THE GLUE BOOK




[Illustration: MODERN GLUE-TESTING LABORATORY]

(Courtesy of A. T. Deinzer, Monroe, Mich.)




  THE GLUE
  BOOK

  HOW TO SELECT
  PREPARE AND
  USE GLUE

  A SHORT, PRACTICAL
  DISCUSSION OF MATTERS
  IMPORTANT TO EVERY
  GLUE USER

J. A. TAGGART, TOLEDO, O.




COPYRIGHT 1913, J. A. TAGGART




AUTHOR’S NOTE


The purpose of this manual is to provide a practical guide for glue
users, to help in eliminating waste and improving the quality of
product.

That there is an enormous waste due to improper preparation and use of
glue is well known to all who are in touch with the subject.

Some authorities estimate that 70% of the glue used in the United
States is improperly handled. The actual waste is said to be in excess
of 25% of the amount of glue used; to say nothing of the loss due to
imperfect condition of the completed work.

The writer knows from actual experience that many glue users are
ignorant of the proper methods to be employed; and that many others are
careless, or indifferent.

The handling of glue is a subject on which much new light has been shed
in recent years. There is no longer any reason why the glue user should
not know the correct methods to follow.

This treatise is intended as a handbook for the glue user who is
interested in increasing the efficiency of his operations.

Technical expressions have been avoided, the whole matter being set
forth as much as possible in the everyday terms in familiar use in the
glue-room.

So far as the author can learn, from an extended investigation, no book
has been published on this subject exactly answering the needs of the
average glue user. Several excellent works are available which would be
interesting to a man technically trained in the subject; but although
they embody many helpful suggestions, they are not in such form as to
be of the greatest value to the practical man. No pretense is made for
the present manual of disclosing new facts; but rather of assembling
in handy and easy reference form a summary of the best modern practice
which the glue user of today may rely upon as a safe and convenient
guide.




TABLE OF CONTENTS


CHAPTER I

IMPORTANCE OF THE INDUSTRY

  Glue industry founded in America by Peter Cooper--increase 
  in capital invested--increase in production--variety of 
  uses--increase in requirements                                 Page 15


CHAPTER II

THE MANUFACTURE OF GLUE

  Sources from which glue is made--boiling the 
  stock--drying--preparation in commercial form                  Page 17


CHAPTER III

TESTING AND GRADING GLUE

  Grades established by Peter Cooper--the tests--viscosity or 
  fluidity test--the jelly test--apparatus for making jelly 
  test--the finger test--a simple, practical test for glue 
  users--sampling--bubbles--surface indications--color 
  indications--alkaline or acid quality--breaking 
  quality--foam--grease--keeping properties--odor--laboratory 
  test                                                           Page 25


CHAPTER IV

CORRECT METHODS IN THE GLUE-ROOM

  Much waste through faulty methods--importance of correct 
  practice--soak glue in cold water before melting--test glue 
  by water absorption--appliance for water absorption 
  test--melting or dissolving glue--do not heat higher than 
  150° F.--apply heat indirectly--live steam ruins glue--use 
  thermometer--heat glue slowly--cleaning the melting 
  pot--importance of using copper, brass or aluminum 
  utensils--guard against evaporation--melt only the amount
  required--importance of cleanliness--keeping the glue-room 
  warm--use by weight--storing--applying glue--securing 
  workers’ co-operation                                          Page 43


CHAPTER V

MODERN GLUE-ROOM EQUIPMENT

  Modern appliances now available for all users--only copper, 
  brass or aluminum should come in contact with glue--the 
  scientific glue-heater--the automatic temperature 
  controller--keep steam away from glue--glue 
  spreaders--clamps and presses--distributing glue in large 
  plants                                                         Page 65


CHAPTER VI

WHICH GLUE TO USE

  Accurate records important--the best glue for wood 
  joints--veneers--sizing--paper boxes--belting and other 
  leather goods--bookbinding--emery purposes--how much to 
  pay--waterproof glue--vegetable glue--quick-setting 
  glue--flexible glue                                            Page 79




THE GLUE BOOK




CHAPTER I

IMPORTANCE OF THE INDUSTRY


Glue is now so extensively used, and for so many different purposes,
that it certainly deserves much more intelligent treatment at the hands
of users than it has received heretofore.

Since 1837, in which year Peter Cooper, who may justly be regarded as
the founder of the glue-making industry in the United States, produced
the first American-made glue, the yearly output has steadily increased.

By 1880, the amount of capital invested in the making of glue had
reached $4,000,000. In 1905, it was $10,000,000, and is now between
$12,000,000 and $13,000,000.

The annual production has increased in about the same ratio. In 1880,
it was $4,000,000; at present it is about $15,000,000.

Glue is an important by-product of the great packing houses. Those
in touch with the industry know how extensively glue enters into the
manufacture of articles of everyday use. The general public hardly
realizes that glue is used not only in making wood-joints and veneers,
but in the production of paper, of silks, hats, carpets, rugs, and
hundreds of other necessities.

America now produces glue of excellent quality to meet practically all
requirements. So great are the requirements that almost the entire
amount of the American-made glue is absorbed by the home demand.




CHAPTER II

THE MANUFACTURE OF GLUE


An understanding of the sources from which glue is derived and of the
processes of manufacture will be found of practical importance to the
glue user. It will give many valuable side-lights on the proper methods
of preparation and handling.

Glue is an organic substance of adhesive properties obtained from the
hides, skins, bones and sinews of cattle, sheep, deer, horses, and
other animals. Tails, snouts, ears, and the pith of the horn are also
used. Some glue is produced from the heads, bones and sinews of fish.

The tendons and intestines of many animals, the swimming bladder of
many varieties of fish; rabbit skins, or “coney,” from which the fur
has been removed; old waste leather, such as gloves, butchers’ offal,
or “country bone;” “junk” bones, and much other apparently worthless
matter, all contribute to the raw material of the glue-maker. In its
broadest sense glue may be understood to include gelatine, but the use
of the word is here confined to the substance known commercially as
glue, and which in contrast with gelatine has greater adhesiveness,
stiffness, and elasticity, and is also darker in color and more nearly
opaque.

Neither gelatine nor glue exists already formed in nature; they are
both the products of the action of heat and water on nitrogenous animal
tissue. It is not definitely known just how this change takes place.
Some writers regard glue as impure gelatine; others believe that there
is a difference in nature between gelatine and glue. This question is
without present importance for our purpose.


BOILING THE STOCK

Glue is produced by boiling the animal substances mentioned above, and
drying the resulting liquor.

