326 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[October 21,1871. 
'Whether the illuminating power is affected by the quan- ' 
lity in which gas is burnt P or in other words, Is it more ! 
economical to use small burners or large ones ? The 
doctrine that the light-giving power of gas varies with 
the quantity burnt, has been held by many eminent 
men, who have maintained that gas gives a larger pro¬ 
portion of light when burnt in large quantities. Mr. 
Farmer, of America, has put forth a proposition, known 
as the “ Farmer Theorem,” that the illuminating power 
increases in a geometrical ratio as the square of the gas 
consumed; i. e. that if two feet of gas give a light equal 
4, three feet of the same gas will give a light equal to 
9, four to 16, etc. This theorem, although accepted in 
America, has received no support in this country. 
The first and most natural suggestion is, to inquire 
whether the observed variations in the illuminating 
power are not due, wholly or in part, to the mechanical 
apparatus employed for developing it. If two tons of I 
identically the same coal do not, when burnt separately, 
give out the same amount of heat, is not the explanation 
to be sought in some difference in the mode of combus¬ 
tion P If two gallons of the same water, when weighed I 
separately, do not show the same weight, must there 
not be some difference in the balances or in the details 
of weighing ? In like manner, if four feet of gas do 
not give exactly two-thirds the amount of light which 
six feet of the same gas gives, is not the difference first 
to be looked for in the nature of the burners employed ? 
Not to take into careful account the influence of the 
burners, when testing the illuminating power of gas, is 
as great an oversight as if, in weighing, one were to 
make no examination of the balances; or as if an en¬ 
gineer were to take no account of the boilers he em¬ 
ployed, and then, finding that a ton of coal in some 
circumstances raised a greater proportion of steam than 
when half a ton was used, were to jump to the conclu¬ 
sion that the heat-giving power of coal became greater, 
relatively to the quantity- consumed, when a ton was 
used than when half that quantity was employed. 
What a boiler is to coal and the generation of steam, 
so is a burner to gas and the development of light. One 
ton of coal in a locomotive of the present day generates 
as much force as six tons did forty years ago, simply 
owing to the superior construction of the locomotive. 
In like manner, as regards the illuminating power of 
gas, there are good burners and bad ones. Moreover, 
as every scicntificalty-constructed boiler is devised spe¬ 
cially for a given amount of coal, by the consumption of 
which the boiler developes its maximum of power rela¬ 
tive to the quantity of fuel used; so every well-constructed 
burner is devised to consume a fixed quantity of gas. 
Indeed, for every burner, wdiether good or bad, there is 
a certain rate of consumption at which the burner does 
more justice to the illuminating power of the gas than 
at other rates, whether greater or less. To disregard 
these considerations, is to render experiments wholly 
useless and misleading. 
As at the same rate of consumption, the light emitted 
by one burner may be much greater or much less than 
that of another, so also a burner which does most justice 
to the gas when the rate of consumption is five feet per 
hour, will, if the rate of consumption be either increased 
or diminished from that point, give out less light in pro¬ 
portion to the quantity of gas consumed. 
Ignorance ot these facts led early experimenters to 
the conclusion that because one Argand burning 4 feet 
an hour gave more light than two precisely similar 
Argands consuming 2 feet each, therefore gas gave more 
light when burned in the former quantity than in the 
latter. Upon similar grounds these experimenters might 
have maintained that because a ball fired out of a rifle 
with a charge of 3 drs. of gunpowder went further and 
had more penetrating force than two smaller balls fired 
out of two similar rifles each with lj drs. charge, 
therefore gunpowder had more explosive force, relative 
to its weight, when fired in the former quantity than in 
the latter. Every kind of burner is fitted to consume a 
special quantity of gas of a given quality, just as much 
as a rifle is specially adapted for a special bail and charge 
of powder. 
In order to ascertain whether the illuminating power 
of gas increased according to the above theory a series 
of experiments was made, when it was found that instead 
of the gas giving more light as the rate of consumption 
increased, in every case there is a point beyond which 
the light decreases relatively to the proportion of gas 
consumed. This point lies always below, sometimes far 
below, the maximum of ordinary gas consumption, and 
varies considerably in different burners. Thus while 
one of the burners used in these experiments yielded its 
maximum proportion of light when the gas was burning 
at the rate of five feet an hour, with another burner that 
point was reached at less than two feet. It was found 
also that one burner gave at its best barely one-fifth of 
the light obtainable from the gas. 
In order to account for the origin of the error the 
referees give some interesting facts. The chief means 
of obtaining the maximum of illuminating power from 
gas is to ensure an exactly adequate supply of air to the 
gas-flame. With Argands this point is easily found, 
for it immediately precedes the stage of combustion at 
which the flame smokes, i. e. when the air-supply be¬ 
comes deficient, and a portion of the gas is not thoroughly 
consumed. Indeed, it may be stated as an absolute rule 
that every burner gives its own maximum of light (relative 
to the quantity of gas consumed) when its flame is just 
upon the point of smoking. With batwings and fishtails 
this point is not easily found, but with Argands (owing 
to the glass chimney which encloses them and regulates 
the air supply) it is always possible to increase the con¬ 
sumption of gas to such a point as will make the flame 
smoke: hence every burner of this kind can be used in 
a manner which will give tho full illuminating power of 
the gas, so far as that is dependent upon an adequate air- 
supply. Now, as the common fault of Argands is that 
the gas issues under too great a pressure— i. c. with too 
great a velocity, thereby bringing the flame in contact 
with too much air—it follows that the worse the Argand, 
the better will it become when a large quantity of gas 
is burnt in it; for the air-supply, as regulated by the 
chimney, being nearly a fixed quantity, any excess in 
the air-supply can be neutralized by increasing the 
quantity of gas consumed. But 'with all Argands, 
whether good or bad, the larger the quantity of gas 
consumed in them (short of smoking), the greater will 
be the proportion of light which they give from the 
gas. 
Other experiments tended to show that the illumi- 
minating power of gas remains the same, in whatever 
quantities the gas is consumed, provided that the right 
kind of burners be employed in the experiments. Every 
burner is fitted, and every scientifically-constructed 
burner is expressly devised, for a certain rate of con¬ 
sumption ; and to use a 6-foot burner with three feet of 
gas would be as absuid as to use a 3-foot burner with 
six feet of gas. 
It was found also in these experiments that there is a 
point in the rate of consumption below which the maxi¬ 
mum of light is not obtained. It has been suggested 
that this was owing to a fixed quantity of gas being 
wasted, so far as illuminating power is concerned, it 
being consumed simply to produce heat in sufficient 
quantity to render the remainder of the gas incandescent 
and light-giving. This theory, however, was disproved ; 
and the application of a rough apparatus for diminishing 
the supply of air, by which in one case the light was 
instantaneously increased nine-fold, showed that this 
too resulted from a supply of air unsuited to the amount 
of gas being used. This leads to the consideration of 
the air supply. 
{To be continued.) 
