260 



GENERAL SCIENCE 



and alcohols are just now in the process of being developed 

 as fuels. 



Wood. Wood is a very impure form of fuel. It con- 

 tains water, resin, starch, cellulose, gum, oil, and mineral 



v Copyright by Underwood & Underwood, N. Y. 



FIG. 225. Cutting Peat, the Vegetable Substitute for Coal, 

 Kiltoom, Roscommon, Ireland. 



matter (ash). Before the wood can burn, the water 

 must be evaporated, and the other substances contained 

 in the wood must be raised to the temperatures at which 

 they decompose, yielding gases of a combustible nature 

 and charcoal. A large amount of heat is required to do 