The following may be noted in connection with the use of skins. The
outer covering, in which the wool, fur or hair is rooted, is of no
importance to the glue-maker. The portion that produces the glue lies
next to it, being composed of fibres which run in every direction and
contain the fluid matter which aids in keeping the skin moist and
pliable. The fat cells are directly beneath the glue-yielding portion,
and as fat is undesirable, because it makes the glue greasy, the shreds
of fat are saponified by being subjected to a lime bath. The lime bath
is also useful in removing any hair still adhering; and is used also in
preparing tissue, to remove bloody and fleshy particles.

This part of the process may consume from one to three days.

It may be noted in passing that the older the animal, the more solid
the glue will be. On this account many manufacturers sort the skins
before using.

Being animal stock, the raw material of glue is subject to
decomposition, and the scraps of hide are therefore carefully
preserved, especially during the summer season.

The tanneries supply most of the hide stock, but only waste pieces
reach the glue manufacturer, as leather is more valuable than glue, and
the larger portion is therefore reserved for the tanner’s use. Various
names are used to describe the parts of hide that the tanner discards
for the glue-maker’s use--the heavy trimmings are “pieces;” the hide
pared off the hair or grain side, “skivings;” the parts scraped from
the flesh side are “fleshings.”

At the packing houses the heads, feet, ribs, and other bony structures
go direct to the glue-room. If bone is sweet and fresh it is known as
“green,” or “packer” bone. The waste of button and knife factories is
also used.

Bones are usually ground, and they are treated with a sulphuric acid
bath to attack and separate the lime and gelatine of which the bone is
composed. Bones, after being treated in this way, become pliable and
soft, and the sulphuric acid is then removed by centrifugal force.

The acid must all be removed, as the glue will granulate if any remains.

Other parts of the stock are always carefully washed before boiling.

After the stock has been prepared, it is placed in a boiler with false
bottom provided with an opening through which the liquid may be run
off. The boiling of the stock is an operation that must be carefully
conducted, as the application of a greater degree of heat, or for a
longer time than is necessary, damages the glue.

The boiler is heated by direct firing. As the boiling proceeds, test
quantities of the liquid are run off for examination, and when a sample
is found on cooling to form a stiff jelly, it is ready to draw off.
The first boiling usually occupies about eight hours. When the liquid
has been run off from this boiling, more water is added and the boiling
is continued. This operation is repeated until the stock has yielded
all of its gelatinous matter. As many as six or eight boilings may be
made.

The liquid first run off--the “first boiling”--is always best, as the
effect of repeated or prolonged application of heat is to weaken the
glue tissue. The later boilings are also as a rule darker in color than
the earlier ones.


DRYING

The glue-solution from the boiling process is run into wooden troughs
or “coolers,” about 6 feet long, 2 feet broad, and a foot deep, in
which the solution sets in a firm jelly.

When set, a little water is run over the surface, the jelly is detached
from the cooler, cut into uniform slices of the thickness desired, and
placed on galvanized or linen nets to dry.

Drying may be done in the open air if weather conditions are favorable,
or in a drying-room. The latter method is preferable. Conditions can be
regulated to insure uniform drying.

Piles of the nets, or “stacks,” are loaded on trucks and taken into the
drying-room, where they are exposed to the effect of warm air currents
induced by blower or pressure fans, or exhaust or suction fans.

The drying is a source of concern to the manufacturer. It is extremely
important to keep the temperature at just the right point, to protect
the glue from dust and dirt, and to avoid the possibility of bacterial
growth in the glue-jelly, which is very susceptible to the development
of harmful organisms.

The final form of the glue will be in sheets, strips or flakes, or
ground. For commercial purposes it is put up in packages, bags and
barrels.




CHAPTER III

TESTING AND GRADING GLUE


There is as yet no uniformity of opinion among glue manufacturers and
glue users as to how glue should be tested and graded. In a general way
the manufacturer knows what kind of glue a certain stock will produce;
but on account of variations that are sure to occur, it is necessary to
subject each glue to certain tests, according to standards more or less
definitely established.

The grades in general use are those originally employed by Peter
Cooper, and are as follows:

  A EXTRA
  No. 1
  1 x
  1¼, 1⅜, 1½, 1⅝, 1¾, 1⅞

The only way to determine which is the best glue to use, is by trying
out various grades in actual practice. The best glues for ordinary
uses are well understood (see pages 79 to 85 for suggestions on this
subject). Between two or more glues of any one type, actual experiment
is the only safe guide. Most glue men will give you good advice; but
above all, keep accurate records of results of the different grades
used. When you have found the right glue, keep to it.


THE TESTS

Glue is graded on physical characteristics rather than on chemical
composition. Various chemical tests have been proposed, but they are
unimportant so far as practical working value is concerned.

The most important physical tests are those for viscosity, and jelly
strength.


VISCOSITY OR FLUIDITY TEST

The test for viscosity, or fluidity, is based on the idea that
the greater the tenacity of the glue, the greater will be its
cohesiveness, and the less will be its flowing power. In other words,
the higher will be its viscosity.

In testing for viscosity, water is used as a standard. A solution is
made of the glue, and the rate of flow of the solution at a certain
temperature is compared with the rate of flow of water under the same
conditions.

Several devices are on the market under the name of “viscosimeter” for
measuring the viscosity of glue.

While they vary in detail they are in principle a pipette from which
the glue-solution flows at a given temperature. The time required for
the glue to run out of the pipette as compared with the time consumed
in the same operation by the same quantity of water gives the relative
viscosity of the glue.

The viscosity test is not entirely accurate in itself, but taken in
connection with the jelly test it forms a very satisfactory basis for
grading.


THE JELLY TEST

The jelly test is based on the comparative resistance power of the
various glue-jellies. Several mechanical devices for determining
jelly-strength have been perfected. One of these consists of a brass
vessel which rests upon the glue-jelly, and into which shot is poured;
the weight of the cup and the contained shot upon having penetrated to
a certain depth in the glue-jelly, gives a figure which expresses the
comparative strength of the jelly with the standard.


APPARATUS FOR MAKING JELLY TEST

[Illustration: Apparatus for Testing Jelly-Strength of Glue.]

Another apparatus that has been found accurate and practical is the
device illustrated on the next page. It consists of a pressure tube
(A), over the mouth of which is stretched a thin rubber diaphragm (B).
The tube connects to a rubber bulb (M) and to a pressure gauge, or
manometer (E) with a scale (F). The pressure tube is filled with water
to the point (C). The manometer tubes also contain water. A three-way 
stop-cock (D) connects the tubes either to the bulb (M), or to the air, 
depending on the position. Below the pressure tube is a brass table (G), 
on which is placed the glass containing the glue-jelly to be tested.

