). For this, except in summer,
the skins must be dried again, either by press or in the shed. This is
another setting out with the sleeker, and, the skin being dried, it
now retains the smoothness and extension which is thus given to it.
The skins are now ready for oiling in the grain, for which whale-oil
or cod-liver oil is generally employed. Olive-oil, castor-oil, and
even linseed-oil may, however, be used, and are sometimes made into an
emulsion with neutral soap and water. After oiling the grain, the skins
are folded and allowed to lie for 2-3 days before oiling the flesh.

The oiling on the flesh is done with a mixture of _dégras_ and tallow,
in such proportions as not to run off during the drying. _Dégras_ is
the surplus oil from the chamois-leather manufacture, which in France
is effected by daily stocking the skins with oil, and hanging in the
air for oxidation. The _dégras_ (_toise_, _moëllon_) is obtained,
not by washing the skins in an alkaline lye, as in the English and
German method, but by simple pressing or wringing. This oil, altered
by oxidation, is so valuable for currying purposes that skins are
frequently worked simply for its production, being oiled and squeezed
again and again till not a rag is left. It is generally mixed in
commerce with more or less of ordinary fish-oil. Eitner recommends,
where the _dégras_ is of indifferent quality, a mixture of 65 parts
_dégras_, 20 of neutral soap (i. e. soap without the usual excess
of alkali), and 15 of soft tallow. After oiling the flesh, which
is accomplished by extending the skin on the marble table with the
sleeker, and applying grease with a sheep-skin pad, it is hung to dry
at a temperature of 65°-70° F. (18°-21° C.). After drying, the surplus
oil is removed by a fine sleeker from both flesh and grain, and the
skins are ready for "whitening" (_blanchissage_). This consists in
taking a thin shaving off the flesh, and was originally accomplished
by the shaving-knife on the currier's beam, and some curriers are
still in favour of this method. It is now, however, usually done
by a sleeker with a turned edge. The grain then undergoes a final
stoning and sleeking, to remove the last traces of adhering oil, and
the skin is grained by rubbing it in a peculiar way under a pommel
covered with cork. It is then coated on the flesh with a mixture, of
which the following is a specimen:--5 parts of lamp-black are rubbed
with 4 of linseed-oil, and 35 parts of fish-oil are added; 15 parts
of tallow and 3 of wax are melted together and added to the mixture;
and, after cooling, 3 parts of treacle. This compound is put on with a
brush, and allowed to dry for some days. Finally, the skins are sized
over with a glue-size, which is sometimes darkened by the addition of
aniline-black.

The preceding account will give some idea of the care and labour
expended on these goods in France. In England, cheaper productions are
more in vogue, and almost every process is accomplished by machinery.
An illustration of the Fitzhenry or Jackson scouring-machine, which is
largely employed both for scouring and setting out, is given in Fig.
53. This is a simple and efficient machine, and has been largely used,
both here and in America.

[Illustration: Fig. 53.]

Fig. 54 shows the improved tool-carriage introduced by C. Holmes of
Boston, in which the brush and sleekers or stones are controlled by
handles which are stationary instead of moving rapidly with the slide,
as in the older form. Spiral springs are also substituted for the older
elliptical ones.

[Illustration: Fig. 54.]

[Illustration: Fig. 55.]

The Fitzhenry machine has also been constructed so as to work in any
direction over a fixed table, being driven by a small direct-acting
steam-cylinder supplied by jointed pipes. But probably the most perfect
scouring and setting machine which has yet been introduced is the
Lockwood Automatic Scourer, which may also be regarded as a development
of the Fitzhenry machine. This has been some years in use in America
with great success, and has received considerable improvements, but has
only very recently been introduced into England by Messrs. Schrader and
Mitchell of Glasgow, who have kindly furnished the annexed illustration
(Fig. 56). In this machine the table is fixed, and the tool-carriage
can be moved over it in every direction. The large projecting carriage,
or cross-head, which supports it, travels on a horizontal rail, which
may be observed below and behind the table. Motion is given to it by a
screw which is driven in either direction by the pulleys at each side
of the cross-head. In a similar way the tool-carriage is traversed
forwards or backwards by a second screw at right angles to the first,
and by a most ingenious interlocking arrangement both screws are
controlled by a single handle. The tool-carriage or "trundle frame"
can also be turned like a turntable, so as to deliver its stroke in
any direction, the tool-holder being driven by a horizontal crank
in the centre of the frame, and immediately above the tools. Though
the machine is complicated, and necessarily expensive, it has not been
found either in America or Scotland difficult to work or liable to
get out of order, while both the quantity and quality of its work are
all that can be desired. Fig. 55 is Gläser's scouring machine. Fig.
57 illustrates the latest English scouring machine, Messrs. Haley and
Co.'s Climax Scourer, which is also ingenious and effective. In it the
table instead of the tool-holder is movable by screws driven by belts
thrown into gear by a handle, and it is provided with two tables of
which one is in work while the hides are being changed and spread on
the other. The oscillating tool-holder, instead of being actuated by
the rise and fall of the connecting-rod, is moved by an adjustable
eccentric.

[Illustration: Fig. 56.]

[Illustration: Fig. 57.]

In the case of strap-butts, the currying is, of course, far less
elaborate. They are well scoured out, heavily stuffed, and stretched in
screw-frames, to prevent their giving afterwards when in use.

In Germany, Switzerland, and Austria, a method of stuffing strap-butts
is frequently employed, which, so far as I am aware, is not in use in
England. It is called _Einbrennen_ or "burning in," and consists in
applying very hot tallow to the dry leather. The butts are washed free
from liquor in a tumbler, boarded to soften them thoroughly, scoured,
set out with a sleeker, nailed on laths, and air-dried. They are then
very completely dried in a room heated to 104°-113° F. (40°-45° C.),
as if any moisture remains in the hide, the fibre will be destroyed by
the heat of the melted tallow. The tallowing generally takes place in
the same room, as a high temperature is required to allow it to soak
in, and the leather would greedily reabsorb moisture if exposed to
damp air. The tallow is heated, generally by steam in a jacketed pan,
to 167°-212° F. (75°-100° C.). There are two ways of applying it. The
melted tallow may be applied on a table to the flesh side of the butt
with a ladle, and rubbed on with a brush or rag. In this case, as soon
as the tallow has sufficiently soaked in, the butts are placed in water
to prevent its striking through to the grain. The second way is to
have the pan of sufficient size and suitable shape, and for two men to
draw the butt through the melted tallow with tongs, and more or less
rapidly according to the quantity it is desired that the leather should
absorb; and in some cases the process is repeated once or more. In this
case, it is useless to wet in water, and the butts are allowed to cool
gradually in pile.

The leather is now impregnated with grease, but it is far from being
properly stuffed. Instead of the grease being spread over the finest
fibres in a minute state of division, it simply fills the spaces
between the larger fibres. To remedy this, the butts are well softened
in water (which, if they have been drawn through the tallow and allowed
to cool, must be tepid), and are then worked in a damp condition in a
drum tumbler, by which they brighten in colour and become uniformly
stuffed. They are then allowed to lie in a pile a day or two, are
stoned and worked out with the sleeker, and hung up to dry. When in
right temper they receive a final setting out with the sleeker, and
when dry are either rolled or glassed. For further details, Nos.
256 and 257 of 'Der Gerber,' 1885, must be consulted, where the
matter has been exhaustively treated by Eitner, in his papers on
"Extract-Gerberei."

[Illustration: Fig. 58.]

In England, curried leathers are generally sold by weight, which
leads to the use of glucose and other materials to add to the weight.
In America, all upper leathers are sold by measure, and this is
now ascertained by a very ingenious machine (Fig. 58). The skin is
laid on a latticed table, and a frame, from which rows of bullets
are suspended, is let down upon it. The total weight of the frame
is indicated by a spring balance, and as the bullets which are over
the skin are supported by it, the diminution of weight indicates the
measurement. Several modified forms of this machine are now made.




CHAPTER XIV.

ENAMELLED, PATENT, OR JAPANNED LEATHER.


These are terms used to designate those leathers, whether of the ox,
the horse, the calf, or the seal, which are finished with a waterproof
and bright varnished surface, similar to the lacquered wood-work of
the Japanese. The name "enamelled" is generally applied when the
leathers are finished with a roughened or grained surface, and "patent"
or "japanned" are the terms used when the finish is smooth. Though
generally black, yet a small quantity of this leather is made in a
variety of colours.

In America, large thin hides are principally used for the purpose.
They are limed and bated in the usual way, stoned after bating, and
tanned with hemlock and oak barks in a paddle tumbler, which is run for
10-15 minutes in each hour. When one-third tanned, they are levelled
on the flesh, and split with the belt-knife splitter, Fig. 52. After
splitting, the portions are drummed with strong gambier liquor for 1/4
hour, and then tanned out with bark. The grains are scoured with the
Fitzhenry or Lockwood machine (Figs. 53 and 56). They are then lightly
oiled and stretched on frames which can be enlarged by screws or a sort
of knuckle-joint at the corners. When quite dry, they are grounded with
a mixture of linseed-oil with white lead and litharge, boiled together
and thickened with chalk and ochre. This is dried in closets heated by
steam, into which the frames are slid face downwards, the heat being
gradually increased from 80° to 160° F. (27° to 71° C.). If it be
desired to employ a higher temperature, the leather is first saturated
with a solution of 2 oz. each of borax and alum in 1 gal. water, when
temperatures of 230°-250° F. (110°-120° C.) may be used. The remaining
treatment is much as above described, but a little turpentine is used
to make the paint work freely. The final varnish is composed of 20
parts spirit of turpentine, 20 linseed oil, 10 thick copal varnish,
and 1 of asphaltum or other colouring material. This must be mixed 2-3
weeks before use, and applied with a brush.

The splits are also often enamelled, and as a preparation receive a
dressing of linseed-oil boiled to a jelly and thinned with turpentine
or naphtha. This is applied with a stiff brush after the splits are
stretched on the frames and are still damp, so that it does not
penetrate the leather, but forms a sort of artificial grain.

Leather destined to be finished in this way requires to be curried
without the use of much dubbing, and to be well softened. The English
practice is to nail the skins thus prepared, and quite dry, on large
smooth boards, fitted to slide in and out of stoves maintained at a
temperature of 160°-170° F. (71°-77° C.), coating them repeatedly with
a sort of paint composed (for black) of linseed-oil, lamp-black, and
Prussian blue, well ground together. Each coating is allowed to dry in
the stoves, before the next is applied. The number of coatings varies
with the kind of skin under treatment, and the purpose for which it is
intended. The surface of every coat must be rubbed smooth with pumice;
finally, a finishing coat of oil-varnish is applied, and, like the
preceding coats, is dried in the stove. The exact degrees of dryness
and flexibility, the composition of the paint, and the thickness and
number of the coats, are nice points, difficult to describe in writing.

This branch of the leather industry, so far as it relates to
calf-skins, is carried on to a larger extent, and has been brought
to greater perfection in Germany and France than in England. In the
former countries, the heat of the sun is employed to dry some of the
coatings. The United States have also brought this style to a high
degree of excellence, especially in ox-hides. There, use is said to
be made of the oils and spirits obtained from petroleum, and without
doubt, French and German emigrant workmen have materially assisted in
attaining this high standard.

Leather finished in these styles is used for slippers, parts of shoes,
harness, ladies' waist-belts, hand-bags, &c., and has now maintained a
place among the varieties of leather for a long period of years.




CHAPTER XV.

MOROCCO LEATHER.


Morocco leather is produced from goat-skins. Rough-haired or
"blue-back" seal-skins are also used, and produce an excellent article;
while an inferior description, called "French morocco," is produced
from sheep-skins. The skins are unhaired by liming in the usual way,
and are then baited with a mixture of dogs' dung and water. The tanning
is done chiefly with sumach, at first in paddle-tumblers, and then in
handlers, lasting about a month in all. Sheep-skins are usually tanned
through in about 24 hours, by being sewn up into bags, grain-side
outwards, and nearly filled with strong sumach infusion. A little air
is then blown in, to completely distend the skin, and they are floated
in a sumach bath, and kept moving by means of a paddle. After the
first day's immersion, they are thrown up on a shelf, and allowed to
drain; they are then again filled with sumach liquor; when this has
a second time exuded through the skin, they are sufficiently tanned,
and the sewing being ripped open, they are washed and scraped clean,
and hung up to dry, making what are called "crust-roans." The dyeing
is sometimes done by brushing on a table, grain-side upwards, but more
usually the skins are folded closely down the back, flesh-side inwards,
so as to protect it as much as possible from the influence of the
colour, and then passed through the dye-bath, which is now generally of
aniline colours. The original oriental method of manufacture for red
morocco was to dye with cochineal before tanning, and this is still
customary in the East, but is quite obsolete in this country. A grain
or polish is given to the leather, either by boarding, or by working
under small pendulum rollers, called "jiggers," which are engraved
either with grooves or with an imitation of grain. A well-cleaned
sumach-tanned skin is capable of being dyed in the finest shades of
colour; and this branch of the manufacture of leather has been brought
to great perfection.




CHAPTER XVI.

RUSSIA LEATHER (Ger., _Juchtenleder_).


This is tanned in Russia with, the bark of various species of willow,
poplar and larch, either by laying away in pits, or handling in
liquors, much like other light leathers, the lime being first removed
by bating, either in a drench of rye- and oat-meal and salt, by
dogs' dung, or by sour liquors. After tanning, the hides are again
softened and cleansed by a weak drench of rye- and oat-meal. They are
then shaved down, carefully sleeked and scoured out, and dried. The
peculiar odour is given by saturating them with birch-bark oil, which
is rubbed into the flesh-side with cloths. This oil is produced by
dry distillation of the bark and twigs of the birch. The red colour
is given by dyeing with Brazilwood; and the diamond-shaped marking by
rolling with grooved rollers.

Much of the leather now sold as "Russia" is produced in Germany,
France, and England. It is tanned in the customary way, occasionally
with willow, but more generally with oak-bark, and probably other
materials. Economy would suggest the use of such materials as, from
their red colour, are objectionable for other purposes, and therefore
cheap. The currying is in the usual manner, care being taken that the
oil used does not strike through to the grain, which would prevent
it taking the dye. The colour is given by grounding with a solution
of chloride of tin (100 parts tin perchloride, 30 parts nitric acid,
25 parts hydrochloric acid, allowed to stand some days, and the
clear solution poured off, and mixed with 12 volumes of water). The
dye-liquor may be composed of 70 parts rasped Brazilwood, 3 parts
tartar, and 420 parts water, boiled together, strained, and allowed to
settle clear. The grounding and dyeing are done on a table with a brush
or sponge (see Glove-kid dyeing, p. 229). The odour is communicated by
rubbing the flesh-side with a mixture of fish-oil and birch-bark oil,
which sometimes contains no more than 5 per cent. of the latter.

[Illustration: PL. VII.

_E. & F. N. Spon, London & New York_

"INK-PHOTO" SPRAGUE & CO LONDON

TREADING AND DYEING THE SKINS.]




CHAPTER XVII.

CHAMOIS OR WASH-LEATHER.


This leather, which is remarkable for its soft felty texture, which it
retains even after wetting, although perfectly porous and free from
greasiness in its finished state, is prepared by the action of oil on
the raw skin. Wash-leather was formerly manufactured from sheep- and
calf-skins, and from those of the chamois, and various deer (hence the
name), from which, after liming, the grain was removed (frized) with a
sharp knife, either with the hair, or after unhairing. The flesh-splits
of sheep-skins are now generally employed for ordinary wash-leather,
and of course no such process is needed, though buff-leather for belts
and military purposes is still so manufactured. The skins receive a
thorough liming, which, where softness is desired, is so conducted as
very thoroughly to remove the cement-substance (coriin) from between
the fibres; and this removal is frequently carried still further by a
short bran-drench, which also secures the complete absence of lime.
After the usual beam-work, the skins are pressed or wrung out to remove
surplus water, and while still moist are oiled on a table and folded in
cushions. Fish-, seal-, or whale-oil is generally used, and vegetable
oils do not seem to answer even in mixture, with the exception perhaps
of olive-oil. The skins are next stocked for 2-3 hours, shaken out,
and hung up for 1/2-1 hour to cool and partially dry. They are then
again folded in bundles, and stocked for a short time, taken out,
oiled again, and returned to the stocks; and this process is repeated,
until the skins lose their original smell of limed hide, and acquire a
peculiar mustard-like odour, and the water at first present has been
entirely replaced by oil. The later dryings are frequently conducted
in a heated room, and when the oiling is complete, the skins are piled
on the floor, and the oxidation of the oil, which has already commenced
during the fullings and dryings above described, is completed by a sort
of fermentation, in which the skins heat very considerably. During this
process, they are carefully watched, and if the heat rises so high as
to endanger the quality of the leather, the pile must be turned over,
so as to cool the skins, and bring those which were originally outside
to the centre. When the fermentation comes to an end, the skins are
no longer susceptible of heating, and are of the well-known yellow or
chamois colour. Where this colour is objectionable, the oxidation is
sometimes completed by hanging the leather in a heated room instead
of by piling. It is now necessary to remove the surplus oil, and this
in France is done by oiling with any sort of oil, throwing into hot
water, and wringing or squeezing. The oil obtained in this way forms
the _moëllon_ or _dégras_ so much prized for currying purposes. The
unoxidised oil still retained by the skins is removed by washing
with soda or potash lye. In England and Germany, the whole of the
uncombined oil is removed in this way, and is recovered from the lye,
in which it exists in a partially saponified state, by neutralisation
with sulphuric acid. It forms the "sod" oil of commerce. About half
the oil employed is obstinately retained by the skin, and cannot be
removed even by boiling with alkalies, while no gelatin is obtained
by boiling water, to which the chamoised skin is much more resistant
than ordinary leather. The nature of the tanning process does not seem
to be well understood. It is generally stated that the fibres of the
skin are unaltered, but are merely coated with the oxidised products of
the oil. It is hard, however, on this hypothesis to understand their
extraordinary indifference to water, even at a boiling temperature,
which speedily converts kid and other tawed leathers into a solution
which gelatinises on cooling; and it seems more probable to the present
writer that some actual chemical combination is formed. Lietzman
('Herstellung der Leder,' p. 164) supposes that the whole of the
gelatigenous tissue has been removed by liming and bating, and that
only the very indifferent yellow elastic fibres (see p. 21) remain.
This view, however, is quite untenable, in consideration of the very
small proportion of these fibres originally present in the skin. Müntz,
in his researches (see p. 17), showed that the fibres insoluble in
boiling water scarcely exceeded 3 per cent, of the dried pelt. Dry
gelatigenous fibre has a considerable resistance to heat, and it is
possible that the action of the oil may consist in preventing the
absorption of water. This, however, will not explain its resistance to
alkalies. Cotton or other vegetable fibres moistened with oil, readily
undergo oxidation, with so much evolution of heat as sometimes to
cause spontaneous combustion; but the oxidation products are easily
and completely removed by alkaline solutions, leaving the fibre in its
original state, as indeed is noted by Lietzman (_loc. cit._).

