26 



Physically, this is the simple case of the 

 diffusion of one gas into another. Ignoring certain 

 minor variations, the establishment of a "steady 

 state" of rate of oxygen movement will see a continuous 

 decrease of the concentration of oxygen from that of the 

 outer air to the zero concentration at the inner end 

 of the passage. The physical theory of the mutual dif- 

 fusion of two gases in contact is applicable, with some 

 possible exceptions which are minor and do not require 

 attention. According to this theory 1 , 



V - Kst J£ 

 dx 



in which formula "V" is the volume of gas diffusing, ex- 

 pressed in cubic centimeters per second; "s" i3 the 

 area across which diffusion is occurring, expressed in 



square centimeters; "t" is the time in seconds; OR is 



dx 



the rate of change of the partial pressure of the dif- 

 fusing gas (which is nearly the same as the rate of 

 change of volume concentration) expressed in atmospheres 

 (760 mm.) per centimeter; and K is the diffusion constant 

 or "coefficient of diffusion". This constant differs 

 with the gases concerned and is directly proportional 



1. See, for instanoe, Chwolson,- Traite 

 de physique, vol. 1, pp. 528-529 (1908), where the ori- 

 ginal investigations are cited. 



