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GAS BURNERS

OLD AND NEW.



GAS BURNERS

OLD AND NEW.

A Historical and Descriptive Treatise

ON THE

PROGRESS OF INVENTION IN GAS LIGHTING;

EMBRACING AN ACCOUNT

OF THE

THEORY OF LUMINOUS COMBUSTION.



BY

"OWEN MERRIMAN."


_Reprinted from the_ JOURNAL OF GAS LIGHTING.


London:
WALTER KING,
11, BOLT COURT, FLEET STREET, E. C.


1884.

W. KING AND SELL, PRINTERS,
12, GOUGH SQUARE, FLEET STREET,
LONDON.




Transcriber's Note: Figure 11 and Figure 12 are identical.



PREFACE.


The little work here presented to the public appeared originally in
the pages of the _Journal of Gas Lighting_. In the hope that it
may thereby become of service to a wider circle of readers, it has
been revised and done into its present shape. The object of the writer
will be attained if it is the means of lessening, in any degree, the
suspicion and prejudice (born of ignorance) which, alas! yet prevail
with regard to gas and gas lighting.




CONTENTS.


                                                       PAGE

INTRODUCTION                                              9

THE FIRST GAS-BURNER                                     13

THE BATSWING BURNER                                      15

THE UNION-JET OR FISHTAIL BURNER                         17

HOW LIGHT IS PRODUCED FROM COAL GAS                      20

IMPROVEMENTS IN FLAT-FLAME BURNERS                       25

BRÖNNER'S BURNERS                                        31

THE HOLLOW-TOP BURNER                                    35

BRAY'S BURNERS                                           38

ARGAND BURNERS                                           44

SUGG'S ARGANDS                                           48

THE DOUGLASS BURNER                                      52

GOVERNOR BURNERS                                         55

REGENERATIVE BURNERS                                     61

INCANDESCENT BURNERS                                     73

CONCLUSION                                               79




CHAPTER I.

INTRODUCTION.


[Sidenote: Gas consumers and gas producers.]

The subject of gas-burners and the development of light from coal gas
is of considerable interest, alike to the consumer and the producer of
gas. When it is known that one burner may develop twice as much light
as another, for the same consumption of gas--the first cost of the one
being no higher than that of the other--its importance to the former
will scarcely be disputed. To the gas consumer it is obviously of great
value to know how he may most effectively and economically develop the
illuminating power of the gas which is supplied to him; and so obtain
the fullest return, in lighting effect, for the money which he expends.
Not quite so obvious is its relation to the latter. To a person totally
unacquainted with the recent history of gas lighting, and ignorant of
the policy which has guided the most prosperous gas undertakings to
their successful issues, it may appear that the manufacturer of gas is
not closely concerned with the utilization of the commodity which he
supplies. Such an one might argue, and with a certain show of reason,
that the sole business of the gas maker is with its production; that
after providing, in the consumer's service-pipe, a full and continuous
supply of gas, of the stipulated quality, his care ends; and that
henceforth the utilization and management of the illuminant rests with
the consumer himself. But, by any one who is at all conversant with the
subject, it will be readily conceded that the interest of the
manufacturer of gas, in this matter, is only second to that of the
consumer. In the gas industry, as in any other business undertaking,
the concern prospers or declines according as the interests of the
customers are considered or neglected. This has been conclusively
demonstrated in the history of many gas undertakings. So long as their
management was conducted in exclusive and selfish regard solely to
their own internal affairs--looking with supreme indifference or
careless apathy upon the needs of the consumers--so long was their
career marked by difficulties and embarrassments. No sooner, however,
were the claims of the consumers recognized, and efforts put forth to
further their interests, than the prospects of the concern brightened;
and by adhering to, and extending the same line of action, the goal of
commercial prosperity was eventually reached.

Seeing, therefore, that the subject is of so supreme importance to
consumers of gas, and that the interests of the consumer are closely
interwoven with those of the manufacturer, it is eminently desirable
that there should be more generally diffused a correct knowledge of the
principles of economical gas consumption, and of the extent to which
these principles are applied in the various burners which, from time to
time, have been invented. No further apology ought therefore to be
required in presenting to the reader the following disquisition on
gas-burners. It may, however, be of advantage for me to state in brief,
at the commencement, what are the objects I have in view, and what the
chief considerations which have led me to write this treatise.

[Sidenote: Waste of gas.]

I purpose, then, to tell of the progress that has been made in
apparatus for the development of light from coal gas; to relate how
the crude and imperfect devices of the early inventors have been
gradually improved upon; and, while not ignoring the drawbacks connected
with recently invented burners, or the defects inherent to their
construction, to show, in the superior achievements of these burners,
how great an advance has been made upon the apparatus formerly in use.
It will be, also, my endeavour to make plain the little understood
phenomenon of the production of light by the combustion of coal gas;
and to show the extent to which the illuminating power developed is
dependent upon the burner employed. That there is need for such
information as I propose to furnish must be sufficiently obvious to any
one who has considered the waste of gas which takes place through
ignorance of the laws of its combustion, and through the use of
defective burners. In a report presented to the Board of Trade by the
London Gas Referees in 1871, it was stated that a number of burners had
been tested, taken from various places of business in the Metropolis;
the major portion of which gave out only one-half, and some of them not
more than one-fourth, of the illuminating power capable of being
developed from the gas. Although, since the time that report was
penned, considerable progress has been made in the construction of
burners, and in the more general adoption of efficient burners by the
public, much yet remains to be done. Doubtless it would still be within
the mark to assert that fully one-fifth of the gas consumed by the
public might be saved by the adoption of better burners, and by the
observance of the conditions necessary for their satisfactory
operation; and when it is borne in mind that the gas-rental of the
United Kingdom amounts to a sum of certainly not less than £9,000,000
per annum, the saving which might be effected assumes truly great
proportions.

The field on which I propose to enter can hardly be said to be already
occupied. Nowhere that I know of is the subject of gas-burners fully
treated of in a manner available for the general reader. With the
exception of the admirable chapter contributed by Mr. R. H. Patterson
to "King's Treatise on Coal Gas," I am not aware that the subject
has been dealt with to any complete extent by recent writers. But,
admirable as is that contribution to the literature of the subject,
being written for technical readers, it is neither so popular in style
nor so elementary in character as to fulfil the purpose which I have in
view in writing the present series of articles. Briefly stated, my sole
purpose is to make the subject of the combustion of gas for the
production of light intelligible to the simplest; and to present an
interesting account of the progress of invention in the perfection of
gas-burners. While passing lightly over many modifications of apparatus
which have been of but limited or temporary service, I shall not
scruple to dwell at length upon such burners as have done much to
further the extension of gas lighting, or whose construction exhibits
a considerable advance upon previous attainments. And while it will
be my endeavour to clothe my remarks in such language as shall be
"understanded of the people," in speaking of the theory of combustion I
hope to be sufficiently explicit to enable my readers to form a clear
conception of the scientific principles underlying the phenomena of
which I treat.

[Sidenote: Progress of gas lighting.]

A further justification--if such, indeed, were needed--for the
appearance of this treatise might be found in the remarkable impetus
which has been given, within recent years, to the perfection of the
details of gas manufacture and the improvement of gas-burners. Of
course, I refer to the beneficial consequences to the gas industry
which have followed the brief, if conspicuous, career of electricity as
an illuminating agent. That the interest in improved illumination which
has been aroused by the short-lived popularity of the electric light,
and the extravagant claims put forward on its behalf, have stimulated
to the development of the resources of gas lighting, is sufficiently
obvious to the most superficial observer. And not only has the
manufacturer of gas been benefited, but the public have reaped no
inconsiderable advantage. At the present day, gas is sold at a far
cheaper rate, as well as of a higher quality, than at any former
period. Nor is the advent of cheap gas the only direction in which the
public have gained. Although not so patent to the majority, the
improvements that have been effected in the methods of burning gas, so
as to obtain the fullest advantage from its use, are calculated to
confer benefits equally real, and not less valuable. It is hardly too
much to say that the last few years have witnessed a greater advance in
the apparatus employed in the combustion of gas than had been effected
during the whole previous history of gas lighting. This being so, it
may not be unacceptable if I attempt to pass in review some of the
various burners that have been invented and used for obtaining light
from coal gas; showing the successive improvements that are exhibited
in their construction, and the extent to which they apply the
principles of combustion. It may be that what I have to relate will
awaken some minds to the consciousness that gas lighting has not
altogether retired into obscurity on the advent of electricity--nay,
that it has even assumed a bolder front; and, with increased resources
and accession of strength, is prepared firmly to maintain its position
as at once the most convenient, economical, and reliable of artificial
illuminants.




CHAPTER II.

FLAT-FLAME BURNERS.


THE FIRST GAS-BURNER.

The first gas-burner was a very simple and unpretentious contrivance.
In one of the earliest works on gas lighting[1] we read: "The
extremities of the pipes have small apertures, out of which the gas
issues; and the streams of gas, being lighted at those apertures, burn
with a clear and steady flame as long as the supply of gas continues."
Familiar as it is to us, and from its familiarity unnoticed, the
phenomenon presented by the flame thus produced continuing to burn "as
long as the supply of gas continued," was doubtless, to the first
experimenters, a wonderful sight. Though we may smile at the question,
it is not difficult to understand the incredulity of the honourable
member who, when Murdock was examined before a Committee of the House
of Commons, in 1809, asked the witness: "Do you mean to tell us that it
will be possible to have a light _without a wick_?" "Yes; I do indeed,"
replied Murdock. "Ah, my friend," replied the member, "you are trying
to prove too much."

          [1] Accum's "Treatise on Gas-Lights." Third edition, 1816.

[Sidenote: The dawn of gas lighting.]

It was but natural, seeing that oil-lamps and candles were the only
forms of artificial illumination in use prior to the introduction of
gas lighting, that the earliest attempts at illumination by gas should
be in imitation of the effects produced by those means. Accordingly we
find that one of the first gas-burners employed was the Argand,
modelled upon the oil-lamp of that name, which had been found to give
superior results; while in more general use, and for some time almost
the sole apparatus available, were single jets, giving a flame similar
in appearance to that of a common candle, together with various
combinations of these jets. A fair idea of the mode of illumination
practised during the earliest period of gas lighting may be gleaned
from the following extract from a paper describing the lighting of
Messrs. Phillips and Lee's cotton-mill at Manchester, read before the
Royal Society, in 1808, by Mr. William Murdock:--

    The gas-burners are of two kinds. The one is upon the principle of
    the Argand lamp, and resembles it in appearance; the other is a
    small curved tube with a conical end, having three circular
    apertures or perforations, of about 1-30th of an inch in diameter,
    one at the point of the cone, and two lateral ones, through which
    the gas issues, forming three divergent jets of flame, somewhat
    like a fleur-de-lis. The shape and general appearance of this tube
    has procured for it, among the workmen, the name of the "cockspur"
    burner.

  [Illustration: FIG. 1.--EARLY GAS-BURNERS.
                 (From Accum's "Treatise on Gas-Lights.")]

Nor was much advance made upon these arrangements down to the year
1816, judging from Accum's "Treatise" (before cited), as the subjoined
extract from that work, together with the above illustrations, will
show:--

    The burners are formed in various ways--either a tube ending with a
    simple orifice, at which the gas issues in a stream, and if once
    lighted will continue to burn with the most steady and regular
    light imaginable, as long as the gas is supplied; or two concentric
    tubes of brass or sheet iron are placed at a distance of a small
    fraction of an inch from each other, and closed at the bottom. The
    gas which enters between these cylinders, when lighted, forms an
    Argand lamp, which is supplied by an internal and external current
    of air in the usual manner. Or the two concentric tubes are closed
    at the top with a ring, having small perforations, out of which the
    gas can issue; thus forming small distinct streams of light.

It is interesting, in view of the present demand for increased
illumination, and for burners of high illuminating power, to note the
amount of light produced by the burners then in use. In Mr. Murdock's
paper we find it stated that each of the Argands in use at Messrs.
Phillips and Lee's establishment gave "a light equal to that of 4
candles (mould candles of 6 to the pound);" and each of the cockspurs
"a light equal to 2-1/4 of the same candles." From which meagre results
we conclude that, besides being burnt in an ignorant and wasteful
manner, the gas consumed was wofully deficient in illuminating power.


THE BATSWING BURNER.

[Sidenote: Who invented the batswing burner?]

A notable advance was made when the batswing burner was invented. To
whom we are indebted for this invention seems involved in some doubt.
Although Clegg, in the historical introduction to his valuable work,[2]
says, very distinctly, that "the batswing burner was introduced by a
Mr. Stone, an intelligent workman employed by Mr. Winsor," it is not so
much as mentioned by Accum, even in the third edition of his
"Treatise;" and Accum, it may be remarked, was for some time closely
associated with Winsor in the promotion of the latter's ambitious and
visionary schemes. Yet, if Clegg's statement be correct, it would
almost appear to fix the date of the introduction of this burner as
prior to 1816. But to whomsoever is due the credit of its invention,
certain is it that the batswing burner was a considerable improvement
upon the old cockspur. Producing a better light for the gas consumed,
it assisted to demonstrate still further the superiority of gas
lighting over other methods of illumination; and as it could be
supplied at a trifling cost, and contained no delicately adjusted nor
easily injured parts, it enabled the benefits of the new method of
lighting to be extended to wherever artificial light was required.

          [2] Clegg's "Treatise on Coal Gas," 1841, p. 21.

  [Illustration: FIG. 2.--BATSWING BURNER.]

[Sidenote: Superiority of the batswing over the cockspur burner.]

From the cockspur and single jet burners the gas ascended in streams,
rising into the air until it came in contact with sufficient oxygen to
completely consume it. In order that this might take place without
producing a flame of an inordinate length, and without much smoke, the
orifices were restricted to a very small size; and the gas issuing from
these at considerable pressure tended to draw in, and mix with the air
in its course. Besides the loss of illuminating power caused by this
mixture of air with the gas flame (similar to what takes place in a
Bunsen burner), the cooling influence upon the small body of flame of
the mass of metal composing the burner, operated still further to
reduce the quantity of light which the gas was calculated to yield.
With the batswing the gas was spread out producing, when ignited, a
thin sheet of flame, by which means the gas was enabled to combine more
readily with the air necessary to effect complete combustion. The size
of the flame being, in comparison with that of the cockspur, so much
larger proportionately to the metal burner, the cooling effect of the
latter was not so apparent. The increased size of flame, also, of
itself, tended to improve the illuminating power; each portion of flame
contributing to elevate and sustain the temperature of the whole, and
so to heighten the intensity of incandescence to which the light-giving
particles were raised.

[Sidenote: Batswing and Argand burners compared.]

Even with the Argands of that day, the batswing compared not
unfavourably. The former burner, having the regulation of its air
supply under complete control, gives the best results when the gas is
supplied to it at a low pressure; as then the requisite quantity of air
to ensure complete combustion of the gas can be delicately adjusted by
means of a chimney of suitable length. When the gas and air have been
nicely adjusted to each other, the flame becomes extremely sensitive to
any change of pressure in the gas supply; a diminution of the supply,
by reducing the quantity of gas issuing from the burner without at the
same time proportionately diminishing the supply of air, tends to
destroy the illuminating power by the cooling action of the surplus
air; while an increased pressure, by allowing more gas to issue than
the air can consume, causes the flame to smoke. But at the time to
which I now refer the principles of combustion were little understood,
still less applied in the construction of burners. Besides this, the
pressure of the gas in the mains was excessive; and there being no
method adopted of controlling it at the burner, the construction of a
good Argand was, under the circumstances, almost impossible. The
batswing was not so prejudicially affected by an excess of pressure.
Pressure to some extent was, indeed, required to enable the flame to
attain its normal shape; while any excess forced the gas through the
flame without permitting it to be raised to incandescence before being
consumed, and although necessitating loss of light, caused no
inconvenience like a smoking flame. Another important advantage which
the batswing possessed over the Argand burner was its simplicity of
construction; and the absence of accessories, such as the glass
chimney--dispensing with the cleaning and attention which the latter
required. Had the benefits of gas lighting been dependent upon the use
of apparatus so fragile, and requiring so much care and attention as
the Argand, the range of its applicability must have been considerably
limited, and its prospects of commercial success much less assured. The
introduction of a series of cheap but effective burners, however,
altered the conditions of gas lighting, and marked the commencement of
a new era in artificial illumination. The possibility of obtaining, by
means of a burner so simple and apparently insignificant as the
batswing, results little, if at all, inferior to what could be obtained
by the use of the most complicated and expensive, was of advantage
alike to the consumer and the producer of gas. To the former it gave
the benefits of an increased illumination, without requiring any
corresponding outlay; to the latter it promised a growing extension of
the use of coal gas, and thus furnished the surest guarantee of future
progress and prosperity.


THE UNION-JET, OR FISHTAIL BURNER.

[Sidenote: Who invented the union-jet burner?]

The batswing had been for some years in extensive use before a burner
was produced worthy in any degree to compare with it in respect to
simplicity and efficiency. The invention of the union-jet, or fishtail
burner, furnished a competitor equally simple; little, if at all,
inferior as regards efficiency; and, to some extent, superior to the
former burner in general adaptability. Although so much behind in point
of time, the new burner speedily rivalled the older batswing in popular
favour; and in its various modifications and improvements may be said,
without fear of contradiction, to have received a wider application
than any other gas-burner. As in the case of the batswing, so with
regard to this burner: few details are recorded of its invention. But,
slight as is the information available, such as we have is more
satisfactory and more authentic than the meagre notice of Clegg, which
is all that is known of the invention of the former burner. It appears
to be established beyond doubt that the union-jet is the joint
invention of Mr. James B. Neilson, the inventor of the hot-blast, and
Mr. James Milne, of Glasgow, founder of the engineering firm of Milne
and Son. About the year 1820, or soon after (as in that year Mr.
Neilson was appointed Manager of the Glasgow Gas-Works), these
gentlemen were experimenting with gas-burners, when they discovered
that by allowing two jets of gas, of equal size, to impinge upon each
other at a certain angle, a flat-flame was produced, with increased
light. This was the origin of the union-jet; so called from the manner
in which the flame is produced. At first separate nipples were employed
for the two jets; but, very soon, Mr. Milne hit upon the expedient of
drilling two holes, at the required angle, in the same nipple. In this
manner, with slight modifications, the burner has continued to be
constructed down to the present day.

