HYDROGEN INTO ATOMS 189 



Table XVI is also satisfactory. The calculated gradual increase in P' with 

 increasing temperature is in full accord with the observations. 



It must be remembered that the observed pressures were those at which 

 the bulbs were sealed off and that the actual pressures in the bulbs while 

 the filaments were heated must have been much higher. The fact that the 

 calculated values are larger than the observed therefore adds support to 

 the theory. 



The value of B obtained above, (68), enables us to calculate the 

 diffusion coefficient D by Equation 32. The shape factor S which is involved 

 in this equation may be calculated from (7), taking d = 0.00706 cm. and 

 b = T).y cm. (see Table Vj. This gives S= i.oi. By substituting this 

 in (32), together with gi = 42000 and the value of B from (68), we find 



Do = 9.6 cm-, per sec. (69) 



This is the value of the diffusion coefficient at 0° C. as obtained by 

 extrapolation downwards from high temperatures by Equation 29. At 

 higher temperatures and at atmospheric pressure, we thus obtain from the 

 same equation, together with (69) : 



D = 2.14 X 10-3 T''^ (70) 



In the "paper of 191 2" D was calculated to be equal to 



^ 0.514 X .0-' T" - ( ) 



1 + 77/T • 



This result was obtained, according to the kinetic theory, on the as- 

 sumption that the free path of hydrogen atoms and hydrogen molecules 

 are the same. At high temperatures the second term in the denominator 

 of (71) becomes negligible and we thus see that the present results show 

 that the diffusion coefficient of hydrogen atoms through molecular hy- 

 drogen is 4.2 times as great as had been previously calculated. 



A very thorough test of the theory is aft'orded by a comparison of the 

 values of Wd calculated according to the theory, with those determined 

 experimentally. In Tables XVII and XVIII the observed and calculated 

 values have been placed side by side. The "observed" values are taken 

 directly from Table III of Part I. The calculated values were obtained by 

 solving Equation 43 for W/j after substituting it in the numerical values 

 of K, F, To and T2. 



For this purpose the values of K were taken from Table XV, which was 

 obtained directly from Equation 65. At O.015 and 0.039 t^^^- pressure To 

 was taken to be 300° K., whereas at pressures from 0.207 to 4.4 mm. the 