When the glass is in position, the table is raised by means of a
threaded wheel until the glue surface forces the water resting on
the flexible diaphragm up to the fixed mark L. Then the stop-cock is
turned to connect the pressure tube and gauge to the rubber bulb. By
pressing the bulb the water is forced down in the pressure tube and so
expands the diaphragm into the jelly, the liquid in the gauge rising
simultaneously. Pressure on the bulb is continued until the water
reaches the mark N.

Thereupon the stop-cock is again turned, the water is held at the point
N, and the pressure is indicated by the height of the liquid in the
gauge. The degree of pressure is the measure of the consistency of the
glue-jelly.

The initial contact between the jelly and the rubber diaphragm is
always the same, all jellies therefore having the same initial
pressure. When the diaphragm is forced down into the jelly, the
pressure required depends entirely upon the resistance that the jelly
offers. The slightest difference in the consistencies of the various
jellies will alter the pressure required, the differences being
accurately recorded by the gauge upon the scale.

Advantages of this apparatus are that the relative value of the jelly
compared with the standard is expressed in concrete figures; the method
of operation is simple; and the instrument is so sensitive that it
will record a change in reading between two samples of glue in which a
difference of 1/100th ounce of dry glue is used. Repeated tests may be
made on the same jelly, as the surface is not broken. With a little
practice a single glue may be tested in twenty seconds, or less.


THE FINGER TEST

One of the most satisfactory methods of determining jelly-strength--and
the one perhaps in most general use, is the finger test.

In this test the various glue-jellies are arranged before the tester,
who presses each with the tip of the finger, comparing it with the
standard as to resistance power. While this may seem to expose the
final decision too greatly to the personal equation, as represented
by the personality of the glue-tester, it is nevertheless true that
an expert develops the most extraordinary precision, arriving at
conclusions that are corroborated by the results of other tests
and by the results in actual practice. The work of the glue-tester
is analogous to that of the coffee-taster and the tea-taster, or
experts in other lines, who through a highly developed and keenly
discriminating sense of taste, or touch, or smell, determine with
extreme nicety the physical characteristics of the substances that they
are accustomed to test.


SOME SIMPLE, PRACTICAL TESTS FOR GLUE USERS

To perform the tests described requires a degree of experience and an
equipment beyond the reach of the ordinary buyer and user of glue.

Certain tests may however be made that are of great value in
determining important facts about the glue it is intended to buy and
use.

These tests could not be used as a basis for grading glue
scientifically, but they are exceedingly valuable in determining its
purity and its adaptability to the work in hand.


SAMPLING

In the first place you should carefully sample your glue with a view to
testing.

Take several samples from various parts of the barrel. Flake glue is
often made up of different varieties, and a single sample may not be
at all representative. Ground glue, from its very nature, is easily
adulterated. It should be examined in a good light, for evidence of
foreign substances. Examine flake glue carefully also for uniformity
of odor and general appearance. If glue has been adulterated while
in original form it is practically impossible to determine the
adulteration by external appearance. Subsequent adulteration may be
detected.


BUBBLES

If you should notice white bubbles, in the shape of round blots, on the
surface of the glue, you have found evidence of decay. If there is any
doubt in your mind you can complete the evidence by moistening the
glue. If it gives off a sour odor you have an additional indication of
putrefaction. Such glue should be avoided.

Bubbles may appear within the glue--not on the surface--without
being an indication of putrefaction. As a matter of fact, bubbles
are practically always found in certain high-grade glues, though
practically never in low-grade bone or hide glues. They are supposed
to be due to the air which gets in when the glue is poured into the
moulds. When glue is originally dried on nets in very cool and dry
weather, such bubbles are frequently found. Always beware of glue
showing surface bubbles.


SURFACE INDICATIONS

Besides being free from bubbles or blots a good glue is smooth, though
not necessarily glossy. Sometimes the very best glue will be of a dull
color, and many inferior glues even have a very shiny surface. The
surface should be uniform in color and in appearance.


COLOR INDICATIONS

These are not important, as a rule. The color of any particular lot of
glue should be nearly uniform; otherwise it is subject to the suspicion
of adulteration.

Bone glues are usually darker than hide glues, but some bone glues
go through an artificial clarifying process which gives them the
appearance of high-grade glues but really detracts from their strength.
Very frequently oxide of zinc is added to glue, the effect being to
make it set quickly, as well as to give it a light color. Some glues
contain so much oxide of zinc that they are milk-white. Zinc oxide is
not harmful except when added in very large quantities.


ALKALINE OR ACID QUALITY

The best glues are neutral as to acid and alkali. Glues with an excess
of acid should be avoided, especially when used with oak or chestnut
or other woods with strong acid qualities, as the acids in the glue
may unite with those in the wood in such way as to have a destructive
effect upon the glue. In such cases the glue will granulate after a
time and the work will pull apart.

When a wood is being used that is strong in acid it is advisable to
use a glue containing enough oxide of zinc to neutralize the acid in
the wood. In making sizing for paper a glue containing either acid or
alkali in excess should be avoided. It is also held by some authorities
that acid in glue tends to bring about decay.

To test for alkali or acid, dissolve a small quantity of glue in water
and dip a piece of litmus paper into the solution. Acid will turn the
paper violet or red. Alkali will turn it blue. Litmus paper may be
procured at any drug store.


BREAKING QUALITY

This is a simple test that affords an important indication of the
quality of glue. Take a small piece between the thumb and forefinger
of each hand and bend it. A very thin piece of good glue will bend
without breaking. When it does break, if the edges are splintery, great
tensile strength is indicated. A clean fracture, on the other hand,
indicates a brittle, low-grade glue, which has been subjected to heat
so long as to destroy the tissue; or else it has been made from bone
stock. High-grade glues never show glassy fractures, but bone glues do.
In making this test, the air conditions of the room should be taken
into account. If the glue has been kept in a dry room it will naturally
break much more readily than if it has been in a moist atmosphere. This
is especially important to bear in mind if comparative tests are being
made.


FOAM

A simple test for foam is to beat a solution of glue with an ordinary
eggbeater. Glue which shows foam, or in which foam does not quickly
subside, probably contains impurities. Foam is especially frequent in
alum-dried glues and in cheap bone glues.

