Biy.Tics : 



even though the percentage pore space does not vary. So much for some 

 of the things about the soil and its atmosphere and the factors in the 

 soil which vri-11 effect pore space. 



Kinetic theory of gases - 



I think if we are going to consider gaseous movement, we perhaps should 

 review very briefly something about the kinetic theory. It is the ki- 

 netic energy that the gas molecules possess whicli will affect to a great 

 extent their movement. The gas molecules are in constant m: Lion and, at 

 a constant temperature, have a constant average velocity. The amount of 

 kinetic energy, or this motion, is a direct function of the absolute 

 temperature. Theoretically, if we reached zero degrees, Kelvin, the ki- 

 netic energy, would be zero, and the molecules would cease to have motion 

 But under normal situations, as the temperature goes up, the average ve- 

 locity of the molecules increases accordingly. 



The molecules of the gas, theoretically, also behave as elastic spheres, 

 and the impacts that they have with one another are instantaneous and 

 thoroughly elastic. They lose none of their energy through the impact 

 of molecules with one another. It is also assumed that the mean free path 

 of the molecules between inpacts is rmch greater than the time for the 

 instantaneous impacts that they have with one ariother. They exert no 

 forces upon one another that would cause them to stick together; each 

 impact is, as I say, thoroughly elastic. ',.'e assume that the duration of 

 the impact is instantaneous or negligable compared to the time interval 

 between these impacts. 



Gases, as you know, also have the property of unlimited and indefinite 

 expansability. That means that they will fill completely any volume into 

 which they are introduced. They exert a pressure on the walls of enclos- 

 ing vessels, due to the impacts the molecules have against the walls of 

 the vessel. The molecular movement that they possess is a manifestation 

 of the kinetic energy in the system. 



It is shovm by the kinetic ener ^y formula that the kinetic energy of a 

 system is equal to: K.E. = m«v^ 



2 , in which "m" is the mass of molecules 

 and "v" is the velocity of molecules. So we sec that this system possesses 

 a certain quantity of kinetic energy. Then, if we increase the mass of the 

 molecules, the Velocity of the molecules will be reduced accordingly. If 

 we have a mixture of gases with a given amount of kinetic energy in that 

 system, the larger gas molecules would be moving at much slower velocity 

 that the smaller molecules. Now this is somewhat important as one goes 

 into consideration of larger and larger molecules. 



The process of diffusion - 



The rate of diffusion at a given temperature would be reduced according 



