112 



AGRICULTURAL CHEMISTRY 



machines suitable for the purpose are made for illuminat- 

 ing dwellings. Five gallons of gasoline will produce about 

 loco feet of gas or vapor. The illuminating power of 

 gas, and of flames in general, is expressed in terms of 

 candle-power. A sixteen candle-power light is one that 

 gives sixteen times as much light as a standard candle, 



Fig. 48. Illuminating gas plant for producing gas from gasoline. A, weight 

 to air-pump B. D, carburetter or generating tank into which air is forced. 



composed of spermaceti, and burned at the rate of 120 

 grains per hour, the comparison being made by means of 

 a photometer. In some localities, hydrocarbons, due to 

 decomposition of organic matter, are given off from the 

 earth as natural gas in amounts sufficient to be used for 

 illuminating and fuel purposes. 



134. Mineral Oils. The heavier products obtained in 



