of Hydrogen through Palladium. 



31 



identical conditions except for the pressure variation, are of most 

 value. It will be observed that the values from Tables XXII 

 and XXV give the greatest constancy with the square root 

 formula, those from Table XXIV agree best with the direct 

 formula, whilst in the case of Table XXVI the agreement is about 

 the same in both cases. We conclude therefore that the range of 

 pressure differences employed by Schmidt is not great enough to 

 settle this question. 



It may perhaps not be out of place to point out that, if we 

 may assume the term involving the square roots of the pressures 

 to be the more important of the two, the values given by Schmidt 

 for the quantity of gas diffusing in unit time at different tempera- 

 tures are in agreement with what we should expect on the dis- 

 sociation theory. On that view the temperature variation of the 

 rate of diffusion depends almost entirely on the variation of k 2 the 

 dissociation constant of the hydrogen inside the metal, which in 

 turn is given by the formula h 2 — C0e~ q,2e , where C is a constant 

 and q is the heat necessary to dissociate one molecule of hydrogen 

 inside the metal. Following the method of calculation in Phil. 

 Mag., Ser. 6, Vol. vin. p. 23 we find 



log lo Z + £log lo = 5+^1/0, 



where L is one of the numbers in column V of the preceding table 

 and B is a constant. 



The following values were obtained by taking the means for 

 neighbouring temperatures of the numbers previously quoted 

 from Tables XIV — XVI of Schmidt's paper. 



I 



II 



III 



Mean Temperature 

 Centigrade 



1/0 absolute 



log lo i + ^log lo 



144° 

 168° 

 225° 

 291° 



2-40 x 10- 3 

 2-27 x 10~ 3 

 2-01 x 10- 3 

 1-77 x 10- 3 



1-796 

 1-570 

 1-273 

 1-0505 



It will be noticed that the numbers in columns II and III come 

 very near to satisfying the linear relation given above. 



If we calculate the value of q for the above figures we get 

 10"88 x 10 s calories. The corresponding value for hydrogen 