Some authorities believe that foam is caused by overheating, due to
scalding by contact with steam jacket, or by steam coming into direct
contact with the glue, or by heating for too long a time, or it may be
due to the fact that all the grease has not been eradicated.

Glue that foams at ordinary temperature should be avoided for good work.


GREASE

A moderate amount of grease may be a good thing when using with clay or
with colors, but a large proportion of grease should be avoided when
making glazed or coated papers, or in general use.

A glue at ordinary temperature which is not overheated on which a scum
rises has an excessive amount of grease. It shows that the glue has not
been properly skimmed in manufacture.


KEEPING PROPERTIES

The keeping property of glue may be determined by letting the
glue-jelly stand for several days exposed to the air, and noting
any deterioration. It is customary to let the jelly stand at room
temperature--but if the glue is to be kept under any special conditions
the test should be made as nearly under these conditions as possible.


ODOR

Deterioration is always accompanied by a sour odor. Avoid using any
glue that does not smell clean and sweet.


LABORATORY TESTS

Up-to-date practice in all the larger concerns using glue demands a
laboratory for making tests. An expert is put in charge and the glue
analyzed chemically as well as for its physical properties. This method
cuts the guess-work down to a minimum. Manufacturers whose output would
not permit the employment of an expert all the year round can have glue
analyzed in laboratories maintained for such purposes. It means often a
great saving of money in the end to learn the exact properties of the
glue you propose to use, or that you may be actually using.

We may also repeat what we have already said about securing competent
advice from manufacturers. The glue user who takes a responsible
manufacturer or glue house into his confidence will secure valuable
counsel.

It is to the glue-maker’s and glue salesman’s interest to have you
secure good results. They have a large experience to draw on, and when
checked up by the results from actual practice in your glue-room their
advice in regard to the selection of glues is usually worth heeding.




CHAPTER IV

CORRECT METHODS IN GLUE-ROOM


It is quite certain that glue-room methods in many factories are years
behind the times. This is due to poor equipment, to ignorance and to
carelessness. Many factories could not continue in business if the
hit-and-miss methods of the glue-room prevailed in other departments.

It is possible to spoil the very best glue by improper methods of
preparation; and not only is a vast amount of glue rendered totally
unfit for satisfactory work, but a great deal is wasted; the total
loss, through faulty methods, being about 25% of the entire amount used.

There is no reason why there should be such loss in the glue-room. The
proper methods of procedure have been definitely established. Putting
them into effect not only saves glue, but it enables better work;
saves time of workmen, and increases greatly the general efficiency
of glue-room operations. The following rules are a guide to correct
practice.


ALWAYS SOAK GLUE IN COLD WATER BEFORE MELTING

The function of soaking is to get back into the glue the liquid it
originally contained.

Soaking in cold water gets the glue into proper condition to dissolve
readily when heat is applied. If glue is soaked in warm water, or
if melted without soaking, the glue on the outside will dissolve at
once, and this will coat the remainder with a film, so that it will
not readily dissolve, except when heat is applied in a degree that is
harmful.

Glue has an affinity for cold water. Good glue will absorb from 1½
times to 2½ times its weight of cold water.

If glue is in flakes or strips, break up into small pieces. Soak the
pieces from 10 to 12 hours in cold water. Soak ground glue 1 to 4 hours
in cold water. Naturally the thinner the glue the less time required
for thorough soaking. The glue should be soaked through thoroughly
and not merely moistened on the outside. You can determine whether
the soaking has been completed by breaking a piece in two and noting
conditions at the centre. If pieces are permitted to stick out beyond
the level of the water, the natural result is that such pieces will be
only partially softened. As the melting proceeds, these will slip to
the bottom of the kettle, and in order to melt them long heating and
high temperature are required. This means damaging the strength and
adhesiveness of the glue.

In soaking ground glue it is a good plan to keep stirring as the glue
is added to the water in the soaking vessel, as this helps to keep the
fine particles of glue immersed in the water, instead of floating on
the top. This is true also of thin-cut, high test glues.


USE ONLY PURE, COLD WATER

In soaking and thinning glue, use only pure, cold water. Unless heater
is provided with pure water attachment or pure water chamber, avoid
using water from the glue-heater. Do not use water from boilers, for
such water contains pipe-rust, acids from boiler compounds, sediment,
and other matter extremely harmful to glue. See to it that all soaking
vessels are scrupulously clean.


TESTING GLUE BY WATER ABSORPTION

The soaking of glue in cold water before using is employed in some
factories as a basis for comparative test of working quality. The
amount of water absorbed may vary as much as 10 ounces in half a pound.
Other things being equal, the glue that absorbs the most water is of
course the cheapest to use. As a comparative test, melt up say 10
pounds of glue and see how much work it will do compared with the glue
you are now using.


A SIMPLE GLUE-TESTER FOR DETERMINING WATER ABSORPTION

A simple and accurate apparatus may be had for determining the amount
of water the glue will absorb for best working results, and also
whether the amount of water actually used is the proper amount for this
particular glue.

It is important to know these facts, since the more water a glue will
absorb under proper working conditions, the cheaper that glue is to use.

The apparatus in question is illustrated on the next page. It consists
of a copper pot and a hydrometer arranged for a temperature of 75° C.,
or 167° F. A sample of the glue to be tested is poured into the pot
and the hydrometer is slowly allowed to sink into the solution until
it finds its correct position. If the glue-solution is, for instance,
1 part glue to 3 parts water, the hydrometer will drop to 25 on the
hydrometer scale. This will show that you have 25% dry glue in the
solution. The hydrometer is fitted with a temperature correction scale
that enables the readings to be adjusted to the temperature of the 
glue-solution.

[Illustration: Apparatus for Testing Glue in Solution]

By noting the working qualities of glue prepared with various
proportions of water, you can determine what is the correct amount
of water to use, and then by using the hydrometer as each batch is
prepared, you can be sure that the correct proportions are always being
used. By making readings from time to time with the hydrometer, you can
also determine the amount of evaporation that is going on, and in this
way guard against the glue becoming too thick for proper use.

No special skill is required to use the hydrometer, and the readings
are so quickly made, that tests can be made in every department in
which glue is used without loss of time.


MELTING, OR DISSOLVING, GLUE

After the glue has been soaked in the manner described, the most
important part of the process is undertaken--that is, the melting of
the glue by application of heat.

