Chemical Affinity in terms of Electromotive Force. 273 



than four microwebers caused an evolution of hydrogen (§ 80) ; 

 with currents less than this amount none was obtained. Since 

 the values of the counter electromotive forces set up by 

 these currents were considerable, especially when the current 

 was near the limiting value of four microwebers, it results 

 that the hydrogen which combined with the oxygen diffusing 

 to the — electrode, and the oxygen combining with the 

 hydrogen that diffused to the + electrode, was the gas oc- 

 cluded within or condensed upon each electrode respectively, 

 and not that produced by the electrolysis reoxidized pari passu 

 with its formation ; for in the latter case the nett work done 

 as electrolysis during the passage of this current would be 

 nil, and hence e would = 0. The action of the " diffusion 

 discharge " is therefore precisely like that of dissolved air 

 present in the fluid electrolysed in the first instance (§ 76), 

 comparable with the " local action " of an ordinary cell. In 

 any given experiment the value of e will rise (the current re- 

 maining constant) until the rate of diminution of aura at each 

 electrode due to this cause just balances the rate of increase 

 through electrolysis. As this latter rises when the current is 

 increased, so will the mean aura-density rise, and the amount 

 of aura dissolved away from the electrode by the surrounding 

 fluid in a given time, and consequently the rate of diffusion 

 discharge, until the aura is at its maximum mean density, 

 i. e. saturated, after which a further increase of the current 

 simply causes free gases to escape. In this case the value of 

 e is still found to increase with the current, obviously indi- 

 cating that the values of the ns (i. e. of the fractions of hy- 

 drogen and oxygen not evolved in the nascent state ab initio) 

 decrease as the current increases. Similarly, when the tem- 

 perature falls the value of e rises {ceteris paribus) and vice 

 versa, indicating that a fall in temperature increases, and a 

 rise decreases, the fractions of gases evolved "nascent" in 

 the first instance. 



The following experiments were then made with the view 

 of investigating the effects produced in the value of e (that is, 

 in the values of the n's) by altering certain of the conditions 

 of electrolysis. 



Effect of Alteration of the Size of the Electrodes. 

 85. It would seem a priori probable that whilst e increases 

 with the current when the electrodes arethesame, and decreases 

 when the size of the electrodes is increased, the current re- 

 maining the same, it will remain constant if the current and 

 size of electrode increase in the same ratio, so that the rate of 

 flow of electricity per unit of electrode-surface (sometimes 



