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



The value of x, thus referred to sulphate of copper, is obtained 

 by examining the amount of heat which the sulphate of copper 

 borrows from the pile during its decomposition in a voltameter 

 with platinum plates placed outside the calorimeter which con- 

 tains the pile and a rheostat offering sufficient resistance. 



This quantity is 38950 thermal units (IV.). 



Replacing x by its value, Table III. gives 



Thermal units. 



V. S0 4 + Cu = 38950 

 S0 4 + Zn = 66296 

 S0 4 + Ee = 57975 

 S0 4 + Cd = 55215 

 S0 4 + H = 46462 



In making a thermal analysis of other salts* (that is, decom- 

 posing them in the same manner as sulphate of copper), I ob- 

 tained the quantities mentioned in the following Table : — 



Thermal units. 



VI. S0 4 + Cu = 38950 

 S0 4 + Zn = 66040 

 S0 4 +Cd = 54470 

 S0 4 +H = 52242 



which refer to the separation of the constituent elements of the 

 salts in the condition in which they exist in their combinations. 



The first three numbers, which are the direct result of experi- 

 ment, agree in a satisfactory manner with those of the preceding 

 Table (V.), which have been calculated on the basis of the result 

 obtained by the electrolysis of sulphate of copper alone. The 

 number referring to sulphate of hydrogen is the single exception, 

 and the interpretation of this result is by no means the least in- 

 teresting. 



If to the quantity of heat disengaged during the formation of 

 the following oxides by means of ordinary oxygen, 



Thermal units. 



VII. Zn + O = 41992 

 Fe+O = 35103 

 Cd+O = 28925 

 Cu + O = 18055 

 H +0 = 34462 



we add the quantity of heat disengaged during the combination 

 of these anhydrous oxides (oxide of iron excepted) with dilute 

 sulphuric acid, 



* I except sulphate of iron, the electrolysis of which offers difficulties 

 which have led me to defer its study. 



