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 deg. to 500 deg. 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.
BROeNNER'S BURNERS.
The credit of having produced the first flat-flame burners designed
upon scientifically correct principles belongs undoubtedly to Herr
Julius Broenner, 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 Broenner
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
Broenner'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.--BROeNNER'S BURNERS.]
[Sidenote: Construction of Broenner's burners.]
The general appearance of Broenner'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 deg.
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 Broenner 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 versa_."
[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
" | 21/2 | 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
" | 31/2 | 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
" | 41/2 | 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
" | 21/2 | 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
" | 31/2 | 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
" | 41/2 | 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 Broenner burner.]
Doubtless the chief cause of the remarkable efficiency of the Broenner
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 Broenner, 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 Broenner'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 Broenner'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 deg.. In Bray's "regulator" burner, introduced in 1869,
they were placed at an angle of 90 deg.; 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 deg.; 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.