  [Illustration: FIG. 3.--FISHTAIL BURNER.]

The explanation of the preference accorded to this burner over its
predecessor, the batswing, is to be found chiefly, I think, in the very
different shapes of the respective flames produced by the two burners.
The batswing, in its original form, produced a flame of great width,
but of no corresponding height. The extremities of the flame,
stretching out from the burner so far on either hand, were easily
affected by an agitation of, or commotion in the surrounding
atmosphere; a slight draught or current of air causing the flame to
smoke at these points. The extreme width of flame also precluded the
use of this burner in globes. The flame produced by the union-jet
burner, as first constructed, was very different to the one just
described. Longer than that of the batswing, and considerably narrower
(but widening gradually from its base, at the burner, to its apex), it
presented somewhat nearly the appearance of an isosceles triangle; or
more closely, perhaps (with its slightly-forked apex), the tail of a
fish, from which resemblance it is commonly designated the fishtail
burner. This form of flame was better adapted for use in globes, and
also better withstood the effects of draughts. And it is perhaps not
unreasonable to suppose that as in shape it approached more closely to
the kind of flame with which the people had been familiar in oil lamps,
the flame produced by the union-jet burner was more agreeable to the
eye than that of the batswing, and that this seemingly trivial
consideration will account, to some extent at least, for the undue
favour shown towards it. For it must not be assumed, because of the
widespread popularity to which the union-jet so early attained, and
which it has continued to enjoy, that it was of necessity a better
burner (in the sense of developing more light for the gas consumed)
than the one which preceded it. On the contrary, in this regard it was
not quite so effective as the batswing. Nor is this result surprising,
looking at the different methods adopted in the two burners for
producing the same effects of light and flame.

[Sidenote: Union-jet and batswing burners compared.]

From the batswing burner the gas issued in a thin but widely-extending
stream, presenting, when ignited, a continuous sheet of flame; its
height and width depending upon the pressure at which the gas was
supplied, but always offering an unbroken surface of flame to the air.
Although, from the excessive pressures which, in the early days of gas
lighting, were generally employed, the flame drew upon its surface too
much air for the attainment of the fullest lighting efficiency
obtainable from the gas; yet the form given to the issuing stream of
gas precluded the air from entering the interior of the flame, and
still further reducing its illuminating power. With the union-jet
burner the conditions were greatly changed; and this latter evil, of
the introduction of cold air into the interior of the flame, was one of
the consequences entailed by the means it employed for producing its
flame. From this burner the gas issued in two narrow streams, like
single jets, which, directly after emerging from the burner, impinged
upon each other at a given angle; the mutual shock given to the streams
of gas when thus arrested causing them to spread out in a lateral
direction, and (the high velocity at which the gas issued being
expended) to unite, and ascend in a sluggish stream until consumed.
That injury to the illuminating power of the flame should result from
causes connected with the manner of producing it will be understood on
considering some of the phenomena associated with the production of a
gas flame.

[Sidenote: How air is drawn upon a gas flame.]

When a jet or stream of gas issues into a still atmosphere, it produces
in its immediate neighbourhood, on all sides, an area of low pressure,
to occupy which the contiguous air rushes in. Induced air currents are
thus set up in close proximity to, and having the same direction as the
issuing stream of gas, and varying in force with the pressure, or
velocity, at which the gas issues. The non-luminous flame of the Bunsen
burner, and of the so-called "atmospheric" burner employed in gas
cooking and heating stoves (which is produced by burning a mixture of
gas and air), is obtained by taking advantage of this tendency of a
stream of gas, issuing under pressure, to draw air upon itself; and it
is to the same circumstance that ordinary illuminating flames owe the
continuous supply of air necessary to keep up combustion. For the
effect is heightened when the gas is inflamed; because, the gaseous
products of combustion being expanded by the intense heat to which they
are subjected, their velocity of ascension is vastly increased. Having
regard to these considerations, it will be clearly perceived how that,
in producing the flame of the union-jet burner, the two streams of gas,
in the act of combining together, drew into the very midst of the flame
a portion of the air with which they were surrounded; and this air,
reducing the temperature of the flame, and diluting the illuminating
gas by the inert nitrogen introduced, as well as by its oxygen causing
a too early oxidation of the carbon particles in the flame, operated to
reduce the illuminating power otherwise obtainable from the gas.

The foregoing remarks, it must be borne in mind, refer to the union-jet
burner in its original form. Numerous improvements have been effected,
from time to time, in its construction, as well as in that of the
batswing, which, by reducing its liability thus to convey air into the
flame, have increased its efficiency; while, at the same time, the
shape of the flame has been improved. Indeed, the result of successive
improvements in the construction of both burners has been so to modify
the shape of their respective flames that, in their latest and most
improved form, the flames produced by the two burners are practically
identical in appearance, although the manner of their production
remains as widely diverse as at the first. The improvements that led up
to, and the causes that produced this result, will be more fully
explained in the sequel.


HOW LIGHT IS PRODUCED FROM COAL GAS.

I have before remarked that, in the early period of its use, one of the
chief obstacles to the development of the lighting power of coal gas
was the excessive pressure at which it was generally supplied. To
understand the action of pressure in influencing the amount of light
which a given quantity of gas will afford, it is necessary to know
something of the nature and properties of flame. Moreover, the
conditions upon which is dependent the illuminating power of a gas
flame are so intimately related to each other, that the precise
functions due to each cannot well be separated from the complete effect
produced by the combined operation of all. I shall not, therefore, be
needlessly digressing from my subject if, at this juncture, I explain
the manner in which combustion takes place in the flame of an ordinary
gas-burner. In doing this, I shall endeavour to clothe my remarks in
very plain language; using no more technicalities than are absolutely
required by the exigencies of the subject. In this way I hope to make
my meaning clear to the simplest. At the same time, without pretending
to be scientifically complete, the explanation of the phenomena of
combustion which I shall furnish will, I trust, be sufficiently
explicit to enable the reader to form a right estimate of the
principles which regulate the production of light when coal gas is
consumed. The end chiefly kept in view is to show clearly the extent to
which the degree of light evolved is dependent upon the burner
employed, and the manner in which the gas is consumed. If my remarks
are the means of causing the reader to look with intelligent interest
upon the familiar phenomena of gaslight, they will not have been
written altogether in vain.

[Sidenote: What is coal gas?]

Seeing that this treatise is compiled especially for those whose
knowledge as to what coal gas consists of is extremely limited, it may
be of advantage to preface my observations on its combustion, and the
production of light therefrom, by a few remarks as to its composition.
Coal gas, as generally supplied, is made up of a variety of distinct
gases; of which, however, only some three or four exist in any
considerable proportion. About 50 per cent., by volume (or half of the
whole), is hydrogen; from 30 to 40 per cent. consists of marsh gas;
while carbonic oxide is usually present to the extent of from 5 to 15
per cent. These three gases, which constitute the great bulk of what is
known as common gas--that is, gas made from ordinary bituminous coal,
as distinguished from that produced from the more costly cannel--are of
little or no value as regards the amount of light they are capable of
affording. The flames produced by the burning of the two former gases
evolve much heat, but are of very feeble illuminating power. The latter
gives a flame of a deep blue colour, producing scarcely any light, but,
like the other two, an intense heat. The power of coal gas to yield a
luminous flame is dependent upon the small quantity of heavy
hydrocarbons which it contains--a constituent, or series of
constituents, of which common gas only contains a proportion varying
between 3 and 7 per cent., although in cannel gas it reaches as high as
15 or 20 per cent. These heavy hydrocarbons are gases composed, like
marsh gas, of carbon and hydrogen; but containing in their composition,
for each unit of volume, a greater aggregate of the two elements, as
well as a relatively higher proportion of carbon, than exists in marsh
gas. One of the simplest members of the series, and that which is
usually present in by far the largest amount, is called olefiant gas.
It contains twice as much carbon, combined with only the same quantity
of hydrogen, as is contained in marsh gas. But besides olefiant gas
there are minute quantities of other gases of the same series, having
an analogous composition, but differing in the amount and relative
proportions they contain of the two elements of which they are
composed. All the gases of this series, when properly burnt, are
capable of affording a brightly luminous flame; but when consumed alone
it is somewhat difficult, on account of the high proportion of carbon
which they contain, to effect their combustion without the production
of smoke. It is, then, to the heavy hydrocarbons which are part of
it--insignificant as their amount may appear--that the luminosity of a
gas flame is solely due. The other constituents which I have mentioned
as forming so much larger a proportion of the whole, besides
contributing to the heat of the flame, serve only to dilute these
richer gases, and so promote their more complete combustion.

[Sidenote: How gas burns.]

The various simple gases which constitute ordinary coal gas do not all
burn together in the flame; the temperature required to effect their
ignition being lower for some of them than for others. Thus, hydrogen
is the first to burn, taking fire readily as soon as it issues from the
burner; while the combustion of the heavy hydrocarbons does not
commence until they enter the hotter portions of the flame, and is not
completed until they reach its farthest extremity. Neither is the
process of combustion in both cases the same. The former gas is at once
completely consumed; the latter first undergo decomposition by the heat
of the flame, being resolved into their elements--hydrogen and
carbon--before being fully consumed. This decomposition of the
hydrocarbons is a factor of supreme importance in the development of
the lighting power of the flame. The hydrogen they contain, being more
easily ignited than the carbon, burns first; and the latter is set
free, in the solid form, as minute particles of soot. These particles
of solid carbon, being liberated in the midst of the flame, are
immediately subjected to its most intense heat; they thus become
white-hot before they reach the outer verge of the flame, and come in
contact with sufficient oxygen to effect their complete combustion.
The amount of light developed by any coal-gas flame is directly
proportional to the degree of intensity to which the temperature of
these carbon particles is raised, and the length of time they remain
in the flame before being finally consumed. It becomes, therefore, a
matter of considerable importance to know the conditions which are
most conducive to the early liberation in the flame of free carbon,
and the attainment by it of an exalted temperature.

[Sidenote: What is a gas flame?]

Looking at the flame (say) of a common slit burner, it is seen to be
divided into two sharply defined and wholly distinct portions. First,
there is--immediately surrounding the burner head, and extending to
some distance from it--a dark, transparent area, which, on closer
examination, is found to consist of unignited gas enclosed in a thin
envelope of bright blue flame. Second, there is (beyond this central
area) a zone, or belt, of brightly luminous flame, white and opaque;
the latter property indicating the presence of solid matter at this
part of the flame. That the dark central portion of the flame consists
chiefly of unignited gas may be shown in various ways, in addition to
the evidence afforded by its complete transparency. Thus, if a small
glass tube be taken, and its lower end inserted in the flame at this
point, the unburnt gas will pass up the tube, and may be lighted at its
upper extremity. A splinter of wood thrust through this portion of the
flame is charred first at the two edges of the flame; while, in like
manner, a piece of platinum foil remains dull in the centre of the
flame, and glows only at the points of contact with the outer air. The
presence of solid carbon in the luminous portion of the flame may be
shown by inserting therein any cold substance (such as a piece of metal
or porcelain), which, reducing the temperature of the heated particles
of carbon below the point at which they are consumed, becomes instantly
coated on its under surface with a deposit of soot. Or, if the flame be
suddenly cooled by gently blowing upon its surface, the same result is
brought about; clouds of soot are given off, and the flame "smokes."[3]

          [3] The behaviour of gas flames when exposed to the action
          of the wind (as exemplified in the naked lights of open
          markets and similar situations) affords an instructive
          illustration of the theory of luminous combustion. A sudden
          gust causes the flame to smoke, by reducing the temperature
          of the liberated carbon below the point at which it can
          combine with the oxygen of the air. A continuous wind
          blowing upon the flame destroys its luminosity altogether,
          because the heat-intensity of the flame is lowered below the
          temperature necessary to decompose the hydrocarbons;
          consequently, these latter burn without the preliminary
          separation of carbon, and a non-luminous flame is
          produced--exactly as in the Bunsen or "atmospheric" burner.

  [Illustration: FIG. 4.--SHOWING THE TWO ZONES OF THE FLAME, AND
  THE METHOD OF DEMONSTRATING THE PRESENCE OF UNBURNT GAS IN THE
  FLAME.]

[Sidenote: How the flame is cooled.]

The existence, in the midst of the flame, of an area of unconsumed gas
is due to the cold gas, as it issues from the burner, cooling the
interior of the flame below the temperature required for its ignition,
as well as to its not at once meeting with sufficient air for complete
combustion. The causes which affect the luminous zone of the flame are
not so readily explained. It has been stated that the luminosity of the
flame is due to the particles of carbon, which are separated out of the
hydrocarbons in the gas, being raised to a white heat. To decompose the
hydrocarbons, a very high temperature is required; and, on account of
the cooling effect of the stream of cold gas, this is not attained
except at some distance from the burner. The abstraction of heat by the
burner itself is also a cause of the reduction of the temperature of
the flame; and, on this account, burners of porcelain, steatite, or
similar composition, being bad conductors of heat, have an advantage
over those made of metal. So considerable is the cooling influence of
the gas stream, that, within certain limits, the distance, from the
burner head, at which the luminosity of a flame commences, is
proportionate to the velocity with which the gas issues; or, in other
words, the pressure at which it is delivered from the burner. The
effect is heightened by the tendency (which has been before remarked)
of a stream of gas, issuing under pressure, to draw upon itself and mix
with the surrounding air. Thus, with each increment of pressure the
luminous zone of the flame is farther removed, until a point is reached
at which the gas is so mixed with air before being consumed that the
luminosity of the flame is completely destroyed.

[Sidenote: Effects of pressure in the gas supply.]

But it must not be assumed, because of the foregoing remarks, that the
pressure at which the gas issues from the burner is altogether an
unmixed evil. In flat-flame burners it fulfils the important function
of promoting intensity of combustion, by bringing the white-hot
particles of carbon into intimate and rapid contact with the air that
is necessary for complete combustion. In Argand burners this duty is
discharged by the glass chimney; but with flat-flame burners it
devolves entirely upon the pressure at which the gas issues from the
burner. It will be seen, therefore, that the pressure of the gas is a
factor of considerable importance in determining the amount of light
afforded by a gas flame, as it is a matter requiring careful adjustment
with each and every burner. On the one hand, with an excessive pressure
the intensity of combustion is increased; but the separated carbon does
not remain so long in the flame. The area of luminosity is thereby
decreased, and the total light yielded is reduced. On the other hand,
with insufficient pressure the combustion is not energetic enough to
raise the particles of carbon to a white heat; consequently, the
illuminating power of the flame is feeble, or else the carbon escapes
unconsumed as smoke.

The thickness of the flame produced by any burner has also an important
bearing upon the degree of light afforded; and this property of
thickness, again, is dependent upon the width of slit, in the case of
batswings (or, in the case of union-jets, upon the size of orifices),
and the pressure at which the gas is supplied. The thickness of the
flame yielded by any burner will obviously vary inversely with the
pressure at which the gas is supplied to it. With a thin flame, all
parts of the flame are so completely exposed to the air, that the
particles of carbon are no sooner raised to the temperature required to
enable them to give out light than they are entirely consumed. With a
thicker flame the carbon separated in the midst of the flame exists for
a sensibly longer period of time in the white-hot state before it
reaches the outside of the flame, and meets with sufficient oxygen for
its complete combustion. Thus we find that the best flat-flame burners
have comparatively wide orifices; while the pressure at which the gas
is delivered from the burner is carefully reduced to the lowest point
at which a firm flame is obtained, without smoke. Similarly, in the
best Argands the pressure is considerably diminished within the burner,
and the gas allowed to issue gently through relatively large holes;
while the chimney is carefully adapted to draw upon the surface of the
flame just sufficient air to completely consume the quantity of gas
which the burner is calculated to deliver.


IMPROVEMENTS IN FLAT-FLAME BURNERS.

Although, there is no doubt, they were made empirically, and in
ignorance of the real effects of pressure upon the flame, the first
steps towards increasing the efficiency of flat-flame burners were in
the right direction of reducing the excessive pressure at which the gas
was formerly allowed to burn. They consisted in the adoption of simple
arrangements for obstructing the passage of the gas through the burner,
and so retarding its flow. The crudeness of the means which were
employed is sufficient evidence that the end aimed at was, at best, but
dimly discerned. The body of the burner was stuffed with wool, or
pieces of wire gauze; which impeded the progress of the gas; reduced
the quantity that would otherwise have been consumed; and,
consequently, diminished the velocity with which it issued from the
burner. Unfortunately, owing to the imperfect methods in use at that
day for condensing and purifying the gas, the burners so constructed
became choked with the tarry matters held in suspension, and carried
forward by the gas; and so, after a comparatively short period of
service, were rendered entirely inoperative. But, altogether apart from
the inconvenience and loss thus entailed (which, when improved modes of
manufacture had removed the cause, ceased to be experienced), the
arrangement was ill adapted for the purpose which it was designed to
serve. The rough and uneven nature of the material employed to stuff
the burner caused the gas to eddy and swirl as it issued into the
atmosphere, and prevented it being supplied equally to all parts of the
flame. The consequence was that the advantages which ought to have been
derived from the diminished pressure were neutralized by the unsteady
flow acquired by the stream of gas; and the illuminating power
developed by the flame was little improvement upon what could
previously be obtained by the manipulation of the tap controlling the
supply of gas to the burner. Besides which, from its unevenness, the
appearance of the flame was not so satisfactory. It was not until the
principles which regulate the production of light from coal gas came to
be known and observed in the construction of burners, that a
modification of the old idea was arrived at, which enabled the benefits
of a reduced pressure to be obtained without any of the attendant evils
hitherto experienced.

