OXIDS OF CARBON, CARBONATES, ETC. 115 



gen and the cyanids are very poisonous. With H, cyano- 

 gen forms hydrocyanic acid, which is used for the destruc- 

 tion of scale insects and in the preparation of pigments. 



141. Carbids. With some of the metals, notably cal- 

 cium, carbon forms carbids, as CaC 2 , which is produced 

 by the fusion of coke and limestone in electric furnaces. 

 In the presence of water CaC 2 is decomposed, forming 

 acetylene gas, C 2 H 2 , and calcium hydroxid. 



CaC 2 + 2H 2 C 2 H 2 + Ca(OH) 2 . 

 Acetylene generators are prepared for illuminating 

 dwellings. Acetylene, like all gaseous hydrocarbons, as 

 methane and benzine, forms explosive mixtures with oxy- 

 gen. All illuminating gases should be dealt with as 

 highly combustible and explosive materials. 



142. Fuels. There are three forms of fuel : ( i ) gas, 

 (2) liquid, and (3) solid. Natural gas, coal gas, and gas 

 generated from gasoline and naphtha, are the principal 

 forms of gas fuel ; kerosene, gasoline, and crude petro- 

 leum are liquid fuels, while coal, coke, lignite, peat, and 

 wood are the chief forms of solid fuel. The composition 

 of coal, coke, lignite, and peat, is discussed in Chapter V. 

 Wood is composed largely of cellulose, and contains, when 

 dry, about 50 per cent, carbon, 6 per cent, hydrogen, and 

 43 to 44 per cent, oxygen. Air-dried wood contains from 

 10 to 15 per cent, moisture. Different kinds of wood 

 vary in density between quite wide limits ; for example, 

 a cord of dry pine weighs about 3000 pounds, while a 

 cord of dry maple or other hard wood weighs from 4500 

 to 5000 pounds, or more. Hence the same volume (as a 

 cord) of soft wood yields less total heat than a cord of 



