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



the voltameters in a second calorimeter. Lastly, in a third series 

 of experiments I suppressed the rheostat. 



Replacing the solution of sulphuric acid in the voltameter 

 with platinum plates by an equivalent solution of nitric acid, and 

 working alternately with each solution, I found that nitric acid 

 borrows for its decomposition about 1062 thermal units less than 

 sulphuric acid, and that consequently the radical N 2 O 6 , in com- 

 bining with ordinary hydrogen, disengages 46462 thermal units 

 (heat of formation of sulphuric acid) — 1062; that is, 45400 ther- 

 mal units. 



I may be permitted, in conclusion, to offer the following con- 

 siderations : — 



The experiments the results of which I now detail by no means 

 invalidate the conclusions I have considered myself justified in 

 drawing from the results of my former experiments*. 



Chemical reactions (combinations or decompositions) are 

 complex; that is, the molecules concerned undergo modifica- 

 tions which precede the combination or which follow the de- 

 composition. These modifications are manifested by a pheno- 

 menon of absorption or of disengagement of heat quite indepen- 

 dent of the thermal phenomenon which accompanies the combi- 

 nation or the chemical separation. 



These modifications which the molecules of bodies, as yet un- 

 decomposed, undergo, and which reveal themselves by the force 

 they develope, explain the necessary action of heat, of light, and 

 of electricity as determining causes of combinations — for instance, 

 in the formation of water, hydrochloric acid, &c. 



The oxyacids only differ from the hydracids in this, that the 

 metalloid they contain is compound. 



The hydracids I have investigated, and in which the metalloid 

 is compound, appear constituted like the hydracids where the 

 metalloid belongs to the natural family that comprehends chlo- 

 rine, bromine, and iodine. They appear formed by the combi- 

 nation without condensation of two volumes of each of the con- 

 stituent elements. 



I give the heat of formation of these acids, and of some of their 

 salts. 



The constituent elements of these compounds are not in the 

 condition we know them in the free state ; for they disengage 

 heat on passing from the nascent to the ordinary state. 



What I have said as to the condition of the constituent ele- 

 ments of saline compounds may also be applied to the condition 

 of the constituent elements of water and of the metallic oxides. 

 Water is not an electrolyte; for it cannot be directly decom- 



* Comptes Rendus des Seances de VAcademie des Sciences, vol. xiii 

 p. 369. 



