CHEillCAL SCIENCE. 245 



14 oz. of water, from 32 to 112, or causing a rise of temperature from 

 60 to 80.8 in a room containing 2,500 cubic feet of air. One cubic foot 

 of carbonic oxide, at the same temperature and pressure, consumes during 

 combustion half a cubic foot of oxygen, generates one cubic foot of 

 carbonic acid, and affords heat capable of raising the temperature of 1 Ib. 

 14 oz. of water from 60 to 66.6. One cubic foot of hydrogen, at the 

 same temperature and pressure, consumes half a cubit foot of oxygen, 

 generates no carbonic acid, and yields heat capable of raising the tempera- 

 ture of 1 Ib. 13 oz. of water from 32 to 212, or that of 2,500 cubic feet 

 of air from 60 to 66.4. This comparison shows the great advantage 

 which hydrogen possesses over the other diluents, especially over light 

 carburetted hydrogen, which is evidently a very objectionable constituent, 

 and shows that a normal gas for illuminating purposes should consist of 

 illuminating hydrocarbons diluted with pure hydrogen. No method is 

 known by which a gas of exactly this composition can be manufactured ; 

 but a very close approximation has been made to this normal gas, by 

 the employment of a process known as White's hydrocarbon method of 

 gas-making. In this process the very ingenious principle is adopted of gen- 

 erating the illuminating constituents in as concentrated a form as possible 

 in one retort, and the diluents, consisting principally of hydrogen free 

 from light carburetted hydrogen, in another. By this arrangement the 

 diluents can be employed for a very remarkable and highly interesting pur- 

 pose ; they are conducted through the retort in which the illuminating 

 constituents are being generated in such a manner as rapidly to sweep 

 out those constituents before they have time to become decomposed by 

 contact with the red-hot interior surfaces of the retort, a mode of destruc- 

 tion which occurs so largely in the usual process of gas-making. This 

 mode of treatment produces a gain in the amount of illuminating power, 

 derived from a given weight of coal, equal to from 50 to upwards of 100 per 

 cent., whilst the increase in quantity of gas is frequently 300 per cent. 

 The gas thus manufactured differs principally from coal gas made by the 

 ordinary process, in having a large portion of the light carburetted hydro- 

 gen replaced by hydrogen ; it is therefore, in a sanatory point of view, the 

 best gas hitherto produced. This is seen in the following table, which 

 exhibits the amount of carbonic acid and heat generated per hour by 

 various sources of light, each equal to 20 sperm candles burning at the 

 rate of 120 grains of sperm per hour. 



Carbonic Acid. Seat. 



Tallow, 10.1 cubic feet. 100 



AVax, .... 



Spermaceti, . . . . $ 8 ' 3 



Sperm oil, (Carcel's lamp,) . 6.4 " 63 



London gases, B, C, D, E, . 5.0 " 47 



Manchester gas, . . . 4.0 " 32 



London gas, A, ... 3.0 " 22 



Boghead hydrocarbon gas, . 2.6 " 19 



Lesmahago hydrocarbon gas, . 2.5 <* 19 



