200 PHENOMENA, ATOMS, AND MOLECULES 



occurs and p2 is the partial pressure of molecular hydrogen after dis- 

 sociation. 



In the present case we may place To = T2; P = 600, S = 1.34, and 

 qx = 42000. From (30) we thus find 



p, = 946Wz,/(DoVT). (80) 



Combining (79) and (80) with (27), we find 



K - W^p(946/DoVT + B) ^ 



^o— Wd (473/DoVT + E) 



where E is given by (34). 



By trial it was found that (81) gives the best agreement between the 

 observed and calculated values of Wp if Do is placed equal to 2.5. 



Calculating E by (54) it is evident that E is negligible compared to 

 4.73/2-5 VT over the whole range of temperatures covered by the experi- 

 ments. Equation 81 thus simplifies to 



Wz, = JSZ X Ji - -^^ W^. (82) 



^144000 y po^T 



This quadratic equation can be conveniently solved for Wd by using 

 a series of approximations, since the second radical is always close to unity. 

 In this way, by taking K from Table XV, the values of Wd for different 

 temperatures and partial pressures have been calculated. The results are 

 placed side by side with the observed values in Table XXI. 



The agreement is entirely satisfactory, considering the crudeness of 

 some of the assumptions made. 



The theory receives additional confirmation through the fact that the 

 observed values of Wd increase in proportion to the square root of the 

 partial pressure as demanded by the theory, whereas at lower temperatures 

 the observed values of We increase linearly with the partial pressure. 



From the value of Do we may conclude by (29) that the diffusion 

 coefficient of hydrogen atoms through nitrogen at high temperatures and 

 atmospheric pressure is 



D = 2.S (Ta/273r^\ (83) 



Comparing this with (69) we see that the ratio of the diffusion co- 

 efficient of hydrogen atoms through hydrogen to that through nitrogen is 

 9.6/2.5 = 3.84. 



If we calculate the free path of In'drogen atoms through nitrogen ac- 

 cording to the principles of the kinetic theory, using Equations 20 and 21 

 on page 865 of the "paper of 1912," we obtain 



Deal. = 2.16 (T/273)^'^ (84) 



