182 Mr. W. H. Patterson on 



heated by a small Bunsen flame ; temperatures were de- 

 termined thermoelectrically. After the method of Haber and 

 B rimer, hydrogen was led into the molten alkali through a 

 platinum tube, and the E.M.F. of this tube measured by the 

 compensation method against a N/10 electrode. In other 

 experiments, the hydrogen was produced by throwing into 

 the molten alkali a little formate and using a platinum wire 

 as electrode. In both cases a value near to that of Haber 

 and Bruner, i. e. —1*5 volt, was attained without perceptible 

 temperature coefficient. 



Experiments were then carried out on the oxy-hydrogen 

 combination, with sodium hydroxide as electrolyte, in order 

 better to establish its dependence on the temperature. 



Haber and Bruner, in the latter communication, have 

 calculated this potential thermodynamically from water- 

 vapour dissociation at high temperature, with the assumption 

 that the molten alkali is in equilibrium with the water-vapour 

 of the air, the latter having an average tension of 0*031 

 atmos. The calculation rests on the integration of the 

 Helmholtz formula for the free energy : — 



which is integrated in the form 



7 A 



dT T 2 ' 



By help of the well-known value of the reaction-heat of 

 the formation of water-vapour from its elements and from 

 the data found by Langen for the mean specific heat of the 

 gases taking part in the reaction, the integral becomes 



*A = 57084-2-976xlog e T + 0'00125T 2 



- 4-56 x T x log -!*£-, + const, x T. 

 Pu 2 x PJ 2 



The constant of this expression follows from the measure- 

 ments carried out by Nernst and Wartenberg on the dis- 

 sociation of water-vapour. It amounts to 7*6. In the 

 equation, T denotes the absolute temperature, and p the 

 partial pressure of the gases. The free energy A is calculated 

 in small calories. 



* For further information relative to the above calculation cf. English 

 edition of Prof. Haber's ' Thermodynamics of Technical Gas Reactions ' 

 (Longmans, Green & Co., 1907). 



