M. P. A. Favre's Electrolytic Investigations. 295 



The compound SO 3 (anhydrous sulphuric acid), when quite 

 pure, placed in a large excess of water, disengages 18639 thermal 

 units (XII.). This experimental datum and the following data 

 are necessary for the discussion of the electrolysis of sulphuric 

 acid : — 



XIII. 



Quantity of water, 

 Solution of in equivalents. 



Thermal 

 units. 



anhydrous sulphate of zinc . 162 

 „ „ copper . 160 

 „ }} cadmium 208 



9553 

 8465 

 5432 



„ hydrogen 110 



8821 



Solution of 





crystallized sulphate of zinc . . 144 

 „ „ copper . 125 

 ,, „ cadmium 140 



2240 

 1393 

 1493 



XIV. 



I have endeavoured to account for the influence which liquids 

 submitted to electrolysis exert upon the distribution of heat in 

 the voltaic circuit. For this I have investigated this action, 

 allowing for (1) their degree of concentration, (2) the distance 

 of the plates immersed, (3) the extent of the moistened surface, 

 (4) the nature of the liquids. 



Thus, for instance, to investigate the influence of the concen- 

 tration of the liquids, I worked with 100 cubic ceutims. of liquid 

 containing 101-55 grms. of sulphuric acid (S0 4 H) in a litre, which 

 served as a standard of comparison, and with equal volumes of 

 this liquid gradually more and more diluted. I reached a dilution 

 of ~- } the liquid containing then only 0*0793 grm. of sulphuric 

 acid in the 100 cubic centims. employed. I took care to have the 

 experiments made with the more or less diluted acid succeeded 

 or preceded by experiments made with the acid which served as 

 standard of comparison. 



I have varied the distances, so as to ascertain the part to be 

 assigned to the heat produced in the work of giving a definite 

 position to the molecules of the electrolyte in the body of the 

 liquid. 



To ascertain the influence of the nature of the liquids, I have 

 worked as follows : — 



I have retarded, as much as possible, the chemical action of 

 the battery, by placing in the calorimeter which contains it a 

 rheostat with great resistance ; and I have successively introduced 

 into the exterior of the circuit voltameters with plates of copper, 

 of cadmium, and of zinc. I have taken care to precede or succeed 

 each of these experiments by another in which the voltameter 

 was dispensed with. In a second series of experiments I placed 



X2 



