184 Dr. C. R. A. Wright on the Determination of 



time, the quantity of electricity conveyed in each interval 

 must at first be nearly the same, but will gradually diminish. 

 These and various other analogous points in connexion with 

 the behaviour of a voltameter as a condenser have recently 

 been quantitatively studied by Herwig (Wied. Ann. ii. p. 601, 

 and vi. p. 305), whose results are perfectly in accordance with 

 the deductions from the general theorem above stated. 



68. It is evident that the considerations that apply to the 

 form of voltaic combination produced by the products of de- 

 composition formed by the passage of a current through the 

 decomposing-cell will equally apply if the same products of 

 decomposition are introduced into the cell in other ways ; 

 so that if two platinum plates are exposed, the one to water 

 impregnated with ordinary oxygen gas, the other to water 

 containing dissolved hydrogen, the two waters meeting, the 

 attractive action of the plates will cause a more or less nearly 

 saturated aura to be formed round each plate, and a difference 

 of potential will be set up between the plates representing the 

 work that would be gained by the combination of the con- 

 densed oxygen and hydrogen : in fact, the form of Grove's 

 gas-battery thus produced will be identical in all respects with 

 that developed when water is decomposed in a voltameter, 

 except that in the latter case the polarization is more or less 

 enhanced by the presence of the " nascent" products of elec- 

 trolysis, at least until these have become wholly converted into 

 the ultimate products. Such a gas-battery must therefore 

 develop an E.M.F. expressed by the value of the formula 



^Ei+tSia-^HI-SOi/O-SCH)]^ 

 now obtaining; that is, since n=l, 



e=-E 1 -{%(h)+S l (a)}xJ, 

 or, since 2(H) must be extremely small, if not wholly negli- 

 gible, practically, 



e=E 1 -S,(h) X J. 



Hence the E.M.F. of a hydrogen and oxygen gas-battery 

 cannot exceed 1*50 volt, which experimentally is found to 

 be the case. Any thing that affects the value of X(A)%J 

 must affect the E.M.F. of a gas-battery; accordingly the 

 E.M.F. is found to vary largely with the temperature, the 

 nature of the plates, the fluid in which the gases are dissolved, 

 the state of concentration of the gas -solutions therein, the 

 presence of other gases, &c. : and in particular it is found to 

 diminish with the strength of the current generated (Morley, 

 loc. cit. supra) ; for the more rapidly the films or auras of 

 gases attracted and those occluded are used up by chemical 