The finishing processes consist in staking during drying to retain
softness, and in whitening and smoothing the flesh (or sometimes both
sides) on the fluffing wheel. Skins for gloves, &c., are bleached
like linen, by sprinkling and exposure to the sun; or more rapidly by
treatment with a weak solution of potash permanganate, and subsequently
with sulphurous, or very dilute sulphuric acid, to remove the brown
manganous oxide formed (Barreswil, Dingl. Polyt. Jour., 161, 312).
Gaseous sulphurous acid from burning sulphur may also be used for
bleaching. The "dyeing" of chamois leather is generally done with
ochres and similar colouring matters, and may be removed by washing.
Treatment with egg-yolk in water, or with an emulsion of olive-oil with
a little soap, and rubbing, or stretching, will restore softness to
chamois leather which has become stiff by washing.




CHAPTER XVIII.

CROWN LEATHER, OR PRELLER'S LEATHER.


The process of manufacture of this leather, which has obtained a
firm position as the most suitable material for certain classes of
belting, picker-straps, &c., was discovered about 35 years since by
Theodor Klemm, a cabinet-maker in Wurtemburg and founder of the present
well-known firm of leather manufacturers, Gebrüder Klemm of Pfullingen.
Klemm, at that time in poor circumstances, sold his patent in Paris to
an Englishman, Preller, who started a manufacture of it in Southwark
and adopted a crown as his trade-mark. Since this time the manufacture
has spread, first to Switzerland and then through Germany; but in
England, to the writer's knowledge, it is confined to one or two firms.

The process of manufacture of crown leather is in principle
intermediate between that of calf-kid (see p. 223), and the pure
oil-tanning, if we may call it so, of which the chamois leather (see
p. 210) is typical. It depends on impregnating the raw hide with a
mixture of fats and albumens, to which salt or saltpetre is added to
prevent putrefaction. The process as described in the original patent
was as follows,--The hides were unhaired by liming or painting (with
sulphides), and cleansed as usual, no plumping lime being given. After
unhairing they were allowed to dry some little time in the air till no
longer plump, and were then worked in a tumbler drum, without water,
till uniformly soft. They were then spread on a table and brushed
over on the flesh-sides with a mixture of 23 parts of ox-brain, 6-1/2
of butter, 28 of soft fat, and 4 of salt or saltpetre, with 26 of
barley-flour and 12-1/2 of milk, of which the leading 4 ingredients
were first to be mixed and the flour stirred in, the milk being last
added. The hides were then returned to the tumbler, which was provided
with tubular axes, through which a portion of exhaust steam was
admitted to warm the drum. After tumbling some hours, the drum was
opened, and the hides were examined. If the tanning was not complete,
the hides were hung in the air for a time to dry, and the process was
repeated till a cut showed that the mixture had completely penetrated
the hide.

From Eitner's researches it appears that the essential tanning
ingredients of the mixture above described are the fat (and butter
which acts simply as fat) and the albuminous matter of the milk
(casein), brains (albumen, &c.), and flour (gluten); the starch serving
at most to assist in the emulsification of the fats. Eitner treated
crown leather with dilute potash solution to remove the albumen
and fats, and after washing and drying obtained a material like an
insufficiently stocked chamois leather. On again stuffing with a
quantity of fat equal to that removed, but without the albumen, the
leather became dark and quite greasy, so that by sharp bending oil
could be pressed out. Good results may be obtained in crown leather
manufactured with fats and flour only, without the use of milk or
brains, so that it is obvious that the same purpose is served by either
vegetable or animal albumenoids. The most important point in the
purposes for which crown leather is employed is toughness, and this is
given by the unaltered hide-fibres, which are merely preserved by the
coating of oily matter with which, like those of chamois leather, they
are surrounded. The albumen serves the purpose of filling the spaces
between the fibres, and giving solidity and firmness, so that the belts
may keep their shape, and not stretch inordinately. It also serves to
make the leather waterproof, and fit it for water-bags for military
purposes (as it gives no taste to the water) and for hose-pipes. The
albumen, which much resembles the hide-fibres in composition, is like
them preserved by the fats.

For the modern process of manufacture, good, even and well-flayed
hides are selected, and unhaired either by sweating, or by a very short
liming, which must be assisted by rockers or some mechanical mode of
moving the hides, so as to get them unhaired in the shortest possible
time and with the least injury to the fibre. Sodium sulphide (see p.
147) may be employed with great advantage. The fleshing and scudding
are performed as usual, according to the mode of unhairing adopted. The
hides are then very commonly rounded, and the bellies tanned in the
usual manner; but sometimes the whole hide is made into crown leather.

As crown leather is naturally almost white, it is usual at this stage
to colour the hide with bark or other liquors. As in this case simply
colouring and not tanning of the grain is required, high-coloured
liquors, made by steaming materials with much colour and little tannin,
are preferable. For this purpose wood extracts, such as chestnut,
quebracho, or oak-wood are said to be very suitable, and beech, pine
or alder bark may also be used. In practice, chestnut and hemlock
extracts, and occasionally cutch are employed; but the last named is
not to be recommended. A chestnut liquor of 7-1/2° Tw. or 5° B. (34°
Bark.), with constant handling or in a paddle-tumbler, will give a
satisfactory colour and grain in 1-2 hours. This rapid colouring is
preferable to the slower process, which occupies 24 hours in weaker
liquors. If sweated, the hides are now plumped with sulphuric acid,
but only to a very moderate extent. This process is best performed
in a paddle-tumbler; about 3-1/2 oz. of sulphuric acid are required
per hide, and a time of 6-12 hours according to the water employed.
The liquor may be several times used, strengthened with the necessary
quantity of acid. Limed hides do not require further swelling. The
hides are washed through clean water, and hung up to dry somewhat.

The hides are next spread on a table, flesh-side uppermost, and
covered with a layer of the tanning paste nearly 1/4 in. thick. The
composition of this paste may be varied according to the relative
prices of different materials, and the amount of hard fats must be
regulated according to whether or not appliances are provided for
heating the tumbler. A good mixture is 7 parts common wheat-flour, 7 of
horse-grease, 1 of salt, and 1-2 of tallow. If too soft, more tallow
may be employed. The salt is first added to the horse-grease, then
the melted tallow, These fats are added little by little to the flour
till a uniform paste is obtained. Another good mixture is 27 parts
wheat-flour, 25 of bone-grease, 4 of tallow, and 4 of salt. Another
recipe gives 28 lb. fine white flour made to a paste with 13-14 pints
water and then worked up to a uniform mass with a tepid mixture of 28
lb. beef tallow and 28 lb. hard horse-fat (_Pferdekammfett_). These
mixtures are all for use in warmed drums; a specimen of one used in a
factory where the mixture was simply trodden in cold into the leather
in open tubs is as follows:--7 parts flour, 9·4 of horse-fat, 2·8 of
fish-oil, 7 of ox-brains and 0·7 of salt. The hides are next folded in
bundles and placed in the drum; or in stocks, which are occasionally
used for the purpose. If a drum be used, it must be of large
diameter, 8-9 ft., provided with pegs inside, and should make about
25 revolutions per minute, so as to work the hides with considerable
force. Much more care is needed in warming the drum, than is required
in ordinary stuffing, and this is best accomplished by warmed damp air.
This may be arranged by the use of an air-pump, which draws air through
water warmed by exhaust steam, and forces it through the hollow axles
of the drum (or drums); or a simple aspirator consisting of a cask
filled with water may be connected to one axle, so that as the water
runs out it will draw air through the drum from the opposite axle,
which is connected with a cask half filled with hot water through which
air is allowed to bubble. Probably the same effect could be reached in
a still simpler and cheaper manner by the use of a steam-jet blower,
such as Körting's. In any case the drum must be warmed to a temperature
of 82°-104° F. (28°-40° C.). Warm dry air may also be used, but is not
so suitable, as it dries the hides too much. The hides are tumbled
8-12 hours, hung up till half-dry, and the process is repeated. For
very heavy hides, 4 tumblings may be required. In the later tumblings,
a lower temperature, 95° F. (35° C.), may be employed, and the time
extended to 15 hours.

The currying of crown leather is very simple. It is set out on flesh
and grain, and boarded to raise the grain. Mossner, before currying,
washes 2 hours in water and brushes with tepid soda solution (1 in
60). The yield of weight is small, only amounting to about 30-40 per
cent. of the raw hide employed, and hence the price per lb. must be
considerably higher than that of tanned leather to yield a profit. The
above information is mostly drawn from articles by W. Eitner ('Der
Gerber,' iv. 1 _et seq._) and Franz Kathreiner ('Gerber Zeitung,' 21st
December, 1875).




CHAPTER XIX.

MINERAL-TANNED LEATHER.


The invention of the earliest form of mineral tanning, that with alum
and salt, dates from remote antiquity; but as it is in large measure
the type of all that has been since done, it deserves examination in
some detail, at least as regards principles. In practice it is used
alone in curing skins with the hair on, and for making white leather
for laces and other purposes; and, in combination with oil and albumen,
which, as we have seen, are the tanning agents in the case of "crown
leather," it forms the process for producing calf and glove kids, as
will be described under those headings (pp. 223, 225).

Careful researches by Reimer (Ding. Polyt. Jour., 205, p. 143 _et
seq._) show (what has long been known in practice) that alum alone
is not capable of making a pliable leather. The salt, nevertheless,
does not enter into combination with the alum, or even with the hide.
Its function is partially physical, increasing the diffusion of the
solution, and partially chemical, as in the presence of acids (and
salts of acid reaction) it precipitates the coriin, and prevents it
from gluing the fibres into a horny mass as it dries. Prof. Knapp
has shown that this is the first essential in producing leather, and
that raw hide may be converted into a pliable material with all the
properties of white leather by simply withdrawing the water with
alcohol, in which coriin is not soluble, and by which it is therefore
precipitated. This leather, containing when dried no added constituent,
is of course at once reconverted into raw hide by soaking in water.
Both the salt and a portion of the alumina is removed from tawed
leather by soaking in water, and it then dries hard and horny, and
by boiling in water will yield a considerable percentage of gelatin.
The alum is not absorbed as a whole. It is a double salt (alumina and
potash sulphate or alumina and ammonia sulphate), and only the alumina
sulphate is absorbed, potash (or ammonia) sulphate accumulating in the
liquor. The alumina salt retained by the hide, especially in presence
of much salt, contains slightly more than its normal proportion of
alumina to acid, or in chemical language is to some extent basic. This
is caused partly by the lime remaining in the skin from the unhairing
process, which neutralises a portion of sulphuric acid, but in part is
the result of the affinity of the hide-fibres for alumina, a certain
small proportion of free sulphuric acid being left in the liquor. The
accumulation of this and of potash sulphate is the reason why such
liquors cannot be used perpetually by mere strengthening with alum, but
must be frequently renewed. The attraction of hide-fibre for alumina
sulphate is so strong, that in presence of a sufficient excess of
hide it may be completely removed even from dilute solutions. Alumina
acetate or sulphate may be substituted for alum with equally good
results in practice, the only advantage of the latter being its easier
preparation. Ferric and chromic salts and iron or chrome alum, may be
substituted for common alum, and are absorbed in a similar manner, and
in presence of common salt give equally pliable leathers, of a buff
and pale greenish tint respectively. Without salt, the leathers are
hard and brittle. In all these cases, the tanning agent may be to a
large extent removed by simple washing with water. The tannage may be
rendered more durable by passing the leather before drying through a
weak bath of sodic carbonate or even lime-water, which precipitates the
alumina, iron, or chrome in a basic form on the hide-fibres. Soap baths
may also be used, by which aluminic, ferric, or chromic stearates and
oleates are formed, possessing considerable toughness and resistance to
water. So far as the writer is aware, no mineral tannage has yet been
produced which will not yield gelatin when treated, first with dilute
acid and then with boiling water; but this is rather a gain than
otherwise, as leather scraps might be utilised for glue. There seems
no reason why good and durable leather, for boot-uppers and for many
mechanical purposes, should not be fabricated with salts of iron and
chromium in conjunction with salt. If eggs and flour were also used,
products similar to calf-kid would be obtained. Iron-leathers may of
course be blacked with infusions of galls or many tanning materials, or
with logwood. Ferrous salts have no tanning properties.

If, instead of using neutral iron salts, basic ferric salts (which may
be obtained by dissolving ferric oxide in solution of neutral ferric
salts, or by oxidising ferrous sulphate with manganese black oxide,
or nitric acid) be employed, much larger quantities are absorbed by
the hide, and if this be fixed with soap baths and finished with a
moderate quantity of oil, a gain of weight--approaching 50 per cent.
of the finished leather, or about the same as that given by bark, may
be obtained. The leather, however, has by no means the same resistance
to wet and decay as bark-tanned leather, and invariably has a tendency
to crack when sharply bent. The process has been most carefully worked
out by Professor Knapp, and was patented and worked commercially for
a short time in Brunswick, but apparently without financial success.
Professor Knapp's method is as follows:--The iron solution is prepared
by adding nitric acid to a boiling solution of ferrous sulphate (green
vitriol) till the iron is completely oxidised to the ferric condition.
To this, ferrous sulphate is again added so long as it continues to
cause effervescence. The resulting solution is a clear orange, and
of more or less syrupy consistence, and may be evaporated without
decomposition or crystallisation to a transparent varnish. The hides
are unhaired and prepared for tanning in the usual way, and are then
handled in solutions of the iron salt, which are at first weak, and
are gradually strengthened. Skins are tanned in 2-3 days, and the
heaviest hides in a week. After tanning, the hides are stuffed in a
drum ventilated through the axes, very similar to that described
under "crown leather," p. 213, with an insoluble iron-soap made by
precipitating soap solution with the iron-liquor; or the iron-soaps may
be formed in the hide by the alternate use of iron and soap solutions,
as already described. The leather is finally saturated with a solution
of stearin and paraffin, to render it waterproof.

A process which has been worked on a larger scale, is that of Dr.
Heinzerling, introduced about 1878, with the usual promise of "complete
revolution" in the leather trade; but which, in spite of the most
determined and persevering efforts of the Eglinton Chemical Company,
who own the English patent, has failed to take any very prominent
position in commerce. The tanning materials employed are alum and salt,
with a varying proportion of potash, soda, or magnesia bichromate.
These salts have a very marked hardening effect on animal tissues, and,
when mixed with gelatin and exposed to light or acted on by acids,
become reduced, and at the same time render the gelatin insoluble even
in hot water, a property which is made useful in many photographic
processes. This is probably due to the formation of salts of chromium,
which, as has been stated (p. 219) have a similar tanning effect, but
perhaps more powerful, than those of alumina. However this may be, the
effect of potash bichromate when exposed to light with gelatin, differs
from that of the addition of chrome salts ready formed, the gelatin in
the first case becoming incapable of even swelling in hot water, while
in the second, though rendered insoluble, it becomes soft and swollen.
The use of potash bichromate in tanning had been previously patented by
Cavalin, who used it in conjunction with alum and salt, and with the
addition of a portion of green vitriol, to give the leather a colour
more similar to that of bark-tanned.

Dr. Heinzerling uses metallic zinc in the salt and alum solution to
assist in the precipitation of amorphous alumina on the hide-fibres.
The same material was used in a similar way by Jennings (No. 2295,
1861), but with the object of whitening the goods. Yellow or red
prussiates of potash (potassic ferrocyanide or ferricyanide), are also
sometimes mixed with the solution, in order to enable the leather to
be blacked with iron-liquor, with which they produce prussian blue. To
fix the tannage on the fibre, and prevent its washing out, the use of
barium chloride, lead acetate, and of soap solution is claimed; the
latter having been also patented for similar purposes by Knapp, and
subsequently by Jennings and others.

In order to render the leather waterproof, it is finally saturated with
solutions of paraffin, stearin, and other fats and hydrocarbons (resin
is employed, though not named in the patent), in petroleum spirit and
similar solvents.

Such is the original patent, which, it will be seen, is rather a
combination of older processes than an original discovery. Whether
it is still worked on the same lines the writer is unable to say,
but he is aware that considerable improvements have been made in
the finish and appearance of the goods. The leather in its present
form possesses considerable resistance to water, is free from the
brittleness so common in mineral tannages, and like other alumed
leathers, considerably exceeds bark-tanned leather in toughness and
elasticity. These make it valuable for many purposes, and among others,
for machine-belting, although it has the disadvantage of elongating
considerably while in use.




CHAPTER XX.

CALF-KID.


Calf-kid is used for light upper-leather, and belongs to a different
class from any yet described, being "tawed" instead of tanned. In this
respect, and in most details of its manufacture, it resembles glove-kid.

The process is as follows. Selected calf-skins, dried or salted, are
the raw material, and after a suitable softening in fresh water, are
limed for 2-3 weeks, or till the hair goes easily. They are then
unhaired and fleshed in the usual manner, pured with a bate of dogs'
dung, scudded, and again cleansed with a bran drench. In Germany, the
bran drench is used alone, and is composed of 33 lb. bran to 100 medium
skins. Before use, the bran should, especially in summer, be well
washed, to free it from adhering meal. The temperature of the drench
should not exceed 100° F. (38° C.), and the skins should remain in for
8-10 hours. Lactic acid is produced by fermentation; this removes lime,
and is itself neutralised by the products of putrid fermentation which
succeeds it.

The tanning is accomplished in a drum with a mixture of alum and salt;
and after drying, the skins are again moistened, and worked in the
drum with a mixture of oil, flour, and egg-yolk. In the German method,
these two operations are combined. Eitner, who has written a series of
articles on the process, gives 40 lb. flour, 20 lb. alum, 9 lb. salt,
250 eggs, or about 1-1/3 gal. of egg-yolk, 7/8 pint (1/2 litre) of
olive-oil, and 12-16 gal. water, as a suitable mixture. The skins are
worked in a drum-tumbler (preferably a square one, see Plate 5) for 20
minutes, then allowed to rest 10 minutes, and this process is twice
repeated. The temperature must not exceed 100° F. (38° C.), and it is
said to be important that the drum should be ventilated by holes at
the axis.

The skins are allowed to drain, are then rapidly dried at a temperature
of 140°-160° F. (60°-71° C.), and, after "samming," or damping with
cold water, are staked by drawing them to and fro over a blunt knife
fixed on the top of a post (see Plate 6). They are then wetted down and
shaved, either with the moon-knife or ordinary curriers' shaving-knife,
and sometimes receive a second dressing of oil, flour, and egg, to
soften them still further.

Dyeing black is accomplished either by brushing on a table, or by
"ridging" or folding, grain-side outwards, and drawing quickly through
baths of the mordant and colour. To prepare them for the colour,
stale urine is generally employed. A deeper colour, and one less
liable to strike through the skin, is obtained by adding 1/4 lb.
potash bichromate to 4 gal. of urine, or the following mixture may be
substituted with advantage, viz. 1/2 lb. Marseilles soap dissolved in
boiling water, 5 or 6 egg-yolks added, and the whole made up to 4 gal.
with water and 1/4 lb. potash bichromate. The colour used is infusion
of logwood or its extract, or two-thirds logwood, which is best
extracted by stale urine or old soak-liquor, with addition of a small
quantity of soda (1 lb. to 25 lb. dye-wood). It is fixed and darkened
by a wash of iron-liquor (1 of iron protosulphate in 75 of cold water).
After being again dried, the skins are grounded with the moon-knife,
and rubbed over on the grain with a composition containing oil, wax,
&c., and are finally ironed with a flat-iron, to give them a fine and
smooth surface. Eitner gives a recipe for the gloss:--1 lb. gum arabic,
1/2 lb. yellow wax, 1/2 lb. beef-tallow, 3/4 lb. Marseilles soap, 2
lb. strong logwood infusion, and 1 gal. water. The water is brought to
a boil in an earthen pot, and then the soap, wax, gum, and tallow are
added successively, each being stirred till dissolved before adding the
next, and lastly the logwood. After boiling for an hour, it is allowed
to completely cool, being incessantly stirred during the whole process.




