76 THE PRODUCTION AND USE OF HEAT 



and is a great saving of wood to the inhabitants. Some say 

 it saves five-sixths, some say three-fourths, others much less. 

 I suppose two-thirds or one-half is saved; my room is twice 

 as warm with one-fourth the wood formerly used." 



As a means of securing comfort, Franklin's invention, with- 

 out doubt, was the greatest single step ever made in perfecting 

 heating devices. With this stove it became possible to heat 

 most of the rooms of a house so that they were fairly com- 

 fortable. Such stoves would hardly be considered of great 

 value today for heating purposes, but at the time of the 

 Revolutionary War they were the king of heaters. In fact, 

 there was no very great improvement over the Franklin stove 

 for a century. In this line of advancement, as well as in many 

 other lines, the world must ever recognize in Benjamin 

 Franklin one of its greatest benefactors. 



II. THE CHEMISTRY OF COMBUSTION 



82. The Classes of Fuels. The wood, coal, kerosene, 

 gasoline, and the various kinds of gases burned for the pro- 

 duction of heat or light are called FUELS. They are commonly 

 classified as SOLID FUELS, LIQUID FUELS, and GASEOUS FUELS. 

 Wood, coal, and coke are common solid fuels; petroleum and 

 its products and alcohol are common liquid fuels, illuminating 

 gas, acetylene, and gasoline gas are common gaseous fuels. 



83. The Fuel Elements. While there are many kinds of 

 fuels, it has been found that they all contain and are made 

 chiefly of two kinds of matter, namely, CARBON and HYDROGEN. 

 Carbon is a solid, black in color, as ordinarly met in CHARCOAL 

 and in the GRAPHITE of the lead pencil, but colorless and 

 sparkling as found in the DIAMOND. Hydrogen is a colorless 

 gas. It is the lightest known substance. Carbon and 

 hydrogen are called the FUEL ELEMENTS. 



84. Chemical Elements. Carbon and hydrogen are also 

 two of the CHEMICAL ELEMENTS because no other kind of 

 matter has ever yet been obtained from either of them alone. 



