230 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



ness. The finer the more difficultly decomposed substance, 

 the more rapidly it oxidized. Easily decomposed substances, pea 

 straw for example, did not oxidize more rapidly when finely 

 divided. 



(3) The Stage of Decomposition of the Material. The more 

 decomposed the substance, the less rapidly it is oxidized. The 

 following figures are some results of Wollny: 



Volume of 



carbon dioxide 



per 100 volume of 



soil atmosphere 



Cattle manure, fresh 13-43 



Cattle manure 8 weeks old 11.71 



Cattle manure 20 weeks old 8. 25 



Peat 0-8 inches deep 2.93 



Peat 9-19 inches deep 2.72 



Peat 19-31 inches deep 2.55 



Peat 31-43 inches deep 2.39 



Peat 43-55 inches deep 2.26 



It is natural to expect the more easily oxidized material to dis- 

 appear rapidly, and the more resistant materials at a slower rate. 



(4) Chemical Composition. Leguminous straws, on account 

 of the presence of more proteids, are oxidized more rapidly than 

 cereal straws. Waxy material hinders the decomposition of turf ; 

 when it is removed by extraction with ether or alcohol, the ex- 

 tracted turf is much more rapidly oxidized than the unextracted. 

 Tannic acid decreases oxidation; rye straw, corn fodder, and soja 

 bean leaves soaked in tannic acid were oxidized less rapidly than 

 the untreated substance. The addition of plant food may 

 accelerate the oxidation. 



(5) Animal residues oxidize more rapidly than vegetable 

 residues. Green materials oxidize more rapidly than the same 

 material dried and moistened. 



(6) The oxidation decreases with the supply of oxygen, though 

 not proportional to the supply ; when the supply decreases beyond 

 certain limits, the oxidation drops rapidly. 



(7) Temperature. The relative effects of different tempera- 

 tures is shown by the following experiment on a compost mix- 

 ture: 



