OXIDATION OF ORGANIC COMPOUNDS. 461 



usually those of low temperatures, and vice versa, so far as increased pres- 

 sure produces an effect it compensates to a slight extent for the low 

 temperature, and decreased pressure detracts to a slight extent from the 

 chemical activity resulting from the high temperatures. 



JOINT WOKK OF AGENTS OF AVEATHERING. 



As a matter of observation, we know that the most important chemical 

 reactions which take place in the belt of weathering, as a result of the 

 action of the various agents, are (1) oxidation, (2) carbonation, (3) hydra- 

 tion, (4) solution, (5) deposition. 



OXIDATION. 



One of the reactions of first importance in the belt of weathering is 

 oxidation. Oxidation is the addition of oxygen to other compounds. The 

 source of the oxygen is the atmosphere, of which it composes 23.12 per 

 cent by weight. This oxygen of the atmosphere acts to some extent 

 directly as a gas, but to a far greater extent through water solutions, and 

 to the greatest extent through water solutions and organisms combined. Of 

 these organisms bacteria are of the greatest consequence, but the molds 

 and fungi are important. 



OXIDATION OF ORGANIC COMPOUNDS. 



The chief elements oxidized in the organic compounds are carbon, 

 hydrogen, and nitrogen. 



oxidation of carbon and hydrogen. — The most abundant organic compound is 

 cellulose (nC c H 10 O g ). Other compounds which contain carbon and hydrogen 

 are the proteids, carbohydrates (starch, sugar, etc.), organic acids, fats, etc. 

 The ultimate oxidation products of all these compounds are carbon dioxide 

 and water. This work of oxidation is almost wholly accomplished through 

 the joint work of bacteria and other microbes (such as the fungi), oxygen, 

 and water. The numbers of bacteria engaged in this work are enormous. 

 Estimates by Wollney, Adametz, Koch, Fullus, and others, of the number 

 of bacteria in one gram of soil connected with the formation of carbonic 

 acid gas alone vary from one-half million to One million. 



During the oxidation of cellulose a large number of organic acids are 

 produced. Of these organic acids humic acid (C 60 H 54 O 2 7, Detmer ; C24H 10 O 6 , 