[Sidenote: The first real improvement of the union-jet burner.]

A modification in the construction of the union-jet which, though
slight, was nevertheless a real improvement, appears to have been made
at an early period in the history of this burner. Instead of having the
top of the burner perfectly flat, it was made slightly concave; more
especially at its centre, where the two jets of gas emerge. The effect
of this alteration was to enable the stream of gas to spread out
better; and thus to cause the flame to become broader at its base. The
shape of the flame was thereby improved; and (what is of more
consequence) its illuminating power increased, because air was not
drawn so readily into the midst of the flame. The value of the
arrangement is shown by the fact that it has been retained ever since,
and is made use of in the latest and most improved burners of this
class.

Prior to 1860, numerous novel contrivances were introduced as
"improved" burners; but all were not equally valuable with the simple
arrangement just described. The construction of many of them, indeed,
betrayed a lamentable ignorance of the first principles of gas
combustion. For instance, one is described as "a fishtail with four
converging holes; and there is an aperture in the centre of the burner
for the admission of atmospheric air into the flame!" Another was a
batswing with two or more slits, producing a series of flames
amalgamated into one; by which means it was supposed that an improved
duty was obtained from the gas--unmindful, or, more probably, in
ignorance of the fact that the same quantity of gas, properly consumed
through one slit, would yield a better light.

[Sidenote: The double-flame burner.]

A burner which, at different times, and under various names, has been
brought repeatedly into notice is the double-flame; consisting of two
batswing or union-jet burners set at an angle to each other, so that
their flames converge, and merge into one. When two gas flames are made
to coalesce in this manner, a greater amount of light is developed than
the sum of that yielded by the separate flames; provided that, in the
combined flame, the gas is properly consumed, without smoke. The reason
for this increase is twofold. First, the increased quantity of gas
burnt in one flame enables a higher average temperature to be
maintained; and, in addition, a smaller surface of flame is exposed to
the cooling action of the atmosphere than when the same quantity of gas
is consumed in two flames. Second, the pressure at which the gas burns
is diminished, because the initial velocity with which the streams of
gas issue from the two burners is expended in impinging against each
other, and a thicker flame results; the apparatus being, as far as its
effect is concerned, a union-jet burner on a large scale. The increase
of light so obtained appears to have been noticed at an early period;
as a burner embodying the same principle is described and figured in
"Clegg's Treatise," published in 1848. In Clegg's burner the gas issued
from two perforated parallel plates inclined to each other; but at a
more recent period two fishtail burners were employed, being mounted on
separate tubes which branched out to a short distance from each other.
Occasionally, for experimental and show purposes, it has been
constructed with the two branches hinged together, so as to show the
different effects produced when the two burners are used separately and
in combination. At the present day it is made, by various makers, as
one burner with two nipples, as shown in the annexed illustration;
which doubtless is its most perfect form.

  [Illustration: FIG. 5.--DUPLEX BURNER.]

The advantages of the double flame are not so obvious under the
conditions which obtain at the present day as at the period when it was
first introduced. The increase of light it affords is most apparent
when the gas is being consumed at an excessive pressure. Although, in
general, it may be taken that any two flames, when combined, will
develop a higher duty, per cubic foot of gas consumed, than separately;
yet it would appear that this is not so in every case. When the gas is
being consumed at the critical pressure which gives the best results,
the flames are so near the smoking point that the slight diminution of
pressure experienced when the streams of gas impinge upon each other is
sufficient to cause the combined flame to smoke. Moreover, to such a
stage of perfection have the ordinary flat-flame burners now been
brought, that, for all ordinary consumptions, it may be safely affirmed
that equal, if not superior results can be obtained with a single as
with a double flame. Where, however, larger quantities of gas are
required to be dealt with than can be effectively consumed in a single
burner, the principle of combining two or more burners together, so
that their flames shall mutually assist each other, may be
advantageously employed; as is seen in the combination of flat-flame
burners in the large lamps now employed in improved street lighting.

  [Illustration: FIG. 6.--SCHOLL'S PLATINUM LIGHT PERFECTER.]

[Sidenote: Scholl's "Platinum Light Perfecter."]

An ingenious device for improving the efficiency of union-jet burners
was brought out some twenty years ago by a Mr. Scholl, of London, and
known as Scholl's "Platinum Light Perfecter," which is shown in the
accompanying illustration. It consisted of a little brass ring,
carrying a plate of platinum about 0·4 inch long by 0·15 inch wide. The
ring fitted on to the top of the burner in such a manner that the
platinum plate was held, in a vertical position, between the two
orifices from which the gas emerged. The jets of gas, instead of
impinging upon each other, impinged against the plate, and united above
to form the flame. By the interposition of the metal plate, the
velocity of the gas was much reduced; and a thicker and more sluggish
flame was produced, with the result of increasing its illuminating
power. When the apparatus was used upon a burner having very small
orifices, and delivering its gas at a high pressure, the increase of
light obtained was very striking; but with lower pressures the
advantage derived from its use was correspondingly diminished. This is
very clearly shown by the following table, which is extracted from a
report, by Captain Webber and Mr. Rowden, on experiments upon
gas-burners, carried out at the Paris Universal Exhibition, 1867.[4]

          [4] See _Journal of Gas Lighting_, Vol. XVIII., p. 88.

  --------------------------+-------+--------+---------------------+--------
  Kind of Burner.           |Cubic  |Pressure| Illuminating Power. |
                            |Feet of|  in    +----------+----------+Increase
                            |Gas    |Inches. |Without   |With      |  per
                            |per    |        |Perfecter.|Perfecter.| Cent.
                            |Hour.  |        |          |          |
  --------------------------+-------+--------+----------+----------+--------
  Leoni's fishtail, No. 2 . |  3    | 0·84   | 1·3      |  4·1     | 215
  Leoni's fishtail, No. 3 . |  {3   | 0·46   | 2·4      |  4·6     |  91
                            |  {4   | 0·70   | 2·8      |  6·5     | 132
                            | {3    | 0·31   | 3·4      |  5·0     |  47
  Leoni's fishtail, No. 4 . | {4    | 0·47   | 4·5      |  7·6     |  68
                            | {5    | 0·71   | 5·0      |  9·2     |  84
                            |  {4   | 0·42   | 5·3      |  6·9     |  30
  Leoni's fishtail, No. 5 . |  {5   | 0·60   | 6·1      |  8·3     |  36
                            |  {6   | 0·81   | 7·1      | 10·0     |  40[5]
  Leoni's fishtail, No. 6 . | {4    | 0·31   | 6·2      |  8·0     |  29[6]
                            | {5    | 0·46   | 8·0      | 10·4     |  30[7]
  --------------------------+-------+--------+----------+----------+--------

          [5] Flame flickers.

          [6] Do.

          [7] Flame flickers a great deal.

Burners were also made with the metal plate forming part of the burner
head; and, instead of being of platinum, it was sometimes formed of
thin steel, or other commoner metal. Where platinum was used, some
advantage probably accrued from its becoming incandescent; but, of
course, any benefit arising from this source was not obtained when
steel was employed. The remarks which have been made respecting the
limited applicability of the double-flame burner will apply, with equal
force, to the apparatus under notice. Although it effected an undoubted
improvement when applied to burners ill adapted to the pressure at
which the gas was supplied, equally good results could be obtained
without its aid, when a burner was employed suited to the quality and
pressure of the gas supplied.

[Sidenote: Leoni's flat-flame burners.]

Perhaps the most efficient flat-flame burners available prior to 1867
were those made by Mr. S. Leoni, of London. One of these is shown in
fig. 7. This maker produced both batswing and union-jets; various sizes
being made of each burner. Besides affording fairly good results from
the gas consumed, the burners were supplied at a very moderate price.
Their distinguishing feature was the peculiar substance of which the
burner-tips were formed. This was a material invented by Mr. Leoni, and
named by him "adamas." (The precise composition of "adamas" is a trade
secret; but it appears to consist of a mixture of various minerals or
earths, moulded in a clayey or plastic condition, and then burnt.)
Previous to his invention, the tip of the burner, or the burner head,
had been made, almost exclusively, of iron or brass. There were,
however, some grave defects inherent in the use of metal for this
purpose. The orifices of union-jets and the slits of batswings in
course of time became much obstructed by the corrosion of the metal;
and the efforts made to remove the obstruction only served to destroy
the burner more quickly, by increasing the size and injuring the
precise shape of the apertures. The "adamas" tips, on the other hand,
perfectly withstood the high temperature to which they were exposed,
were quite incorrodible, and were sufficiently hard to endure a
considerable degree of even rough usage. By constructing the tip of
this material, the efficiency of the burner was improved in many ways.
The liability of the burner to corrosion being removed, and the
inconvenience due to this cause done away with, the life of the burner
was prolonged, and the expense of renewal consequently reduced. But, in
addition to these advantages, there was yet another direction in which
the "adamas" tip contributed to enhance the utility of the burner. This
was in maintaining a higher temperature of the flame; and arose from
its inferior capacity, compared with metal, for conducting heat from
the flame. That the advantage derived from this source, although
unimportant, was not altogether imaginary, will be apparent when it is
mentioned that metal burners, when in operation, usually attain to a
temperature of from 400° to 500° Fahr.--an indication of the amount of
heat being continuously abstracted from the flame. The adoption of a
non-conducting material for the burner-tip, while it did not entirely
prevent, considerably reduced the loss of heat.

  [Illustration: FIG. 7.--LEONI'S FLAT-FLAME BURNER.]

Two varieties of each class of burner were made by Mr. Leoni. In the
one burner, the "adamas" tip was inserted into an iron stem; in the
other, the tip was inserted in a brass body, which fitted on to the
iron stem. Between the brass body and the iron stem of the latter
burner there was affixed a layer of wool, designed to check the
pressure at which the gas was supplied. Owing, very probably, to the
unsuitability of the material (wool) used for this purpose, the result
was not satisfactory; as, according to the statements of Messrs. Webber
and Rowden, in the report previously cited, no difference could be
detected, in many experiments, between the results yielded by the
burner with or without the layer of wool. Some light is shed upon this
apparent anomaly by certain experiments made by the writer to determine
the pressure at which gas issues from various burners. With one of
Leoni's No. 4 union-jets, under an initial pressure of 1 inch (the
pressure at the inlet when the burner is in operation), the pressure at
the outlet of the burner, when the layer of wool was employed, was 0·11
inch; but from the same burner, when the layer of wool was removed, the
gas issued at a pressure of only 0·07 inch. Thus the effect of
inserting the layer of wool in the burner was exactly the opposite of
that which it was intended to produce; the pressure of the issuing gas
stream being increased instead of diminished.


BRÖNNER'S BURNERS.

The credit of having produced the first flat-flame burners designed
upon scientifically correct principles belongs undoubtedly to Herr
Julius Brönner, of Frankfort-on-the-Maine. Long before the date of his
invention, efforts had been made to reduce the pressure of the gas
within the burner. But these endeavours were carried out in so
hap-hazard a fashion as to lead to the belief that no definite
conception was entertained as to what was really required. As we have
seen, layers of wool had been employed; but the area of the
interstices, or the gas-way through the material, was a matter of the
merest accident. And there was not the slightest guarantee that the
same conditions should prevail in any two burners. Herr Brönner
shrewdly detected the cause of former failures, as he clearly perceived
the end which it was requisite to attain, and towards which previous
inventors had been but blindly groping. Having formed a right estimate
of the requirements to be fulfilled, and the difficulties to be
surmounted, he set about accomplishing the desired result by other
means. There were two causes which had chiefly contributed to the
unsuccessful issues of previous attempts. One was the uncertain and
indefinite operation of the means employed for diminishing the
pressure; the other was the inadequate provision for enabling the gas
to lose the current, or swirl, acquired in passing the diminishing
arrangement, and come to a state of comparative rest before issuing
into the atmosphere. Both these errors were successfully avoided in
Brönner's invention--the former by making the inlet to the burner of
restricted and definite dimensions, and of less area than the outlet,
or slit; the latter by enlarging the chamber, or place of expansion
within the burner, as well as by the different arrangement adopted for
diminishing the pressure.

  [Illustration: A TOP.
                 B TOP.
                 FIG. 8.--BRÖNNER'S BURNERS.]

[Sidenote: Construction of Brönner's burners.]

The general appearance of Brönner's burner is pear-shaped; and in size
it is considerably larger than an ordinary burner designed to pass an
equal quantity of gas. It consists of a cylindrical brass body
surmounted by a steatite top, and tapering to a very small diameter at
its lower end, or inlet; the latter being closed by a plug of steatite,
in which is a rectangular slot, or aperture, of accurately defined
dimensions. The size of this aperture determines the quantity of gas
which, at any particular pressure, is admitted to the burner; and the
slit, or outlet of the burner, being of greater area than the inlet,
ensures the gas being delivered from the burner at a lower pressure
than that at which it enters it. By varying the respective dimensions
of these two openings, and their relation to each other, the burner may
be regulated to deliver its gas at any required pressure short of the
initial pressure at the entrance to the burner. The enlargement of the
cylindrical body provides an expansion chamber, wherein the velocity of
the stream of gas which rushes through the narrow opening at the inlet
of the burner is checked, and any agitation or unsteadiness which may
have been imparted to it is subdued before the gas issues into the
atmosphere and is consumed. There are two kinds of tops for the
burners, which are distinguished by the letters A and B. The B top is
of the ordinary semi-spherical type, giving a true batswing-shaped
flame; the A top is flatter, almost square in form, and yields a flame
taller than, but not so broad as the former. In consequence of this
difference in the shape of its flame, the latter burner is better
adapted for use in globes. The general appearance of the burners, and
their distinguishing peculiarities, will be clearly understood from the
illustrations.

[Sidenote: Properties of steatite.]

The material of which the more important parts of the burner are
constructed is eminently adapted for the purpose. Steatite is a mineral
which, as found in nature, is so soft as to be readily turned in a
lathe, and shaped to any design; but when heated up to about 2000°
Fahr. it becomes almost as hard and durable as flint, while perfectly
retaining its form and colour. These properties peculiarly qualify it
for receiving a slit or orifice, which, though of minute proportions,
must be accurately formed to precise dimensions. Besides which, like
"adamas," its capacity for conducting heat away from the flame is so
limited that, in this respect, it has a considerable advantage over
metal for the purpose of being formed into gas-burners.

[Sidenote: Varied adaptability of the Brönner burner.]

The following tables, which are extracted from the report of the
Committee of the British Association appointed to investigate the means
for the development of light from coal gas of different qualities,[8]
exhibit the very satisfactory results obtained by the use of these
burners. In Table I., the gas operated upon was cannel gas (such as is
generally supplied in Scotland), and possessed an illuminating power,
when employed in the standard burner, of 26 candles per 5 cubic feet.
Table II. contains the results of determinations with common gas (such
as is used in London, and generally throughout the greater part of
England); 5 cubic feet of which, in the standard burner, gave an
illuminating power of 16 candles. The first and second columns of the
tables refer to the different sizes of the tops and bottoms of the
particular burners employed; there being in all some 16 sizes of the
one, and 11 sizes of the other. These, being interchangeable, permit of
a great variety of combinations; and enable a burner to be selected
suited to any particular quality or pressure of gas. For as with
pressure, so with illuminating power: In order to obtain the utmost
lighting efficiency, different burners are required for gases differing
in quality or their degree of richness. A burner which, with gas of one
quality, will yield excellent results, may, under the same conditions
of pressure and supply, be totally unsuited to gas of another quality.
That this should be so will be evident from a consideration of what has
been said as to the theory of burning gas to the best advantage; and,
in brief, results from the richer gas containing in its composition a
greater proportion of carbon, and so requiring an increased supply of
air for its thorough combustion. This increased supply of air can only
be obtained (with flat-flame burners) by causing the gas to issue into
the atmosphere at a higher pressure; and so it comes about that,
compared with the quantity of gas to be delivered through them, the
slits of batswing and the orifices of union-jet burners must be
considerably narrower when intended for cannel gas than when common gas
is to be consumed. In other words, in order to develop its full
illuminating power, it is essential that the pressure at which the gas
issues from the burner should be proportioned to its quality. The gist
of the matter is set forth in the general statement that "the poorer
the quality of the gas, the lower must be the pressure at which it is
consumed; and _vice versâ_."

          [8] See _Journal of Gas Lighting_, Vol. XXXII., p. 423,
          and Vol. XXXVI., p. 376.

  TABLE I.

