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



meter is indicated by the special calorimeter which contains it, 

 while in experiments X. this heat is developed in the calorimeter 

 of the battery itself, and is necessarily added to the quantity of 

 heat which expresses the work consumed there. 



That is the reason why there is restored to the calorimeter 

 No. 2 a quantity of heat so considerable borrowed from the 

 pile — heat the origin of which cannot be attributed to the phy- 

 sical resistance of the voltameter ; for this may be almost neg- 

 lected, since a rheostat presenting an adequate resistance has 

 been introduced into one of the muffles of the calorimeter in 

 which is the battery. 



To what are we to attribute the very discrepant results in ex- 

 periments VI., IX., and X. when the conditions are varied in 

 which bodies of the same name are associated or dissociated? 



This I shall more fully discuss in a more extended memoir ; 

 and I will restrict myself to giving the conclusions in a subse- 

 quent part of this paper. I will merely mention here that the 

 cause of these differences is to be sought in the particular con- 

 dition of the bodies (oxygen, hydrogen, &c.) concerned in the 

 action, and which are considered sometimes in the nascent and 

 sometimes in the ordinary state. 



In the experiments in which a quantity of heat sufficient to 

 decompose an equivalent of sulphate of zinc in a voltameter is 

 brought into play, I was not long before I saw that the couples 

 of the battery can act more or less as voltameters, and decom- 

 pose part of the sulphate of zinc they produce. Thus there is 

 deposited on theplatinum a quantity of zinc which at first is very 

 small, and which increases in proportion as the quantity of sul- 

 phate of zinc increases in the liquid of the battery, a quantity 

 which always replaces an equivalent weight of hydrogen, the for- 

 mation of which is no longer due to electrolysis. The zinc thus 

 deposited in the battery itself, and from which it borrows the 

 heat necessary for its separation, dissolves immediately in the 

 ratio of its production, replacing the heat which has been bor- 

 rowed. This action, in fact, is completely local, and does not 

 aid the current, the enfeeblement of which is indicated by a 

 smaller deflection of the needle, and by a retardation of the che- 

 mical action. 



When the operations succeed one another without renewing 

 the acid of the battery, the quantity of zinc in solution conti- 

 nually increases, and the electrolysis we have mentioned is evi- 

 denced by a smaller deflection of the needle, and by the retarda- 

 tion of the chemical action. A moment is attained at which 

 the zinc is deposited in too large a quantity to dissolve immedi- 

 ately in sulphuric acid which is gradually weaker, and an end 

 must then be put to the operation. 