CHAPTER XXI.

GLOVE-KID.


This branch of leather manufacture is mainly carried on in Germany,
Austria, and France. In Germany and Austria, lamb-skins are principally
employed; in France, kid-skins. For fine gloves, the skins of very
young animals only can be used. The ordinary style of manufacture is as
follows:--The soaking of the dried skins is effected in large wooden
tubs (_Kufen_, _Bottichen_), and occupies on the average 3-4 days,
according to the character of the soak-water, the size of the skins,
and the time they have been stored. The skins, when thoroughly and
uniformly softened, are unhaired, either by painting the flesh-side
with a thin paste of lime, or in lime-pits. In unhairing by painting
(_Schwöden_), the skins, after coating the flesh-side with lime, are
folded together, so that the lime comes as little as possible into
contact with the wool, and these bundles or "cushions" are placed in
a tub, in which they are most frequently covered with water. After
unhairing on the beam with a blunt knife, the skins must be limed for
some days, in order that the leather may stretch well, a quality which
the Germans denominate _Zug_. By this method of unhairing, the wool
is preserved uninjured, but it is not suitable for the finer sorts
of leather. The unhairing in lime-pits is done either with gas-lime
(Grünkalk), or, as is now almost exclusively the practice, with the
so-called "poison-limes" (_Giftäscher_). These are prepared by mixing
red arsenic (arsenic sulphide) with lime, while it is being slaked, and
is at its hottest. The calcic sulphydrate (and perhaps sulpharsenite)
thus formed hastens the unhairing, and gives the grain a higher gloss.
Well-conducted establishments now avoid as much as possible the use of
old limes, which produce a loose, porous leather, with a rough, dull
grain. The liming lasts on the average 10 days, and is of the greatest
importance. It is essential that the interfibrillary substance shall
be dissolved, that the leather may have the quality known as _Stand_,
that is to say, may be strongly stretched in either length or breadth
without springing back. It also depends upon the liming (and this is of
special importance in the case of lamb-skins), whether the tissue of
the fat-glands is well loosened, so that the fat, either as such, or as
lime- or ammonia-soap, may be readily and completely worked out. Skins
in which this is neglected can never be properly dyed.

When the hair (or wool) is well loosened, the skins are rinsed in
water, and then unhaired on the beam with a blunt knife. The water
employed in washing should not be much colder than the limes, or it
will prevent the hair from coming away readily. The wool or hair is
washed and dried for sale. The skins are thrown into water, to which a
little lime-liquor has been added, to prevent precipitation of the lime
in the skins by the free carbonic acid of the water, which would have
the effect of making them rough-grained.

Next comes the first fleshing (_Vergleichen_) or "levelling." By this,
the loose cellular tissue on the flesh-side is removed, together
with the head, ears, and shanks, and the flanks are trimmed. The
skins are then again thrown into water, softened with lime-liquor as
above described, and then into a bate of dogs' dung. This is prepared
by stirring up white and putrid dogs' dung with boiling water, and
straining it through a sieve or wicker basket. The bate must be used
tepid, and not too strong. The skins "fall" (lose their plumpness) in
it rapidly, and become extremely soft and fine to the touch; and the
fat-glands, remaining hairs, and other dirt, can now be very readily
scudded out. So far no completely satisfactory substitute has been
found for this somewhat disgusting mixture, but it has been noted that
guano will produce similar effects. With regard to the mode of action
of the dung bate, much has been speculated without proof, and exact
analytical evidence is wanting; but, no doubt, a weak putrefactive
action goes on, as may be deduced from the presence of _bacteria_;
further, the ammonia and weak organic acids present in the putrefying
dung are capable of acting on fat and lime; and finally, a direct
mechanical effect seems to be produced, difficult to describe, but
favourable to the succeeding manipulation. Too strong bates, or too
long continuance in them, produces evident putrefactive effects on the
skins. (See also p. 184.)

When the skins come out of the bate, they are stretched and worked
(_abgezogen_) on the flesh with a sharp knife, and any remaining
subcutaneous tissue is removed. This constitutes the second
fleshing. They are then rinsed in warm water, and beaten with clubs
(_Stoss-keule_), see Plates 3 and 4, in a tub, or worked in a
tumbler-drum (_Walkfass_), in either case with a very little water
only; and finally brought into a tank of water, not too cold, and kept
in constant motion with a paddle-wheel.

The skins are next cleansed on the grain-side by working on the beam
with plates of vulcanite with wooden handles, so as to remove fat,
lime- and ammonia-soaps, and other lime compounds, together with all
remaining hair or wool. The skins are now a second time washed in the
"paddle-tumbler," first in cold, and then in tepid water; and after
allowing the water to drain from them, they are transferred to the bran
drench.

This is prepared by soaking wheaten bran in cold water, diluting with
warm water, and straining the extract through a fine hair-sieve.
Sufficient of the liquid must be employed to well cover the skins, and
the temperature may range from 50° F. (10° C.) to 68° F. (20° C.).
These conditions are favourable to bacterial activity, which comes
into play, and, on the one hand, evolves formic, acetic, lactic, and
butyric acids, which dissolve any remaining traces of lime, and on the
other, loosens and differentiates the hide tissue, so as to fit it
to absorb the tawing solution (_Gare_). Much care is required in the
management of the bran drench, especially in summer, since the lactic
readily passes into the butyric fermentation (see also p. 186). The
tawing mixture is composed (like that employed in the fabrication of
calf-kid, q. v.) of alum, salt, flour, and egg-yolks, in a quite thin
paste. The skins are either trodden in it with the feet, or put into
a tumbler-drum with it (Fig. 48). Kathreiner pointed out, some years
since (in vol. i. of 'Der Gerber'), that a mixture of olive-oil and
glycerine might be partially substituted for the egg-yolks, in both the
tanning and dyeing of glove-kid leather.

The tawed skins are now dried by hanging on poles, grain inwards.
Rapid drying in well-ventilated, but only moderately-heated, rooms is
essential to the manufacture of a satisfactory product.

[Illustration: Fig. 59.]

[Illustration: Fig. 60.]

The dry leather is rapidly passed through tepid water, and after being
hung for a very short time, to allow the water to drain off, is trodden
tightly into chests, and allowed to remain in them for about 12 hours,
so that the moisture may be uniformly distributed. It is then trodden
on hurdles (_Horden_), composed of square bars of wood, joined corner
to corner, so as to make a floor of sharply angular ridges, Fig. 59.
The next operation is stretching over a circular knife, called the
_Stollmond_ (_stollen_, Eng. "staking"), shown in Fig. 60; then the
leather is dried nearly completely, and staked again.


Dyeing.

The dyeing of glove-kids is done in 2 ways:--_a._ The skins are plunged
into the dye-bath (_Tunkfarben_). In this way, all light colours are
ordinarily produced, such as _gris-perle_ (pearl-grey), _paillé_
(straw-yellow), _chamois_ (reddish yellow), silver-grey, aquamarine,
&c. _b._ The skins are spread on an inclined or rounded table of stone
or metal, and brushed over, on the grain side, first with a mordant
(_Beize_), then with the dye-liquor, and lastly, with a solution of
a mineral salt (Plate 7). The mordant serves to fix the colour on
the surface of the skin, to prevent its striking through, to produce
certain modifications of colour, and to enable any parts of the skin
which yet contain fat to take the colour evenly with the rest. To
satisfy these conditions, the composition of the mordants is very
varied. Potash bichromate, ammonia, potash, soda, and stale urine are
among the most frequently employed, seldom separately, but usually in a
mixture containing 2 or more.

Dye-stuffs of vegetable origin have always held the first place. Those
most in use are logwood (_Blauholz_), Brazilwood (_Rothholz_), the two
fustics--_Cuba Gelbholz_ (_Morus tinctoria_) and _Ungarisches Gelbholz_
(_Rhus cotinus_), several species of willow-bark and of berries,
indigo-carmine, and indigo dissolved in sulphuric acid.

Aniline colours used alone remained in fashion for a short time only,
but are now usefully employed as top-colours (_Ueberfarben_), viz.
brushed in very dilute solution over vegetable colours. In this way,
particularly tasteful shades of green, violet, and marine-blue may be
produced.

After the mordant has been applied once or twice, and the colour
3-6 times, a wash (_Ueberstrich_) containing some metallic salt is
generally applied, with the object either of bringing out the special
tone required, or of making the colour more lively and permanent.
The so-called "vitriols" are mostly employed: "white vitriol" (zinc
sulphate), "blue vitriol" (copper sulphate), "green vitriol" (iron
sulphate), and occasionally other salts.

Before dyeing, the greater part of the flour, salt, and alum must
be removed from the skins by washing with tepid water; and they
therefore require a second feeding (_Nahrung_) of egg-yolk and salt.
In the case of the skins which are dyed by plunging into the dye-vat
(_Tunkfarben_), this is done after the dyeing is completed; in that of
brush-dyeing, before the dyeing process.

After the dyeing, the skins, if dipped, are wrung out; if brush-dyed,
sleeked out with a brass plate, to get rid of superfluous water. They
are then dried in an airy room. Before staking (stretching), the skins
are laid or hung in a damp cellar, or in moist saw-dust. They are
staked twice: once damp, and once nearly dry.

Skins which are much damaged on the grain, or otherwise faulty, are
smoothed with lump pumice on the flesh-side, either by hand or machine.
They are then dyed on this side, mostly by dipping, but occasionally
with the brush, in which case, the method described is slightly
modified.

Indebtedness is acknowledged to F. Kathreiner, of Worms, and David
Richardson, of Newcastle, for much information on the production of
light leathers. The Plates 1 to 8 represent the works of Messrs.
Tréfousse et Cie., at Chaumont (Haute-Marne).




CHAPTER XXII.

CONSTRUCTION AND MAINTENANCE OF TANNERIES.


As few architects have specially studied the construction of tanneries,
and in most cases much of the arrangement depends on the knowledge of
the tanner himself, a short chapter on the subject will not be out of
place.

In the selection of a site, a clay or loamy soil is to be preferred
to a gravelly or sandy one, as lessening the liability to leakage,
and waste of liquor. Perhaps, however, the first consideration of all
is the water supply, since for manufacturing purposes town water is
generally very expensive. With regard to quality and impurities of
water, information may be found on p. 83; but, as a general rule, the
softer and purer the supply the better. It is also of great advantage
when the source is at such a level as to flow into the tan-yard, or
at least into the beam-house, without pumping. Filtration too, when
needed, is much facilitated by a sufficient head of water.

Of scarcely less importance than the water supply is the drainage of
the yard. It not unfrequently happens that tanneries are prohibited
from discharging their refuse liquors, limes, and soaks into rivers
and watercourses, and it is sometimes a matter of extreme difficulty
to find any other way of getting rid of them. In default of an outlet,
recourse must be had to precipitation and filtration, but this is a
costly expedient, and in fixing a site for a new yard it is far better
to provide against such a possible contingency. Should, however, such
means become necessary, it may be borne in mind that limes and liquors
in great measure mutually precipitate each other, and that if all the
various refuse is run into one tank, mixed, and settled, much is
accomplished in the direction of purification. The further treatment of
the effluent water must be determined by its nature and composition.

The site chosen, the next question is the arrangement of the buildings.
It is very doubtful, where ground is not inordinately expensive,
whether it is wise to erect drying-sheds over the pits. In case of
fire, very serious damage is done to liquor and leather by the heat
and burning timber. If the turret form of drier be decided on, strong
foundations are required, and the ground-floor or basement is occupied
with heating apparatus; and, on the other hand, the tan-house may
be easily and cheaply covered with slated roofs, with sections of
glass, to the north, if possible, like a weaving-shed, through which
sufficient light for convenient work and cleanliness is admitted. The
direct rays of the sun should be avoided, but in the writer's opinion
the balance of advantage is largely in favour of a liberal supply of
light. Iron roofs are unsuitable, since the moisture condenses on, and
rusts them; and particles of oxide fall into the liquors, and cause
iron-stains.

Good ventilation along the ridge of the roof should be provided,
wherever there is any steam or hot liquor used; or the condensed
moisture soon leads to decay.

As regards the general plan of the buildings, much depends on local
circumstances; but as far as possible, they must be so arranged that
the hides and leather work straight forward from one department to
another with as little wheeling or carrying as possible; that the
buildings where power is used be near to the engine, so as to avoid
long transmissions, which are very wasteful of power; and that the
different buildings be so isolated as to diminish the risk of the whole
being destroyed in case of fire.

As regards the first of these conditions, if the various soaks,
limes, bates, and handlers are well arranged, it is hardly necessary
to do more than draw the goods from one pit into the next throughout
the whole of the process. To, and from the layers, the goods must
generally be carried or wheeled. In the sheds, if it be a sole-leather
tannery, the butts should first come into turrets or open sheds for
the rough drying; then into a room sheltered from draughts to temper
for striking. The striking machines or beams should be in an adjoining
room, or immediately below; then a small shed-space for drying before
rolling; next the roller room; and then the warm stove for drying
off. If two of these can be provided to be used alternately, it will
allow the goods to be aired off without taking down, and they may then
be immediately handed or lowered into the warehouse, without fear of
over-drying, which is sometimes difficult to avoid where leather must
be taken direct out of the hot drying-room.

To fulfil the second condition named, the engine should be at the
centre of the main range of buildings, with perhaps the grinding
machinery on one side, and the leather-finishing on the other; but
this would be rather contrary to the third requirement. A very good
plan would be to have the engine-house in the centre as suggested, but
separated from the buildings on each side by brick gables; and with the
boiler-house behind it, and under a separate roof, say of corrugated
iron. Figs. 61, 62, from Eitner's book on American Tanning, show the
arrangement of a sole-leather tannery in the United States. If it be
impossible to have the engine near its work, it is in most cases better
to employ a separate high-pressure engine, which may be within a glass
partition, and will work all day with scarcely any attention. The loss
of power in carrying steam for moderate distances through sufficiently
large and well-clothed pipes is much smaller than that of long lines
of shafting. The writer has known cases where fully half the indicated
power of the engine was consumed in friction of the engine, shafting,
and belts. High-pressure engines are as a rule to be preferred to
condensing for tannery use, since the waste steam can generally be
employed for heating, and both the first cost and that of maintenance
are smaller. Where much fuel is used, it is quite worth while to have
the cylinders indicated occasionally, both running light, and driving
the machinery; much information is gained in this way as to the power
spent on the various machines, and very frequently large economy is
effected by proper adjustment of the valves. To work economically, an
engine should be of ample power for all it has to do; and adjusted to
its work, not by lowering the pressure of steam, or by checking it
at the throttle-valve, but by setting the slide-valves to cut off as
early in the stroke as may be. As to how early this is possible, an
indicator-diagram will at once give information. In arranging shafting,
moderate speeds, say 100-150 rev. per min., should be chosen for main
lines, and when higher speeds are necessary, they should be got up by
light and well-balanced counter-shafts, with wrought-iron pulleys. In
calculating speeds, it must be remembered that they vary inversely as
the size of the pulleys. Thus a 3 ft. pulley running at 100 rev., will
drive a 2 ft. one at 150 rev., and a 12 in. one at 300. Of course the
higher its speed, the more power any shaft will transmit, but increased
friction and wear and tear soon limit this advantage. The velocity
of a belt in feet per min. is obtained by multiplying the number of
revolutions per minute by the girth of the pulley in feet or by its
diameter multiplied by 3-1/7, or more accurately, 3·1416.

[Illustration: Fig. 61.]

[Illustration: Fig. 62.]

Pulleys should always be of ample breadth for the power they have to
transmit; and it is more economical both in power and cost, to use
broad single belting than the same strength in double. If the pulley
will not take a belt broad enough for the work it has to do, a second
belt may be made to run on the top of the first, and will do its share
of the work. Belts should be washed occasionally with soap and tepid
water, and oiled with cod-oil; but if of sufficient breadth, should
not require the use of rosin, or adhesive materials, to make them grip
the pulley. Makers of machines often err in constructing their driving
pulleys too small both in breadth and diameter.

The horse-power which a belt is capable of transmitting obviously
varies extremely with circumstances, but may be approximately
calculated by the formula

  (_a_ · _v_)/66000,

where _a_ is the area of contact of the belt with the smallest pulley,
and _v_ its velocity in feet per minute. Another rule is, that at a
velocity of 1000 ft. per min. each inch of breadth of belt should
transmit 2-1/2 horse-power on metal pulleys, or 5 on wooden ones,
on which the adhesion is greater. Adhesion may also be increased
by covering the pulleys with leather or india-rubber. Both rules
assume that the belt is of ample strength. One horse-power would be
transmitted by a belt running 1000 ft. per min. with a pull of 33 lb. A
good single belt should not break with a much less strain than 1000 lb.
per inch of breadth, and should stand about 1/10 as much as a working
strain.

Countershafting and high-speed machinery, such as disintegrators,
striking machines of the Priestman type, &c., should run without
material jar or vibration. If this occurs, it is generally a sign that
the running part is not equally balanced. In this case, the shaft must
be taken out of its bearings, and supported on two exactly horizontal
straight-edges, when it will roll till the heaviest part is downwards;
and weight must be taken off or added till it will lie in any position.
In this way, the writer had recently to add fully 2 lb. of iron to the
drum of a striking machine before equilibrium was secured, and a most
troublesome vibration prevented. Of course all machinery should be
supported as solidly as possible; and if circumstances permit, most
machines are better on a ground-floor. In placing bark mills, however,
it is frequently convenient to fix them in the top of a building, so
that the ground material may be sent down shoots by its own weight to
the required places. An alternative plan is to set the mill on the
ground-floor, and to raise the ground material with a bucket-elevator.
This may be done successfully by letting the material fall directly
from the mill into the buckets; but otherwise it must be thrown in
with a shovel, as buckets will not pick up ground bark, even from
a hopper; and in any case such elevators are often troublesome. In
a grinding plant designed by the writer, the unground material is
filled on the basement floor into an iron barrow, which may be wheeled
into an iron bow working between upright guide-rails. On pulling a
brake-line, the barrow is raised to the top of the building, and its
contents are tipped into a large hopper, after which the barrow rights
itself, and descends for another load. In the bottom of the hopper is a
sliding shover, which forces the material on to vibrating screens, by
which it is guided either into a disintegrator, or crusher rolls, at
pleasure. Both these discharge through iron spouts into large hoppers
on the outside of a brick gable, from which, powdery materials like
myrabolanes and valonia, can be run direct into barrows or trucks.
It is very desirable that such hoppers should be separated from the
main building by a fireproof partition. The writer is glad to say, he
does not know of a case of fire from disintegrators grinding tanning
materials, but he is informed that a Carter's disintegrator employed in
grinding bones in a manure works has repeatedly set fire to the flannel
bag into which the dust was allowed to escape. If this were to occur
with a dry and dusty tanning material, it is not unlikely that it might
result in an explosion such as sometimes happens in flour-mills from
a similar cause. On the whole, however, mills of the coffee-mill type
are probably more dangerous than disintegrators; since if they become
partially choked, the heat caused by friction is very great.