  -----------------------------------+-----------------------------------
         |    AT 0·5-INCH   |    AT 1·0-INCH      |    AT 1·5-INCH
         |      PRESSURE.   |      PRESSURE.      |      PRESSURE.
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
  No.    |No. |Cubic|Illumi-|Illumi- |No.    |No. |Cubic|Illumi-|Illumi-
  of     |of  |Feet |nating |nating  |of     |of  |Feet |nating |nating
  Burner.|Top.|per  |Power. |Power   |Burner.|Top.|per  |Power. |Power
         |    |Hour.|       |per Five|       |    |Hour.|       |per Five
         |    |     |       |Cub. Ft.|       |    |     |       |Cub. Ft.
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
     2   |  2 | 1·20|  5·07 | 24·13  |   2   |  2 | 1·40|  5·25 | 18·75
     2   |  3 | 1·40|  6·64 | 23·71  |   2   |  3 | 1·95|  7·37 | 18·90
     2   |  4 | --  | Smokes|  --    |   2   |  4 | 2·30| 10·33 | 22·46
     2   |  5 | --  |   "   |  --    |   2   |  5 | 2·40| 11·24 | 23·42
     2   |  6 | --  |   "   |  --    |   2   |  6 | --  | Smokes|  --
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
   2-1/2 |  2 | 1·40|   5·53| 19·75  | 2-1/2 |  2 | 1·90|  8·30 | 21·84
   2-1/2 |  3 | 1·70|   8·48| 24·94  | 2-1/2 |  3 | 2·30| 10·14 | 22·04
   2-1/2 |  4 | 2·03|  10·33| 25·49  | 2-1/2 |  4 | 2·70| 12·08 | 22·37
   2-1/2 |  5 | --  | Smokes|  --    | 2-1/2 |  5 | 2·85| 14·29 | 25·07
   2-1/2 |  6 | --  |   "   |  --    | 2-1/2 |  6 | 3·00| 15·21 | 25·35
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
     3   |  2 | 1·45|   6·27| 21·62  |   3   |  2 | 2·00|  8·48 | 21·20
     3   |  3 | 1·90|   8·66| 22·79  |   3   |  3 | 2·40| 11·34 | 23·63
     3   |  4 | 2·13|  11·24| 26·39  |   3   |  4 | 2·80| 14·84 | 26·50
     3   |  5 | --  | Smokes|  --    |   3   |  5 | 3·15| 17·04 | 27·20
     3   |  6 | --  |   "   |  --    |   3   |  6 | 3·25| 18·07 | 27·80
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
   3-1/2 |  2 | 1·50|   5·81| 19·36  | 3-1/2 |  2 | 2·12|  8·85 | 20·87
   3-1/2 |  3 | 1·95|   8·30| 21·28  | 3-1/2 |  3 | 2·55| 12·63 | 24·76
   3-1/2 |  4 | 2·55|  12·08| 23·68  | 3-1/2 |  4 | 3·00| 14·47 | 26·12
   3-1/2 |  5 | 2·80|  14·38| 25·68  | 3-1/2 |  5 | 3·50| 18·07 | 25·81
   3-1/2 |  6 | 3·00|  15·58| 25·97  | 3-1/2 |  6 | 3·60| 19·45 | 27·01
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
     4   |  2 | 1·60|   6·36| 19·87  |   4   |  2 | 2·30|  9·77 | 21·24
     4   |  3 | 2·10|  10·69| 25·45  |   4   |  3 | 2·90| 13·83 | 23·84
     4   |  4 | 2·65|  13·37| 25·23  |   4   |  4 | 3·30| 17·06 | 25·85
     4   |  5 | 3·45|  17·61| 25·52  |   4   |  5 | 4·10| 21·57 | 26·30
     4   |  6 | 3·55|  18·07| 25·45  |   4   |  6 | 4·20| 22·40 | 26·66
  -------+----+-----+-------+--------+-------+----+-----+-------+--------
     5   |  2 | 1·77|   7·38| 20·85  |   5   |  2 | 2·60|  9·68 | 18·81
     5   |  3 | 2·30|  11·90| 25·87  |   5   |  3 | 3·30| 13·64 | 20·67
     5   |  4 | 3·30|  15·40| 23·33  |   5   |  4 | 4·00| 19·91 | 24·14
     5   |  5 | 4·10|  20·74| 25·29  |   5   |  5 | 5·00| 25·36 | 25·36
     5   |  6 | 4·30|  22·68| 26·37  |   5   |  6 | 5·30| 27·66 | 26·10
  -------+----+-----+-------+--------+-------+----+-----+-------+--------

  TABLE II.

  ----+----+----------------------+---------------------+------------------
      |    |    AT 0·5-INCH     |    AT 1·0-INCH      |    AT 1·5-INCH
           |      PRESSURE.     |      PRESSURE.      |      PRESSURE.
      |    +-----+-------+------+-----+-------+-------+-----+-------+------
  No. |No. |Cubic|Illumi-|Illum.|Cubic|Illumi-|Illum. |Cubic|Illumi-|Illum.
  of  |of  |Feet |nating |Power |Feet |nating |Power  |Feet |nating |Power
  Top.|Bot-|per  |Power. |per   |per  |Power. |per    |per  |Power. |per
      |tom.|Hour.|       |Five  |Hour.|       |Five   |Hour.|       |Five
           |     |       |Cub.  |     |       |Cub.   |     |       |Cub.
           |     |       |Ft.   |     |       |Ft.    |     |       |Ft.
  ----+----+-----+-------+------+-----+-------+-------+-----+-------+------
  A2  | 1  | --  |  --   |  --  | 1·5 |   2·7 |  9·0  | 2·0 |   4·0 | 10·0
   "  | 2  | 1·6 |  2·9  |  9·1 | 2·4 |   5·2 | 10·8  | 3·1 |   6·8 | 11·0
   "  | 2½ | 2·0 |  3·9  |  9·8 | 2·9 |   6·8 | 11·7  | 3·8 |   9·4 | 12·4
  A3  | 3  | 2·1 |  4·4  | 10·5 | 3·2 |   7·8 | 12·2  | 4·4 |  10·6 | 12·0
   "  | 3½ | 2·5 |  4·8  |  9·6 | 3·8 |   9·2 | 12·1  | 4·9 |  12·2 | 12·4
   "  | 4  | 2·5 |  5·4  | 10·8 | 3·8 |   9·6 | 12·7  | 5·2 |  13·6 | 13·1
   "  | 4½ | 3·0 |  6·4  | 10·7 | 4·5 |  10·8 | 12·0  | 5·9 |  14·8 | 12·5
   "  | 5  | 3·2 |  7·7  |  2·0 | 5·1 |  13·2 | 13·0  | 6·8 |  18·0 | 13·2
   "  | 6  | 3·7 |  8·7  | 11·8 | 5·8 |  15·5 | 13·3  | 7·7 |  21·0 | 13·6
   "  | 7  | 3·5 |  8·6  | 12·3 | 5·9 |  16·0 | 13·6  | 8·4 |  23·0 | 13·7
   "  | 8  | 3·7 |  9·0  | 12·2 | 6·2 |  16·8 | 13·5  | 8·6 |  23·4 | 13·6
  B1  | 1  | --  |  --   |  --  | 1·3 |   2·3 |  8·8  | 1·8 |   3·5 |  9·7
  B2  | 2  | 1·3 |  2·3  |  8·8 | 2·1 |   4·4 | 10·5  | 2·8 |   6·4 | 11·4
   "  | 2½ | 1·6 |  3·0  |  9·4 | 2·5 |   6·0 | 12·0  | 3·4 |   8·4 | 12·4
  B3  | 3  | 2·0 |  3·8  |  9·0 | 3·0 |   7·2 | 12·0  | 4·1 |  10·1 | 12·3
   "  | 3½ | 2·3 |  4·3  |  9·3 | 3·4 |   7·7 | 11·3  | 4·5 |  11·0 | 12·2
  B4  | 4  | 2·3 |  4·7  |  0·2 | 3·6 |   8·8 | 12·2  | 5·0 |  13·0 | 13·0
   "  | 4½ | 2·7 |  5·9  | 10·9 | 4·3 |  10·4 | 12·1  | 5·6 |  15·0 | 13·4
  B5  | 5  | 3·1 |  7·0  | 11·3 | 4·9 |  12·9 | 13·2  | 6·5 |  18·0 | 13·8
  B6  | 6  | 3·8 |  9·6  | 12·6 | 5·9 |  16·4 | 13·8  | 8·0 |  23·0 | 14·4
  B7  | 7  | 4·0 | 10·2  | 12·8 | 6·6 |  19·0 | 14·4  | 9·0 |  26·0 | 14·4
  B8  | 8  | 4·7 | 11·8  | 12·6 | 7·3 |  22·0 | 15·1  | 9·6 |  30·0 | 15·7
  ----+----+-----+-------+------+-----+-------+-------+-----+-------+------

[Sidenote: Pressure of gas with the Brönner burner.]

Doubtless the chief cause of the remarkable efficiency of the Brönner
over previous burners is to be found in the pressure at which the
gas flows from the burner and is consumed. In the course of some
experiments made to determine the pressure at which gas is delivered
from various burners, the writer found that from a No. 4 Brönner, with
an initial pressure--_i.e._, the pressure at the inlet when the burner
is in operation--of 1 inch, the gas issued at a pressure of only 0·05
inch; and with an initial pressure of 0·5 inch, the outlet pressure was
only 0·03 inch. On the other hand, a No. 4 steatite flat-flame burner,
without any arrangement for retarding the flow of the gas, under the
same initial pressure gave at the outlet 0·16 inch and 0·05 inch
respectively. The absence of anything within the burner to cause the
gas to swirl, or to issue with an unsteady flow, must also be credited
with contributing, in no slight degree, to the favourable results
yielded by these burners.


THE HOLLOW-TOP BURNER.

In the hollow-top burner we have one of the most notable improvements
which have been effected in flat-flame burners. A simple modification
of the batswing--the earliest of flat-flame burners--it is not more
complicated in its details than is that burner. Yet, simple as it
is, its construction exhibits an important advance upon the original
batswing. Indeed, this burner may be said to embody the only
considerable improvement that has been made in the distinctive features
of the batswing since the introduction of the latter burner, which, as
we have seen, took place as early as the year 1816.

[Sidenote: The hollow-top an improved batswing burner.]

In its outward form, the hollow-top burner differs little, if at all,
from the batswing; but a slight modification which has been adopted in
the arrangement of its interior has produced a very marked result in
improving the shape of the flame yielded by the burner, and, to some
extent, in the results, as regards illuminating power, which it is
capable of affording. In this burner, as its name implies, the
interior of the top or head of the burner is hollowed out, forming an
enlargement of the cavity or chamber within the burner, and (what is
chiefly important) making the shell of the dome-shaped burner head of
equal thickness throughout. In the ordinary batswing, in consequence
of the varying thickness of the burner at this part, the slit is much
deeper in the middle than at any other part of its length, and
gradually decreases in depth towards each end. As the resistance to
the passage of the gas, or the friction which it encounters, increases
with the depth of the slit, the gas passes out from the burner at the
ends of the slit more readily than in the middle; producing a
wide-stretching flame, of scanty height in proportion to its width.
From the same cause the flame is not of equal thickness throughout;
being thinner in the middle than at the ends. Moreover, the outer
extremities of the flame, extending so far beyond the body of the
burner, are unable to retain the form given to them by the lateral
flow of the gas at the ends of the slit; the resistance, presented by
the atmosphere, together with the natural tendency of the gas to
ascend, causing the under portion of the flame to fold back upon
itself. As one result of this combination of untoward circumstances,
the flame is liable to smoke with a slight agitation of the
surrounding air.

In the hollow-top burner, the slit is of equal depth throughout its
length; and the resistance offered to the passage of the gas being the
same in all parts of the slit, the gas flows through the middle as
readily as at the ends--nay, in reality rather more so, owing to the
innate ascensive power of the gas, due to its being lighter than air.
The peculiar hollowing-out of the head of the burner, also, withdraws
the ends of the slit out of the direct course or current of the gas
through the burner; so that the tendency of the stream of gas to issue
at these points, in preference to going through the middle of the
slit, is further checked. The consequence is that the shape of the
flame is considerably improved; it being taller, more compact, and not
so broad as that of the batswing. In addition, the flame being of
equal thickness throughout, its illuminating power is somewhat
improved; while, from its compactness, it is better enabled to resist
atmospheric influences. With this alteration in the shape of the flame
all original resemblance to a batswing is entirely destroyed; but the
appearance of the flame of the new burner is much more agreeable to
the eye than that of the older batswing.

  [Illustration: FIG. 9.--ORIGINAL HOLLOW-TOP BURNER.
                 (From Wadsworth's Specification.)]

[Sidenote: Who invented the hollow-top burner.]

As has been exemplified in so many instances in the history of
invention, the hollow-top burner was not appreciated at its true value
until long after it had been brought into existence. It appears to
have been originally invented by Joseph and James Wadsworth, of Marple
and Salford, and was patented by them in 1860. According to the
specification of the inventors, the burners might be made either
in solid or sheet metal, as will be seen from the accompanying
illustrations, copied from the drawings in the specification. But
there were difficulties in the way of casting the burners in solid
metal which do not seem to have been surmounted; and those produced
under the patent appear to have been made exclusively of sheet brass.
For many years these burners were made and sold without their
peculiarities attracting any marked attention; which would seem to
imply that their faulty construction precluded the attainment of all
the advantages afforded by the burner as we know it.

[Sidenote: Sugg's hollow-top burner.]

The superior results which the hollow-top burner was calculated to
afford did not become fully apparent until the burner was made of
non-conducting material, and greater care exercised in its
construction. This appears to have been done in Germany earlier than
in this country. But, in England, it was undoubtedly Mr. Sugg who
first turned his attention to the improvement of the burner, and
demonstrated its merits. Mr. Sugg commenced the manufacture of this
burner in steatite in the year 1868; and since that time the burner
has been extensively employed, and its advantages widely recognized.
The superiority of hollow-top burners produced by Mr. Sugg to those
previously manufactured, is chiefly the result of their being made in
steatite instead of in metal. With this material, greater exactness
and uniformity are obtained in the shape and dimensions of the burner
than when metal is employed; besides which there is (what has been
before referred to) the advantage arising from its inferior conductive
capacity for heat, and its non-liability to corrosion. Another
improvement, also due to Mr. Sugg, and which is productive of
noticeable results, consists in cutting the slit of the burner with
a circular saw, applied from above, so as to make the ends of the
slit curved instead of horizontal; by which means the tendency of
the gas to issue laterally at the ends of the slit, and form horns
to the flame, is lessened. Mr. Sugg's table-top burner (which was
introduced in 1880), in addition to the characteristic features
of the hollow-top, has a rim-like projection from the burner, below
the slit; its object being to protect the flame from the disturbing
influence of the uprush of air in its immediate vicinity, and so
preserve its shape unaltered, while diminishing its liability to
smoke. Prior to Mr. Sugg--namely, in the early part of 1879--Mr. Bray
had successfully obviated this injurious action upon the flame of the
ascending current of air, by affixing to the burner two arms of brass,
so placed as to be immediately under the projecting wings of the
flame.

  [Illustration: 1868 BURNER.
                 1874 BURNER.
                 TABLE-TOP BURNER.
                 FIG. 10.--SUGG'S HOLLOW-TOP BURNERS.]


BRAY'S BURNERS.

The burners of Messrs. George Bray and Co. have deservedly acquired a
world-wide reputation, and are in extensive use wherever gas lighting
is known. Their distinguishing characteristic, and that which has won
for them the high repute in which they are held, is the union of
cheapness with remarkable efficiency. In all the various descriptions
and classes of burners which are produced by this firm, the
characteristic referred to is preserved; although it is needless to
add that the different varieties are not equally efficient. Of the
three forms of flat-flame burners we have been considering--batswing,
union-jet, and hollow-top--the one which, more than any other, has
been the speciality of the firm is the union-jet; and it is with the
development of this class of burner that the name of Bray is most
intimately and honourably associated.

  [Illustration: UNION-JET.
                 HOLLOW-TOP OR SLIT-UNION.[9]
                 BATSWING.
                 FIG. 11.--BRAY'S "REGULATOR" BURNERS.]

          [9] The name "slit-union," by which Mr. Bray prefers to
          designate this burner, he states to be derived from the
          resemblance of its flame to that of the union-jet burner;
          while it is produced by means of a slit.

[Sidenote: Bray's "regulator" burner.]

[Sidenote: Bray's "special" burner.]

The "regulator" union-jet, which was the first notable burner produced
by Messrs. Bray, has received, perhaps, a wider application than any
other single gas-burner. It consists of a cylindrical brass case,
screwed at one end for insertion into the fittings, and at the other
containing a tip of "enamel"--a material invented by Mr. Bray, and
apparently of somewhat similar composition to the "adamas" of Mr.
Leoni--the "enamel" tip being perforated, in the usual manner, with
two holes, set at an angle to each other, for the outflow of the gas.
The distinctive feature of this burner is the introduction into the
lower part of the brass case of a layer, or layers, of muslin;
designed to check in some degree, and to steady the current or flow of
the gas through the burner. At the time of its introduction, this
burner compared very favourably, as regards the results it yielded,
with other burners in common use; and its fairly good performances,
together with the very low price at which it can be sold, cause it
still to be extensively employed wherever the attainment, from the gas
consumed, of the highest obtainable results may be subordinated to
cheapness, or in situations where, from delicacy of construction or
from the care and attention demanded, a more efficient burner may not
be so suitable. But in the matter of developing the illuminating power
of the gas employed, the "regulator" is far surpassed by the more
recently introduced "special" burner of the same makers.

  [Illustration: UNION-JET.
                 HOLLOW-TOP OR SLIT-UNION.
                 BATSWING.
                 FIG. 12.--BRAY'S "SPECIAL" BURNERS.]

Mr. Bray's series of "special" burners--embracing union-jet,
hollow-top, and batswing--are constructed upon the principle of, and
in form are somewhat similar to Brönner's burners, which have already
been fully described. Apart from its being of greater bulk, the main
divergence in the construction of the "special" burner from that of
the earlier "regulator" is the introduction, into the lower part of
the brass case, of a plug or washer of enamel, pierced by a small
circular hole for the admission of gas into the burner; the diameter
of this hole determining the quantity of gas which, at any particular
pressure, is admitted into the burner. Just above the enamel washer, a
layer of muslin is inserted, as in the "regulator" burner; which, in
this case, is for the purpose of subduing the agitation, or swirl,
acquired by the current of gas in passing through the narrow aperture
in the washer. A tip of enamel, made of the particular description
(union-jet, hollow-top, or batswing) required, fitting into the upper
part of the brass case, completes the burner. The objects aimed at in
the "special" burner are to cause the gas to be consumed at the lowest
pressure compatible with the maintenance of a firm flame, and with the
least agitation, or swirl, in the current of gas as it issues from
the burner. The former is attained, as in Brönner's burners, by
diminishing the area of the opening admitting into the burner, without
a corresponding diminution of the orifices through which the gas
issues into the atmosphere; the latter, by the interposition of
the layer of muslin which is immediately above the diminishing
arrangement, as well as by the enlargement of the gas chamber in
the upper part of the burner. The improvement thus effected in the
illuminating power developed from the gas is well shown in the
following tables extracted from an exhaustive series of tests of
gas-burners carried out by Mr. T. Fairley, F.R.S.E., Borough Analyst
of Leeds, and embodied by him in a report presented to the Leeds
Corporation. The full text of the report will be found in the _Journal
of Gas Lighting_ for February 6, 1883.

