480 THE COMBUSTION OF GAS FOR ECONOMIC PURPOSES. 
So that, when we wish to economize the radiant heat of burning gas, it is best to use 
it with some solid body, as fragments of pumice or pieces of asbestos. 
The last point to which I would refer is the available or convertible motive power of 
burning gas. 
The calculations of Dr. Mayer, of Heilbronn, and the experimental inquiries of 
Mr. Joule, of Manchester, show that the mechanical power of heat is 772 lbs,, raised a 
foot high for the heat necessary to raise the temperature of a pound of water 1° Fahr. 
A cubic foot of hydrogen in burning has therefore the mechanical power of (329 x 
772 = )253,9881bs.; and the same quantity of common gas has the power of (650 x 
772 = )501,800 lbs.; while the power of a cubic foot of cannel gas is (760 x772 = ) 
586,720 lbs., raised a foot high. But if the same quantity of these gases is exploded 
with air or oxygen in a closed chamber, the mechanical power is somewhat different. I 
have here tabulated the expansive force of such a mode of combustion, and I may say 
that the calculations are deduced from the temperatures of combustion and from the 
volumes of the products—allowance having been made for the specific heats of the 
several products. It would seem, therefore, that the explosive powers of the several 
constituents of coal gas, when mixed with their proper proportions of air or oxygen, 
are as follows:— 
Explosive Power of Mixed Gases. 
Hydrogen . . 
Mixed with Air. 
(Ats.) 
. . 12-5 . 
Mixed with Oxygen. 
(Ats.) 
. . . 25-6 
Marsh gas . . 
. . 14-0 . 
. . . 370 
Olefiant gas . . 
. . 15T . 
. . . 42-9 
Propylene gas . 
. . 22-5 . 
. . . 67-3 
Butylene gas . 
. . 30-2 . 
. . . 85*8 
Carbonic oxide . 
. . 11*7 . 
. . . 21-8 
Common gas . . 
. . 14-6 . 
. . . 29-2 
Cannel gas . . 
. . 18-0 . 
. . . 38-8 
These are the theoretical pressures exerted upon the sides of the containing vessel when 
these several gases are exploded with their proper proportions of air or oxygen ; but as 
the explosion is never instantaneous, but proceeds from particle to particle, and therefore 
occupies time, and as the walls of the vessel always cool the products of the exploded 
gas to a great degree, this theoretical value is never obtained in practice, the highest 
pressure in the exploding chamber of a gas-engine being only 75 lbs. on the square inch, 
or five atmospheres. The power of this has been determined experimentally by Mr. 
Evans, who informs me that with a cubic foot of a mixture of nine air and one gas he 
has propelled a wooden shot (three inches by four) 50 yards ; and he ascertained that 
the same effect was produced with an ounce of gunpowder. The motive power, there¬ 
fore, of the exploding mixed gas is considerable. 
In the gas-engines of Lenoir it has been found that the best proportions of air and gas 
are eight volumes of air to one of common gas; theoretically the best proportion for 
London (13-candle) gas is 5'6 volumes of air to one gas. A larger portion of air is re¬ 
quired for cannel gas, as 11 to 1; but in practice it is found that cannel gas does not 
produce so good an effect as common gas. The time of the explosion is about the 27th 
part of a second, and the temperature of it is about 2474° Fahr. instead of from 5228° 
to 7000°—the calculated temperatures for open and closed chambers. 
The machines which are used for practically employing this power are all modifica¬ 
tions of the original engine of Lenoir. They consist of a cylinder with a double-action 
piston, receiving the mixed gas alternately on either side of the piston. The arrange¬ 
ment is such that in the movement of the piston the air and gas, in proper proportions 
(8 to 1), are drawn into the cylinder by a suitable side valve, and when the piston has 
made half a stroke it shuts off the valve; at that moment the mixed gas is fired in the 
cylinder by means of an electric spark from a Kuhmkorff’s coil passing between the 
points of two wires in the cylinder. One of these wires is insulated by traversing a rod 
of porcelain fixed in the cylinder, and, being in connection with a make-and-break con¬ 
trivance, called a distributor, attached to the fly-wheel of the engine, it receives the 
charge of electricity, and so fires the mixed gas at the right moment. The expansion 
caused by the explosion and heat of combustion drives the piston through the rest of 