The words “most important” are used advisedly. It is safe to say that
most of the damage done to glue occurs in the melting process. There
are all kinds of ways of melting glue, but many of them absolutely
ruin glue for practical work. As this is a very important subject, it
is well to get the rudiments thoroughly in mind--and for this purpose
the reader should remember what has been said about the nature of
glue--that it is made from animal matter; and that it is composed of
innumerable small fibres on whose strength the holding power of the
glue depends.

Whatever injures and breaks down these fibres inevitably weakens the
glue; so that in melting, every care must be observed to avoid the
breaking down of the glue-fibres.

The most common destructive agent is heat. Just as the application of
heat breaks down the fibres of a roast of beef, rendering it “tender”
as the saying is, so the prolonged application of heat, or heat of
too great an intensity, will destroy the glue-fibres, and therefore
radically impair their value for actual use.

So, it is absolutely necessary to employ no more heat in melting glue
than is required to reduce the soaked mass to the proper working
consistency.


DO NOT HEAT GLUE HIGHER THAN 150° F.

By actual experience it has been determined that a temperature of 130°
to 150° F. is all that is required to melt the glue to the requisite
consistency; any greater heat is actually harmful, as it assists just
so much more in the process of disintegration.

The term “boiling,” or “cooking,” never should be applied to the
process of glue melting. These words imply a temperature of 212°
F.--and such a temperature is ruinous to glue. In producing glue from
the original stock--from the hides, bones, sinews, etc.,--boiling is
necessary, in order to extract the gelatinous matter--but as we have
already seen, the longer the stock is boiled, the weaker the product.
“First boilings” are always best. In preparing for use, however,
boiling is not necessary; therefore, never heat glue above 150° F.


APPLY HEAT INDIRECTLY

Heat never should be applied directly, as this results in burning, or
scalding, the glue.

Some glue-melting appliances have been constructed in which steam is
turned directly upon the glue mass. This is bad practice of the most
harmful kind.

Steam never should come into direct contact with glue. The temperature
of steam is always at least 212° F.--under pressure it is much
higher--and consequently it cooks the glue and destroys the fibres.
Live steam burns glue just as it burns your hand if turned directly
upon it.

The destructive effect of live steam upon glue may not be noticed at
once, but work on which overheated glue has been used will eventually
pull apart on account of the destruction of the glue-fibres.


LIVE STEAM RUINS GLUE

One of the largest glue manufacturers in the country makes the
following comment on this subject:

“In regard to the effect of live steam turned into a pot of glue,
whether flake, ground, or jelly--the glue would become overheated, and
you know that always has a disastrous effect. The temperature of live
steam is 212°, and under pressure it is even higher, so that at least
the glue around the pipe will attain a temperature of 212°. The effect
will be that the glue will be cooked to death and lose its strength. We
would certainly discourage the application of live steam for dissolving
glue as there is nothing to gain by it and everything to lose.”

Opinions of other manufacturers are unanimous on this point.

“We know of factories where they have made a careful test,” writes
one, “and the results obtained from glue where it was melted with a
live steam jet and where it was dissolved in a jacketed kettle were
so greatly in favor of the latter method that it is used universally
today.”

A further vital objection to the use of steam direct is that the steam
contains acids from boiler compounds, dirt, pipe-rust and sediment,
all of them injurious to the strength and to the elasticity of glue.

Then too, glue always takes up moisture from steam. This changes the
consistency of the glue. It leads to guess-work. The quantity of water
added to glue must always be exactly regulated. Turning live steam on
glue prevents proportions of glue and water remaining constant.


USE A THERMOMETER

The only safe procedure in melting glue is to use a thermometer. If
glue is melted in an open pot, or one in which the contents of the glue
chamber can be reached easily, an ordinary drop thermometer, encased in
a frame for protection, may be used.

It is preferable, however, to have the thermometer a part of the
apparatus, with the mercury tube extending into the glue chamber. In
this way it is easy to keep watch on the temperature of the glue mass
at all times.

An improvement even on this method is found in the automatic
temperature controller that may be had with some glue-melting
appliances, by which the supply of heat is automatically regulated.
When the temperature in the glue chamber passes 150° F.--the absolute
maximum of safe temperature--the valve automatically closes and shuts
off the heat, re-opening again when the temperature has lowered from
5° to 10°. By the use of the automatic temperature controller the
temperature is kept at the proper point, and there is no necessity
of making observations with the thermometer except to verify your
controller.

The temperature controller not only permits the scientifically correct
preparation of glue, preventing overheating and ruined work, but saves
also in expense of supervision.


HEAT GLUE SLOWLY

Glue should be heated slowly, requiring about 30 minutes. Rapid heating
dissolves the outer portions of the glue quickly, and a scum is then
formed over the rest of the glue, preventing its proper melting.

The following precautions will be found useful to put into practice.


CLEANING THE MELTING POT

Dirt enters the melting-pot through the glue itself, the introduction
of dirty brushes, or the exposure of the pot to dust, etc. If glue is
melted in a dirty pot, the skin forming on the surface of the glue
liquor gradually accumulates at the sides of the kettle and slowly
decomposes. This may or may not fall into subsequent melts, thus
contaminating them. The only way to make sure that it will not do so is
to clean the pot.

Much unnecessary waste of glue may be avoided through observance of
the following procedure. The contents of the melting-pot exhausted,
scraps of dried glue, as well as scraps of partially dried jelly
adhering to the sides should be detached mechanically, as thoroughly as
possible, and examined. If clean, they may be replaced in the bottom of
the kettle; if dirty, they are to be set aside temporarily.

In the first instance, they are covered with the minimum of water
necessary to soften, and the sides of the kettle swabbed with a little
water in order to soften any glue that has dried and has not been
detached mechanically. The pot is then gently heated in order to bring
the scraps into solution, this solution used in work, and the pot
thoroughly washed out with hot water and cooled before soaking a fresh
portion of glue.

If the scraps have proved dirty, but not sour, they may be kept warm
enough to permit the dirt to settle, when the glue may be used without
risk. If sour they must be thrown away. If the glue-pot is properly
cleaned there is no danger of souring and all the glue may be used
without waste.

It may be contended that much labor may be saved by adding sufficient
water for the next melt, and through this means soften all glue
adhering to the kettle in connection with that added fresh. It will be
found, however, that the freshly added glue will absorb the bulk if not
all of the water, leaving adhering scraps practically unsoftened, which
in this way continue to accumulate, interfering with the proper working
of the glue.

Pots, kettles, brushes, everything that comes into contact with glue,
should be regularly and rigidly inspected, and kept absolutely free
from dust and dirt. This is extremely important.


