262 



GENERAL SCIENCE 



these products are wood alcohol and acetic acid. Char- 

 coal made at a low temperature is very inflammable and 

 burns with an intense heat. It is very porous and is able 

 to absorb many times its own volume of certain gases. 



Coke bears the same relation to soft coal that charcoal 

 does to wood. Coal is heated in a retort from which air 

 has been excluded, until everything that has been driven 

 off by heat has escaped. Other valuable products of the 

 process are illuminating gas, ammonia water, benzene, 



creosote, carbolic acid, pitch, and 

 tar-camphor. 



Charcoal and coke are used as 

 fuels and in the reduction of the 

 ores of iron and other metals. 

 The oxide of a metal when heated 

 with carbon decomposes ; the 

 oxygen unites with the carbon 

 and releases the metal. 

 , Hydrocarbons. A compound 

 of carbon and hydrogen is called 

 a hydrocarbon. There are a 

 number of hydrocarbons. Marsh 

 gas, composed of one atom of 

 carbon and four atoms of hydro- 

 gen, is formed in the rotting vegetable matter at the 

 bottom of a marshy pool. Figure 227 shows a method 

 of collecting this gas. It is a colorless, combustible gas 

 and burns with a pale blue flame. In mines this gas is 

 called fire damp. 



In the manufacture of coke a number of gases are 

 produced. The coal gas which we use for heating and 

 lighting is about one third marsh gas (methane), forty- 

 five per cent hydrogen, some carbon monoxide, and nitro- 



FIG. 227. Collecting Marsh 

 Gas. 



