56 



and 0.74 percent, and nitrogen contents between 78.80 

 and 80.24 percent. All figures are in volume-percent. 

 The atmospheric air at the same time and place was 

 found to contain 20.95 percent oxygen, 79.03 percent 

 nitrogen, and .025 percent carbon dioxide. In these 

 observations the highest contents of carbon dioxide in 

 the soil air were found in compost material or in soils 

 which had been recently ma a our ad . However a content of 

 1.79 percent carbon dioxide was found in the air from the 

 soil of a pasture and several samples from cultivated 

 soils ran over one percent. In general the nitrogen 

 remains approximately constant, the oxygen and carbon 

 dioxide rising and falling reciprocally. 



The first analyses of soil air from different 

 depths were made by Pettenkofer^, who determined the 

 percentage of carbon dioxide in air samples from 1.5 nu 

 and from 4.0 m. deep. Air from the lesser depth carried 

 •243 to 1.198 percent; that from the greater depth car- 



1. The average composition of the atmosphere 

 by volume is oxygen = 20.941 percent, nitrogen = 78.122 

 percent. The carbon dioxide is more variable. The 

 normal is about .03 percent. It seldom falls below 

 .025 percent or rise$(above .055 percent, unless in case 

 of exceptional polution by smoke or the like. See 

 Clarke,- Data of Geochemistry, 3rd ed. , U. S. Geol. Sur- 

 vey, Bull. 616, pp. 41-47, where other literature is cited. 



2. Eeue Rep. Pharm. 21; 677-702 (1873). 



