66 



same concentration and a porosity of .7^ to .0«2 cubic 

 foot and 1.01 cubic feet for a concentration gradient of 

 1.0 percent per inch and porosities of .2 and .7, 

 respectively. Calculations for two actual cases, on 

 analytical data by Belz, gave, respectively, .10 to .15 

 and about .04 cubic foot of carbon dioxide escaping per 

 day from one square foot of soil surface. 1 It should be 

 noted that the diffusion of carbon dioxide and of oxygen 

 in the soil is not given exactly by the diffusion co- 

 efficient for these gases diffusing into each other. 

 In the soil they are diffusing, side by side but in op- 

 posite directions, through an atmosphere of about 79 

 percent of nitrogen, This alters the rate of diffusion, 

 but the alteration can be predicted by the theory of 

 Stefan and is found to be approximately 1.12 times 

 the rate of diffusion of carbon dioxide and oxygen with- 

 out the nitrogen. This correction is taken into account 

 by Buckingham,whose paper may be consulted for details. 

 The similar disturbances due to the presence of water 

 vapor are much smaller and may be neglected. The con- 

 clusion that the carbon dioxide and oxygen diffuse at 

 nearxy equal rates follows from theory and is indicated^ 



1. loc. cit. . page • 



2. Sitzungsber. Akad. V/iss., V/ien, math.- 

 naturw. kl.. 65 ; 63 ( J. 



