M. P. A. Favre's Electrolytic Investigations. 291 



about 50 millims. I may, however, mention that, working under 

 these conditions, I could never transfer outside the battery more 

 than about three-quarters of the heat it developes. A quantity 

 representing about 6000 units remains obstinately confined there. 

 It is this unexpected result which, after having long engaged my 

 attention, has directed my researches in their present path, having 

 led me to suspect the existence of secondary phenomena which 

 render the reactions complicated. 



Experiments. 

 Let us consider the following numbers furnished by the reac- 

 tion of sulphuric acid and of sulphate of copper on various 

 metals : — 



Thermal 

 units. 

 I. One equiv. of zinc, in replacing 1 equiv. of hydrogen! iqqq^ 



in SO 4 H, gives J 



One equiv. of zinc, in replacing 1 equiv. of copper 1 07^4^ 

 in S0 4 Cu, gives J 



One equiv. of iron 



,, cadmium 







19025 

 16265 



IT. We are led to conclude that 







If the metalloid radical SO 4 , in 

 with H, gives . * . 

 in combining with 

 )> » 



combining! Thermal units. 



• • • r 



Zn it gives x-t 19834 



Fe „ a; + 19025 -7512 



Cd „ ^ + 16265-7512 



If we take as the value of x the heat corresponding to the 

 formation of another sulphate (sulphate of copper for instance), 

 we shall conclude — 



III. That the radical SO 4 , in combining with Cu, giving x, 



the radical SO 4 , in combining with Zn, should give x-\- 27346 



Fe „ a7+19025 



„ „ „ Cd „ a7 + 16265 



H „ x + 7512 



It will be sufficient, then, to find the value of x to calculate the 

 heat of formation of the other sulphates. 



It is better to choose the value of x by referring it to the for- 

 mation of sulphate of copper rather than of sulphate of hydrogen, 

 because, in the decomposition of the latter sulphate, the thermal 

 phenomenon due to the metal H set at liberty, and which passes 

 from the nascent to the ordinary state, is exhibited in a much 

 more pronounced manner than in the case of the other metals. 



