CHEMICAL CHANGES 



229 



carbon dioxide comes partly from easily reducible substances 

 containing it, partly from the substance itself. In consequence 

 of this loss of oxygen, the substance becomes richer in carbon. 

 The following analyses 1 of three samples of peat of different ages 

 show this enrichment in carbon : 

 PERCENTAGE COMPOSITION OF ASH-FREE PEAT OF DIFFERENT AGES. 



The older the peat, the richer it is in carbon and also in 

 nitrogen. 



Conditions of Decomposition of Organic Material. Various 

 experiments have been made to study decomposition of the 

 organic matter of the soil. Many experiments have been 

 carried out by Wollny 2 with the following method: A 

 mixture of sand or earth and the organic material was placed in 

 U tubes, moistened with water, and kept in a constant tempera- 

 ture bath. The carbon dioxide formed was drawn out every 24 

 hours and collected in a solution of barium hydroxide of known 

 strength. The unused barium hydrate was treated with standard 

 acid, and the quantity of carbon dioxide evolved calculated. 



The following are some of the results of these experiments : 



1 i ) Effect of Ratio of Organic Matter to Soil. Varying quan- 

 tities of powdered horse dung were added to the same quantity of 

 sand, other conditions remaining the same. The oxidation was 

 decreased when the carbon dioxide formed exceeded certain 

 limits, and was less rapid, the greater the proportion of organic 

 substance. 



(2) Effect of Fineness of Division. These experiments were 

 made with peat and with pea straw of different degrees of fine- 



1 Detmer, Landw. Versuchs-stat., 1871. 



2 Die Zersetzung d. Organischen Stoffe. 