USE COPPER AND BRASS OR ALUMINUM UTENSILS

An important aid to cleanliness is the use of copper, aluminum or brass
for all parts of the apparatus with which glue comes into contact.
Not only are copper, aluminum and brass the cheapest materials to
use in the long run, due to their resisting acids in glue, water and
steam which quickly corrode iron, but copper, aluminum and brass are
practically self-cleaning.

Iron equipment is especially bad. It is most expensive in the end, for
iron is quickly eaten away by acids in glue and water. Iron rusts, and
the rust impairs the color and quality of the glue liquid. Do not use
iron vessels under any conditions.


GUARD AGAINST EVAPORATION

A great deal of waste in the use of glue is due to evaporation. If glue
is heated in open pots, evaporation is very great. Evaporation weakens
glue; makes it too thick for use, and also makes it very uneven in
quality. Glue should always be melted in a closed vessel.


DO NOT MELT TOO MUCH AT ONE TIME

As glue deteriorates quickly if allowed to stand, no more should be
prepared than is needed for a single day’s work. It is even better to
prepare it twice or oftener during the day.

If glue is dissolved at the proper temperature and kept at that same
temperature after melting, no noticeable deterioration results during
the course of the working day. But if allowed to stand over night its
value decreases, and it should not be mixed with fresh glue, as it is
not of the same consistency.

With practice and observation you can easily determine each day’s needs
in advance and prepare each morning just the right amount.


CLEANLINESS OF FIRST IMPORTANCE

Glue is extremely sensitive to impurities.

Cultures of germs are grown by bacteriologists in gelatine glue because
they afford an ideal breeding place for germs.

Glue quickly absorbs odors, and decays rapidly if exposed to impurities.

Decayed or decaying glue is not only extremely unpleasant to handle,
but it is worthless to work with. Keep your glue clean. Keep it away
from strong odors. Glue will keep sweet and clean before melting just
as long as you care to keep it so.


KEEP GLUE-ROOM WARM AND FREE FROM DRAFTS

Glue can not be expected to do good work if not kept at uniform
temperature. See that the glue-room is of a temperature that
facilitates uniform consistency of glue. Avoid possibility of drafts
and consequent chilling of the melted glue.

Do not let glue freeze. If glue-jelly is frozen through it will crumble
and act about like overheated glue. Glue frozen only around the edges
does not show pronounced deterioration. Do not take any chances. Keep
the glue-room temperature above freezing at all times.


USE BY WEIGHT

Glue is sold by the pound and should be used by the pound. Weigh not
only the glue, but weigh the water as well. Keep an accurate record of
weights.


STORING

Glue should be stored in a dry place. Barrels should not be unheaded
prematurely, and after having been opened should be kept covered when
not in use.


APPLYING GLUE

All surfaces to which glue is to be applied should be warm and dry.
Hot glue will chill if applied to a cold surface, and if wood is being
glued, moisture will have the effect of clogging the pores of the
wood. Heat dries and expands the pores, allowing the glue-fibres to
penetrate deeply, thus insuring perfect adhesion.

At the same time there is danger of getting wood too dry, making it
absorb too much glue, and too speedily. This causes a very quick
setting, and may result in “starving” the glue joint.

Some users on this account recommend adding a little moisture to the
surface of stock, by steaming or by application of a little warm
water. There is more or less uncertainty on this subject. As a general
conclusion it is safe to say that stock must always be warm; surplus
moisture must be expelled; no “green” stock must be used.

Here again, as in so many other problems of the glue-room, observation
of results under actual conditions should be the guide to practice.


SECURING WORKERS’ CO-OPERATION

One more thing of extreme importance--the employer should do
everything possible to secure the co-operation of every worker in the
glue-room, from the foreman down, in using proper methods. A little
personal interest here will be rewarded a thousand fold. Provide your
workmen with proper equipment, which in itself encourages cleanliness,
and show them how the quality of work may be improved.

Show them that an unclean, ill-smelling glue-pot is unnecessary. Show
them that there is a right way, and a wrong way, to prepare glue--and
the right way is the way to use. Introduce system into the glue-room,
as into every other part of the plant.

Many workers are still ignorant of modern glue methods. It is the duty
of the employer to know what the correct practice is, and to see that
it is employed in his glue-room.




CHAPTER V

MODERN GLUE-ROOM EQUIPMENT


With the increased knowledge of the nature of glue, and of proper
methods of handling, has come a great improvement in apparatus used.
The primitive way of melting glue was to heat it in an open pot over
a fire. No heed was given to the loss through evaporation; nor to the
scalding of glue; nor to the dirty condition of the glue-pot, and
consequently contamination of fresh glue by the remains of former melts
frequently occurred.

We say “primitive” methods advisedly in speaking of this old-time way
of melting glue; for in the light of modern knowledge such methods
belong to a day gone by. Yet some glue-rooms still use the old open
glue-pot, and many others use apparatus which shows little, if any,
improvement.

Modern glue-room appliances are now available for every glue-room, for
every purpose. No glue user, large or small, can afford to use any but
modern, scientific equipment. The saving in time, and in materials, and
in improved quality of the completed work, and in the greater respect
and increased efficiency of workers in the glue-room, all these things
result in quickly repaying the increased outlay required.


ONLY COPPER, BRASS, ALUMINUM SHOULD COME INTO CONTACT WITH GLUE

The advantage of using copper, brass, and aluminum in glue-room
appliances, due to their self-cleansing properties, already has been
mentioned.

In apparatus designed for melting glue the use of copper, brass, and
aluminum is absolutely required for economy and good results. Copper,
brass, and aluminum are the only materials available that are not
affected unfavorably by the action of acids in glue, steam and water;
by boiler compounds, dirt, pipe-rust and sediment.

An iron agitator or stirrer in a glue-heater is corroded so quickly by
the acids in glue, water and steam that in six months it is unfit for
use.

A brass agitator, on the other hand, will last practically forever. So
it is with every part of the glue-heater with which glue comes into
direct contact.

The glue user who has had experience with galvanized iron heaters
does not need to be told that the iron quickly is eaten away and the
apparatus rendered unfit for use. It is certainly the part of wisdom to
invest in copper, brass, and aluminum equipment, to which metals there
is practically no “wear-out.”

Glue-room equipment of iron is still sold, but only because there are
still some users who are so blinded by the initial small saving in
outlay, as not to see the saving that accrues in the end from using
indestructible materials--and the additional saving due to good work
and economy of glue.