For lubricating purposes, mineral oils of high density are not more
dangerous than animal or vegetable, but rather the reverse; as, though
they are possibly more inflammable, their mixture with cotton-waste
and other porous vegetable materials is not spontaneously combustible,
while vegetable and animal oils occasionally are. Heavy mineral oils
should always be used as cylinder oils in high-pressure engines, in
preference to other oils or tallow, since they are not decomposed
by steam, and do no harm if blown into the feed-water, but serve to
loosen and prevent scale and deposit. Ordinary oils and tallow, on the
other hand, when submitted to the action of high-pressure steam, are
separated into glycerin and fatty acids (see p. 60), and the latter
corrode the valve faces and seatings, and in combination with temporary
hardness in the boilers form a very dangerous porous deposit, which
often leads to overheating of the tubes.

Next to the machinery, the pits demand special consideration. The
chapter on the subject in Mr. Schultz's book on 'Leather Manufacture,'
is well worth attentive study as giving American practice on the
subject.

The old-fashioned method of sinking pits is to make them of wood, and
carefully puddle them round with clay, which should be well worked
up before use. Such pits, if made of good pine and kept in constant
use, are very durable, some of the original pits at Lowlights Tannery,
constructed in 1765, being still in use. Loam mixed with water to the
consistence of thin mortar may also be employed, the pits being filled
up with water, to keep them steady, at the same rate as the loam is run
in. Probably the best materials for pit-sides are the large Yorkshire
flagstones. Where these are not attainable, very durable pits may be
made of brick, either built with Lias lime, and pointed with Portland
cement, or built entirely with the latter. Common lime cannot be used,
as it spoils both liquors and leather; and even cements with too large
a percentage of lime are unsatisfactory. Brick and common mortar are,
however, suitable for lime-pits.

The writer has constructed wooden pits in two ways. In the one case,
after making the excavation, beams were laid in a well-puddled bed of
clay; on these a floor of strong tongued and grooved deals was laid,
and on this the pits were constructed of similar wood to the floor, and
puddled round with clay. In the second case the pits were built like
large boxes above ground, and when finished, lowered on to a bed of
clay prepared for them, and then puddled both around and between. It
may have been from defective workmanship in the first case, but those
made on the last-named plan, which is that adopted from very early
times, have certainly proved the tightest and most satisfactory. Mr.
Schultz describes a plan as the Buffalo method, in which a floor is
laid as just described, and grooves cut with a plane for the reception
of the sides, which are formed of perpendicular planks, each end and
side being finally tightened up by the insertion of a "wedge plank."

If bricks be used, great care must be taken that the cement is not
merely laid so as to fill the joints towards the two surfaces of the
wall, as is the habit of modern bricklayers, but actually floated into
all the joints so as to make the wall a solid mass; or leaks can hardly
be avoided. Cement pits are very good, and, though not particularly
cheap in material, which must be of the best, are readily made by
intelligent labourers under good supervision. The first step is to lay
a level floor of good concrete, in which glazed pipes for emptying
the pits may be embedded; care being also taken that all joints in
these are thoroughly tight, since future repairs are impossible. The
next step is to make frames, the exact length and breadth of the pits
required, and perhaps 15 in. deep. These are arranged on the floor
where the pits are to be, and the intervening spaces are filled with
concrete of perhaps 1 of cement to 3 or 4 of crushed stone or brick.
Rough stones and bricks may also be bedded in the concrete as the work
goes on, to help to fill up. After the first layer has set, the frames
may be raised and a second added, and so on. The work is generally
finished by floating over it, while still damp, a little pure cement,
to give a smooth surface. Before using, the cement should be tried
on a small scale, to be sure that it does not discolour leather or
liquors, and the pits should always be seasoned with old or cheap
liquor before actual use.

If possible, both latches and handler-pits should be provided with
plugs and underground pipes, communicating with a liquor-well some
feet below their levels. Glazed fire-clay is very suitable both for
pipes and plug-holes, which should be in the pit corners. Some means
should also be provided for the ready clearing of the pipes when choked
with tanning materials. A good plan is to let each line of pipes end
in a liquor-well large enough for a man to go down. As it is almost
impossible to make plugs fit without occasional leakage, it is not
well to run pits with very different strengths of liquors to one well,
but the layers, handlers, and different sets of leaches should each
have their own, so as to avoid mixture. A good means of clearing pipes
consists in a series of iron rods 3-4 ft. long, connected by hooks
fitting into double eyes, as shown in Fig. 63. It is obvious that in a
narrow pipe or drain, these cannot become disconnected.

[Illustration: Fig. 63.]

It is, as Schultz points out, of questionable advantage to lay wooden
troughs for supplying liquor to each pit under the alleys, since it is
almost impossible to preserve them from decay; but the same objection
would not apply to glazed pipes, well clayed or cemented. A very good
and cheap plan in practice, is to let the liquor-pump, or a raised
liquor-cistern, discharge into a large and quite horizontal trough
raised 5 or 6 feet above the level of the yard, and provided with
plug-holes at intervals, under which short troughs may be set to run
the liquor into the various pits.

[Illustration: PL. VIII.

_E. & F. N. Spon, London & New York._

"INK-PHOTO." SPRAGUE & CO. LONDON.

RUBBING-DOWN DYED SKINS.]

In tan-yard construction, iron should, as far as possible, be avoided
wherever it can come into contact with liquor, as it discolours the
leather. In default of underground pipes, india-rubber suction hose
may be employed. Direct-acting steam pumps without fly-wheels are not
suitable for tanneries, as they "hammer" when the pit is nearly sucked
up. Steam-jet elevators and the pulsometer are very useful for some
purposes, but slightly warm, and dilute the liquors with condensed
steam.

[Illustration: Fig. 64.]

Much that has been said about pits applies also to leaches. They may
be constructed either of wood, or brick and cement, and where heat is
employed the latter is the better. They are also to be provided with
plugs and pipes leading to a liquor-well. About 6 in. from the bottom
of the pit is a false bottom B made of boards, perforated with holes
or set a little distance apart; and in the corner is an "eye" C (Ger.
_Pfaff_) consisting of 2 boards set at right angles, so as to preserve
a vertical channel communicating with the space under the false bottom.
This serves, in pits provided with pipes, for the insertion of the
plug; and where this is absent, for that of a suction hose to pump
off the liquor. In the American Press-leck System, the eye of one
pit communicates by a horizontal spout with the top of the next (see
D, Fig. 64). The Allen and Warren Sprinkler Leck (Fig. 65) has very
much superseded this arrangement in America, though it is doubtful
if it spends the bark so completely. The round tubs, however, have
several advantages and may well be used for many purposes in English
yards. Their construction is described in some detail in Mr. Schultz's
book above cited. Some details will also be found on p. 209 of the
'Manufacture of Leather' by Davis. The rule for finding the capacity
of a round tub with perpendicular sides in cubic feet is to square the
diameter and multiply by ·7854, and by the depth in feet; or roughly,
to square half the diameter and multiply by the depth and by 3-1/7.

[Illustration: Fig. 65.]

Leaches and liquors are generally heated by blowing in steam direct. In
this case, the condensed water mixes with the liquor, and in heating
a liquor to boiling point it may be taken that about 20 per cent. of
water will be thus added. Where strong liquors are to be heated, it
is therefore obviously much better to pass the steam into a closed
copper coil in the liquor. Such a coil, with steam at 30 lb. pressure,
will heat about 27-1/2 gal. per hour per square foot of surface from
46° F. to boiling, and evaporate about half that quantity of liquor
already at boiling temperature. (See Box, 'Treatise on Heat,' p. 176.)
Heating coils must of course be provided with steam traps to carry off
condensed water; and in boiling by open steam it is very desirable
to let the steam pass through such a trap before use, to stop water
condensed in the pipes, which usually contains iron, and discolours the
liquors.




CHAPTER XXIII.

DRYING-SHEDS FOR LEATHER.


The primitive way of drying leather was to hang it on poles in the
open air, but this in our uncertain climate has become quite obsolete.
The oldest plan now actually in use is to hang on poles in a shed
generally raised some height above the ground, so as to catch the wind,
and provided on all sides with louvre boards arranged so as to open
and shut as required. These sheds, to give good results (especially on
mixed tannages, which need much more care in drying than bark), demand
very watchful management. In windy weather, and with wet leather at
all times, the louvres must be kept nearly or quite closed, and on the
sunny side of the shed the same precaution is generally necessary.
Again, in very damp weather the leather does not dry at all, and in
frosty seasons it is apt to freeze, by which sole leather is made soft
and spongy, and dressing leather, though whitened, is said to be less
capable of carrying grease. To prevent freezing, and to enable leather
to be dried in damp or cold weather, it became customary to provide
sheds with ranges of steam-pipes on the floor; this, though decidedly a
valuable addition, has not proved by any means an entirely satisfactory
solution of the problem of leather drying. No sufficient means are
provided for controlling the ventilation, and the upward currents of
hot air dry the leather irregularly, and produce bad colour. A much
more satisfactory shed is the American turret drier.

This consists of a lofty building, 3 to 8 stories high, without
louvres, but with latticed floors. J. S. Schultz recommends 5 stories,
of 7 ft. clear between beams, as a convenient height, and the building
should be divided by partitions from top to bottom into 4 or more
series of chambers one above another, each of which is capable of
having the heat and ventilation separately regulated. The Americans
usually fill one of these series at once, and dry off the whole in
about 10 days, so that as many will be required for a tannery as will
hold a 10 days' production. For ventilation, each of these sets of
chambers is provided with a lantern ventilator at the top for the exit,
and shutters or dampers on the bottom floor for the admission of air.
The bottom floor is also provided with steam-pipes, of which those for
each set of compartments are controlled by a separate cock. When warmth
is applied at the bottom, the tall building acts like a chimney, and a
continuous current of air passes from the ventilators at the base up to
those at the top. The usual American practice is, after filling one of
these ranges of compartments, to apply no steam-heat for the first 3
or 4 days, and, if the weather be dry or windy to keep the ventilators
also closed. After the third or fourth day, a moderate degree of heat
is given, and this is increased so that at the end of about 10 days the
stock is fully dry.

This is in accordance with a common American practice, in which the
leather is fully dried before rolling, in order to fix the soluble
colour, and prevent it striking out to the surface in the finishing.
The wet leather is raised by an elevator, consisting of an endless
chain provided with hooks, to which the leather is attached at the
bottom, and from which it is taken at the top. Various ways are adopted
to lower the leather from these tall turrets to the room where it is
stored prior to damping down for rolling. In some cases, the lattice
floors are made movable, and the whole contents of the room, including
the sticks from which the leather is hung, are allowed to fall into the
lowest room. This method is of very questionable advantage, if we take
into account the labour of separating the sticks and carrying them back
to their places. Another plan is to have shoots from each loft, down
which the sides are slid to the rolling-room. The floors should have
what light is necessary supplied through glass windows, so arranged as
not to admit direct sunlight.

To adapt the turret drier for English requirements, some slight
modification is needed, since we do not dry our leather right off,
and then damp back, but, when it is suitably dry, lay it in a pile to
"sammy" for striking; then, perhaps, after striking, hang up again for
a short time to temper for rolling, possibly again between rollings,
and finally to dry off at a temperature of, say, 68-77° F. (20-25° C.).
Perhaps on this account, the writer has seen no complete turret-driers
in use in England, though a portion of one of the large sheds at
Dartford belonging to Messrs. Hepburn was converted by them some years
since into a very good turret, which gave excellent results both
for sole leather and kip butts in stuff. This turret is represented
in section in Fig. 66, and is about 56 ft. × 24 ft. in area, and
50 ft. high from the ground-line to the top of the roof, which is
ventilated by a dormer, _a_, with fixed louvres at the top, while air
is admitted at the bottom through ventilators with sliding flaps, _b
b_. It is heated by 10 rows of 4-in. steam-pipe, _c c_, each 54 ft.
long, making a total of 540 ft. run, or about 640 ft. superficial (a
4-in. pipe being about 4-5/8 in. diameter outside). I am informed
by Mr. J. G. Hepburn that he considers 4-in. pipes inferior for the
purpose to smaller ones, giving too much heat in one place, and without
sufficiently distributing it, and were he constructing a new turret he
would replace them by 1-1/2 in. wrought-iron, using about 3 of 1-1/2
in. to replace 2 of 4 in., small pipes being much more effective (as
will be seen by table, p. 250) than larger ones, in proportion to
their surface. He considers, however, that the best way of heating
drying-sheds, though more expensive in first cost, is by means of hot
water, which is much more constant in temperature than steam. Mr.
Hepburn, to whom I am much indebted for the above information, informs
me that the turret still acts very well, drying kip butts on the
upper floor a good colour in all weathers in about a week. He finds,
however, that the steam-pipes as described are hardly sufficient in
very cold weather, and intends to increase them, or replace with
1300-1400 ft. of hot water pipe heated by a saddle boiler. At Lowlights
tannery, a shed arranged on the turret principle (though much less
completely carried out from want of height in the buildings) has been
for many years in operation, principally for drying off sole-leather,
with the most satisfactory results.

[Illustration: Fig. 66.]

It is noted by Box ('Practical Treatise on Heat,' p. 166) that an exit
for the moist air should not be placed at the top of a drying-chamber,
but at the bottom, since in the first case, the hot dry air tends to
rise at once to the opening, and pass away unsaturated with moisture,
while that cooled by evaporating water from the goods, being heavier,
tends to form downward currents and remain in the chamber. To this it
may be objected that aqueous vapour is much lighter than air; this
is true, other things being equal, but in practice the evaporation
of a given quantity of water cools the air and makes it heavier in a
materially greater degree than the admixture of aqueous vapour lightens
it. This source of waste of heat exists in the turret drier, but is
there, from its great height, reduced to a minimum. In lower sheds it
becomes very material, and the air currents formed are productive of
much harm by causing irregular drying. This difficulty has been met by
Mr. Edward Wilson, of Exeter, to whom the leather trade owes several
very useful inventions, by an ingenious drying-room constructed on
the lines indicated by Box, though I do not know that he was in any
way indebted to that writer for the idea. In this Mr. Wilson arranges
the steam-pipes, instead of on the floor, in a vertical compartment
partitioned from the chamber, through which air is admitted and heated.
This hot air fills the top of the chamber and from its lightness floats
in a horizontal layer, only descending and escaping by apertures in the
floor as it becomes cooled by evaporating the moisture of the hides.
Mr. Wilson states that the method answers well in practice, and it is
certainly the most scientific in conception, but it might be feared
that, as applied to a single floor, the upper parts of the butts,
suspended near the ceiling, would dry more rapidly than those near
the floor. If applied to a double-floored building, this disadvantage
would, from the stronger draught, and consequent larger supply of air,
be less likely to show itself, and the upper floor with its uniform
warm air would be well adapted for drying off finished sole-leather,
while the cooler and milder drying of the ground floor would be fitted
both in character and situation for that wet out of the yard. Special
precaution would be needed to prevent the heated air escaping by doors
opening into the upper floor. There is little doubt that as regards
heat this is the most economical system which has yet been invented.

A method has been introduced in the United States of drying wet and
finished leather all together, in drying-rooms heated to a considerable
temperature, and closely shut up. This is found to answer fairly on
leather from sour liquors, but that from strong and sweet liquors is
darkened, as might be expected. The drying is accomplished in much
shorter time than by the turret drier. The mixture of wet and dry
leather, and the lack of ventilation produce an atmosphere nearly
saturated with moisture, and hence the drying is not nearly so harsh as
might be supposed from the considerable temperatures made use of. There
does not, however, seem anything in the principle to recommend its
general adoption.

Another invention, of which we have as yet heard little definite in
England, consists in drying at a low temperature by air artificially
deprived of its moisture. This may be accomplished in several ways.
Experiments have been made in drying in a closed chamber provided
with trays of calcium chloride to absorb the moisture evaporated. Air
when artificially cooled by compression and subsequent expansion, as
in the case of ice-making machines, parts with a large portion of its
moisture, which is condensed in the form of ice in the tubes of the
machine. Such air, if subsequently warmed, would dry powerfully and
rapidly.

Before leaving the subject of drying-sheds, a few words on the
mechanics of drying in general may not be out of place. Air-drying
is dependent on the condition that the air must be capable of taking
up more moisture than it already contains. It is a matter of common
experience that there are warm days when the air is so saturated with
moisture in the form of invisible vapour, that scarcely any drying
takes place; and similarly, cool dry days, when leather dries rapidly.
The relative amount of moisture in the air is easily ascertained by
the simple instrument known as the wet and dry bulb hygrometer; an
instrument which ought to be in every drying-shed, especially where
steam heat is used. It consists of two similar thermometers, side by
side, of which one has the bulb covered with muslin and kept wet by a
piece of lamp-cotton attached to it, and dipping in a cup or bottle of
water. This water evaporates more or less rapidly, according to the
dryness of the air; and as heat is consumed by it in passing into the
gaseous condition, the wet thermometer falls more or less below the dry
in proportion to the rapidity of the evaporation. On a summer's day,
the difference may amount to 9°-12° F. (5°-7° C.), and this is about
the extreme dryness permissible in a drying-room for finished leather.
Wet leather should of course be dried much more slowly. The influence
of heat on drying is two-fold. It increases the capacity of the air
for moisture, and it replaces the heat consumed by evaporation. The
following tables give the capacity of air for moisture at different
temperatures, and the percentage of saturation as shown by the wet and
dry thermometer. At Greenwich, the mean humidity for the year is 82 per
cent.; or for the day-time only 76 per cent., varying from 62 in summer
to 86 in winter:--


Table I.--Capacity of Air for Moisture.

  ───────────┬──────────────────┬──────────────────────┐
             │ Weight in Pounds │  Weight in Pounds of │
  Temp. Fahr.│ of a Cub. Ft. of │ Moisture contained in│
             │      Dry Air.    │      a Cub. Ft. of   │
             │                  │      Saturated Air.  │
  ───────────┼──────────────────┼──────────────────────┤
     32°     │     ·0807        │      ·000304         │
     42      │     ·0791        │      ·000440         │
     52      │     ·0776        │      ·000627         │
     62      │     ·0761        │      ·000881         │
     72      │     ·0747        │      ·001221         │
     82      │     ·0733        │      ·001667         │
     92      │     ·0720        │      ·002250         │
    102      │     ·0707        │      ·002997         │
  ───────────┴──────────────────┴──────────────────────┘


Table II.--Hygrometer Table.

