THE BURNING OF WOOD AND COAL 89 



chlorate among others. It causes many substances to burn. 

 Oxidation is the union of oxygen with the material burned. 



(11) The rate at which the substance burns is determined, in 

 part, by the concentration of the oxygen, and, in part, by the 

 temperature of the material burning. All substances must 

 be heated to a certain temperature before they will burn 

 in air. This temperature is called the kindling temperature. 



(12) When the fuel element, carbon, burns in oxygen it forms 

 carbon monoxide, or carbon dioxide. When the fuel element, 

 hydrogen, burns in oxygen it forms water. (13) The hydro- 

 carbons are compounds of hydrogen and carbon. They rep- 

 resent man's chief supply of fuel hydrogen. Petroleum is a 

 complex mixture of hydrocarbons. 



III. THE BURNING OF WOOD AND COAL 



100. The Burning of Wood. Wood is composed chiefly 

 of carbon, hydrogen, and oxygen. These elements are 

 present in various compounds which make up the wood. 

 When the wood is heated to the kindling temperature in the 

 presence of the air containing oxygen, a complicated series 

 of changes take place which may be understood in part at 

 least, by means of Exs. 28 and 29. 



Exercise 28. Heating Wood in the Air 



Place two or three thicknesses of wire gauze on a ring attached to a 

 ring stand and lay a piece of wood about 3^ by ^ by 1 in. in size on 

 the gauze. By means of a flame apply heat to the wood from beneath 

 the gauze. If the flame from the burner passes through the gauze, 

 more thicknesses of the gauze must be used. While the wood is 

 smoking strongly, remove the flame and apply a lighted match to the 

 escaping smoke. Does the smoke catch on fire? (Fig. 69.) How 

 high above the wood can you cause the smoke to ignite? 



This smoke consists of VOLATILE MATTER produced by the action 

 of the heat on the wood. The volatile matter consists in part of 

 hydrocarbons, and in part of water, acids, and wood alcohol. It is 

 the burning of the volatile matter which causes the flame when wood 

 is burned. 



The black material, left on the gauze after the volatile matter is 