  _Medium Lighting Power Union-Jets._

  -----------------------------------+-----------------------------------
        "Regulator" Burners.         |      "Special" Burners.
  ------+------+-----+-------+-------+------+------+-----+-------+-------
  No.   |Pres- |Cubic|Illumi-|Illumi-|No.   |Pres- |Cubic|Illumi-|Illumi-
  of    |sure  |Feet |nating |nating |of    |sure  |Feet |nating |nating
  Burner|in    |per  |Power  |Power  |Burner|in    |per  |Power  |Power
        |Inches|Hour |in     |per 5  |      |Inches|Hour |in     |per 5
        |      |     |Stand. |Cubic  |      |      |     |Stand. |Cubic
        |      |     |Candls.|Feet.  |      |      |     |Candls.|Feet.
  ------+------+-----+-------+-------+------+------+-----+-------+-------
     3  |  0·5 | 3·50|   6·8 |  9·7  |   3  |  0·5 | 3·43|  11·3 | 16·4
     3  |  1·0 | 4·80|   6·9 |  7·2  |   3  |  1·0 | 4·90|  15·6 | 15·8
     3  |  1·5 | 6·20|   7·5 |  6·05 |   3  |  1·5 | 6·03|  17·6 | 14·6
     4  |  0·5 | 4·65|  12·2 | 13·1  |   4  |  0·5 | 3·73|  13·3 | 17·8
     4  |  1·0 | 6·67|  14·2 | 10·6  |   4  |  1·0 | 5·15|  17·4 | 16·9
     4  |  1·5 | 8·16|  14·2 |  8·8  |   4  |  1·5 | 6·57|  22·4 | 17·1
     5  |  0·5 | 5·72|  17·0 | 14·9  |   5  |  0·5 | 4·80|  17·6 | 18·3
     5  |  1·0 | 7·97|  20·0 | 12·6  |   5  |  1·0 | 6·67|  24·4 | 18·3
     5  |  1·5 | 9·73|  21·8 | 11·2  |   5  |  1·5 | 8·30|  30·0 | 18·2
     6  |  0·5 | 5·90|  18·0 | 15·2  |   6  |  0·5 | 5·48|  20·1 | 18·3
     6  |  1·0 | 8·35|  23·0 | 13·8  |   6  |  1·0 | 7·65|  28·4 | 18·6
     6  |  1·5 |10·60|  28·0 | 13·2  |   6  |  1·5 | 9·20|  34·2 | 18·7
  ------+------+-----+-------+-------+------+------+-----+-------+-------

  _Medium Lighting Power Slit-Unions._

  -----------------------------------+-----------------------------------
        "Regulator" Burners.         |      "Special" Burners.
  ------+------+-----+-------+-------+------+------+-----+-------+-------
  No.   |Pres- |Cubic|Illumi-|Illumi-|No.   |Pres- |Cubic|Illumi-|Illumi-
  of    |sure  |Feet |nating |nating |of    |sure  |Feet |nating |nating
  Burner|in    |per  |Power  |Power  |Burner|in    |per  |Power  |Power
        |Inches|Hour |in     |per 5  |      |Inches|Hour |in     |per 5
        |      |     |Stand. |Cubic  |      |      |     |Stand. |Cubic
        |      |     |Candls.|Feet.  |      |      |     |Candls.|Feet.
  ------+------+-----+-------+-------+------+------+-----+-------+-------
    3   | 0·5  | 4·22|  13·8 |  16·4 |   3  |  0·5 | 3·04|  10·8 | 17·8
    3   | 1·0  | 6·37|  20·2 |  15·9 |   3  |  1·0 | 4·61|  16·4 | 17·6
    3   | 1·5  | 8·14|  25·8 |  15·9 |   3  |  1·5 | 5·88|  19·9 | 16·9
    4   | 0·5  | 4·25|  14·8 |  17·4 |   4  |  0·5 | 3·82|  14·2 | 18·6
    4   | 1·0  | 5·88|  20·6 |  17·5 |   4  |  1·0 | 5·69|  20·8 | 18·3
    4   | 1·5  | 7·95|  26·5 |  16·6 |   4  |  1·5 | 7·35|  25·6 | 17·5
    5   | 0·5  | 5·25|  19·0 |  18·2 |   5  |  0·5 | 4·12|  15·4 | 18·7
    5   | 1·0  | 8·14|  28·4 |  17·45|   5  |  1·0 | 6·37|  23·4 | 18·4
    5   | 1·5  |10·20|  36·4 |  17·8 |   5  |  1·5 | 7·94|  28·5 | 18·0
    6   | 0·5  | 5·67|  22·2 |  19·6 |   6  |  0·5 | 5·00|  19·6 | 19·6
    6   | 1·0  | 8·60|  33·6 |  19·4 |   6  |  1·0 | 7·55|  29·0 | 19·2
    6   | 1·5  |11·10|  39·5 |  17·8 |   6  |  1·5 | 9·70|  37·0 | 19·1
  ------+------+-----+-------+-------+------+------+-----+-------+-------

  _Medium Lighting Power Batswings._

  -----------------------------------+-----------------------------------
        "Regulator" Burners.         |      "Special" Burners.
  ------+------+-----+-------+-------+------+------+-----+-------+-------
  No.   |Pres- |Cubic|Illumi-|Illumi-|No.   |Pres- |Cubic|Illumi-|Illumi-
  of    |sure  |Feet |nating |nating |of    |sure  |Feet |nating |nating
  Burner|in    |per  |Power  |Power  |Burner|in    |per  |Power  |Power
        |Inches|Hour |in     |per 5  |      |Inches|Hour |in     |per 5
        |      |     |Stand. |Cubic  |      |      |     |Stand. |Cubic
        |      |     |Candls.|Feet.  |      |      |     |Candls.|Feet.
  ------+------+-----+-------+-------+------+------+-----+-------+-------
     3  |  0·5 | 4·16|  12·6 |  15·1 |   3  |  0·5 | 3·37|  12·4 | 18·4
     3  |  1·0 | 5·64|  16·6 |  14·8 |   3  |  1·0 | 5·25|  20·4 | 19·4
     3  |  1·5 | 7·83|  21·0 |  13·4 |   3  |  1·5 | 7·13|  24·0 | 16·8
     4  |  0·5 | 4·26|  14·0 |  16·4 |   4  |  0·5 | 3·67|  13·0 | 17·7
     4  |  1·0 | 6·74|  21·2 |  15·6 |   4  |  1·0 | 5·55|  20·6 | 18·6
     4  |  1·5 | 7·81|  24·0 |  15·3 |   4  |  1·5 | 7·13|  26·0 | 18·2
     5  |  0·5 | 4·76|  15·4 |  16·2 |   5  |  0·5 | 3·86|  14·6 | 18·9
     5  |  1·0 | 6·93|  20·4 |  14·7 |   5  |  1·0 | 5·85|  22·6 | 19·4
     5  |  1·5 | 8·72|  25·8 |  14·7 |   5  |  1·5 | 7·53|  28·0 | 18·6
     6  |  0·5 | 6·04|  20·0 |  16·5 |   6  |  0·5 | 4·86|  19·4 | 20·0
     6  |  1·0 | 8·82|  29·4 |  16·6 |   6  |  1·0 | 7·53|  31·6 | 21·0
     6  |  1·5 |11·10|  31·6 |  14·2 |   6  |  1·5 | 9·60|  39·0 | 20·4
  ------+------+-----+-------+-------+------+------+-----+-------+-------

The quality of the gas operated upon averaged about 19 candles when
tested with the Standard London Argand Burner.

In a former part of this treatise it was remarked that the flames
produced by the modern representatives[10] of the batswing and fishtail
burners have lost the original resemblance to the objects whence the
names of those burners were derived; and that the two flames have
gradually approached each other in shape, until, in their latest
developments, they are practically identical. We have seen how that,
by the invention of the hollow-top, a burner is obtained apparently,
to all outward appearance, the same as the batswing, yet giving a
greatly improved form of flame. We have now to learn how the fishtail,
or union-jet burner has been modified so as to yield a flame closely
agreeing with that produced by the improved slit burner.

          [10] Although the true batswing is still in common use, I
          look upon the hollow-top as being its "modern representative;"
          seeing that, in a great many instances, it has superseded
          the former burner--of which, indeed, it is only an improved
          form.

[Sidenote: How the union-jet burner has been improved.]

As first constructed, the union-jet burner gave a tall, narrow flame;
its extremity being forked and jagged like the tail of a fish. Besides
being unsightly, this form of flame was ill-adapted to develop, to
anything like its full extent, the illuminating power of the gas. In
order to obtain the best results, as regards illuminating power, the
heat-intensity of the flame must be very high, so as to bring up the
temperature of the particles of carbon liberated in the flame to the
necessary degree of incandescence. To this end there must be
concentration of the flame, in order to utilize to the full the heat
of combustion. With the tall flame produced by the original union-jet
burner there was too much exposure to the atmosphere for the flame to
attain to the requisite intensity of heat; as well as considerable
liability of the gas being brought too early into intimate contact
with air, and so oxidized, or fully consumed, before its carbon had
been raised to the temperature necessary to enable it to give out
light. With the burner in its improved form the height of the flame is
much curtailed, while it is broadened, and made more even and compact.
This alteration has been chiefly brought about by two modifications in
the construction of the burner-tip--first, by hollowing out its flat
upper surface; and, second, by altering the angle at which the two
streams of gas emerge from the burner. By scooping out the central
portion of the flat top of the burner, so as to form a hollow or
depression where the gas emerges, the flat sheet of flame which is
formed when the two streams of gas impinge upon each other obtains a
broader base, and at the same time is preserved from drawing air into
its midst. But the chief share of the improvement is due to the
alteration in the angle formed by the two channels in the burner-tip.
It will be readily apparent that the more obtuse this angle--that is,
the nearer the two streams of gas are to impinging against each other
in a horizontal line--the more will the flame tend to spread out, or
the lower the pressure required to obtain any desired spread of flame.
It is by taking advantage of this circumstance that Mr. Bray has been
enabled to improve the union-jet burner. Twenty years ago this burner
was usually made with the two channels in the burner-tip placed at an
angle of about 60°. In Bray's "regulator" burner, introduced in 1869,
they were placed at an angle of 90°; with the result of obtaining a
more satisfactory flame, both as regards its appearance and
illuminating power. In the "special" burner, which was not brought out
till 1876, the angle is increased to 120°; thus enabling the necessary
spread of flame to be obtained with the gas issuing at a low pressure.
Another minor improvement in the latter burner consists in making the
holes in the burner-tip elliptical instead of circular.




CHAPTER III.

ARGAND BURNERS.


[Sidenote: The premier gas-burner.]

The premier position among gas-burners undoubtedly belongs to the
Argand; and it is from no unwillingness to recognize its claims, much
less from ignorance of its merits, that I have left the consideration
of this burner until now. It occupies this honourable position as much
by virtue of the importance it has acquired through being accepted by
Parliament as the test burner, and the peculiar relation in which it
consequently stands to other burners, as for any marked superiority in
operation. For while, in general, the Argand gives superior results to
other burners, this is not always the case. There are circumstances
and conditions to which the Argand is quite inapplicable, and where a
simpler and less pretentious burner will give excellent results.
Indeed, some of the simple flat-flame burners which we have had under
notice have now been brought to such a stage of perfection, that, when
intelligently used, they not unsuccessfully rival the Argand. But it
has been in the direction of demonstrating the illuminating power
which it was possible to obtain from gas, and stimulating to the
attainment, by other and simpler burners, of the same level of
excellence, that the influence of the Argand has been most beneficial.
For, by reason of its peculiar construction, and more especially its
mode of obtaining the air necessary for combustion, the Argand lends
itself, more readily than any other burner, to the work of
investigating and experimenting upon the conditions necessary for
economical combustion, and the development of the highest illuminating
power from the gas consumed. In this burner, the air supply to the
flame is under complete control; and thus one of the chief elements of
uncertainty and difficulty which are experienced in dealing with other
burners is eliminated. The delivery of gas to different parts of the
flame is also more susceptible of variation; and the results of such
variation more fully exposed to observation. The consequence has been
that the most remarkable advances in developing improved illuminating
power from coal gas have been made with this burner. But after the
possibility of obtaining an improved duty from the gas has been
demonstrated by means of the Argand, and the conditions necessary for
its attainment determined, equally good results have been achieved by
other burners.

  [Illustration: PLAN OF GLASS-HOLDER AND BURNER TOP.
                 SECTION OF BURNER.
                 FIG. 13.--ARGAND BURNER.]

In thus showing the benefits to be derived from a more scientific mode
of combustion, and leading the way to the fuller attainment, by other
burners, of the illuminating power obtainable from the gas, the Argand
burner has acted as a pioneer in the development of gas lighting. For,
on account of its complexity, and its delicacy of construction, this
burner has never been, nor, indeed, can ever hope to be generally
employed. Besides the inconvenience and expense entailed by the
cleaning and renewal, when broken, of the glass chimney which is
indispensable to this burner, its very perfection as a burner
precludes its being adopted under the conditions which appertain to
the great majority of situations in which gaslight is required. For
while, under the particular conditions as to pressure of gas, &c., for
which it has been constructed, the Argand may give results surpassing
any other burner, a very slight divergence from these conditions is
productive of far more damaging results to the illuminating power of
the flame than is the case with other and less efficient burners. The
cause of this seeming anomaly will be apparent when we come to
consider in detail the construction of the Argand, and the conditions
which must be observed to ensure its satisfactory operation. For the
present it will suffice merely to make mention of what appear to be
well-established facts--viz., that the most perfect burners are the
least adapted for use under uncertain and varying conditions; and that
in proportion to the efficiency of a burner, under the conditions for
which it has been constructed, is the injury to the illuminating power
of its flame which is experienced when these conditions are departed
from.

[Sidenote: What is an Argand burner?]

Resolved into its simplest form, the Argand burner may be said to
consist of a hollow ring of metal, or other suitable material,
provided with the necessary tubes or connections for communicating
between its interior and the gas supply, and perforated on its upper
surface with a number of holes for the emission of the gas. Through
these holes the gas issues in a series of jets, which immediately
coalesce to form one cylindrical sheet of flame. The burner is
surmounted, and the flame enclosed, by a glass chimney, which is
supported on a light gallery connected with the burner; the chimney
serving the double purpose of shielding the flame from draughts, or
currents of air (thus enabling the gas to burn uniformly and
steadily), and of drawing upon the surface of the flame the supply of
air necessary for its proper and complete combustion. For in the
Argand the air supply is produced under conditions totally different
from those which govern its production in all the other burners we
have had under consideration. In flat-flame burners, the quantity of
air supplied to the flame is determined by the pressure of the gas;
or, in other words, the velocity with which it issues from the burner.
In Argand burners, on the contrary, the air supply is obtained quite
independently of the pressure at which the gas issues; and the
conditions most effective for the economical combustion of the gas,
and the development from it of the highest illuminating power
attainable, are only secured when the pressure of gas is reduced to a
minimum.

It has been shown, in speaking of flat-flame burners, how the
illuminating power of the flames yielded by such burners is
injuriously affected by an excess of pressure in the gas, as it issues
into the atmosphere, causing a too great intermingling of gas and air.
With such burners, however, some degree of pressure is needed, in
order, by bringing the flame into contact with sufficient of the
oxygen of the air, to promote the requisite intensity of combustion;
whereas with the Argand the draught that is produced through the
agency of the glass chimney enables the necessary supply of air to be
obtained for the support of the flame without adventitious aid from
the pressure of the gas. Consequently, one of the chief objects to be
aimed at in the construction of the latter burner is to so reduce the
pressure of the gas within the burner that it may issue with little or
no greater velocity than that due to its own specific lightness. In
some of the best Argands this object is attained very successfully;
and the ingenious devices which have been made use of to gain this end
will be duly described in the sequel. But, in addition to causing the
gas to issue from the burner at the minimum of pressure, it must be
delivered evenly and equally at all parts of the ring of holes; so
that there shall not be an excess of gas supplied to one portion of
the flame, and an insufficiency to others. Then the area of the
opening in the centre of the ring, through which the air supply is
obtained to the inner surface of the flame, as well as the length and
diameter of the glass chimney, must be so proportioned that the exact
quantity of air needed to enable the flame to yield its maximum
results shall be drawn upon it. These, and other equally essential
requirements, have to be taken into consideration, and provided for,
in constructing an efficient Argand burner. It is no wonder,
therefore, that the development of the powers of this burner has taken
up so much time and labour and inventive skill; and the remarkable
degree of efficiency to which it has now been brought testifies to the
thought and the accurate knowledge of the principles of combustion
which have been brought to bear upon it.

[Sidenote: The earliest Argands.]