  ───────────┬───────────────────────────────────────────────┐
  Temperature│     Degrees between Wet and Dry Thermometers. │
  of Air.    ├───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┬───┤
             │ 1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 │ 8 │ 9 │ 10│ 11│ 12│
  ───────────┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───┤
      32° F. │ 87│ 75│ ..│ ..│ ..│ ..│ ..│ ..│ ..│ ..│ ..│ ..│
      42     │ 92│ 85│ 78│ 72│ 66│ 60│ 54│ 49│ 44│ 40│ 36│ 33│
      62     │ 94│ 88│ 82│ 77│ 72│ 67│ 62│ 58│ 54│ 50│ 47│ 44│
      82     │ 95│ 90│ 85│ 80│ 76│ 72│ 68│ 64│ 60│ 57│ 54│ 51│
             │                                               │
             │   Per cent. of moisture, saturation being 100.│
  ───────────┴───────────────────────────────────────────────┘

As regards the heat consumed in evaporation; it requires about 1000
times as much heat to convert 1 lb. of water into vapour, as it does
to raise the temperature of the same quantity 1° F. At least as much
heat as this must be supplied if the air which has been used in drying
is to retain the same temperature it had at the outset, and therefore
if a turret is to keep at a higher temperature than the air, which is
necessary to create a draught, this is the minimum amount of heat which
must be supplied per pound of water to be evaporated. In practice much
more will be needed.

The following table shows the heat given out by different sizes of
pipes at different temperatures, and steam pressures, in units equal to
the heat required to raise 1 lb. of water 1° F., and the cubic feet of
air which they will heat.[V]

[Footnote V: To illustrate the use of such tables, the following
example may be given. To dry 100 butts in a turret, each containing 20
lb. of moisture, at least 20 × 1000 × 100 = 2,000,000 units of heat
will be required to replace the loss by evaporation alone. As a 4-in.
pipe at 300° gives off 669 units per foot per hour (see Table III.),
about 125 ft. would give off 2,000,000 units per day. If we compare
this with Mr. Hepburn's practical experience, supposing the 4 working
floors of his turret to hold 100 butts each (a low estimate), and to
dry in 10 days; we have 540 ft. for 40 butts or 1350 ft. for 100 butts
a day; showing that more than 10 times the minimum is required in
practice. Of course this allows for weather in which the air must be
heated considerably before it will dry at all, for heat that escapes
uselessly at the top and sides of the building, and for the fact that
the pipes are not heated the whole time, and probably, on the average,
to a much lower temperature.]


Table III.--Heating Effect of Pipes freely exposed to Air at 60° F.

  ──────┬─────────┬──────────────────────────┬──────────────────────────────┐
        │         │Units of Heat per Ft.-run │  Cub. Ft. of Air at 60° F.   │
        │         │ of Pipe per Hour.        │ (15-1/2° C.) heated 1° per   │
  Temp. │ Pressure│                          │ Ft.-run of Pipe per Hour.    │
    of  │ of Steam├──────┬─────┬──────┬──────┼───────┬───────┬───────┬──────┤
   Pipe.│ per In. │2 in. │3 in.│ 4 in.│ 6 in.│ 2 in. │ 3 in. │ 4 in. │ 6 in.│
  ──────┼─────────┼──────┼─────┼──────┼──────┼───────┼───────┼───────┼──────┤
   ° F. │   lb.   │      │     │      │      │       │       │       │      │
    300 │   53    │  403 │  545│  669 │  938 │ 22235 │ 28713 │ 36919 │ 51760│
    280 │   35    │  355 │  480│  587 │  825 │ 19582 │ 26490 │ 32387 │ 45521│
    260 │   21    │  312 │  421│  515 │  723 │ 17218 │ 23233 │ 28421 │ 39952│
    240 │   10    │  271 │  366│  448 │  627 │ 14946 │ 20199 │ 24717 │ 34594│
    220 │    2·5  │  233 │  313│  384 │  537 │ 12858 │ 17271 │ 21184 │ 29629│
    200 │   ..    │  195 │  263│  322 │  452 │ 10775 │ 14507 │ 17780 │ 24967│
    180 │   ..    │  160 │  216│  264 │  369 │  8830 │ 11920 │ 14573 │ 20368│
    160 │   ..    │  128 │  172│  210 │  295 │  7070 │  9487 │ 11590 │ 16300│
  ──────┴─────────┴──────┴─────┴──────┴──────┴───────┴───────┴───────┴──────┘

It may be taken that 1/20 of the above volumes may be heated 20°, from
50° F. to 70° F., and so on; but if the average temperature is higher
than 60° F., the duty will be less, and to obtain the same effect the
pipe must be heated so much hotter as to keep the same difference as
before between the pipe and air. Thus a pipe at 300° F. will only heat
as much air at 80° F. as one of 280° F. will of air at 60° F.

[Illustration: Fig. 67.]

It will be noted that the efficiency of small pipes is much greater
than that of larger ones, and in these days of high-pressure steam,
much may be said in favour of the use of comparatively small
wrought-iron steam-pipes instead of the larger cast metal ones. The
first cost is small, the pipes are easily obtained ready screwed, and
in the lengths required, and may be put together by any intelligent
workman. The risk of fracture by the concussion of condensed water
is very trifling, as compared to that of metal, and much lighter
pipes are safe for high pressures. Steam-pipes must always be laid
with an incline of say 1 in. in 10 ft. from the end where the steam
is admitted, so that the condensed water may get away, and at the
lowest point a steam-trap must be provided for its escape. In the
writer's experience, the best form is that of Holman, made by Tangye
of Birmingham, of which the principle will readily be understood from
Fig. 67. The cup-shaped vessel _a_ floats on the water in the outer
casing, and so closes the valve _b_ until _a_ gets full, when it
sinks and allows the water to escape until it floats up again. It is
important that this trap should be set level, or the valve will not
close properly. Each pound of condensed water is equivalent to about
1000 units of heat given off (see Table III.). In planning steam-pipes,
it is not necessary that they should be arranged in a single line.
Even if in gridiron form the steam will still reach every part, in
proportion to the condensation which takes place. A series of large
pipes may be supplied by small pipes from a common main, and discharge
their condensed water into a common waste-pipe with branch from each.
A 1/2-in. pipe from a high-pressure boiler will supply a considerable
range, say 100 ft. of 4-in. pipe, though a larger size is advisable. At
the farther end of a range of steam-pipes a small tap must be provided
to let out the air which accumulates in them. In employing the exhaust
steam of an engine for heating purposes, the pipes must be of ample
size and freely open at the ends to avoid back-pressure. For this
purpose the gridiron form is a very good one.

The planning of hot-water pipes is much more difficult than that of
steam-pipes, but the general principle is that the pipes must rise
all the way from the boiler to the farther end, where there must be
an expansion-box or supply-cistern to allow the water to rise and
fall and dissolved air to escape. From this the pipes must fall more
or less, throughout the distance, back to the boiler, entering it at
the bottom. If at any point the pipe has to fall, leaving an upward
bend, a tap must be provided for the escape of air, but such upward
bends are a fertile source of difficulty and failure of action. With
long runs of either steam or water pipes, arrangements must be made
to allow of expansion and contraction, which will amount to 1-2 in.
per 100 ft., according to the temperature employed. If one end of the
system can be left free, all that is needed is to support the pipes on
rollers (pieces of old pipe may be used); if not, stuffing-boxes must
be provided.

The air heated by boilers, and other sources of waste heat, may often
be utilised for heating purposes, but generally requires to be driven
by a fan, unless the drying-room can be arranged directly above the
source of heat. If air has to be conveyed, the air-ways must be of
ample size, and if the ascending force of heated air be relied on,
passages less than 2 ft. sq. are seldom of much use. This ascending
force is generally much overrated where the differences of temperature
are so small as those employed in a drying-room. In a boiler chimney,
where the temperature of the escaping gases is 552° F. (289° C.), the
specific gravity of the air is about half that outside, and a chimney
of 50 ft. in height gives a draught equal to the pressure of a column
of about 1/3 in. of water, and the hot gases theoretically have a
velocity of about 80 ft. per second; whereas the same chimney with a
difference of temperature of 30° F. would have a draught equal to 1/300
in. of water only, and a velocity of 8 ft. per second.

The following table will enable the reader to calculate approximately
loss in friction in air-passages and the pressure required to pass a
given volume of air. The pressure needed increases in proportion to the
length of the pipe and the square of the velocity of the current of air
to be passed. Thus if we double the length of the pipe we must double
the pressure to pass the same quantity; and in order to double the
quantity of air through a given pipe, the pressure must be quadrupled.


Table IV.

 Head, or Difference of Pressure at the two ends of a Circular Pipe 1
 yd. long in inches of water required to pass 1000 cub. ft. of air per
 minute.

  ────────────┬────────────┬─────────┬─────────────────────────────────
  Velocity in │ Diameter of│  Head.  │
  Ft. per Sec.│    Pipe.   │         │
  ────────────┼────────────┼─────────┤
              │    in.     │         │
    84·8      │     6      │ ·186    │ }
    37·7      │     9      │ ·02442  │ } To pass 100 ft. per min. these
    21·2      │    12      │ ·00579  │ }   figures must be divided by
     9·4      │    18      │ ·000763 │ }   100. To pass 10,000 ft. they
     5·3      │    24      │ ·000181 │ }   must be multiplied by 100.
     3·4      │    30      │ ·0000593│ }
  ────────────┴────────────┴─────────┴─────────────────────────────────

To calculate the head required for a long pipe, multiply the head given
by the table by the length in yards. The air passed by square pipes of
the same diameters will be 1·273 times greater with the same heads.

To be added to the pressure required to overcome friction is that
needed to force the air out at the end of the pipe. This varies with
the shape of the tube, &c., but for our purpose may be taken as given
in the following table:--


Table V.

Approximate Pressure needed to force Air out of a Pipe with a Velocity
of--

  Ft. per Sec.    Head in Inches,
                     Water.

    84·8             1·8
    37·7             0·36
    21·2             0·13
     9·4             0·02
     5·3 under       0·01
     3·4 under       0·005

Air-passages should be, as far as practicable, of uniform area
throughout their length, as much velocity is lost in passing even from
a smaller to a larger tube. Of course sharp bends must be avoided.




CHAPTER XXIV.

COMMERCE, STATISTICS, AND BIBLIOGRAPHY.


=Skins.=--The trade in skins possesses no small importance. Many of the
statistics relating to skins are collective, and not specific; these
will be grouped under the heads of the respective countries, after all
accessible details have been given upon each kind of skin.

_Alligator._--In the Southern United States, notably Florida, the
supply of alligator-skins amounts to many thousands annually, and
the "farming" of the reptiles for their skins is even spoken of. The
principal market for them is Europe, but no statistics of the trade
are published. The alligators often attain a length of 18-20 ft. The
hides are stripped off, and the belly and sides, the only portions fit
for use, are packed in barrels in a strong brine, and shipped to the
Northern tanner, who keeps them under treatment for 6-8 months, when
they are ready to be cut up. So far the leather has been principally
used in the manufacture of boots and shoes, for which it is especially
adapted.

_Armadillo._--The skins of this animal were exported from Brunei
(Borneo) to Singapore to the value of 121 _dol._ (of 4_s._ 2_d._) in
1879.

_Ass._--Hankow exported 2402-1/2 _piculs_ (of 133-1/2 lb.) of asses'
skins in 1878, and 1068 _piculs_ in 1879.

_Buffalo._--Manilla (Philippines), in 1878, exported 379 tons of
buffalo-skins, value 12,130_l._, and 274 tons of cuttings, 6579_l._
Hankow exported 1091 _piculs_ in 1878, and 1238 in 1879. Brunei
(Borneo) sent 1362 _dol._ (of 4_s._ 2_d._) worth to Singapore
in 1879. The approximate London market values of buffalo-skins
are:--Batavia, 4_d._-7_d._ a lb.; Bengal, 3_d._-6_d._; other sorts,
2-1/2_d._-6-1/2_d._

_Calf._--Hamburg exported to Great Britain of calf and other skins
in 1876, 20,731 cwt.; in 1877, 27,550; in 1878, 14,583; and in 1879,
19,287 cwt. The Hawaiian Islands sent 168 pieces to Germany in 1879.
Christiania shipped 31,000 _kroner_ (of 1_s._ 1-1/2_d._) worth to Great
Britain in 1878, and 300 _kr._ in 1879. The exports from Archangel
(including seal) in 1878 were 335 pieces to Holland, and 23,108 to
Germany: total value, 2343_l._ Honolulu, in 1878, exported 651 pieces,
being 500 to Germany, 135 to China, and 16 to the United States. Memel,
in 1879, sent landwise over the Russian frontier for German markets,
34,400 pieces, value 5450_l._ The approximate London market value of
calf-skins is 15_d._-34_d._ a lb.

_Deer._--San José (Costa Rica) exported 12,121 lb. in 1878. Kiungchow
(China) exported 17,544 pieces, value 541_l._, in 1879. Ciudad Bolivar
(Venezuela), in 1879, sent 77,305 pieces (168,176-1/2 lb.) to New York,
and 14,695 pieces to Germany. Guatemala, in 1879, exported 2353 pieces
to Germany, 693 to New York, and 100 to Belize. Panama shipped 765_l._
worth of deer and other skins to the United States in 1879. Costa Rica
exported 82,168 lb. in the year ended April 30, 1879. Puerto Cabello
(Venezuela), in 1879, shipped 2466 _kilo._ (of 2·2 lb.) to Great
Britain, 11,619 to Germany, 6182 to the United States, and 1281 to
Holland. The Commercial Society of Mozambique sold 41 deer, 391 buck,
2168 blesbok, and 3071 other antelope skins at Rotterdam in June 1876.
The approximate London market values of deer-skins are: Blesbok, Cape,
6-17_d._ a lb.; Deer, East Indian, 22-50_s._ a doz.

_Dog._--Dog-skin makes a nice, thin, tough leather, but most of the
gloves sold as dog-skin are made of lamb-skin.

_Dugong and Manatee._--The skins of these animals, more important
perhaps as oil-yielders, are smooth, bluish-black in colour, and nearly
1 in. thick. They are well adapted for machine-belting. About 50 are
shipped annually from Queensland.

_Fish._--Although the skins of fish are chiefly gelatinous, and
easily soluble in water, some are of a firm, strong texture, and of a
useful character. Up to within a few years, however, their employment
for practical purposes has been rather limited, and it is only
comparatively recently that attention has been more generally directed
to their utilisation on an extended scale. At a Maritime Exhibition
held at the Westminster Aquarium in 1876, a Norway exhibitor showed a
variety of tanned fish-skins, among which were:--Tanned whale-skins;
upper leather, made from the white whale, the source of the so-called
porpoise hide used for laces; skins of flatfish, prepared for gloves;
skins of soles, tanned and dressed for purses; skins of thornbacks,
prepared as a substitute for sandpaper; and skins of eels, dressed and
dyed, suitable for braces, &c. Shoes have been made at Gloucester,
Mass., from the skins of the cusk or torsk (_Brosmus vulgaris_), the
use of which has been patented, and an industry is said to be carried
on at Colborn, Canada, with the skins of species of siluroids for glove
making. In Egypt, fish-skins from the Red Sea are used for soles of
shoes. The skin of the losh or burbot (_Lota maculata_) is used by the
people in many parts of Russia and Siberia to trim their dresses. It
is also utilised by some of the Tartar tribes as material for their
summer dresses, and the bags in which they pack their animal skins.
The spiny and tuberculous skins of many sharks and allied fishes are
largely employed, under various trade names, for polishing woods, and
for covering boxes, cases, &c. From a certain portion of the skin of
the angel shark (_Squalina angelus_) the Turks make the most beautiful
sea-green watch cases. Turners, ebonists, and carpenters in Europe
use the rough skin of the blue dog-fish (_Squalus glaucus_), like
emery paper, for smoothing their work and preparing it for polishing.
This shark-skin is also made into shagreen. That most used at present
appears to be the skin of the ray (_Hypolophus sephen_), which is
very common on the Malabar coast. The house of Giraudon, Paris, makes
excellent use of them for morocco and _tabletterie_. At the recent
Paris Exhibition this establishment exhibited numerous illustrations of
the ornamental application of the prepared skin in large office-table
inkstands, candlesticks, boxes and caskets, paper-knives, reticules,
card-cases, photograph frames, bracelets, scent bottles, &c. The fish
called _chat_ (_Squalus catulus_) at Marseilles is smaller than the
angel fish, and furnishes a product known as _peau de rousette_. This
skin is reddish, and without spots, and of a uniform grain, flat, and
only used to make cases and other articles known as shagreen. _Peau de
chien de mer_ is another name given to some species of _Squalus_. That
found on the French coasts is known under the names of _chien marin_,
_rousette tigrée_, &c. Turners, cabinet makers, and carpenters use the
skin for scraping and smoothing their work, and it is also used for
like purposes by metal workers. This skin, when worked up with the
tubercles with which it is studded, takes the name of _galuchat_, and
is usually dyed green, to cover cases, sheaths, and boxes. Under the
name of _chagrin_, these skins used to be much employed in Turkey,
Syria, Tunis, and Tripoli--that made in Tripoli being considered the
best. It was coloured black, green, white, and red. France imported
18,000 lb. of ray-skins in 1863, chiefly from Portugal.

_Goat and Kid._--Our imports of undressed goat-skins in 1883
were:--From Russia 18,355, 2523_l._; Sweden 1296, 229_l._; Norway
19,391, 3316_l._; Denmark 11,012, 1856_l._; Germany 52,571, 5856_l._;
Holland 13,336, 1858_l._; Belgium 40,518, 4632_l._; France 81,798,
14,121_l._; Italy, 5708, 987_l._; Austrian territories 37,827,
3844_l._; Turkey 38,166, 4580_l._; Egypt 16,228, 933_l._; British
Possessions in South Africa 1,176,535, 139,632_l._; Aden 39,800,
4797_l._; British India: Bombay 122,242, 10,487_l._; Madras 169,642,
17,895_l._; Bengal 2,568,526, 203,256_l._; China 93,738, 5864_l._;
Australasia 44,340, 5518_l._; United States of America 6822, 845_l._;
Chile 16,756, 2553_l._; Brazil 159,949, 16,189_l._; Argentine Republic
12,000, 952_l._; other countries 3239, 229_l._; total 4,749,795,
452,952_l._ Ciudad Bolivar (Venezuela) sent 317 pieces (284 lb.) to New
York in 1879. Tripoli exported 7000_l._ worth in 1879, and 3000_l._ in
1880. In 1880, a number of raw goat-skins were sent from the Marche
and Romagna to the United States, weighing about 1-1/2 _kilo._ (of 2·2
lb.) each, and to be used chiefly for ladies' shoes and pocket-books.
Shanghai, in 1878, exported 164,285 pieces. Tangier, in 1879, sent 12
cwt., 60_l._, to Great Britain; 3637 cwt., 18,185_l._, to France and
Algiers; 10 cwt., 50_l._, to Spain; total, 14,636 doz., 18,295_l._;
and 3046 cwt., 13,707_l._, in 1880. The Hawaiian Islands, in 1879,
shipped 24,940 pieces to the United States (Pacific ports). In 1879,
Christiania exported 65,000 _kroner_ (of 1_s._ 1-1/2_d._) worth of
goat and sheep skins to Great Britain. The shipments of goat and kid
skins from the French East Indies fell from 5500 in 1876, to 4894 in
1877, and 300 in 1879, with none since. The shipments from the Cape
to Great Britain were 794,637 in 1878, 657,509 in 1879, and 934,810
in 1880. Cadiz, in 1877, sent 404 _kilo._ (of 2·2 lb.) of kid skins,
value 84_l._, to Great Britain, and 3866 _kilo._ 805_l._, to France.
Puerto Cabello (Venezuela), in 1879, despatched 28,684 _kilo._ to
Germany, 124,964 to the United States, 14,295 to France, and 18,536
to Holland. Honolulu sent 64,525 pieces to the United States in 1878.
Samsoun (Turkey) exported 130,700 _kilo._, 6796_l._, to France in
1878. The Cape exports fell from 1,478,761 pieces in 1874, to 687,570
in 1879. Memel sent by sea 7 cwt., 73_l._, in 1879. Tientsin (China)
exported 38,107 _piculs_ (of 133-1/3 lb.) in 1879. Mogador (Morocco)
forwarded 112,974 doz., 59,243_l._, to Marseilles in 1878, and 8407
bales, 48,000_l._, in 1880; these skins are used for the manufacture of
morocco leather, for which they are peculiarly suitable, owing to their
fineness of grain, caused, it is said, by the rich diet, consisting
of the fruits of the argan tree. The approximate London market values
of goat-skins are:--East Indian, 4-15_d._ a lb.; best tanned, 2_s._
4_d._-3_s._ 8_d._; inferior to good tanned, 9_d._-2_s._ 5_d._; Cape,
best, 11-18_d._; Cape, inferior to good, 8-14_d._ Turkey is one of the
largest rearers of goats, and consequently the manufacture of morocco
leather is extensively carried on in that country. Formerly, nearly
all the buck-skins found their way to London, but they were displaced
by Indian goat-skins; and, for a time, the exportation of Turkish
buck-skins experienced a check, the result being the establishment
of a large number of manufactories in Vienna and the different
Austro-Hungarian provinces. These establishments have prospered and
been enlarged, and get the major portion of their goat-skins from
the London market. It is, however, proposed in Austria to do without
the London market in future, and to institute at Trieste periodical
sales of goat-skins, which will be, especially for Vienna, of great
advantage from the point of view of cost of transport. Notwithstanding
the exportation of buck-, goat-, and sheep-skins from Turkey, there
are still sufficient remaining in the country to form the basis of a
very flourishing and entirely indigenous industry. The Turk is very
unskilful in the manufacture of sole leather; but the article in which
he excels is morocco leather for slippers, tanned exclusively with
sumach. The production of tanned buck-skins reaches yearly a total of
nearly a million skins, and of sheep half a million; the best kinds are
those of Philippopolis, Samakof, and Peristra. The Bulgarian skins are
not so well tanned as those mentioned, although the quality of the raw
skins is superior. The best at the present day are those of Sophia.

