THE COMBUSTION OP GAS FOR ECONOMIC PURPOSES. 
477 
And if instead of atmospheric air a jet of oxygen is used, as I will now show you, 
the temperature is still higher. This is the principle of Deville’s furnace, which is a 
jet of oxygen blowing into a large flame of coal-gas, and directed down upon the 
refractory substance, the whole apparatus being enclosed in a chamber of non-conduc¬ 
tors. With this furnace large masses of platinum are easily melted, the platinum being 
placed upon a hollow bed of lime. I have seen a mass of platinum, weighing about 
350 lbs., which had been melted in this manner; and I was informed by Messrs. John¬ 
son and Matthey, the platinum assayers of Hatton Garden, that the mass required six 
hours for its fusion. During that time about 360 cubic feet of coal-gas and the like 
quantity of oxygen were used; in fact, Deville found in his experiments at the Ecole 
Normale that it required a little more than a cubic foot of gas and a cubic foot of 
oxygen to melt a pound of platinum. The temperature of the flame must be enormous; 
calculated from the thermotic powers of gas with air and oxygen, it may be said that 
it is equal to about 5228° of Fahr. when air is used, and 14,320° with oxygen. 
The temperature of different combustibles is shown on the diagram on the following 
page, and you will notice that the highest temperature produced by the various consti¬ 
tuents of coal gas is that of acetylene, or the vapour of benzole when burned in oxygen, 
the heat of which exceeds 17,000° Fahr.; the lowest temperature of all the constituents 
is about 12,700^ Fahr., the temperature of burning carbonic oxide. 
On the same diagram I have tabulated the thermotic power of a great number of 
substances. It is expressed in the number of pounds of water raised 1° Fahr. by a pound 
of the substance, and when the body is capable of being converted into gas or vapour, 
I have also expressed it in the cubic foot at common temperatures and pressures. Hy¬ 
drogen, you perceive, is the most powerful thermotic agent, and carbonic oxide is the 
weakest; a pound of the first of these gases will raise 62,030 lbs. of water 1°, whereas 
a pound of the latter will only heat about 4325 lbs. of water to that extent. Examined 
by the cubic foot, and considering that for every pound of w'ater raised 1°, about 
48 cubic feet of air are raised to the same extent, we may say the chief constituents of 
coal gas have this thermotic power:— 
^Pounds of Water and Cubic Feet of Air raised 1° Fahr, by a Cubic Foot of the 
Gas Burning in Air. 
Cubic Foot of 
Lbs. Water 
raised 1° Fahr. 
Cub. Ft. Air 
raised 1° Fahr. 
Hydrogen . . . 
heats 
329 . 
. 15,837 
Marsh gas . . . 
55 
996 . 
. 47,946 
Olefiant gas . . 
55 
1585 . 
. 76,299 
Propylene . . . 
55 
2376 . 
. 114,378 
Butylene . . . 
55 
3168 . 
. 152,502 
Acetylene . . 
55 
1251 . 
. 60,220 
Benzole vapour . 
5 } 
3860 . 
. 185,814 
Carbonic oxide gas 
53 
320 . 
. 15,403 
Common coal gas . 
55 
650 . 
. 31,290 
Cannel coal gas 
33 
760 . 
. 36,585 
From this we can determine the practical thermotic pow'er of any of these agents. A 
cubic foot of common gas will heat 65 gallons of water 1°, or 6-5 gallons 10°, or 
3-25 gallons 20°; so that a bath containing 250 gallons of water would require about 
77 cubic feet of common gas, or 66 of cannel, to raise its temperature from 558 to 75°. 
In practice, however, this is rarely attained, because of the faulty construction of the 
heating apparatus. I find, indeed, that a bath in my own house, made by Phillips, of 
Skinner Street, takes nearly twice this proportion of gas to heat it, and being in a closed 
room the atmosphere is almost poisoned before the bath is ready; and the circulation of 
the hot water is so imperfect that the top layer becomes boiling hot before the bottom 
of the water is warm. This is a subject which requires attention, for it is open to much 
improvement. 
‘Again, with regard to the boiling power of gas, although in good practice a cubic 
foot of gas should boil off about 4712 grains of water, or about 22 times its own weight, 
yet this is not often attained, for in an open vessel we rarely evaporate more than 
2866 grains of water, or about 13 times its weight. 