It is, however, only within comparatively recent years that its true
principles of construction have been at all fully recognized, as
evinced by the burners which have been produced. For a long period,
Argand burners were made upon wholly empirical and arbitrary rules.
During the early years of gas lighting, the makers of gas apparatus,
and such persons as professed to have a special knowledge of the
production and utilization of the new illuminant, appear to have been
ignorant of even the most obvious of the conditions required for the
successful working of the burner. In one of the earliest works which
appeared relating to gas lighting,[11] we find the Argand burner
described as consisting of "two concentric tubes closed at the top
with a ring having small perforations, out of which the gas can issue;
thus forming small distinct streams of light." According to this
description, the burner referred to cannot have been an Argand in the
strictest sense of the word; but, in reality, must have consisted
chiefly of a series of single jets placed in a circle, and surrounded
by a glass chimney. But the great improvement in the amount of light
developed, which resulted from bringing the jets of flame closer
together, so as to cause them to coalesce and produce one homogeneous
mass of flame, could not long escape notice; and accordingly we find
that in "Clegg's Treatise," which appeared twenty-five years later,
the proper disposition of the holes in the ring, necessary for the
successful operation of the burner, is clearly recognized. In this
work, speaking of the Argand burner, it is remarked (p. 193) that "the
distance between the holes in the drilled ring should be so much that
the jet of gas issuing from each shall, when ignited, just unite with
its neighbour."

          [11] Accum's "Treatise on Gas-Lights."

Before a really efficient burner could be produced, there were,
however, to be successfully encountered other problems, the precise
nature of which was not so clearly apparent as that of the one above
referred to; otherwise their solution would not have been so long
delayed. Of these, the most important, and at the same time the most
difficult, were two--namely, the right adjustment of the air supply,
and the most advantageous pressure at which to consume the gas. In the
earliest Argands, not the slightest provision was made for diminishing
the pressure of the gas before it was consumed. It was thought that
everything had been accomplished that was necessary if the holes for
its emission were sufficiently minute to allow of no more than the
required quantity of gas passing through them at the extreme pressure
at which it was supplied to the burner. The consequence was that the
gas, issuing from the burner at a very high velocity, became so
intermingled with air before it was consumed, that its flame was
excessively cooled; and only a small fraction of the illuminating
power available was developed. Then as to the air supply. In nearly
every burner produced prior to Mr. W. Sugg's invention of the "London"
Argand in 1868, this was greatly in excess of the requirements; nor is
it to be wondered at. Had the supply of air been delicately adjusted,
while yet there was no provision for diminishing the pressure of gas
at the burner, the flame would have been liable to smoke on any sudden
increase in the pressure of gas in the mains; and the annoyance and
inconvenience occasioned by a smoking flame were greater drawbacks
than the loss of light experienced through having the air supply
greatly in excess. Thus, although during this period there were many
so-called "improved" burners brought into notice, in none of them were
these two cardinal requirements in the production of an efficient
burner clearly recognized and seriously grappled with; and,
consequently, the high level of excellence to which the Argand is
capable of being brought was not attained.


SUGG'S ARGANDS.

[Sidenote: The 'London' Argand.]

The invention by Mr. W. Sugg, in 1868, of the famous "London" Argand
constitutes an important epoch in the history of gas lighting. Prior
to that time, the construction of this class of burners had been
carried out in a wholly empirical manner; and such improvements as had
been effected must be looked upon as being rather the fortuitous
issues of hap-hazard endeavours, than as resulting from the
acquirement of clearer views as to the conditions to be complied with
in order to ensure the successful operation of the burners. The
invention of the "London" Argand was the first earnest attempt to
abandon the former chance methods, and to proceed upon more scientific
lines. Its construction shows that its inventor possessed a thorough
acquaintance with the principles of combustion; while, in many
particulars, it exhibits an intelligent discernment, and a successful
application of the precise means required to attain a desired end. In
this burner, the extreme importance of causing the gas to issue at a
low pressure is for the first time clearly recognized; and the manner
in which this object is so successfully attained is as simple as it is
ingenious. At the entrance to the burner the gas is divided among
three narrow tubes, the combined capacity of which is much smaller
than that of the pipe supplying the burner. Through these tubes the
gas is conducted into a concentric cylindrical chamber (forming the
main body of the burner), where its rapid flow is checked; the
current, or swirl, which it may have acquired, is subdued; and the gas
comes to a state of comparative rest before it issues into the
atmosphere and is consumed. The top rim of this concentric cylinder is
pierced with 24 holes, the aggregate area of which is considerably
greater than that of the three supply-tubes; thus ensuring that the
gas shall be delivered at a much lower pressure than that at which it
enters the burner. By dividing the gas into three streams, which enter
the cylindrical chamber at equidistant points in its circumference,
the supply is equally distributed throughout the entire ring of holes;
and a flame of even and regular shape is the result.

The arrangement by which, in this burner, the air supply is obtained
and regulated is as noteworthy as are the means adopted for
controlling the pressure of the gas. The opening within the circular
ring of holes is much smaller than in previous Argands; thereby
proportionately reducing the quantity of air supplied to the inner
surface of the flame. The space between the cylindrical body of the
burner and the glass chimney is occupied by a truncated cone of thin
metal, the upper edge of which is on a level with, and reaches to
within a very short distance of the rim of the burner; while its base
rests upon the gallery supporting the chimney. By means of this cone,
all the air entering between the burner and the chimney is directed
upon the immediate surface of the flame; thereby promoting intensity
of combustion, and a higher illuminating power of the flame. Then the
chimney itself is of such dimensions that, with the quantity of gas
for which the burner has been constructed, just sufficient air is
drawn upon the flame to completely consume the gas by the time the top
of the chimney is reached; a flame of such length as to nearly reach
to the top of the chimney, without smoking, being the most effective
and economical for the quantity of gas consumed.

  [Illustration: FIG. 14.--SUGG'S "LONDON" ARGAND.
                 (_Full Size._)]

Another matter which tended not a little to enhance the results
yielded by this burner was an alteration in the material of which the
body of the burner was constructed. In previous Argands, this had, in
almost every instance, been metal; whereas in the "London" burner
steatite was employed. How the illuminating power of the flame is
affected by the material of which the burner is constructed has been
gone into so fully before (in relation to flat-flame burners), that it
is unnecessary to dwell upon the matter here; only remarking that as
in Argands the contact surface between the burner and the flame is
relatively so much greater than in flat-flame burners, the cooling of
the flame due to this cause is proportionately increased.

[Sidenote: The standard test burner.]

[Sidenote: The improved "London" Argand.]

So great was the improvement effected by this burner in the
illuminating power developed from the gas consumed, so obvious its
superiority to every previous Argand, that it was immediately adopted
by the Metropolitan Gas Referees as the standard burner for testing
ordinary coal gas within the area of their jurisdiction; and from that
time down to the present it has continued to be prescribed in Acts of
Parliament as the burner to be employed in testing ordinary coal gas,
not only in the Metropolis, but generally throughout the United
Kingdom. But although, as the standard test-burner, the original
"London" Argand can still be obtained, it has been far surpassed, in
the results yielded, by a new series of Argands, in which the same
ingenious inventor has still further applied the principles first put
into practice in the former burner. In this newer series of burners,
the details of construction before adopted are modified in two or
three particulars; but without departing from the general principles
embodied in the arrangement of the earlier burner. Thus the holes in
the ring are considerably larger, while the three supply-tubes remain
of exactly the same capacity as before; by which means the gas is
delivered at a much lower pressure. As the increased size of holes
necessitates that the cylindrical body of the burner should be of
enlarged diameter, the opening in the centre becomes of greater area
than before. Were it to remain so, it would permit too large a
quantity of air to be drawn upon the inner surface of the flame; to
obviate which result a metal spike rises in the centre, reducing the
area of the opening, and proportionately diminishing the quantity of
air which would otherwise be admitted at this part of the burner. The
arrangement for regulating the air supply to the outer surface of the
flame is likewise modified, but in a different direction. The upper
edge of the cone is brought nearer to the rim of the burner, and
slightly curved, so as to direct the air more completely upon the
flame; while the base of the cone, instead of extending to the glass
chimney in an unbroken surface, is pierced by a number of holes, which
admit air between the cone and the chimney. The action of this third
current of air is to keep the chimney cool, and to steady the flame;
and, in addition, it may be that it provides a supply of air to
support and intensify combustion at the upper extremity of the flame.
The combined effect of these alterations is to cause the burner to
develop from 7 to 12 per cent. more light from the gas consumed, than
is yielded by the original "London" Argand.

[Sidenote: Silber's Argand burner.]

The Silber Argand, which is a remarkably efficient burner, in the main
features of its construction is very closely related to Mr. Sugg's
later Argands just described. The air is directed on to the outer
surface of the flame, as in those burners, by a curved deflector, of
which the upper edge is, however, at a higher level than in Mr. Sugg's
burners. Air is also admitted between the deflector and the glass
chimney. The most striking divergence in its construction from that of
Mr. Sugg's burners is contained within the opening in the centre of
the burner. Instead of a solid metal spike, there is a brass tube,
through which, as well as between its circumference and the
cylindrical body of the burner, air can enter to feed the inner
surface of the flame. In addition to promoting the steadiness of the
flame, it would appear that the air entering through this inner tube
supports the combustion of the gas at the tail of the flame. The
arrangements for diminishing the pressure of the gas within the
burner, and for ensuring its equable distribution to all parts of the
ring of holes, though quite different, seem to be scarcely less
complete than those employed in the "London" burner. From the nipple
which connects the burner to the gas supply, the gas enters (by four
minute perforations) into a horizontal chamber, where its velocity is
checked, and whence it is conveyed into the cylindrical chamber
forming the main body of the burner. The very satisfactory
performances of the burner (which are in advance of those of the
standard Argand) sufficiently attest the correctness of its
construction.

[Sidenote: Multiple Argands.]

For consuming large quantities of gas, double or treble Argands are
constructed. These consist, in effect, of two or three Argand burners
placed concentrically to each other within one chimney. Mr. Sugg
has produced a series of burners of this class, designed to pass
quantities of gas ranging from 15 to 55 cubic feet per hour; and, in
some instances, exceeding even the latter figure. These burners, with
ordinary (16-candle) coal gas, give a light equal to 4 candles per
cubic foot of gas consumed; which is a considerably better result than
is afforded by the standard burner. The cause of their yielding
results so superior to the ordinary Argand is found in the
circumstance that their flames present a much smaller surface area to
the cooling action of the air, in proportion to the quantity of gas
consumed. The arrangement of these burners differs from that of the
improved single Argands, which have been described, only in that there
are two or more steatite cylinders, each fed by its own supply-tubes,
and having its own distinct ring of holes; while the space between the
cylinders is so proportioned as to admit no more than the quantity of
air required to produce the necessary intensity of combustion.

  [Illustration: FIG. 15.--THE DOUGLASS ARGAND.
                 (_A A, Focal Plane, or Belt of Strongest Light._)]


THE DOUGLASS BURNER.

The multiple or concentric Argand invented by Mr. (now Sir) J. N.
Douglass, the Engineer to the Trinity House, may be mentioned here.
This burner is of the type of those last noticed, but possesses
certain peculiar features which give it a distinct claim to novelty.
As will be seen by the accompanying illustration, the concentric
cylinders of which the burner is composed terminate at different
heights; their tops forming a regular gradation of steps, of which the
innermost is the highest. These cylinders are of considerable depth,
permitting the gas and air to be heated by contact with their surfaces
before the point of ignition is reached. The essential feature of the
invention, however, is a series of deflectors of peculiar shape,
which, in addition to directing air on to the surfaces of the flames,
are so formed "as to force the outer flame or flames on to the inner
flame or flames in the manner illustrated." By this means the flames
are concentrated and united into one, and combustion is quickened;
and, a greater intensity of heat being thus attained, the illuminating
power is much augmented. When this burner was first brought into
notice, in 1881, high hopes were entertained as to its future. The
results which it was said to afford, being far in advance of anything
previously obtained from a simple Argand, seemed to promise for the
burner a speedy and unequivocal success. At the North-East Coast
Marine Exhibition, held in 1882, a burner with ten rings was
exhibited, which was reported to develop, from 16-candle gas, 6
candles per cubic foot--a truly remarkable result to be given by so
simple a burner. But, notwithstanding its apparently successful
introduction, the burner has made little or no headway in the
direction of its practical application. Indeed, it may almost be said
to have faded altogether out of public view. This would seem to imply
that there are difficulties in the way of its successful working, when
brought under ordinary conditions, which were not foreseen at the time
of its invention.




CHAPTER IV.

GOVERNOR-BURNERS.


[Sidenote: Effects of excessive pressure with Argand and flat-flame
burners.]

Throughout this treatise, much has been said of the relation which the
pressure of gas, at the point of its delivery from the burner, bears
to the illuminating power of the flame yielded--sufficient to show
that the maintenance of a low and equable pressure in the gas supply
is one of the conditions most imperative to be observed for the
attainment of economy in combustion. Ordinarily, however, this
condition does not obtain at the consumers' burners. The exigencies of
distribution require that, in order to maintain a sufficient supply
wherever gas is needed, a much higher pressure should be kept in the
mains than is requisite for developing, at the burner, the best
results from the gas consumed. Moreover, the pressure at any one point
is subject to continual fluctuations from the variations in the
consumption of gas going on in the neighbourhood. For instance, where
a number of burners are in operation in a house, consuming about the
exact quantities of gas for which they have been constructed, when
part of them are shut off the gas supply to the remainder is in excess
of what is required; and, consequently, the burners do not develop the
same proportion of light from the gas consumed as formerly. Where a
large consumption of gas is suddenly discontinued (as in the business
parts of a town, when the shops and warehouses are closed), the
increase of pressure that is experienced at the burners which remain
in operation is very manifest. The effect of this increase in the
pressure of the gas supply is seen in different directions in Argand
and flat-flame burners. In the former, it causes the flame to smoke,
by permitting more gas to pass through the burner than can be properly
consumed; in the latter, by cooling the flame below the temperature
required for effective combustion, it reduces, in proportion to the
extent to which it is higher than the original pressure, the
illuminating power developed per cubic foot of gas consumed.

[Sidenote: The gas regulator.]

Seeing that economy in combustion can only be attained under the
conditions of an equable pressure, it becomes necessary to subdue the
fluctuations above referred to, or at least to prevent their reaching
the burner. To this end the regulator, or governor, is employed. In
this instrument, a bell dipping into, and sealed in liquid--or else a
flexible leather diaphragm--is actuated by the pressure of the
entering gas, and so connected with a valve as to reduce the area of
the opening which permits gas to enter the instrument in proportion to
the pressure of gas at the inlet; by which means an equable pressure
is maintained at the outlet, no matter what the quantity of gas which
is being consumed, or how the pressure may vary in the inlet-pipe. By
the aid of a governor, fixed on the service-pipe at the entrance to a
building, the pressure of gas at the various burners is rendered
fairly uniform; yet, even then, perfect equality of pressure is not
obtained. The slight friction which the gas experiences in flowing
through the pipes causes the burners to be supplied at somewhat lower
pressures, the farther they are removed from the burner. And, again,
owing to its low specific gravity, gas tends to gain in pressure with
an increased elevation; each rise of 10 feet adding about 1-10th of an
inch to its pressure. From this cause a higher pressure is experienced
in the upper than in the lower rooms of a building. This peculiarity
was observed at an early period in the history of gas lighting; as
Clegg mentions that, in cotton-mills, check-taps were employed to
regulate the pressure of gas at each floor.[12] In order, therefore, to
obtain the desired regularity of pressure in the gas supply, governors
must be employed for each storey; or, what is better still, each
burner must have its own separate governor. And this brings us back to
the subject with which we are more closely concerned.

          [12] Clegg's "Treatise on Coal Gas," 1st Ed., p. 197.

The governor-burner, as its name implies, consists of a governor, as
described above (but, of course, on a smaller scale) combined with a
gas-burner; the governor being adjusted so as, whatever excess of
pressure there may be in the gas-supply pipes, to permit only the
quantity of gas to pass which the burner is intended to consume.
Obviously, the principle herein contained is capable of receiving
numerous applications. It can be, and is applied with equal success to
Argand and flat-flame burners; while the modifications which obtain in
the manner of constructing the regulating portion of the apparatus are
almost as numerous and as varied as are the burners themselves. As the
main features exhibited by one are common to all, it is unnecessary to
go into the details of their several constructions. It will suffice to
take two or three of the most successful, or the best known, as
representatives of the whole.

[Sidenote: Giroud's Rheometer.]

Among the first in order of time--and still retaining no unworthy
position in order of merit--is the "rheometer," or "flow-measurer," of
M. Giroud. In this instrument a light metal bell is sealed in
glycerine contained in a cylindrical case; the bottom of this latter
containing the inlet-pipe, screwed for connecting to the ordinary
fittings, while from the centre of its cover rises a tube leading to
the burner. The bell is pierced by a small hole for the passage of the
gas, and is surmounted by a cone-shaped projection, which constitutes
the valve of the instrument. As the pressure of the entering gas lifts
the bell, it causes this cone-valve to enter the mouth of the tube
leading to the burner; reducing the area of the opening in proportion
to the pressure of gas acting upon the under side of the bell, and so
permitting only the required quantity of gas to pass to the burner. It
might be thought that the presence of liquid would constitute an
objection to the use of the instrument; but, as glycerine does not
evaporate, when once the instrument is fixed and properly adjusted, it
needs no further attention. With an excessive initial pressure, there
is, however, a liability of the gas to bubble through the sealing
liquid, and so destroy the efficiency of the instrument; but this
might be obviated by increasing the depth of the bell, and so giving
it a greater seal. The instrument is very reliable for the purpose
which it is intended to fulfil; delivering, through a considerable
range of pressure beyond that required to raise the bell, the exact
quantity of gas for which it has been adjusted. It may be added that
the rheometer has an advantage over many instruments of its class, in
that it presents so little obstruction to the downward rays of the
flame.