_Horse._--Shanghai exported 458-1/2 _piculs_ in 1878. Rio Grande do Sul
exported 10,714 pieces salted, and 601 dried, in 1879. The approximate
London market values of horse-hides are:--English, 9-14_d._ a lb.;
River Plate, 6-21_s._ a hide.

_Kangaroo._--The skins of this animal are largely exported from
Australia and Tasmania, forming some of the most pliable leather known.
To prepare them for market, they should be carefully taken off, pegged
out, and dried slowly in the shade.

_Lamb._--The exports from Asterabad (Persia) viâ Gez in 1879 were 788
bales Bokharan, 60,613_l._ Calamata and Messenia (Greece) produced in
1880, 137,500 lb., 2680_l._ Dedeagatch (Turkey), in 1878, exported 500
bales of lamb- and kid-skins, value 4000_l._ The exports from Ancona
(Italy), including kid and rabbit, in 1878, were 609,826 _kilo._ (of
2·2 lb.) to Italy, 41,480 to Austria, 2714 to Germany, 2655 to Greece,
19,486 to England, 3180 to Turkey; total, 679 tons, 50,321_l._ Tientsin
(China), in 1879, shipped 35,008 _piculs_ (of 133-1/3 lb.).

_Llama._--The skin of the llama is growing in importance in Parisian
shoemaking. It weighs on an average 6 lb., and contains 18 sq. ft. of
leather, costing about 1_l._ The source of supply is the Peruvian Andes.

_Ox and Cow._--Coquimbo (Chili) exported 4709 ox-hides in 1879.
Santos (Brazil) in the year ending Sept. 30, 1879, exported 316,940
_kilo._ salted, valued 5800_l._, and 1282, 25_l._ The shipments from
Christiania to Great Britain fell from 47,500 _kroner_ (of 1_s._
1-1/2_d._) worth in 1877, to 3500 _kr._ in 1879. San José (Costa Rica)
despatched 449,870 lb. in 1878. The exports from the Cape, including
cow, fell from 150,875 pieces in 1878, to 104,281 in 1879. Rio Grande
do Sul, in 1879, shipped 455,315 pieces salted, and 499,960 dried. Of
cow-hides, Hankow exported 35,265 _piculs_ (of 133-1/3 lb.) in 1878,
and 21,063 in 1879. The Kiungchow exports (including buffalo) in 1879
were 490 _piculs_, 818_l._ From Shanghai (including buffalo) went
26,070 _piculs_ in 1879. Chinkiang fell from 7262 _piculs_ in 1877,
to 3974 in 1878, and none in 1879. Memel, in 1879, sent away by sea,
75 cwt., 136_l._; and over the Russian frontier for German markets,
3000 pieces, 3000_l._ The approximate London market values of ox and
cow hides are:--Buenos Ayres and Monte Video, 1st dry, 9-(10-1/2)_d._
a lb.; 2nd dry, 7-(8-1/2)_d._; best light, 8-(9-1/2)_d._; salted,
(5-1/4)-(7-3/4)_d._; Brazil, dry, 7-(10-1/2)_d._; dry salted,
(4-1/2)-9_d._; West Indies, salted, (3-1/2)-7_d._; United States,
salted, (3-1/2)-(6-1/2)_d._; East India, best, 4-13_d._; 2nd,
(1-3/4)-(11-1/4)_d._; 3rd and 4th, (1-1/4)-9_d._; Australian, salted,
(2-3/4)-6_d._; Cape, wet salted, (2-1/2)-(7-1/2)_d._; Continental,
salted, (3-3/4)-5_d._; English, (2-3/4)-7_d._

_Seal._--Our imports of undressed seal-skins in 1883 were:--From
Norway 112,809, 35,267_l._; Denmark 866, 138_l._; Germany 28,669,
8428_l._; Channel Islands 1048, 305_l._; France 2798, 2002_l._; British
Possessions in South Africa 7020, 5635_l._; British India: Bombay 830,
1850_l._; China 2083, 4000_l._; Japan 11,943, 17,369_l._; Australasia
1487, 890_l._; British North America 341,778, 88,413_l._; United States
of America 98,566, 256,018_l._; Central America 563, 563_l._; Chile
1974, 1803_l._; Uruguay 13,950, 4884_l._; Whale Fisheries: Northern
44,474, 15,208_l._; Other Countries 426, 253_l._ Total, 671,284,
443,026_l._ The exports from Christiania in 1879 were 74,090 pieces;
to Great Britain, the value was 254,400 _kroner_ (of 13-1/2_d._) in
1878, and 172,900 _kr._ in 1879. Our total imports from Norway rose
from 29,912 pieces in 1877, to 63,540 in 1878, and receded to 54,005 in
1880. From the Cape, they were 11,065 in 1877, 15,128 in 1879, and 7731
in 1880. And from Newfoundland, 413,057 in 1879, and 253,656 in 1880.
The approximate London market values of seal-skins (not fur seals)
are 1_s._ 9_d._-10_s._ 6_d._ each for Newfoundland, and 2-11_s._ for
Greenland.

_Sheep._--Our imports of undressed sheep-skins in 1883 were:--From
Russia 7374, 820_l._; Sweden 16,780, 1446_l._; Norway 23,756, 2469_l._;
Denmark 80,226, 7803_l._; Germany 126,867, 12,476_l._; Holland
34,213, 4182_l._; Belgium 94,966, 14,479_l._; Channel Islands 9579,
2900_l._; France 644,080, 66,510_l._; Spain 147,480, 19,730_l._;
Italy 41,743, 3790_l._; Austrian Territories 41,011, 4031_l._; Turkey
244,579, 23,593_l._; Egypt 8870, 517_l._; British Possessions in
South Africa 2,521,109, 339,374_l._; Aden 29,780, 2720_l._; British
India 190,202, 17,745_l._; Australasia 2,693,064, 267,289_l._; United
States of America 45,692, 4367_l._; Bermudas 2342, 365_l._; Peru 7220,
1692_l._; Chile 3582, 681_l._; Brazil 18,616, 2453_l._; Uruguay 92,499,
21,303_l._; Argentine Republic 985,268, 176,900_l._; Falkland Islands
26,747, 3105_l._; Other Countries 7086, 747_l._ Total, 8,145,431,
1,003,487_l._

Bosnia Serai, in 1879, exported about 10 tons. Shanghai, in 1878,
50,285 pieces (including lamb). Coquimbo (Chili), in 1879, 45 tons
(including goat). Bagdag, in 1878, 86,351 pieces, 4071_l._, to India
and Europe (including lamb). Falkland Islands, 1940_l._ worth in 1879.
Cape, 1,480,875 pieces in 1879. Hankow, 7606 pieces, 9276_l._, in 1879.
Tientsin, 206,777 _piculs_ (of 133-1/3 lb.) in 1878, 8737 in 1879.
Mollendo (Peru) 79 _quintals_ (of 2 cwt,) in 1878. Mogador, in 1880,
15 bales, 80_l._, to Great Britain; 345, 1700_l._, to France; 2, 3_l._,
to Spain. Our imports from the French East Indies have fallen from 5600
pieces in 1876, to 3762 in 1877, 410 in 1879, and none since; from
Italy, from 339,973 in 1876, to 39,751 in 1880; from European Turkey,
from 230,922 in 1876, to 63,236 in 1880; from Asiatic Turkey, they have
risen from 93,965 in 1876, to 185,543 in 1880; from Brazil, 41,604 in
1876, 2623 in 1877, 5730 in 1880, and none in the intermediate years;
from the Argentine Republic, 3,539,589 in 1876, 898,155 in 1879,
1,248,553 in 1880; from the Cape, 1,496,039 in 1877, 1,819,772 in
1880; from India, 3,927,934 in 1876, 2,911,974 in 1880; from Victoria,
1,667,330 in 1876, 1,158,686 in 1880; from New South Wales, 83,167
in 1878, 36,995 in 1880; New Zealand, 168,984 in 1878, 334,792 in
1880. The approximate London market values of sheep-skins are:--Cape,
10-34_s._ a doz.; fine wool, 28-59_s._; superior, 40-82_s._; Mogador,
14-27_s._; Buenos Ayres, 4-13_d._ a lb.; Australian, 4-16_d._; tanned
East Indian, best, 2-4_s._; ordinary to good, 1_s._-2_s._ 9_d._

_Walrus._--Our imports of walrus skins from Christiania in 1879 were
valued at 7900 _kroner_ (of 13-1/2_d_).

_Unenumerated._--Our imports of unenumerated skins and hides in 1883
were as follows:--

Dressed skins, not leather.--From Russia 410, 645_l._; Germany 5249,
559_l._; Holland 5917, 795_l._; Belgium 16,524, 2658_l._; France
41,069, 2680_l._; British India 2005, 218_l._; Australasia 2925,
795_l._; British North America 300, 313_l._; United States of America
502, 225_l._; Other Countries 94, 40_l._ Total 74,995, 8928_l._

Undressed skins:--From Denmark 15,950, 2418_l._; Germany 10,815,
3391_l._; Holland 7700, 765_l._; Belgium 10,400, 800_l._; France
3162, 309_l._; British Possessions in South Africa 4699, 422_l._;
British India 21,846, 3260_l._; China 86, 410_l._; Australasia 65,305,
3274_l._; British North America 1698, 255_l._; United States of America
3575, 1295_l._; Brazil 12,853, 1097_l._; Other Countries 7457, 559_l._
Total 165,546, 18,255_l._

Wet hides.--From Sweden 1945 cwt., 6133_l._; Norway 1561 cwt.,
4197_l._; Denmark 4757 cwt., 10,873_l._; Germany 33,617 cwt.,
86,210_l._; Holland 19,006 cwt., 47,859_l._; Belgium 74,288 cwt.,
210,698_l._; Channel Islands 2478 cwt., 4724_l._; France 64,212 cwt.,
178,941_l._; Portugal 18,031 cwt., 52,328_l._; Gibraltar 888 cwt.,
2616_l._; Italy 13,411 cwt., 37,431_l._; Austrian Territories 940 cwt.,
2260_l._; British Possessions in South Africa 23,881 cwt., 66,779_l._;
Japan 806 cwt., 2300_l._; Australasia 93,891 cwt., 209,158_l._; United
States of America 11,590 cwt., 31,610_l._; Bermudas 923 cwt., 2257_l._;
British West India Islands 3329 cwt., 8105_l._; Brazil 64,406 cwt.,
191,051_l._; Uruguay 99,391 cwt., 308,940_l._; Argentine Republic
25,142 cwt., 73,518_l._; Falkland Islands 1434 cwt., 4100_l._; Whale
Fisheries: Northern 782 cwt., 4985_l._; Other Countries 2024 cwt.,
4660_l._ Total 562,733 cwt., 1,551,733_l._

Dry raw hides and pieces.--From Russia 10,829 cwt., 79,940_l._; Sweden
193 cwt., 1233_l._; Denmark 1641 cwt., 10,677_l._; Germany 13,022
cwt., 62,248_l._; Holland 10,874 cwt., 37,716_l._; Belgium 3791 cwt.,
15,355_l._; France 3393 cwt., 12,262_l._; Gibraltar 225 cwt., 1000_l._;
Italy 451 cwt., 1366_l._; Austrian Territories 555 cwt., 2813_l._;
Turkey 925 cwt., 3327_l._; Egypt 468 cwt., 1493_l._; West Coast of
Africa, not particularly designated 673 cwt., 1398_l._; British
Possessions in South Africa 39,501 cwt., 160,716_l._; East Coast of
Africa (Native States) 2990 cwt., 8808_l._; Madagascar 2850 cwt.,
8773_l._; Mauritius 2669 cwt., 8433_l._; Aden 6745 cwt., 22,282_l._;
British India: Bombay 33,548 cwt., 105,081_l._; Madras 3860 cwt.,
13,248_l._; Bengal and Burmah 370,369 cwt., 1,329,822_l._; Straits
Settlements 51,456 cwt., 130,244_l._; Ceylon 2314 cwt., 6468_l._;
Java 3288 cwt., 10,670_l._; Cochin China, Camboja, and Tonquin 2236
cwt., 5153_l._; China 18,892 cwt., 63,192_l._; Australasia 7009 cwt.,
15,506_l._; United States of America 17,842 cwt., 56,536_l._; British
West India Islands 953 cwt., 3713_l._; United States of Colombia 1053
cwt., 4955_l._; Peru 1120 cwt., 3577_l._; Chile 1118 cwt., 4089_l._;
Brazil 9125 cwt., 31,089_l._; Uruguay 2937 cwt., 9924_l._; Argentine
Republic 3556 cwt., 12,426_l._; Other Countries 1645 cwt., 5596_l._
Total 634,116 cwt., 2,251,129_l._.

Undressed leather.--From Germany 89,073 lb., 5563_l._; Holland 86,048
lb., 6239_l._; Belgium 25,650 lb., 1943_l._; France 62,799 lb.,
4655_l._; Spain 42,773 lb., 3555_l._; Aden 21,280 lb., 1853_l._;
British India: Bombay 3,663,452 lb., 274,625_l._; Madras 17,859,652
lb., 1,375,484_l._; Bengal and Burmah 1,821,925 lb., 124,193_l._;
Straits Settlements 3,957,651 lb., 147,962_l._; China 37,923 lb.,
2068_l._; Australasia: West Australia 12,750 lb., 487_l._; South
Australia 238,249 lb., 11,283_l._; Victoria 7,175,550 lb., 357,032_l._;
New South Wales 2,428,147 lb., 120,675_l._; Queensland 11,980 lb.,
621_l._; Tasmania 40,863 lb., 1986_l._; New Zealand 1,573,289 lb.,
74,776_l._; British North America 155,500 lb., 7405_l._; United States
of America 17,329,692 lb., 778,392_l._; Other Countries 186,333 lb.,
11,121_l._ Total 56,820,579 lb., 3,311,918_l._

Dressed leather.--From Russia 1669 lb., 252_l._; Germany 1,397,928 lb.,
369,719_l._; Holland 1,809,262 lb., 293,196_l._; Belgium 260,657lb.,
41,146_l._; France 5,187,323 lb., 725,485_l._; Turkey 6226 lb.,
339_l._; British Possessions in South Africa 700 lb., 250_l._; British
India 156,802 lb., 15,720_l._; Australasia 2812 lb., 423_l._; British
North America 779,321 lb., 57,326_l._; United States of America
7,858,956 lb., 533,419_l._; Other Countries 5183 lb., 543_l._ Total
17,466,839 lb., 2,037,818_l._

Varnished, japanned, or enamelled leather.--From Russia 44,088
lb., 9725_l._; Germany 18,236 lb., 3895_l._; Holland 209,707 lb.,
56,667_l._; Belgium 648 lb., 200_l._; France 67,724 lb., 25,598_l._;
Turkey 190 lb., 50_l._; British North America 6868 lb., 1151_l._;
United States of America 83,387 lb., 19,377_l._ Total, 430,848 lb.,
116,663_l._

Boots and Shoes.--From Germany 3766 dzn. pairs, 10,413_l._; Holland
23,321 dzn. pairs, 85,585_l._; Belgium 38,203 dzn. pairs, 81,253_l._;
Channel Islands 464 dzn. pairs, 2327_l._; France 53,437 dzn. pairs,
233,038_l._; Turkey 350 dzn. pairs, 149_l._; Australasia: New South
Wales 29 dzn. pairs, 100_l._; British North America 3080 dzn. pairs,
6706_l._; United States of America 331 dzn. pairs, 1400_l._; Other
Countries 77 dzn. pairs, 243_l._ Total, 123,058 dzn. pairs, 421,214_l._

Gloves.--From Sweden 350 dzn. pairs, 237_l._; Norway 50 dzn. pairs,
58_l._; Denmark 19,320 dzn. pairs, 16,093_l._; Germany 3090 dzn. pairs,
2693_l._; Holland 309,416 dzn. pairs, 321,080_l._; Belgium 197,444
dzn. pairs, 222,946_l._; Channel Islands 10 dzn. pairs, 16_l._; France
1,138,343 dzn. pairs, 1,375,988_l._; Italy 232 dzn. pairs, 280_l._;
Australasia: Victoria 43 dzn. pairs, 96_l._ Total, 1,668,298 dzn.
pairs, 1,939,487_l._

Unenumerated leather manufactures.--From Sweden 108_l._; Norway
109_l._; Denmark 236_l._; Germany 22,705_l._; Holland 119,462_l._;
Belgium 35,762_l._; France 48,308_l._; British Possessions in South
Africa 198_l._; British North America 931_l._; United States of America
19,388_l._; Other Countries 571_l._ Total, 247,778_l._

Our imports of hides from the undermentioned countries have fluctuated
as shown:--

Abyssinia.--Undressed, 7289 cwt. in 1876, 327 in 1878, 2159 in 1879,
and 324 in 1880.

Aden.--Undressed, 8190 cwt. in 1876, 113 in 1879, 8294 in 1880.

Algiers.--Raw, 2,051,701 _kilo._ (of 2·2 lb.) in 1879.

