12 SCIENCE OF HOME AND COMMUNITY 



a lower price, hence it is quite possible that a hundred years 

 from now, electricity may be the common method of heat- 

 ing. As the stoves and furnaces of to-day have taken the 

 place of the fireplaces formerly in common use, so in the 

 future, electric radiators may take the place of stoves and 

 furnaces. 



The chemistry of burning. The source of heat in any 

 of these systems, excepting electricity, is the burning of the 

 fuel. In coal the chief element is carbon. In wood, too, this 

 is found, together with other elements including a gas called 

 hydrogen, which also burns. The burning of coal consists in 

 the union of the oxygen of the air with the carbon, forming an 

 invisible gas called carbon dioxid, and consists to a lesser ex- 

 tent in a union with hydrogen, forming water. In breathing 

 we give off the same gas, which is formed in our bodies in a 

 similar way, but not so rapidly, by the union of oxygen and 

 carbon. This process of uniting with oxygen takes place in 

 all ordinary types of burning, as in the candle and the kero- 

 sene lamp. 



Fuels are of three kinds : solid, such as coal and wood ; 

 liquid, such as kerosene ; and gaseous, such as illuminating 

 gas. Coal and wood are the fuels most commonly used for 

 heating purposes. 



Coals are divided into two classes, the hard and the soft. 

 The hard coal contains a larger per cent of carbon, and the 

 soft coal a larger per cent of volatile substances that are 

 .driven off when the coal is heated. These substances are 

 not completely burned, and as a result a large amount of 

 smoke is formed. In order that the fire may continue to 

 burn, the various products formed must be carried off through 

 the chimney ; and a new supply of oxygen must be furnished. 

 The fire is controlled by means of dampers which regulate 

 the amount of air that enters. The important part of the 

 air for the purpose of burning is oxygen. This constitutes 

 about one fifth of the air. Experiments with pure oxygen 



