29 



ENVIRONMENT OF LIVING THINGS 



ignites the sulphur, and finally the wood of the match, composed largely 

 of the element carbon, is lighted and oxidized. If we could take out the 

 different chemical elements of which the match is formed and oxidize them 

 separately, we should find that the amount of heat needed to start the oxi- 

 dation of the substances would vary greatly. The element phosphorus, for 

 example, is kept under water in a glass jar be- 

 cause of the extreme readiness with which it ig- 

 nites in the presence of oxygen.' 



Slow Oxidation. — Oxidation may take 

 place slowly, as may be seen in the rusting 

 of an iron nail. Rust is iron oxide, and is 

 formed by the union of iron and oxygen. 

 This kind of oxidation is said to be a slow 

 oxidation. Slow oxidations are constantly 

 taking place in nature and are a part of the 

 process of decay and of breaking down of 

 complex materials into simpler materials. 



Heat given off as Result of OxidationT^^^ 

 One of the most important effects of oxida- 

 tion lies in the fact that, when anything 

 is oxidized, heat is produced. This heat 

 may be of the greatest use. Coal, when 

 oxidized, gives off heat; this heat boils the 

 water in the tubes of a boiler; steam is 

 generated, wheels of an engine turn, and 

 work is performed. The energy released 

 by the burning of coal may be transformed 

 into any kind of work power. Energy is 

 the ability to perform work. We shall later 

 find that the oxidation of certain materials 

 in the bodies of plants or animals releases 

 energy. The heat of the human body is 

 maintained by constant oxidation of food 

 materials within the body. 

 The Composition of Water. — If an electric current is passed 

 through water ^ by means of the apparatus shown in the Figure, it 



' The teacher may later introduce experiments in chemistry to demonstrate the 

 physical appearance of such other elements as are used by plants in food making. 

 2 A little sulphuric acid must be added to make the liquid a better conductor. 



Apparatus for separating 

 water into the two ele- 

 ments hydrogen and 

 oxygen. 