Argentine Republic.--Undressed, 94,479 cwt. in 1877, 32,961 in 1879,
34,905 in 1880.

Austro-Hungary.--Vienna, 24,672 metrical _centners_ in 1878, 48,950 in
1879; Fiume, raw, 1400 _kilo._ in 1879.

Bahamas.--167_l._ worth in 1879.

Barbados.--363_l._ worth in 1877, 913_l._ in 1878.

Belgium.--Undressed, 51,069 cwt. in 1877, 82,021 in 1878, 68,123 in
1880. Dressed, 176,635 lb. in 1878, 418,906 in 1880.

Brazil.--Undressed, 137,351 cwt. in 1878, 115,137 in 1880. Pernambuco
in 1878-9 exported, dried, 31,717 _kilo._ to Great Britain, 28,077
France, 25,606 Portugal, total value, 3002_l._; salted, 383,691 _kilo._
Great Britain, 937,976 United States, 585,868 France, 40,770 Spain,
463,269 Portugal, total value 75,523_l._; in 1880, 61 tons, 2267_l._
Maceio exported in 1877, 4728 pieces (average 28 lb. each) to Great
Britain, 1440 New York and Lisbon; in 1879, 36,775; in 1880, 11,405.
Bahia exported 1,432,864 _kilo._ in 1877-8, and 1,773,965 in 1878-9,
principally to the United States and Germany. Santos exported 397,000
_kilo._ in 1879. Ceara exported in 1878, 372,808 _kilo._ to England,
31,966 Havre, 775,863 Hamburg, 7800 New York.

British India.--Undressed, 281,198 cwt. in 1876, 463,764 in 1880;
dressed, 14,835,979 lb. in 1878, 6,178,370 in 1880.

Bulgaria.--Rustchuk, in 1879, exported 254,196 _kilo._ (250 tons) to
Austria.

Canada.--Dressed, 939,759 lb. in 1876, 372,359 in 1879, 1,066,043 in
1880.

Cape.--Undressed, 15,370 cwt. in 1876, 44,503 in 1878, 29,442 in 1880.

Central America.--Undressed, 72 cwt. in 1876, 1113 in 1878, 356 in 1880.

Chili.--Undressed, 318 cwt. in 1876, 17,042 in 1879, 1566 in 1880;
dressed, 33,026 lb. in 1876, 3929 in 1877, 199,965 in 1878, 224 in
1879, 2930 in 1880.

China.--Undressed, 5671 cwt. in 1876, 60,871 in 1878, 2705 in 1880.
Hankow exported in 1879, 7797 pieces, 1656_l._; Kiungchow, 490 _piculs_
(of 133-1/3 lb.), 818_l._; Newchwang, 17,665 pieces; Tientsin, 4354
_piculs_; Canton, in 1878, 653 pieces of skins, 873-3/4 _piculs_ of
hides.

Costa Rica.--San José exported 308,794 lb. in 1879.

Denmark.--Undressed, 20,806 cwt. in 1877, 5632 in 1880; Copenhagen
exported 1,166,172 lb. to Great Britain in 1878.

Ecuador.--Undressed, 680 cwt. in 1876, 18 in 1877, 115 in 1879, 89 in
1880. Guayaquil exported in 1878, 5711 _quintals_ raw, 17,133_l._,
to the United States, and 12,504 halves tanned, 8752_l._, to South
America; and in 1880, 8859 _quintals_ raw, 22,148_l._, and 4861 tanned,
2916_l._ Manabi, in 1878, exported 1321 _quintals_, 3963_l._

Egypt.--Undressed, 1250 cwt. in 1877, 718 in 1878, 1286 in 1880. In
1879, the values were 620_l._ to Austria, 380_l._ France, 1950_l._
Great Britain, 45,500_l._ Greece, 280_l._ Italy, 62,500_l._ Turkey.

Falklands.--Undressed, 4315 cwt. in 1878, 2679 in 1880. The value of
the exports was 5020_l._ in 1879.

France.--Undressed, 26,866 cwt. in 1876, 57,305 in 1880; dressed,
2,727,190 lb. in 1876, 4,338,485 in 1880. Calais in 1878 sent 2188
_kilo._ prepared to Great Britain, and 76,811 _kilo._ in 1879.

French East Indies.--Dressed, 24,600 lb. in 1876, 12,713 in 1877, none
since.

Gambia.--Exported 15,380 pieces in 1878.

Germany.--Undressed, 45,002 cwt. in 1876, 21,143 in 1878, 44,383 in
1880; dressed, 1,269,143 lb. in 1876, 954,578 in 1878, 1,318,659 in
1880. Hamburg sent to Great Britain, 33,458 cwt. dry and salted in
1877, 13,972 in 1879. Königsberg exported 1535 cwt. raw in 1878, 424 in
1879.

Greece.--Dressed: Syra in 1877 sent 60,217_l._ worth to Turkey,
23,259_l._ to the Danubian Principalities, 2748_l._ to Austria; in
1879, 492_l._ Turkey, 251_l._ Austria, 200_l._ Russia.

Guatemala.--Exports in 1877, 62,343 _dol._ worth; in 1878, 844-1/2
_quintals_ to England, 1293 France, 2476 Germany, 822 New York, 149
California; 1879, 412,605 Germany, 12,360 New York.

Hawaiian Islands.--Exports 1880, 24,885 pieces.

Holland.--Undressed, 55,705 cwt. in 1876, 53,568 in 1880; dressed,
941,372 lb. in 1876, 896,734 in 1880.

Java.--Exports 1878-9, 357,353 pieces and 1240 _piculs_ to Holland,
7212 pieces to the Channel for orders, 1200 pieces to France, 7369
pieces to Italy, 5695 pieces and 872 _piculs_ to Singapore.

Madagascar.--Undressed, 252 cwt. in 1877, 3088 in 1879, none since.

Mauritius.--Undressed, 5341 cwt. in 1876, 2945 in 1880.

Morocco.--Undressed, 0 in 1877, 5445 cwt. in 1878, 1014 in 1880.
Tangiers exported in 1879, 2727 cwt., 6000_l._, to Great Britain; 1818
cwt., 4365_l._, France; 21 cwt., 42_l._, Spain. Mogador, in 1880,
sent 44 bales, 150_l._, to Great Britain; 667, 2250_l._, France; 243,
770_l._, Portugal.

Natal.--Undressed, 32,555 cwt. in 1876, 17,496 in 1878, 23,908 in 1880.

New Granada.--Undressed, 12,217 cwt. in 1878, 574 in 1879, 6059 in
1880.

New South Wales.--Undressed, 9386 cwt. in 1878, 79,972 in 1880;
dressed, 2,257,041 lb. in 1877, 1,694,015 in 1880.

New Zealand.--Undressed, 39 cwt. in 1878, 6335 in 1880; dressed,
140,448 lb. in 1878, 446,102 in 1880.

Persia.--Bushire exported in 1879, 4000 _rupees'_ worth to England,
5000 _r._ India; Lingah, 2800 _r._ India, 1950 _r._ Persian coast;
Bahrein, 6000 _r._ Koweit, Bussora, and Bagdad.

Peru.--Undressed, 2859 cwt. in 1876, 622 in 1878, 1235 in 1880.
Mollendo exported 538 _quintals_ in 1878, and 1307 _q._ dry in 1879.

Philippines.--Undressed, 1024 cwt. in 1876, 102 in 1880. Manilla, in
1879, exported 7976 _piculs_, 12,761_l._, to China and Japan.

Portugal.--Undressed, 17,456 cwt. in 1877, 10,983 in 1880.

Queensland.--Undressed, 1315 cwt. in 1879, 5019 in 1880.

Roumania.--Galatz exported 341 bales in 1879.

Russia.--Undressed, 482 cwt. in 1876, 6020 in 1880; dressed, 88,225 lb.
in 1876, 46,694 in 1880. Riga shipped 14,839 _poods_ (of 36 lb.) in
1877, 11,311 in 1879. Poti, in 1877-8, sent away 5654 _poods_, and 2149
from Persia.

Saigon.--Exports in 1879, 10,582 _piculs_.

San Domingo.--Exports in 1878, 630 pieces to Great Britain, 490 France,
3100 Italy, 3980 Spain, 460 United States, 560 West Indies; in 1880,
1340 Italy, 2541 Spain, 7142 United States, 97 West Indies.

South Australia.--Dressed, 38,108 lb. in 1878, 303,143 in 1880.

Spanish West Indies.--Puerto Rico exported in 1878, 167 _quintals_
United States, 5673 Spain, 637 Germany.

Straits Settlements.--Undressed, 28,444 cwt. in 1876, 48,213 in 1880;
dressed, 603,389 lb. in 1876, 2,778,159 in 1880.

Surinam.--Exports in 1878, 9221 _kilo._

Sweden and Norway.--Christiania exported 95,200 _kroner_ worth in 1875,
4200 _kr._ in 1878. Gothenburg exported 10,960 cwt. in 1879.

Tasmania.--Dressed, 65,803 lb. in 1878, 38,141 in 1880.

Tripoli.--Bengazi, in 1878, sent 50,000 pieces, 4000_l._, to Malta.
The value of the exports was 2000_l._ in 1879, and 4500_l._ in 1880.

Turkey.--Aleppo exported in 1878, 181 tons, 10,824_l._, to France;
5, 320_l._, Italy; 11, 704_l._, Austria; 52, 3328_l._, Turkey; 12,
768_l._, Egypt. Thessaly exported 15,000_l._ worth in 1880. Samos
sent 19,300_l._ worth tanned to Turkey and Egypt in 1879. Van
exported 1500_l._ worth in 1879. Kerasund shipped by steamer in 1879,
557 bales, 3899_l._ Trebizond in 1879 sent 940 bales (of 12 and 60
pieces), 6580_l._, to Turkey; 1567, 10,969_l._, France; 501, 3507_l._,
Russia; 80, 560_l._, Greece. Dedeagatch, in 1879, exported 1300 bales,
40,000_l._ Alexandretta, in 1879, sent 280 tons, 16,800_l._, to France;
3, 180_l._, Austria; 10, 600_l._, Russia; 96, 6720_l._, Turkey; 29,
2030_l._, Egypt. Adana, in 1879, sent 250 tons, 7500_l._, to France;
140, 4200_l._, Turkey; 27, 810_l._, Greece. Jaffa exported 18,000
_okes_ (49,500 lb.), 666_l._, for Turkey in 1879.

United States.--Undressed, 115,767 cwt. in 1876, 7888 in 1879; 14,358
in 1880; dressed, 16,716,711 lb. in 1879, 22,543,033 in 1880. Savannah
exported 8758 bundles in 1880. Galveston exported in 1879-80, 9878
bales and 7510 single, dry; and 6905 bundles wet-salted. Texas State in
1878-9 exported 28,104,065 lb., 562,081_l._

Uruguay.--Undressed, 116,738 cwt. in 1876, 65,846 in 1879, 104,691 in
1880.

Venezuela.--Puerto Cabello exported in 1879, 10,126 _kilo._ to Great
Britain, 8817 Germany, 75,794 United States, 5756 France, 696 Holland,
1023 Spain. Ciudad Bolivar sent 35,562 pieces, 762,234 lb., to New York
in 1879.

Victoria.--Undressed, 0 in 1878, 2710 in 1879, 8705 in 1880; dressed,
3,506,562 lb. in 1876, 5,096,696 in 1880. The values of the exports in
1878 were 9417_l._ hides, and 19,706_l._ skins and pelts.

_Tanning Materials._--Our imports of bark in 1883 were:--From Sweden
6410 cwt., 1281_l._; Norway 8858 cwt., 1687_l._; Holland 12,855 cwt.,
3246_l._; Belgium 59,936 cwt., 15,987_l._; France 3323 cwt., 2138_l._;
Algeria 46,052 cwt., 19,577_l._; British East Indies 4605 cwt.,
3321_l._; Australasia 183,777 cwt., 119,292_l._; United States of
America 36,203 cwt., 12,368_l._; Other Countries 3087 cwt., 1852_l._
Total, 365,106 cwt., 180,749_l._

Our imports of cutch and gambier in 1883 were:--From British India:
Bombay 277 tons, 7682_l._; Bengal and Burmah 8115 tons, 221,651_l._;
Straits Settlements 17,477 tons, 453,804_l._; Philippine Islands 47
tons, 1227_l._; United States of America 877 tons, 25,149_l._; Other
Countries 44 tons, 1208_l._ Total, 26,837 tons, 710,721_l._

Our imports of myrobalans in 1883 were:--From Germany 1133 cwt.,
503_l._; British India:--Bombay 349,275 cwt., 184,983_l._; Madras
120,262 cwt., 54,997_l._; Bengal 23,579 cwt., 9663_l._; Straits
Settlements 214 cwt., 107_l._; Ceylon 1105 cwt., 483_l._; Japan 306
cwt., 146_l._ Total, 495,874 cwt., 250,882_l._

Our imports of extracts in 1883 were:--From Denmark 2773_l._; Germany
36,638_l._; Holland 54,600_l._; Belgium 7353_l._; France 261,690_l._;
Spain 1000_l._; Italy 4571_l._; British North America 33,311_l._,
United States of America 66,114_l._; Mexico 3937_l._; Other Countries
1625_l._ Total, 473,612_l._

Our imports of galls in 1883 were:--From Austrian Territories 474 cwt.,
1022_l._; Turkey 9056 cwt., 23,388_l._; Egypt 2435 cwt., 6210_l._;
Persia 269 cwt., 770_l._; British India 1572 cwt., 1062_l._; China
22,625 cwt., 66,731_l._; Japan 2936 cwt., 9276_l._; Other Countries 185
cwt., 486_l._ Total, 39,552 cwt., 108,945_l._

Our imports of valonia in 1883 were:--From Holland 100 tons, 1600_l._;
France 59 tons, 947_l._; Austrian Territories 178 tons, 2732_l._;
Greece 3101 tons, 46,526_l._; Turkey 27,030 tons, 432,423_l._ Total,
30,468 tons, 484,228_l._

Our imports of sumach in 1883 were:--From France 688 tons, 8979_l._;
Spain 54 tons, 616_l._; Italy 12,395 tons, 184,152_l._; Austrian
Territories 1707 tons, 21,121_l._; Other Countries 32 tons, 430_l._
Total, 14,876 tons, 215,298_l._


Literature.

The chief works relating to the tanning, currying, and dressing of
leather, and the tanning materials employed, are as follows:--

  Abridgments of Specifications: Skin, Hides, and Leather, 1627-1866.
                                                             London: 1872.

  Bernardin (R. J.).
    Classification de 350 Matières Tannantes.                  Gand: 1880.

  Brüggemann (A.).
    Weissgerberei.                                            Quedlinburg.

  Brüggemann (A.).
    Saffian Fabrikation.                                      Quedlinburg.

  Brüggemann (A.).
    Glacéleder Färberei.                                      Quedlinburg.

  Councler (Dr. C.).
    Bericht über die Verhandlungen der Commission zur Feststellung
      einer einheitlichen Methode der Gerbstoffbestimmung.   Cassel: 1885.

  Das Ganze der Lederbereitung.                               Quedlinburg.

  Davis (C. T.).
    Manufacture of Leather.                            Philadelphia: 1885.

  Dussauce (F.).
    Tanning, Currying, and Leather-dressing.           Philadelphia: 1865.

  Eitner (W.).
    Leder-Industrie: Bericht über die Welt-Ausstellung in
      Philadelphia, 1876.                                    Vienna: 1877.

  Hansen (A.).
    Die Quebracho Rinde.                                     Berlin: 1880.

  Höhnel (F. R. von).
    Die Gerberinden.                                         Berlin: 1880.

  Knapp (Fr.).
    Natur und Wesen der Gerberei und des Leders.            München: 1858.

  Lange (J. C.).
    Lederbereitung.                                           Quedlinburg.

  Lietzmann (J. C. H.).
    Herstellung des Leder in ihren Chemischen und Physikalischen
      Vorgängen.                                             Berlin: 1875.

  McMurtrie (W.).
    Culture of Sumac, and preparation for market: Department of
      Agriculture Special Report, No. 26.                Washington: 1880.

  Morfit (C.).
    The Arts of Tanning, Currying, and Leather-dressing.
                                                       Philadelphia: 1852.

  Neubrand (J. G.).
    Die Gerbrinde.                               Frankfurt-on-Maine: 1869.

  Olivet (P.).
    Lederfärberei.                                            Quedlinburg.

  Schultz (J. S.)
    Leather Manufacture: a Dissertation on the Methods and
      Economics of Tanning.                                New York: 1876.

  Sonnenfeldt (Dr.).
    Färben der Pelzwaaren.                                    Quedlinburg.

  Villain (H.).
    Cuirs et Peaux: Tannage, Corroyage, et Mégisserie.        Paris: 1867.

  Vincent (C.).
    Fabrication et Commerce des Cuirs et Peaux.               Paris: 1872.

  Wattle Bark: Report of the Board of Inquiry.            Melbourne: 1878.

  Wiener (F.).
    Die Lohgerberei, oder die Fabrikation des Lohgaren
      Leders                                                Leipzig: 1879.

  Wiesner (J.).
    Die Rohstoffe des Pflanzenreiches.                      Leipzig: 1873.

  Wittmack (L.).
    Die Nutzpflanzen aller Zonen.                            Berlin: 1879.

  Leather Trades Circular and Review.                              London.

  Tanners' and Curriers' Journal.                                  London.

  Scottish Leather Trader.                                        Glasgow.

  Shoe and Leather Reporter.                                     New York.

  La Halle aux Cuirs.                                               Paris.

  Der Gerber.                                                      Vienna.

  Gerber Zeitung.                                                  Berlin.

  Deutsche Gerber Zeitung.                                         Berlin.

  Gerber Courier.                                                  Vienna.

  Gazetta dei Pellami.                                              Milan.




INDEX.