  [Illustration: FIG. 16.--GIROUD'S RHEOMETER.]

[Sidenote: Sugg's Christiania governor-burner.]

Mr. William Sugg, in his regulator or governor, adopts an entirely
different arrangement to the foregoing. The valve is placed at the
inlet of the governor; and not at its outlet, as in the instrument
just described. Instead of a metal bell, a diaphragm of thin and very
flexible leather is employed, which is raised by the pressure of the
entering gas, and, in turn, actuates the valve; closing the entrance
to the governor in proportion to the pressure of gas acting upon it.
The orifice communicating between the under and the upper side of
the leather diaphragm is controlled by a screw, whereby the quantity
of gas delivered to the burner can be regulated according to
requirements; but when once it has been adjusted to give any desired
pressure of gas at the burner, this pressure will be strictly
maintained, no matter with what excess of pressure (within reasonable
limits) the gas may be supplied to the instrument. The improved
"London" Argands produced by Mr. Sugg (the details of the construction
of which have been already described) are too delicately adjusted to
be applied with advantage directly to the ordinary consumer's
gas-fittings, or wherever any variation in the pressure of the gas
supply is likely to be experienced. However, with the addition to them
of the above governor, their use becomes as easy and simple as that of
other burners; and thus the gas consumer is enabled to obtain the
benefit of the most improved apparatus without being called upon to
exercise the constant care and attention which, without the aid of the
governor, would be necessitated. Besides being applied to Argands,
this governor is successfully applied by its inventor to his
flat-flame burners. In conjunction with a simple steatite burner of
the latter class, it has received a very extended application, under
the name of the Christiania governor-burner.

[Sidenote: Sugg's Steatite-float governor-burner.]

Recently, however, a new type of governor, for application to burners,
has been brought out by the same manufacturer, the construction of
which is very different to that of the instrument referred to above;
and as it is somewhat simpler in its details, and withal appears to be
cheaper in construction, it seems destined to supersede the former
instrument. In this new governor, instead of a leather diaphragm,
there is a bell (or float) of steatite, which is free to move, in the
manner of a piston, within an inner cylindrical chamber contained
within the outer case of the instrument. Attached to the centre of the
float, and on its upper surface, is a tube sliding within another tube
of somewhat larger area; the latter forming a continuation of the
inner cylindrical chamber. The smaller tube is open at both ends, and
thus communicates from below to above the float; the outer tube is
closed at the top, but has an orifice in its side. The action of the
instrument is as follows:--The gas, entering below the float, passes
through the inner tube to the upper part of the cylindrical chamber,
and thence, through the orifice in the outer tube, to the burner. As
the pressure of the entering gas exceeds that required to overcome the
weight of the float, the latter is raised; the tube which is attached
to it being propelled farther into the outer tube in which it slides,
and, in so doing, partially closes the orifice in the side of the
latter. In this way, according to the pressure of the gas acting upon
the under side of the float, the area of the opening through which it
must flow to get to the burner is reduced; and so the quantity of gas
which issues from the burner remains the same under all pressures
above that required to actuate the float. The instrument appears to be
as reliable as it is simple, and to contain few parts calculated to
get out of order; but, of course, whether or not it will retain its
good qualities after long-continued use can only be proved by
experience.

  [Illustration: FIG. 17.--SUGG'S STEATITE-FLOAT GOVERNOR.]

[Sidenote: Peebles's needle governor-burner.]

[Sidenote: Efficiency of the needle governor-burner.]

Another instrument of this class--the last which I shall notice--is
Peebles's needle governor-burner. For simplicity combined with
remarkable efficiency, it is undoubtedly ahead of all its compeers.
Somewhat similar in principle to Giroud's rheometer, it differs from
that instrument in many of the details of its construction; and while
dispensing with the use of liquid, maintains equal efficiency in
operation. It was described as follows by Dr. W. Wallace, in a lecture
on "Gas Illumination," delivered before the Society of Arts in
January, 1879:[13]--"In a little cylinder stands a so-called needle, on
the point of which rests a flanged cone of exceedingly thin metal. At
one side of the cylinder there is a small tube leading away the gas,
and the orifice of which is influenced in area by the action of the
cone. The instrument, by means of a screw leading into the side tube,
can be made to deliver any desired number of cubic feet, which it does
with surprising accuracy, provided that the pressure of the gas is not
less than 6-10ths of an inch." As to the efficiency of the instrument,
Dr. Wallace proceeded to state:--"In trials that I have made, I have
not found the variations of volume at different pressures to exceed 1
per cent." For situations where this extreme nicety of operation is
not absolutely essential, or where the rate of consumption is to be
invariable, the instrument is constructed in a somewhat modified and
simpler form. The small tube on the side of the instrument is
dispensed with, and the gas permitted to pass through perforations in
the lower part of the cone. With this alteration there is a nearer
approach to the construction of the rheometer; but, as in that
instrument, there is no provision for altering the rate of consumption
to suit different circumstances.

          [13] See _Journal of Gas Lighting_, Vol. XXXIII., p. 162.

  [Illustration: FIG. 18.--PEEBLES'S NEEDLE GOVERNOR.]




CHAPTER V.

REGENERATIVE BURNERS.


[Sidenote: Temperature of a gas flame.]

As was remarked in the introduction to this treatise, recent years
have witnessed a very considerable advance in the construction of
gas-burners, and in the amount of light capable of being developed
from each cubic foot of gas consumed. Undoubtedly the most noticeable
feature of this advance is the successful application of the
regenerative, or, as it would be more appropriately designated,
recuperative system. Briefly stated, this consists in utilizing the
heat of the products of combustion from the gas flame (which otherwise
would be dissipated into the atmosphere) to raise the temperature of
the gas before it is ignited; and, likewise, of the air necessary for
combustion. The temperature of an illuminating gas flame is usually
estimated to be between 2000° and 2400° Fahr.; and as the products of
combustion must leave the flame at a temperature little, if at all,
inferior to the former figure, it must be evident that there is an
ample margin of heat for employment in this direction. A considerable
proportion of the large amount of heat conveyed by those products of
combustion which, under ordinary circumstances, is imparted to the
surrounding atmosphere--often elevating its temperature to an
unnecessary and prejudicial extent--is, by this method, returned to
the flame; intensifying the process of combustion, and augmenting, in
a remarkable degree, the illuminating power developed from the gas
consumed. Thus the ultimate effect of the operation is to produce a
concentration of heat in the flame, and the conversion of superfluous
heat into beneficial light. Within a comparatively recent period, the
utility of this process was strongly disputed; and it was stoutly
maintained, by many persons, that as the immediate effect of ignition
was to cause a temperature of more than 2000° Fahr. to be attained,
the heating of the gas and air prior to their combustion could produce
little or no beneficial effect upon the illuminating power of the
flame. However, the falsity of this view of the case is conclusively
demonstrated by practical experiment; the remarkably high results
yielded by burners that have been constructed upon the regenerative
system sufficiently attesting the correctness of the principles upon
which they are founded.

Although, in general, both the gas and air supplies are heated, it is
chiefly due to the latter that the beneficial effect noticed is
produced; and this for two reasons. First, because the quantity of air
is so much greater than the gas it is required to consume; being, at
the nearest approach to theoretical perfection, fully six times its
volume. Second, because four-fifths in volume of the air consists of
inert nitrogen, which does not contribute anything to the heat of the
flame, but, when applied in its normal, cold condition, abstracts no
inconsiderable proportion of heat from it. Yet the heating of the gas
itself is not without very appreciable influence. In an ordinary
gas flame there is always an area of non-illumination around, and
extending to a variable distance from the burner head. This is caused
partly by the conduction of heat from the flame by the burner; but, in
a greater degree, by the cooling action of the issuing stream of cold
gas, as is shown by its extending farther from the burner in
proportion to the pressure or velocity with which the gas issues. The
prejudicial effect due to the former is obviated to a great extent by
constructing the burner of steatite, or other non-conducting material.
To remedy the latter, nothing will avail but the heating of the gas
supply.

[Sidenote: Effects of heating the gas and air.]

The effect of heating the gas is to enlarge the area of the
illuminating portion of the flame, and, in a minor degree, to enhance
the intensity of incandescence to which the carbonaceous particles are
raised. When the gas issues from the burner at a temperature little
inferior to the temperature of ignition, the hydrocarbons it contains
are immediately decomposed; the liberated particles of carbon are
raised to the temperature of incandescence; and the illuminating area
of the flame is extended downwards, even to the surface of the burner.
The heating of the air operates chiefly to produce and maintain a more
elevated temperature of the flame; and, in this manner, contributes to
the development of a higher illuminating power from the same area of
flame. In the case of ordinary gas flames, the cold atmosphere by
which they are surrounded, by abstracting heat from the flame,
prevents the most favourable conditions for the development of light
from being attained. When, however, the air immediately surrounding
the flame has been previously heated, the particles of carbon (the
incandescence of which furnishes the desired illuminating power)
attain to a much more exalted temperature; and, consequently, give out
a greater degree of light.

But there is yet another direction in which the prior heating of the
air supply contributes to the development of improved illuminating
power. Being heated, its density is lowered; so that in any given
volume of air there is less weight of oxygen than when cold. The
consequence is that as less oxygen is presented to a given surface
area of flame, the separated particles of carbon remain for a longer
period of time in the incandescent condition before being entirely
consumed. Thus there are three distinct results produced by heating
the gas and air before combustion--namely, first, the particles of
carbon are liberated earlier in the flame; second, they are raised to
a more exalted temperature; and, third, they remain for a longer time
in the incandescent condition. The combined effect of all three is the
improved illuminating power developed from the gas consumed.

  [Illustration: FIG. 19.--BOWDITCH'S REGENERATIVE GAS-BURNER.]

[Sidenote: Bowditch's regenerative burner.]

So far back as the year 1854, the principle of heating the air supply
to an Argand burner, by means of waste heat from the flame, was
partially applied, with some success, by the Rev. W. R. Bowditch,
M.A., of Wakefield. Mr. Bowditch's burner, which is shown in the
accompanying diagram, contained, in addition to the ordinary chimney,
an outer glass chimney, which extended for some distance below the
inner one, and was closed at the bottom; so that all the air needed to
support the combustion of the gas was required to pass down the
annular space between the chimneys, and in its passage became
intensely heated by contact with the hot surface of the inner chimney,
as well as by radiation from the flame itself. This burner contained
many defects. Amongst others, the inner chimney could not long
withstand the intense heat to which it was subjected, and, in
consequence, had to be frequently renewed; the heating of the air was
not effected solely by the products of combustion, but, perhaps in a
greater degree, by the abstraction of heat from the flame itself;
while, at best, this heating was but partial. Yet, these defects
notwithstanding, the burner showed very clearly the beneficial results
attending even a partial application of the principle; as, in the
illuminating power it developed from the gas consumed, a clear gain of
67 per cent. over the ordinary Argand burner was obtained. Although
the drawbacks connected with the construction of Mr. Bowditch's burner
prevented its ever receiving general, or even extensive adoption, its
simplicity has gained for it the distinction of being freely copied by
so-called inventors of a later day.

[Sidenote: Invention of the Siemens regenerative burner.]

It was left to Herr Friedrich Siemens, of Dresden, to produce a burner
which, while applying the principle of regenerative heating in the
most scientific and complete manner, should also be adapted to the
ordinary conditions of gas lighting. After much experimenting on the
subject, a burner embodying the essential features of the regenerative
system was invented by this gentleman in 1879; and so great was the
advance which its performances manifested over anything previously
attained, so wide the prospect of further achievements which was
opened out, that it may fairly be said to have inaugurated a new era
in gas illumination. In this burner the products of combustion were
made to give up a considerable portion of their heat to the gas and
air, as the latter passed to the point of ignition; the flame itself
not being called upon to contribute in any degree to this result.
Although, as was but natural, the first attempts towards the
construction of such a burner were very crude, and but partially
successful in their results, the inventor persevered in his endeavours
to work out his ideas into practical and thoroughly satisfactory
shape. It was not until after it had gone through many modifications
that the burner acquired the peculiar form which now distinguishes it,
and attained to its present stage of perfection. Before proceeding to
describe an example of the burner as now constructed, it is necessary
to state that the principles embodied in Herr Siemens's invention are
equally well adapted--and, indeed, are applied with equal success--to
the construction of flat-flame and Argand burners; but as the
distinctive features of the invention are common to both classes of
burners, it will be quite sufficient to describe in detail one of the
latter type.

A prominent feature in the appearance of the Siemens burner, as will
be seen from the annexed illustration, is a large metal chimney, for
creating a draught to carry away the products of combustion. The
entrance to this chimney is situated a little above the apex of the
flame; but there is a branch flue connecting the main chimney with the
interior of the burner. The body of the burner is of metal, and its
interior is divided into three concentric chambers. Of these, the
innermost is open at the top, and is surmounted by a porcelain
cylinder, which, when the gas is lighted, is surrounded by the flame.
This chamber is closed at the bottom, but communicates at the side
with the before-mentioned branch tube, or flue, leading to the main
chimney. The intermediate chamber communicates, at its lower
extremity, with the gas supply; and terminates, a short distance from
the top of the burner, in a number of small metal tubes, which convey
the gas to the point of ignition. The outer chamber is open both at
top and bottom, and is for conveying air to support the combustion of
the gas. In order to promote greater intensity of combustion, there is
a notched deflector at the summit of the latter chamber, and another
on the lower part of the porcelain cylinder, which cause the air to
impinge more directly upon both sides of the flame. There is also an
arrangement for introducing air between the outer casing of the air
chamber and the glass chimney which encloses the flame; its object
being to keep the chimney cool.

  [Illustration: ELEVATION.
                 ENLARGED SECTION OF COMBUSTION CHAMBERS.
                 FIG. 20.--SIEMENS'S REGENERATIVE GAS-BURNER.]

[Sidenote: Action of the Siemens burner.]

The action of the burner is as follows:--When the gas is ignited at
the ring of tubes, the heated air and products of combustion, which
rise from the flame, create a draught in the main chimney. Through the
communication established by means of the lateral flue, a partial
vacuum, or area of low pressure, is induced in the innermost chamber
of the burner, and within the porcelain cylinder which surmounts it.
As the flame terminates close to the mouth of the latter, the greater
portion of the products of combustion, instead of going into the main
chimney, are sucked into the porcelain cylinder; and thus a current is
set up through the interior of the burner, and by the lateral flue, to
the main chimney. The heat carried away by the products of combustion
is communicated, through the walls of the chambers, to the entering
gas and air; and by this means the latter are heated to a very high
temperature before they issue from the burner and are consumed. The
consequence is that a much greater intensity of combustion is
maintained; the carbon particles are separated earlier in the flame,
and are raised to a more exalted temperature; and the ultimate effect
is a higher yield in illuminating power per cubic foot of gas
consumed. Independent tests by various experienced photometrists have
conclusively shown that a light equivalent to that from 5 to 6 candles
is obtained per cubic foot, from gas which, in the standard "London"
Argand, yields a light of only from 3 to 3-1/2 candles.

[Sidenote: Defects of the Siemens burner.]

While the advantages of the Siemens burner are many and obvious, it is
not without its disadvantages. These partly arise from causes
connected with the very observance of the conditions necessary to
secure the efficiency of the burner. With every advance in the more
efficient operation of gas-burners, increased care and attention are
demanded in their employment, in order to obtain the benefits they are
calculated to yield. Indeed, it would almost appear that the nearer
the approach to perfection which is made in the construction of a
burner, the greater must be the drawbacks to its general adoption.
Thus, in the burner under notice, if the gas supply is allowed to
become in excess, the tail of the flame enters the porcelain cylinder,
and soot is deposited in the interior of the burner; obstructing the
passages, and impairing the burner's action. Then, to cause the burner
to yield its highest results, it is necessary that the air supply be
accurately adjusted to the quantity of gas being consumed. To this end
the entrance to the air chamber, at the bottom of the burner, is
covered by a perforated semi-circular cup, by turning which the
quantity of air entering the burner can be increased or diminished as
required. Moreover, the bulky construction of the burner, with its
accompaniment of chimney and flue, and its complicated arrangement of
tubes and chambers, imparts to it a somewhat clumsy and inelegant
appearance, which is calculated to impair the favour with which its
remarkable performances cause it to be regarded. But these drawbacks
are far outweighed by the undoubted advantages conferred by the
burner--in improved illumination combined with economy of combustion,
and the facilities it affords for securing perfect ventilation.

Encouraged by the success of Herr Siemens, other inventors have
followed in his footsteps; with the result that there are now a
variety of burners before the public, embodying the same principles,
but differing in the details of their construction and in the measure
of their efficiency. Of these may be mentioned Grimston's, Thorp's,
and Clark's; and without describing in detail the construction of the
several burners (of which further particulars will be found in the
"Register of Patents" in the _Journal of Gas Lighting_[14]), it must
suffice to refer to the salient points and distinctive features of
each.

          [14] See Vol. XL., pp. 786, 950; and Vol. XLII, p. 836.

[Sidenote: Grimston's regenerative burner.]

Grimston's burner (shown on the next page) consists, in effect, of an
Argand burner turned upside down; the gas issuing from the bottom ends
of a number of small tubes placed in a circle. The jets of
flame--first directed downwards from the mouths of these tubes--by a
conoidal deflector in the centre of the ring, are caused to spread
outwards, and assume a horizontal direction; and by their amalgamation
with each other a continuous sheet or ring of flame is produced. The
horizontal direction of the flame is maintained by its passing
underneath a metal flange, faced with white porcelain, or other
refractory material; the supply of gas being adjusted so that the
flame just terminates at the outer edge of this flange. Before
entering the chimney, the products of combustion are caused to flow
through a number of vertical tubes contained in a cylinder, which is
concentric to an inner cylinder containing the gas-supply tubes. The
outer cylinder is traversed by the air needed for the support of
combustion, which is to become heated before reaching the point of
ignition; and in order the more completely to enable the products of
combustion to impart their heat to the entering air, the cylinder is
further intersected by strips of wire gauze, which pass around and
between the tubes (see fig. 22, on next page). By these means the air
is intensely heated; and, passing among the narrow burner tubes
through which the gas is conveyed, gives up a portion of its heat to
the latter before the point of ignition is reached. Thus, in a very
simple manner, both air and gas are raised to a considerable
temperature before combustion takes place.

