Intelligence and Miscellaneous Articles. 77 



at its minimum value when the vacuum is made and the causes 

 indicated below do not intervene. 



The oxygen of the air attacks the zinc directly, a corresponding' 

 quantity of water escapes decomposition, and the negative work of 

 the reduction of hydrogen is diminished by so much. In one of my 

 experiments the electromotive force of an aerated pile was 19,320, 

 the same pile deprived of air giving 18,796. The difference, 524, 

 corresponds, with a mean current equal to 500, to a consumption of 

 y-i-y of a milligramme of oxygen during the ten minutes that each of 

 my experiments lasted. 



This influence of the air is one of the principal causes of the varia- 

 tions of the constants of the pile, noted successively by MM. Fechner 

 Ohm, Jacobi, Despretz, De la Rive, PoggendorfF, and, lastly, by M. 

 Du Moncel. The air only dissolves in limited quantity in water; 

 its relative influence is therefore more marked when, the current 

 being feebler, the battery consumes less. It follows that the electro- 

 motive force ought to increase with the resistance of the circuit. 



2. Influence of the sulphate dissolved. — The laws of the conducti- 

 bility of saline solutions could alone give me the key to the effects 

 produced by the zinc-salt formed in Smee's battery. The water, 

 acid, and sulphate are all separately conductors ; each conducts and 

 is decomposed. The water and the acid concur in producing the 

 normal effect, because both produce hydrogen. This is not the 

 case with the sulphate : zinc is reduced ; now this reduction of zinc 

 gives rise to a negative work equal to 53,260 instead of 34,460, the 

 negative work of the reduction of hydrogen. The reduced zinc does 

 not, it is true, usually appear, because as soon as an atom of the free 

 metal touches the platinum, a local couple is produced which redis- 

 solves it ; but the work thus restored does not improve the general 

 current, which remains diminished. 



The electromotive force of a Smee's element with acidulated water 

 being 18,796, was reduced to 18,069 by the solution of 5 deci- 

 grammes of pure sulphate of zinc in the liquor. The difference, 727, 

 supposes that the conductibility of acidulated water was twenty-five 

 times as great as that of the dissolved sulphate of zinc. 



The influence of the sulphate of zinc is more marked, as this salt 

 is more abundant, and the solution is less acid, and consequently 

 less conducting. Neglecting the influence of the air, it is to the 

 presence of sulphate of zinc that the gradual enfeeblement of Smee's 

 pile is due. 



3. Influence of the concentration of the acid. — So long as the acid 

 solution contains more than 25 equivalents of water for 1 of acid, 

 the electromotive force remains constant ; but when the proportion 

 of acid is greater, the electromotive force is increased by the quan- 

 tity of heat which would be disengaged by mixing the solution with 

 its complement of water in the proportion of 25 equivalents. When 

 the acid is too concentrated, traces of sulphurous acid maybe formed. 

 Thus a Smee's element mounted with concentrated acid, simply 

 diluted with its weight of water, gave 20,279, difference 1483, 

 while, according to M. Favre, this difference ought to be only 743. 