  Abies bark, 53
  ---- tannin, 31
  Acacia barks, 34-8
  ---- fruits, 53
  ---- tannin, 23-5
  Acetic acid, examining, 102
  Achromatic condenser, 9
  Acid, digallic, 76-8
  ----, dioxysalicylic, 69-71
  ----, ellagic, 71
  ----, ellagitannic, 78
  ----, gallic, 69-71
  ----, gallotannic, 76-8
  ----, quercitannic, 78
  ---- solutions, preparing standard, 95-7
  Acids, decomposition of tannins by, 68-73
  ----, examination of, 101
  ----, free, in tan-liquor, determining, 108-11
  Acorn cups, 50-3
  ---- galls, 27
  Adipose tissue, 8
  Adjustment for thickness of cover-glasses, 11
  African kino, 34
  Air, capacity for moisture, 249
  Albumen, 20
  Alder bark, 54
  Aleppische Gallen, 26-8
  Aleppo galls, 26-8
  Algarobilla, 23
  Algarrobo, 23
  Alkaline solutions, preparing standard, 95-7
  Allen and Warren sprinkler leck, 241
  Alligator skins, 255
  Alnus tannin, 54
  Alum in tanning, 218-22
  Amboyna kino, 33
  American press leck, 241
  ---- rocker, 169
  ---- union splitter, 188
  Ampelopsis hæderacea, 67
  Analysing tannins, 118-31
  ----, methods for the tannery, 90-131
  Analysis, indicators, 91
  ----, instruments, 91-5
  ----, standard solutions, 90
  Anatomical structure of hide, 2-16
  Aphis punctures, 28
  Areca-nut cutch, 25
  Armadillo skins, 255
  Artificial light for microscope, 12
  Ash of leather, estimating, 107
  Aspidosperma wood, 39
  Ass skins, 255
  Australian kino, 34

  Babul tannin, 53
  Bahera, 38
  Balance, 93
  Balsamocarpon pods, 23
  Bark, commerce, 270
  ---- elevators, 162
  ---- mills, 158-61
  Barkometer, 169
  Bates for dressing leather, 184-6
  Beaming dressing leather, 187
  ---- hides, 151
  Bengal kino, 33
  Bibliography, 272-4
  Blood vessels, 8
  Bloom, source of, 62
  Bloomers for butts, 176
  Blue-back seal-skins, 206
  Boots and shoes, commerce, 265
  Botany Bay kino, 34
  Breaking the nerve, 8
  Bristol finishing, 183
  Buffalo method of unhairing, 144
  ---- skins, 255
  Bulls'-eye condenser, 12
  Burettes, 92
  Burning-in strap butts, 201
  Butea kino, 33
  Butts, cleansing lime from, 155
  ---- defined, 155
  ----, striking, 179

  Cachou, 23-5
  ---- jaune, 29-31
  Cæsalpinia pods, 25, 54
  Calf kid, 223
  ---- skins, 256
  Camata valonia, 52
  Camatina valonia, 52
  Cascalote tannin, 54
  Castanea extract, 23
  Catechin, 79-81
  Catechol, 67
  Catechu, 23-5
  Catechutannic acid, 81
  Cellular structure of hide, examining, 12
  Chagrin, 258
  Chamada valonia, 52
  Chamois leather, 210-2
  Charcala valonia, 52
  Chemical composition of hide, 17-22
  Chemistry of tannins, 57-82
  Chestnut extract, 23
  ---- ---- for sole leather, 158
  Chinese galls, 28
  Chlorine in water, estimating, 98
  Chromic and osmic acids for hardening and staining hide sections, 14
  Churco bark, 55
  Cleaning drains in tannery, 240
  Climax scourer, 200
  Commerce, 255-71
  Commercial tanning materials, 23-56
  Composition, chemical, of hide, 17-22
  Comptonia tannin, 54
  Condense-water trap, 251
  Connective tissue, 7
  ---- ----, nature of, 18
  Constitution of tannins, 76-82
  Construction of tanneries, 231-42
  Conveyors for bark, 162
  Coriaria tannin, 54
  Coriin, 19
  ---- in lime-liquors, determining, 104
  Corium, 2, 7
  Cork-tree bark, 38
  Cover-glasses, 11
  ----, screwing objective down on, 11
  Cow skins, 261
  Crown leather, 213-7
  Crust roans, 206
  Curried leather, measuring, 202
  Currying, 193-202
  ---- crown leather, 217
  ---- defined, 1
  Cutch, 23-5
  ----, commerce, 271
  Cutting hide-sections, 12-5
  Cynips punctures, 26

  Decomposition of phlobaphenes by fusion with caustic alkali, 73-5
  ---- ---- tannins by acids, 68-73
  ---- ---- ---- by heat, 65
  ---- ---- ----, products of, 65-8
  Deer skins, 256
  Dégras, 211
  Depilatories, various, 150
  Derma, 2
  Dhak kino, 33
  Diffuseur for exhausting tan, 167
  Digallic acid, 76-8
  Dioxysalicylic acid, 69-71
  Diplolepis punctures, 26
  Disintegrators, 158-61
  Dissolving extracts, 168
  Dividing hides, 155
  Divi-divi, 25
  ---- ---- for sole leather, 157
  Dog skins, 256
  Drainage of tanyard, 231
  Drains from latches and pits, 240
  Dressed leather, commerce, 265
  ---- skins, commerce, 263
  Dressing leather, 184-92
  Dry raw hides, commerce, 264
  Drying, principles, 248-54
  ---- -sheds, 243-54
  ---- sole leather, 183
  Dugong skins, 256
  Dyeing calf kid, 224
  ---- chamois leather, 212
  ---- glove kid, 229

  East Indian kino, 33
  ---- ---- kips, 191
  Écorces de Chêne, 38
  Eichenrinden, 38
  Einbrennen, 201
  Elæocarpus tannin, 54
  Elastic fibres, 8
  ---- ----, nature of, 21
  Elevators for bark, 162
  Ellagic acid, 63, 71
  Ellagitannic acid, 78
  Enamelled leather, 203-5
  ---- ----, commerce, 265
  Ephreda tannin, 54
  Epidermis of hide, 2
  Epithelial layer of hide, 2
  Erectores pili muscles, 2, 7
  Espinillo tannin, 54
  Estimating ash of leather, 107
  ---- chlorine in water, 98
  ---- grease in leather, 105
  ---- hardness of water, 97
  ---- sulphur in sodium sulphide, 104
  Eucalyptus kino, 34
  ---- tannin, 54
  Eugenia tannin, 54
  Examination of acids, 101
  ---- of lime and lime-liquors, 102-4
  ---- of water, 97-100
  Examining cellular structure of hide, 12
  Exhausting tanning materials, 161-8
  ---- tannins, 117
  Extracts, commerce, 271
  ----, dissolving, 168
  ----, preparing, 32

  Fat glands, 6
  Fish skins, 256-8
  Fitzhenry scouring machine, 196
  Flasks, 91
  Fleshing hides, 152-5
  Focus of microscope, 10
  French morocco, 206
  Frizing by hard water, 85
  Fuchsia tannin, 54
  Furnaces for burning tan, 164

  Galläpfel, 26-8
  Galle d'Alep, 26-8
  Gallic acid, 69-71
  Gallotannic acid, 76-8
  Galls, 25-9
  ----, commerce, 271
  Galuchat, 258
  Gambia kino, 34
  Gambier, 29-31
  ----, commerce, 271
  Gambir, 29-31
  Gammuzza sumach, 46
  Gelatin in lime liquors, determining, 104
  ----, nature of, 17
  Gerbersumach, 40-50
  Glands of skin, 2, 6
  Glove kid, 225-30
  Gloves, commerce, 266
  Goat skins, 258-60
  Grain of tanned leather, 6, 8
  Graining dressing leather, 189
  Grease in leather, estimating, 105
  Grinding tanning materials, 158-61

  Hair cuticle, 4
  ----, growth, 2
  Handler liquors, table of determinations, 111
  Handlers, 169, 173
  Handling hides, 169
  Har, 38
  Hardening hide for cutting, 14
  Hardness of water, 84-6
  ---- ---- ----, estimating, 97
  Harra, 38
  Hartnack's objectives and eye-pieces, 10
  Head required to pass air in pipes, 253
  Heat, decomposition of tannins by, 65-8
  Heating effect of pipes, 250
  ---- leaches, 242
  ---- liquors, 242
  Hemlock, 31
  ---- extract for sole leather, 158
  Henle's layer, 5
  Hide albumen, 20
  ----, anatomical structure, 2-16
  ----, chemical composition, 17-22
  ----, examining cellular structure, 12
  ----, hardening, for cutting, 14
  ----, holding, for cutting, 13
  ----, influence of water in plumping, 85
  ----, microscopic examination, 9-16
  ----, section, 2
  ----, sections, cutting, 12-15
  ---- ----, mounting, 14
  ---- ----, rendering transparent, 13
  ---- ----, simultaneous hardening and staining, 14
  ---- ----, staining, 14
  ---- substance in leather, determining, 108
  Hides, beaming, 151
  ----, dividing, 155
  ----, fleshing, 152-5
  ---- for sole leather, preparing, 132-8
  ----, handling, 169
  ----, imports, 266-70
  ----, liming, 139-45
  ----, preparing for tanning, 133-8
  ----, rounding, 155
  ----, soaking, 133-6
  ----, softening, 138
  ----, stocking, 136
  ----, sweating, 145-7
  ----, unhairing, 139-56
  ----, ---- by sulphides, 147-50
  High-power objectives, 11
  Hiusache tannin, 53
  Holding hide for cutting, 13
  Holmes' tool carriage, 196
  Horny layer of hide, 2
  ---- tissues, nature of, 21
  Horse skins, 260
  Hot air pipes, 252
  ---- water pipes, 252
  Howard scrubber, 176
  Huxley's layer, 5
  Hyaline, 6
  Hydrochloric acid, examining, 101
  Hydrometer, 169
  Hygrometer table, 249
  Hymenæa pods, 23

  Illuminating apparatus, 10
  ---- microscope, 12
  Immersion lenses, 9
  Indicators for analysis, 91
  Infusions for Löwenthal's analytical method, 130
  Inga tannin, 55
  Instruments for analysis, 91-5
  Iodina wood, 40
  Iron in tanyards, 241

  Jackson scouring machine, 196
  Japanese galls, 28
  Japanned leather, 203-5
  ---- ----, commerce, 265
  Jiggers, 207
  Juchtenleder, 208

  Kamai bark, 56
  Kangaroo skins, 260
  Kát, 23-5
  Keratin, 21
  Kid skins, 258-60
  Kifushi galls, 28
  Kino, 32-4
  Kinoin, 81
  Kiri-hinau tannin, 54
  Kiri-toa-toa bark, 55
  Knoppern galls, 27
  Kut, 23-5

  Lamb skins, 260
  Lancashire finish, 183
  Latches, construction, 241
  ---- for exhausting tan, 164-8
  Laurus tannin, 55
  Layers for butts, 176
  Leaches, heating, 242
  Leather, chemical examination of, 105-8
  ----, determining hide substance, 108
  ----, estimating ash of, 107
  ----, estimating grease in, 105
  ----, estimating matters soluble in water, 106
  ---- manufacture defined, 1
  Lecks for exhausting tan, 164-8
  Levantische Gallen, 26-8
  Levelling glove kid, 226
  Libi-dibi, 25
  Lime, examination of, 102
  ---- for unhairing, 139-45
  ---- -liquors, determining gelatin and coriin in, 104
  ---- ----, examination of, 102
  Liquors, heating, 242
  Literature, 272-4
  Llama skins, 261
  Lockwood automatic scourer, 197
  London finish, 183
  Löwenthal's modified process for analysing tannins, 127-31
  Loxopterygium wood, 39
  Lymph vessels, 8

  Machærium wood, 40
  Maintenance of tanneries, 231-42
  Malphigia tannin, 55
  Manatee skins, 256
  Mangrove bark, 55
  Manquitta bark, 55
  Measuring curried leather, 202
  Methods of analysis for the tannery, 0-131
  Microscope, artificial light for, 12
  ----, choice of, 9
  ----, illuminating, 12
  ----, price of, 10
  Microscopic examination of hide, 9-16
  Mills for grinding bark, 158-61
  ---- ---- ---- sumach leaves, 49
  Mimosa bark, 34-8
  ---- ---- for sole leather, 158
  ---- tannin, 23-5
  Mineral tanning, 218-22
  Miscellaneous tannins, 53-6
  Mise au vent, 194
  Moëllon, 211
  Molinier's hide-working machine, 187
  Morocco leather, 206
  Mounting hide-sections, 14
  Myrobalans, 38
  ----, commerce, 271
  ---- for sole leather, 157

  Naucite tannin, 55
  Nauclea extract, 29-31
  Nerve, breaking the, 8
  Nitrogen bulb, 103
  Noix de galle, 26-8
  Nut-galls, 26-8

  Oak-bark for sole leather, 157
  ---- ---- tannin, 78
  ---- -barks, 38
  ---- -galls, 26-8
  ---- -wood extract for sole leather, 158
  Objective, screwing down on cover, 11
  Objectives, 8
  Oiling in currying, 195
  Osmic acid solution, preserving, 15
  ---- and chromic acids for hardening and staining hide-sections, 14
  Ox skins, 261
  Oxalic acid, examining, 102
  Oxalis tannin, 55
  Oxyphenic acid, 67

  Palas kino, 33
  Pale catechu, 29-31
  Panniculus adiposus, 15
  Pars papillaris, 2
  ---- reticularis, 2
  Patent leather, 203-5
  Pay-pay pods, 55
  Permanganate process for analysing tannins, 128-31
  Persea bark, 55
  Phlobaphenes, 72
  ----, decomposition by fusion with caustic alkali, 73-5
  Phloroglucin, 74
  Phloroglucol, 74
  Phyllocladus bark, 55
  Pipes, heating effect of, 250
  Pipettes, 92
  Pits, construction, 238-40
  Plan of tannery, 232-6
  Plumping hide, influence of water on, 85
  Pokako tannin, 54
  Polygonum leaves, 55
  Pomegranate tannin, 55
  Preller's leather, 213-7
  Preparation of tannins, 58
  Preparing hides for sole leather, 132-8
  Preparing hides for tanning, 133-8
  ---- standard solutions, 95-7
  Preserving osmic acid solution, 15
  Price of microscope, 10
  Priestman's striking machine, 180
  Prosopis pods, 23
  Protocatechuic acid, 75
  Pterocarpus kinos, 33, 34
  Pumps for tannery, 241
  Punica tannin, 55
  Pures for dressing leather, 184-6
  Purification of tannins, 58
  Putz's patent filling, 22
  Pyrocatechin, 67
  Pyrocatechol, 67
  Pyrogallic acid, 66
  Pyrogallol, 66

  Quebrachia wood, 40
  Quebrachitannic acid, 82
  Quebracho, 39
  ---- catechin, 81
  Quercitannic acid, 78
  Quercus acorn cups, 50-3
  ---- barks, 38

  Reagents for analysing tannins, 120-3
  Rete malpighi, 2
  Retenage, 194
  Rhabdisto valonia, 52
  Rhizophora bark, 55
  Rhus galls, 28
  ---- leaves, 40-50
  Roble Colorado bark, 56
  Rocker, 169
  Rounding hides, 155
  Rove galls, 28
  Russia leather, 208

  Salt in water, effect of, 86
  Salts for tanning, 218-22
  Sampling tannins, 116
  Sangue del drago, 34
  Schmack, 40-50
  Screwing objective down on cover, 11
  Seal skins, 261
  Sebaceous glands, 6
  Section of hide, 2
  Sections of hide, cutting, 12-15
  Shafting in tannery, 236
  Shagreen, 258
  Shaving dressing leather, 187
  Sheep skins, 262
  Shumac, 40-50
  Site for tannery, 231
  Skins, trade in, 255-70
  Soaking hides, 133-6
  Sod oil, 211
  Sodium sulphide, estimating sulphur in, 104
  Softening hides, 138
  Sole-leather, 132-83
  ---- ----, preparing hides, 132-8
  ---- ----, tanning materials, 157-68
  ---- ----, treatment in the shed, 179-83
  ---- ----, treatment in the tan-house, 169-78
  ---- ----, unhairing hides, 139-56
  Soluble matters in leather, estimating, 106
  Splitting dressing leather, 188
  Staining hide-sections, 14
  Standard solutions, 90
  ---- ----, preparing, 95-7
  ---- ----, table of, 97
  Statistics, 255-71
  Steam pipes, 250
  ---- power in tannery, 236
  ---- trap, 251
  Stieleiche bark, 38
  Stocking hides, 136
  Stretching dressing leather, 191
  Striking butts, 179
  Structure, anatomical, of hide, 2-16
  Stuffing strap-butts, 200
  Sudoriferous glands, 6
  Sulphides for unhairing, 147-50
  Sulphur, estimating, in sodium sulphide, 104
  Sulphuric acid, examining, 101
  Sumach, 40-50
  ----, commerce, 271
  ---- extract, 50
  ---- mill, 49
  ---- plantations, 40-8
  Suspender liquors, 172
  ---- pits, 169
  Sweat glands, 6
  Sweating hides, 145-7
  Sweet-fern tannin, 54

  Table, analyses of spring and river waters, 89
  ----, capacity of air for moisture, 249
  ----, head for passing air, 253
  ----, heating effect of pipes, 250
  ----, hygrometric, 249
  ----, reactions of tannins, 112
  ----, standard solutions, 97
  Tan burning furnaces, 164
  ---- liquor, determining free acids in, 108-11
  Tanneries, construction, 231-42
  ----, maintenance, 231-42
  Tanning defined, 1
  ---- materials, commerce, 270
  ---- ----, commercial, 23-56
  ---- ----, exhausting, 161-8
  ---- ---- for sole leather, 157-68
  ---- ----, grinding, 158-61
  Tannins, action on gelatin, 57
  ----, analysing, 118-31
  ----, bloom from, 62
  ----, characters, 57-8
  ----, chemistry of, 57-82
  ----, classification, 64
  ----, constitution, 76-82
  ----, decomposition by acids, 68-73
  ----, ---- by heat, 65
  ----, exhausting, 117
  ----, general chemistry, 59-64
  ----, ---- methods of examination, 65-75
  ----, preparation, 58
  ----, products of decomposition by heat, 65-8
  ----, purification, 58
  ----, qualitative detection, 111-4
  ----, quantitative determination, 114-31
  ----, reagents for analysing, 120-3
  ----, sampling, 116
  ----, table of reactions, 112
  Taps for exhausting tan, 164-8
  Tawed leather, 223
  Tawhero towai bark, 56
  Tawing defined, 1
  Tecoma bark, 56
  Terminalia fruits, 38
  Terra japonica, 23-5, 29-31
  Tiffany's bate, 185
  Tipuana wood, 40
  Trade in skins, 255-70
  Transparent hide-sections, 13
  Traubeneiche bark, 38
  Turkey galls, 26-8
  Turret driers, 245
  Tutu tannin, 54

  Uncaria extract, 29-31
  Undressed leather, commerce, 265
  ---- skins, commerce, 263
  Unhairing hides, 139-56
  ---- ---- by lime, 139-45
  ---- ---- by sulphides, 147-50
  ---- ---- by sweating, 145-7

  Valonia, 50-3
  ----, commerce, 271
  ---- for sole leather, 157
  Varnished leather, commerce, 265
  Vélanèdes, 50-3
  Ventilation of drying-sheds, 246
  Virginia creeper, 67

  Wagatea pods, 56
  Walrus skins, 263
  Wash leather, 210-2
  Water as used in tanning, 83-9
  ----, counteracting chlorides in, 87
  ----, detecting various impurities in, 99
  ----, dissolved mineral matters in, 84
  ----, effect of salt in, 86
  ----, estimating chlorine in, 98
  ----, ---- hardness of, 97
  ----, examination of, 97-100
  ----, filtering, 83
  ----, hardness of, 85
  ----, influence on plumping, 85
  ----, permanent hardness of, 84
  ----, suspended matters in, 83
  ----, table of spring and river, 89
  Wattle-bark, 34-8
  ---- ---- plantations, 36-7
  Weinmannia bark, 56
  Wet hides, commerce, 263
  Whawhako tannin, 54
  Whitening in currying, 195
  Wilson's spring butt-roller, 181
  ---- striking machine, 181
  Wu-pei-tze galls, 29


                                LONDON:

             PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,
                  STAMFORD STREET AND  CHARING CROSS.




       *       *       *       *       *


Transcriber Note


Illustrations were moved to avoid splitting paragraphs. Hyphenization
was standardized to the most commonly used form. Several minor typos
were corrected. This file was produced from images generously made
available by The Internet Archive.






End of Project Gutenberg's A Text-book of Tanning, by Henry R. Procter