With regard to the efficiency of the burner, at the exhibition of gas
appliances held at Stockport in 1882 (where a gold medal was awarded
to it, as well as to Thorp's burner, to be referred to hereafter),
with a consumption per hour of 9·84 cubic feet of 17·5 candle gas, an
illuminating power of 60·67 candles was obtained (equal to 6·16
candles per cubic foot); while, on another occasion, when the burner
was consuming 8·94 cubic feet per hour, an illuminating power of 51·5
candles (equal to 5·76 candles per cubic foot) was obtained from gas
of the same quality. It is claimed for this burner that equally good
results are obtained with small sizes as with large; and this, if
borne out in actual practice, should go far towards ensuring the
success and extensive adoption of the burner.

  [Illustration: FIG. 21.--GRIMSTON'S REGENERATIVE GAS-BURNER.]

  [Illustration: FIG. 22.--GRIMSTON'S BURNER.
                 PLAN, SHOWING REGENERATING ARRANGEMENT.]

  [Illustration: FIG. 23.--THORP'S REGENERATIVE GAS-BURNER.]

[Sidenote: Thorp's regenerative burner.]

Thorp's burner produces a cylindrical flame, like that of the Argand,
but without the aid of a glass chimney which is a necessary adjunct to
the latter burner. By means of a deflector on the inner side of the
flame, the latter is made to curve outwards and assume a somewhat
convex form, so as to obviate the shadow which otherwise would be cast
by the gas chamber at the bottom of the burner. Above the flame is a
cylindrical chimney, divided by a vertical partition into two
concentric chambers, which are intersected by a series of metal gills,
or projections, continued through both chambers. The outer chamber is
for conveying away the products of combustion; the inner one for the
passage of air to feed the flame; while down the centre of the inner
chamber there passes a tube conveying the gas to the point of
ignition. The hot products of combustion pass up from the flame
through the outer chamber, and give up the greater portion of their
heat to the projections; by which it is conducted into the inner
chamber, and transferred to the incoming air. A common imperfection of
regenerative burners is that, in consequence of the diminished rate at
which the gas flows through the burner when expanded by heat, when
starting the burner the gas must be only partially turned on, and the
quantity gradually increased as the burner becomes heated; thus
necessitating considerable attention. To prevent the need for this
attention, there is in Thorp's burner an ingenious contrivance for
automatically regulating the quantity of gas admitted to the flame.
The central gas-tube, which is referred to above, contains a brass
rod, fixed at one end, and at the other connected to a valve
controlling the quantity of gas that enters the tube. At first, when
the gas is lighted, this valve is almost closed; but as the rod
becomes heated it elongates, gradually opening the valve until the
full quantity of gas is admitted which the burner is intended to
consume. At the Stockport exhibition, Thorp's burner was tested with
the following results, as recorded in the Judges' report. After it had
burned about two hours, "it gave an illuminating power of 183 standard
candles, while burning 27 cubic feet of gas per hour (equal to 6·77
standard candles per cubic foot), with gas of 3·5 candles per cubic
foot.... In another experiment with the same quality of gas, after
burning half an hour it yielded, under similar conditions, 154 candles
with a consumption of 25·29 cubic feet per hour, which gave an
illuminating power of 6·02 candles per cubic foot."

[Sidenote: Clark's regenerative burner.]

There is nothing in Clark's burner that calls for special notice. In
its main features it appears to be constructed upon similar lines to
Grimston's burner, although the coincidence is doubtless only
accidental.[15] It must, however, be added that in the details of its
construction it is much simpler than the latter burner; and certainly
it appears to lose very little in efficiency from its greater
simplicity, as the following extract from a report by Mr. F. W.
Hartley, the well-known photometrist, will show:--"With a consumption
rate of 5·3 cubic feet of gas per hour, the amount of light yielded
horizontally was equal to 29·79 times that of a standard candle. The
light yielded per cubic foot of gas burned per hour was therefore
equal to 5·62 times that of a standard candle." And the amount of
light delivered immediately downwards is said to be "very sensibly
greater than the amount of light delivered horizontally." Like the
Grimston burner, it is of the inverted Argand form; the gas issuing
from a chamber at the bottom of a tube which descends through the
centre of the burner. The products of combustion escape through a
chimney; and in so doing give up a portion of their heat to the
entering air, which is conveyed to the point of ignition through
horizontal tubes that intersect the chimney. The burner is enclosed in
a suitable lantern, the lower half of which consists of a
semi-globular glass; a similar arrangement being adopted in connection
with the Grimston and Thorp burners.

          [15] In justice to Mr. Clark it should be mentioned that,
          since the above appeared in the _Journal of Gas Lighting_,
          the attention of the writer has been called to the fact
          (which had been overlooked by him) that Clark's patent was
          taken out some months before that of either Grimston or
          Thorp.

  [Illustration: FIG. 24.--CLARK'S REGENERATIVE GAS-BURNER.]

The three burners last mentioned have not been before the public
sufficiently long to enable a reliable opinion to be formed as to
their value in actual and prolonged use. Although there is no reason
for supposing that such will occur in the present instance, it so
often happens that the results indicated by apparatus in the
experimental stage, or while still under the control of the inventor,
are not borne out in practice, that it would be unwise to express any
decided opinion as to their ultimate worth from existing information.
It is, however, to be earnestly hoped that the marked favour with
which they have been received will not be impaired on improved
acquaintance; but that further experience will justify the
anticipations that have been excited by the excellent performances of
the burners hitherto, and demonstrate at once their durability and
real usefulness.


Since writing the above, considerable activity has been shown by
inventors in producing new burners upon the regenerative principle, or
in improving upon existing models. Of course, as yet it is too early
to arrive at a satisfactory estimate of their actual value or relative
worth; but it may be hoped that, from the increased attention being
devoted to the subject, some real and practical results will flow, by
which the gas-consuming public will be the gainers. So far, the most
promising of this class of burners that has been brought into actual
use, since the introduction of the Siemens burner, is the one
represented below.

  [Illustration: FIG. 25.--BOWER AND THORP'S REGENERATIVE GAS-BURNER.]

It is a modification, in the direction of greater simplicity, of
Thorp's former burner, illustrated and described on p. 69 of this
treatise; and as its construction is based upon the same lines as that
burner, further description is not required.




CHAPTER VI.

INCANDESCENT BURNERS.


A review of gas-burners would scarcely be complete without some
reference to the incandescent burners of M. Clamond and Mr. Lewis.
Although their dependence upon an artificially produced blast or
current of air removes them from the list of appliances applicable to
ordinary conditions, the remarkable results which they afford, not
less than their originality, demand for them at least a passing
notice. The production of light by the agency of these burners is
brought about in a manner altogether different, and is due to quite
other causes than those which are concerned in the production of an
ordinary illuminating gas flame. In the latter case, the illuminating
power developed is solely due to the hydrocarbons contained in the
gas, which are decomposed by the heat of the flame, the separated
carbon being raised to a white heat. In the former, the illuminating
power is not obtained directly from the gas; but advantage is taken of
the heat of the flame, enhanced by the application of a blast of air,
to raise to incandescence some refractory foreign material, which
latter is thus made to give out light. In the Clamond burner this
refractory substance is a basket composed of magnesia, spun into
threads; in the Lewis burner it is a cage of platinum wire.

To the unthinking reader it may perhaps appear somewhat surprising
that results so remarkable as are yielded by these burners should be
obtained, while disregarding, as a source of light, the hydrocarbons
contained in gas, and employing them, in common with the other
constituents, solely as a source of heat. An explanation, however, is
readily forthcoming. As was shown in a former part of this
treatise,[16] the great bulk of ordinary coal gas consists of
constituents which, in the act of combustion, produce considerable
heat, but scarcely any light; the illuminating power developed in an
ordinary gas flame being almost wholly dependent upon the very small
proportion of heavy hydrocarbons which the gas contains. Thus, the
quantity of heat-producing elements contained in the gas being quite
disproportionate to the light-yielding hydrocarbons, there is always
produced, in an ordinary gas flame, more heat than is necessary for
effectively consuming the free carbon, which is liberated in the flame
by the decomposition of the heavy hydrocarbons. This is shown by the
fact that coal gas can usually be naphthalized--that is, impregnated
with the vapour of naphtha--to a considerable extent before the limit
of effective combustion is reached. The object aimed at in the
incandescent burners about to be described is to utilize, in the
development of illuminating power, the combined heat produced by the
combustion of all the constituents of the gas. To this end the heat
of combustion is brought to bear upon, and caused to raise to
incandescence, some refractory material, extraneous to, but brought
within the operation of the flame.

          [16] See Chap. II., p. 21.

[Sidenote: Effect of injecting a blast of air into a gas flame.]

A further explanation of the superior results yielded by these burners
may be found in the employment of an artificial blast or current of
air. Indeed, without some such arrangement the desired end could not
be attained. The heat developed by the unaided flame is diffused over
too wide an area to raise the temperature of the heated substance to
the necessary degree of incandescence to enable it to give out
sufficient light. By injecting a current of air into its midst, the
flame is condensed into a smaller compass; and is brought to bear more
directly upon the precise locality where its heat may be most
effectively employed. Thus, although the total quantity of heat
developed remains exactly the same as before, it is concentrated upon
a smaller surface of the refractory substance; and the latter is
consequently more intensely heated, or, in other words, raised to a
more exalted temperature. The very superior illuminating power which
is thereby obtained is due to the circumstance that the quantity of
light yielded by an incandescent body increases in a higher ratio than
the temperature to which it is raised.

[Sidenote: Lewis's incandescent gas-burner.]

Proceeding now to describe the burners. The one invented by Mr. Lewis
(various forms of which are illustrated on the next page) consists of
an upright tube, connected at its base to the gas supply, and
surmounted by a cap or cage of platinum wire gauze; which latter
constitutes a combustion chamber, as it is there that the mixture of
gas and air is consumed. Into the lower part of the upright tube the
nozzle of an air-pipe is inserted, through which a supply of air can
be injected, under pressure, into the burner, after the manner of a
blowpipe. There are also small branch tubes leading into the upright
gas-tube, and open to the atmosphere. Through these an additional
quantity of air enters the burner; being drawn or sucked in by the
agency of the main current, which flows through the upright tube. The
resemblance to an ordinary Bunsen burner is, therefore, very close.
The mixture of gas and air thus produced, when ignited, burns at the
platinum cap; the heat which is developed causing the latter to become
highly incandescent, and so to give out a brilliant light. To prevent
the conduction of heat from the incandescent platinum, through the
upright tube, a non-conducting material--such, for instance, as
steatite or porcelain--is interposed between the gauze cap and the
metal tube.

  [Illustration: FIG. 26.--LEWIS'S INCANDESCENT GAS-BURNER.]

The light produced by this burner is said to approximate more closely
to daylight than that yielded by an ordinary gas flame (the colours of
textile fabrics, for instance, being shown as well by its aid as by
daylight); while, on account of its resulting from the incandescence
of a fixed body, instead of being emitted from a flame, it is
unaffected by a gust of wind, and maintains perfect steadiness under
every condition of weather. The illuminating power developed is stated
to be equal to 5 standard candles per cubic foot of gas consumed.

[Sidenote: Clamond's incandescent gas-burner.]

M. Clamond's burner, which is shown in fig. 27, is a much more
complicated apparatus than the preceding one, and not so easily
described; but its main features may be briefly enumerated as
follows:--The air (which, as in Mr. Lewis's burner, is supplied under
pressure) is divided, as it enters the apparatus, into two portions.
One portion is at once mixed with the gas; the remainder being
conveyed, through a peculiarly constructed tube composed of small
pieces of refractory material, to the combustion chamber, or "wick,"
as it is termed, of the burner. This "wick" is a small conical basket,
made of a kind of lacework of spun magnesia, which, when raised to
incandescence by the heat produced by the combustion of the gas,
furnishes the desired illumination. The mixture of gas and air is
subdivided, by a "distributor," into two portions, one of which goes
direct to the magnesia "wick," there to be burnt, while the other is
distributed among a number of tubes, forming so-called "auxiliary
burners," the flames of which are utilized to heat the chief air
supply; being directed upon the sides of the before-mentioned tube of
refractory material, through which it is conveyed. By this means the
air is raised to a very high temperature (1000° C., or 1800° Fahr., it
is said) before it impinges upon the flame. The result is the
production of a most intense heat within the magnesia basket; the
latter being raised to brilliant incandescence, and so developing a
high illuminating power.

  [Illustration: FIG. 27.--CLAMOND'S INCANDESCENT GAS-BURNER.]

The magnesia basket must be renewed after being in use a period of
from 40 to 60 hours, as it gradually deteriorates by the action of the
intense heat to which it is subjected; but as the cost is said to be
insignificant, this should not be a great drawback. The basket is
placed at the base of the burner, in order to obviate the shadow which
would otherwise be cast by the apparatus; and it is attached to the
main body of the apparatus by platinum wires. As to illuminating
power, the only particulars which have been made public refer to the
first two models constructed; one of which was said to develop a light
equal to that from 6·208 candles, and the other to 9·72 candles per
cubic foot of gas consumed.

  [Illustration: FIG. 28.--CLAMOND'S IMPROVED INCANDESCENT BURNER.]

[Sidenote: Clamond's new burner.]

In a recently designed modification of the burner (which is shown in
the accompanying illustration) M. Clamond dispenses with an artificial
supply of air under pressure, and endeavours to obtain similar results
by other and simpler means. To this end the position of the magnesia
"wick" is reversed (it being placed at the top of the apparatus); the
current of gas is allowed to draw in upon itself a quantity of air by
a precisely similar arrangement to that adopted in the Bunsen burner;
while an additional supply of air is drawn upon the flame by the
accelerated draught produced by the aid of a glass chimney. As in the
more complicated and complete burner, the air supply is heated by
means of auxiliary burners in the interior of the apparatus. It has
been stated, on the authority of M. Clamond, that this modified burner
develops, from the gas consumed, a duty of about 6 candles per cubic
foot; being equal to the results yielded by the more complicated
apparatus. Should this be borne out in practice, M. Clamond will
have achieved a noteworthy success. It is, however, advisable to
reserve expressing any definite opinion of its merits until further
information is received, or until the burner has been tried in this
country.




CHAPTER VII.

CONCLUSION.


The burners last mentioned may be said to mark the extent of the
progress that has been made, down to the present time, in the
construction of apparatus for developing light from coal gas; and they
remind me that I have arrived at the conclusion of my subject. From
the unpretending gas-jet described by Accum--burning, with
wonder-provoking steadiness and constancy, "so long as the supply of
gas continued"--to the complicated apparatus of M. Clamond, is a long
stretch of invention; embracing the labours of many distinct and
original workers in the same field, and including numerous variations
in the details of burners that have not been touched upon in the
foregoing remarks. As was announced in the introduction, I have dealt
in this treatise only with the more important or the more successful
of the modifications that have been made from time to time in the
construction of the gas-burner. In addition to the burners that have
been referred to, there have been invented many others, which could
not be adequately noticed without prolonging the treatise to an undue
length. Some of these (the fruit of much thought and careful
experiment) have obtained, in the commercial success that has attended
them, no more than their merited reward; others (devoid of any real
merit, and in their construction disregarding the most elementary
principles of economic combustion) have been brought into somewhat
extensive use by the misleading statements and false representations
of their inventors, and are only tolerated through the ignorance of
the public; while not a few of the latter class of burners have
speedily found the oblivion which they richly deserved. Sufficient,
however, has been said to show that many real improvements have been
effected in the construction of gas-burners, and to prove that, with
the apparatus now available, a far higher duty may be obtained from
the gas consumed than was possible only a few years ago.

But although the great advance that has been made in the construction
of gas-burners is undoubted, the benefits which ought to result
therefrom have not been realized by the gas-consuming public; nor are
they likely to be to their full extent. While the ingenious and
effective inventions for utilizing the waste heat of combustion, and
for lighting by incandescence, may, and doubtless will, in the course
of a few years, be far more extensively adopted than at present, it is
hardly to be expected that they will be generally employed. Two causes
operate to preclude the latter result--namely, their first cost, and
the care and attention demanded in their employment. It seems
tolerably certain that for a long time yet the great bulk of coal gas,
used for lighting purposes, will be consumed through the simple
flat-flame burners that have done so much hitherto for the furtherance
of gas lighting. Fortunately so much has been done towards the
perfection of this class of burners, that, for a very slight
expenditure, results may now be obtained far in advance of what could
formerly be produced only by the most costly and delicate apparatus.
For ordinary situations and requirements, the improved flat-flame
burners produced by Bray, Brönner, and Sugg, when intelligently
employed, leave scarcely anything to be desired. _When intelligently
employed_, I repeat, and with cautious emphasis; for the best of
burners will be extravagant and ineffective if employed without due
regard to the conditions for which it was made. That which is most
needed at the present day, and which will best ensure the continued
use of coal gas for the purposes of illumination, is the more general
diffusion amongst gas consumers of a knowledge of the principles of
combustion, and of the simple precautions to be taken and conditions
to be fulfilled in the employment of gas-burners. The apparatus that
is available is both varied and effective; what is wanted is the
knowledge to use it aright. By contributing to the freer dissemination
of that knowledge, purveyors of gas will confer no inconsiderable
benefits upon their customers, and, at the same time, will assuredly
promote their own interests.