A SCIENTIFIC GLUE-HEATER

The facts already mentioned about the melting of glue should be borne
in mind in choosing a glue melter, or glue-heater--always remembering
in particular that it is of utmost importance that the heating agent
should not come into direct contact with glue, and that the glue should
not be overheated in preparation.

The glue-heater that has been proved most economical and efficient in
wide-spread use has an air-tight glue chamber (to prevent evaporation),
surrounded by a water-jacket (to prevent burning or scalding glue),
the water in the jacket being heated either by direct injection of
steam or by the use of copper heating coils. Electricity is also used
successfully as a heating agent.

The heater is made of copper and brass throughout, and is therefore not
affected by the harmful effect of acids in glue, steam and water, dirt,
grease, pipe-rust, sediment and other harmful substances. In this
heater glue is reduced to a uniform and correct working consistency,
and with unusual speed, if desired; 5 gallons of glue may be melted in
less than 15 minutes, and as much as 50 gallons in less than one hour.

It has already been noticed that excessive speed in heating requires a
degree of heat that is injurious.

A thermometer is provided with this heater that gives accurate readings
of the temperature within the glue chamber, so that the heat may be
turned off when the danger point of 150° F. is reached.


THE AUTOMATIC TEMPERATURE CONTROLLER

A still more recent and valuable improvement is the automatic
temperature controller, a thermostatic valve which operates
automatically to keep the temperature in the glue chamber between 145°
F. and 150° F., or at any temperature for which it is set.

Not only overheating of the glue is prevented, but expense of
supervision is reduced. The heater does not need to be constantly
watched for fear glue will not be kept at correct temperature.

This particular heater is also provided with a brass agitator (hand
or power) for keeping glue thoroughly mixed while melting, and with a
special faucet by means of which the melted glue is drawn off without
dripping or clogging. It is made in sizes from 2 gallons to 500 gallons
liquid capacity, and for use with any heating agent--gas, electricity,
or steam.

An apparatus of this kind not only facilitates economical melting of
glue, by preventing evaporation, waste, formation of scum, sour and
dirty glue, but it also insures uniform “spread.” Furthermore, it is
a great incentive to accuracy and cleanliness on the part of workmen,
encouraging them to good work by providing them with a neat and clean
glue-melting appliance, in contrast with the old-fashioned, unsightly
and ill-smelling “glue-pot;” and providing them also with glue that has
been properly prepared.


KEEP STEAM AWAY FROM GLUE

Above all, keep steam away from glue. Some glue-melting devices are
on the market in which glue is prepared by subjecting to the direct
application of steam. This produces only bad results. All authorities
are now agreed on this subject. It is safe to say that the chief
development in glue-room methods of the past ten years hinges entirely
on the discovery of these facts: that steam ruins glue; that glue
never should be heated above 130° to 150° F. at the utmost; that the
other properties in steam--boiler compounds, acids, dirt, pipe-rust,
sediment, and grease--are absolutely injurious to glue.

Do not let the argument of speed blind you to the damage resulting
from the live steam type of dissolver. If you want speed, use a type
of instantaneous dissolver that prevents steam from coming directly
into contact with glue. The very best practice, the one generally
recommended by experts, is to heat glue slowly, with a heat not above
130° to 150° F. Then the glue is in the very best possible condition
for work.

The effect of acids is such that they have been known to turn a pot of
good glue black.


GLUE SPREADERS

In wood-working establishments where much glue is used, it should be
applied mechanically, by means of glue spreaders.

Some spreaders are made with Brussels carpet covering for rolls, but
this is not good practice. The carpet covering absorbs dirt quickly,
is difficult to keep clean, is liable to tear, is sure to stretch and
eventually rots and wears out.

The simplest, cleanest, and cheapest method in the long run is to have
rolls with corrugated surface; even spread is thus assured, and there
is practically no “wear-out” to them.

In order to keep glue at right temperature during use, it is best to
have the glue-pans surrounded by heating coils. These may easily be
connected with the steam boiler or gas heater; or electricity may be
used.

A further improvement is to have the spreader connected with the 
glue-heater, as then only a minimum quantity of glue need be carried in 
the pans. By this method a quantity of glue sufficient for a day’s work 
or half-day’s work may be melted in the morning and maintained steadily 
at uniform thickness and temperature until used. The melted glue is fed 
to the pans only as needed, through open copper troughs.

Glue pans should of course be made of copper, for the reasons already
mentioned. Another advantage is that copper pans are self-cleaning, as
glue does not adhere to this material.

Spreaders may be had as a single-roll machine, for coating one side of
stock, or as a double-roll, for coating both sides, or as a combination
single and double-roll. They may be operated by hand or with power.
When used with power a good operator can coat 13,500 lineal feet per
day, with a good machine. The results with a glue spreader are largely
due to the proper adjustment of the scrapers.

Glue spreaders can be used to coat flats, edges, straights and mitres
equally well.

For coating plain and straight surfaces, use a solid roll. For tongued
and grooved pieces, V-shaped stock, dovetails and other irregular
shapes, use a brush roll. Some spreaders are fitted with combination
solid and brush roll; a very convenient and economical arrangement.

The spreaders should be kept scrupulously clean, and also the brushes,
if any are used. Clean brushes by filling glue pan with hot water and
revolving the brush in it until all the glue has been removed.


CLAMPS AND PRESSES

After gluing, the work should be kept under pressure for a sufficient
length of time to insure perfect adhesion. In the case of hide glues
the time required is from three to four hours. The time varies with
variations in the glue, in condition of stock, and in temperature of
room. No general statement can be made to cover the case; experience is
the best guide. Either retaining clamps or presses are used.

Pressure should be distributed as evenly as possible. Presses may be
had in almost every style for every need--open on one side, or on two
sides; for veneered stock; sectional presses; etc. Very excellent
presses are being made of structural steel. They are practically
indestructible, very efficient, and yet simple in operation.

In selecting a veneer press equipment the amount of pressure per
square inch must first be determined. Opinion varies with different
manufacturers, some using 100 pounds, some 200 pounds, per square
inch. The best general results are obtained by using 150 pounds per
square inch. All presses made with a 2-inch screw should be designed to
withstand a pressure of 8 tons or 16,000 pounds per screw. To find the
tonnage of press that you require, multiply the length by the width of
stock, this by the pressure per inch you desire and divide the results
by 2,000. This will equal the tons pressure required. The number of
screws per press can then be determined.


DISTRIBUTING GLUE IN LARGE PLANTS

Glue is used in the wood-working industry mainly for making joints and
veneers.

In large establishments, where many workmen are employed, a good plan
for distributing the melted glue is to arrange a battery of small
glue-pots, or warmers, strung along a pipe line running from the steam
boiler or gas heater.

