HYDROGEN INTO ATOMS 195 



The dissociation at higher temperatures would cause an increase in this 

 mean specific heat amounting to 



02 X 



T — 27S''.i2—xy 



In Table XIX are given the mean specific heats for a few temperatures, 

 as calculated from Pier's formula, together with those calculated by taking 

 into account the increase due to dissociation. For this calculation the values 

 of X iwere taken from Table XV and ^2 was taken to be 8400 calories. 



Siegel, in a recent paper,^^ discusses in detail the errors of the explosion 

 method. He points out that, owing to a faulty method of calculation, the 

 temperatures given by Bjerrum are considerably too high, in some cases 

 as much as 400°. He then shows that Bjerrum's experiments exhibit certain 

 discrepancies which could be readily explained by assuming a dissociation 

 of the hydrogen. He then says (pages 649-50) : 



"In order to reconcile Langmuir's results with those of the explosion 

 method, one -must assume that in the calculations thus far, the capacity 

 of the system (in the explosion chamber), that is, ChoO + MCH2, has 

 been taken about 30% too high. 



"Such an assumption ... is impossible. However, if we take for 

 the heat of dissociation Qf hydrogen, the value 140000 calories instead 

 of the 1 31000 calories given by Langmuir, we then find by the Nernst 

 approximation formula : 



log K = Q/4.57 T + 2v . 1 .75 log T + 2vC 



that at 2850° and atmospheric pressure the dissociation is about 11%, 

 which is the value given by Langmuir for 2700°. With this assumption 

 it can be shown that the heat capacity of the system at 2850° would be 

 13% less than previously taken. This result is no longer irreconcilable 

 with the other results of the explosion method. However, I am of the 

 opinion that the heat of dissociation of hydrogen should be at least 



^* Z, phys. Chem., 87, 641 (1914). 