Individual pots of copper which are filled at the central source of
supply fit into cast-iron jackets, kept warm by steam which comes from
the pipe line. The requisite temperature is thus maintained at minimum
cost.

The valves may be so arranged as to cut off any warmer not in use,
avoiding waste of heat. The arrangement is very satisfactory even in
comparatively small establishments, and may be adapted to any number of
individual pots.


ADVANTAGES OF ELECTRICAL EQUIPMENT

When steam is used as the heating agent, only about one-fifth the
amount of heat generated is actually used for heating the glue.
Four-fifths of it radiates through the pipes and creates a heat so
intense that the efficiency of the workmen is reduced fully one-half
in summer. With gas as the heating agent, the same conditions are
present as with steam, plus the fire risk, which in itself is so great
as to make gas extremely inadvisable.

Electricity is coming into greater favor every year, with the
improvement of electrical glue-heating appliances. Electricity is still
too expensive to justify its use as a heating agent, except for the
exact purpose desired, but modern electrical devices, including the
jacketed, heat-retaining glue-pot, make it possible to use electricity
without waste.

The cost is less than either steam or gas and its advantages are so
great that thousands of institutions are now using these “fireless”
glue-heaters. The best electric glue-heaters are made of copper and
brass, the greatest conductors of heat. They require much less heat
than any other pot and the heat is required for just about one-fifth
the time, owing to the heat-retaining jacket.




CHAPTER VI

WHICH GLUE TO USE


The answer to this question depends so largely on the individual
conditions, that only very general suggestions may be given. We have
already suggested the need of experimenting and accurately recording
the results of using various kinds of glue. Once again, your dealer
will give you good advice nine times out of ten--and your own
experience should afford the most valuable check on his suggestions.

In general, the following glues are indicated:

Wood joints--High test hide glues. They make strong, firm joints, which
is extremely important, as joints are subject to more or less tension;
and they set rapidly.

Veneers--A moderately high test mixture of bone and sinew or bone
and hide. The higher test glues set too quickly for this particular
kind of work. If a spreading machine is used, avoid a glue that tends
to foam. Sometimes foaming is caused by its spreading too fast.
Overheating glue also tends to foam it. This can be overcome by the
addition of sweet oil or vaseline, paraffine or wax candle, but it is
objectionable when veneering. It is best to be sure you have a glue
that will not foam. Your dealer can tell you what glue to use.

Sizing--Use a glue free from grease and foam and one that flows freely.

Paper Boxes--A quick-setting hide glue is indicated for setting-up. For
covering, a lower test bone glue is preferred, as it does not set so
quickly. Paper box manufacturers are troubled more or less with foaming
glue and can use the remedy suggested in the paragraph on veneers, as
this will not be objectionable in paper box work.

Belting and Other Leather Goods--Here the principal requirements are
flexibility, resistance to moisture and tenacity. The higher test glues
are generally preferred.

Bookbinding--For pasting covers, a low-grade bone glue answers all
requirements sufficiently well. For rounding and backing, where strain
is exerted, a high-grade hide glue should be used.

For Emery Purposes--Very high-grade glue that has been carefully
prepared to eliminate all acids, alkalies and impurities. A good
emery glue possesses superior water-absorbing qualities. To test a
glue for emery purposes, soak an ounce in about five times its weight
of water at room temperature for 48 hours. If at the end of the time
the water shows discoloration, or if decomposition is evidenced by a
disagreeable odor, the glue is not adapted to emery use; otherwise it
may safely be used. Weigh glue after the operation, to get an idea of
its water-taking properties.


HOW MUCH TO PAY FOR GLUE

While the high test glues cost more per pound, they go farther and do
better work, except in cases when their quick-setting characteristics
are an objection.

How much you can afford to pay for your glue is a question that you
must answer from your own observation and tabulation of results. In
certain lines it would be foolish to use a high-grade glue, where the
work would not benefit in proportion to the increased expenditure. Any
attention given to the subject will be well repaid.


KEEP ACCURATE RECORDS

Always keep accurate records, and base your future purchases upon the
demonstrated comparative results already attained by the various glues
you have used in actual practice.

No glue is good to use unless properly prepared. A 16-cent glue may be
reduced to the grade of an 8-cent glue by overheating. The grade of
the glue at the time it is used is the important thing.

Do not by faulty methods of preparation impair the working quality of
your glue. A glue of moderate high-grade properly prepared is better
for practical purposes than a high-grade glue whose working quality has
been destroyed by excessive or prolonged heating.


WATERPROOF GLUE

Sometimes it is desired to use glue with waterproof qualities. Glue
is rendered practically waterproof by adding a small quantity (about
1%) of ammonium or potassium bichromate to the glue liquid. Upon
hardening, the glue then becomes waterproof. Adding a small quantity of
formaldehyde to the liquid glue will help it to resist the action of
water after it has dried for some time.

Others suggest dissolving glue in an equal quantity of water and adding
about as much linseed oil as water, with the aid of heat, until a
jelly is formed. This mixture is said to be practically waterproof.

A patented process has recently been put out for which the claim is
made that it can be applied to any glue irrespective of grade or make,
rendering it absolutely waterproof. The result is attained by mixing
the glue with certain chemicals in specified proportions, and then
adding a certain amount of formaldehyde. Any amount of glue can be
treated and the process is said to be most effective.


VEGETABLE GLUE

Of recent years efforts have been made to find a substitute for
animal glue. The effort has met with success to a certain extent for
particular kinds of work. Probably the newest addition to the list of
vegetable glues is the mineral glue-silicate of soda. Liquid silicates
were first sold for the manufacture of soap. In recent years certain
forms have been used for light adhesive paper work. It is used in
places where glue is too slow setting.


QUICK SETTING GLUES

When a glue is desired to set very quickly the manufacturer can usually
furnish glue with the setting qualities desired for the particular
work in hand. If this cannot be done, for any reason, remember that
the temperature of the glue is an important factor. A low temperature
aids in quick setting. Some paper box manufacturers have had successful
results in quick setting by adding a small quantity of turpentine to
the liquid glue. Some add silicate of soda.


FLEXIBLE GLUES

Specially made glues are supplied by manufacturers for work in which
flexibility is needed. An easy way to increase the flexible quality of
glue is to add a little glycerine to the liquid glue.




The Republican Publishing Co., Hamilton, Ohio




TRANSCRIBER’S NOTES

Inconsistent hyphenation has been standardized throughout.