L92 Dr. 0. 1\. A. Wright on the Determination of 



a voltameter till the liquids surrounding the electrodes were 

 saturated with oxygen and hydrogen respectively, for which 

 purpose a battery of two Minotti cells was used. One Minotti 

 cell was then excluded from the circuit, a resistance of 50,000 

 ohms being included therein (the current being measured by 

 determining the difference of potential set up between the ends 

 of this resistance, as described in § 69), and the voltameter- 

 plates shortcircuited for a few seconds. After removing the 

 shortcircuiting wire, the current passed at a rapidly slackening 

 rate in the direction due to the Minotti cell ; but in a very 

 few minutes it ceased to flow altogether, and then began to 

 flow in the opposite direction. The shortcircuiting of the vol- 

 tameter-plates was then repeated for two minutes, after which 

 the current flowed in the normal direction at a gradually 

 slackening rate : after one hour the current still flowed in the 

 normal direction and had a value of +0*0000034 weber; but 

 soon it became reduced to zero again, and then flowed in the 

 reverse direction, having a value of — 0*0000017 weber after 

 two hours had elapsed since the second shortcircuiting. After 

 twenty hours more the current was so small that its direction 

 was inappreciable; but on removing the electrodes and igni- 

 ting them and then replacing them, it flowed continuously in 

 the normal direction. Similar results were obtained in many 

 other analogous experiments. 



The gradual setting-up again of an E.M.F. after short- 

 circuiting the electrodes of a voltameter has been already 

 previously noticed by Ayrton and Perry, and the effect gene- 

 rally compared by them to the residual charge of a Leyden 

 jar ; they do not, however, appear to have observed the gra- 

 dual extinction and reversal of the current just described. 



74. It should further result from the general theory of elec- 

 trolysis above stated, that if the electrodes of a voltameter are 

 shortcircuited whilst still in contact with the fluid saturated 

 with gases surrounding them, on removing the shortcircuiting 

 wire the reproduction of an aura round each electrode will 

 take place much more rapidly than will be the case were the 

 electrodes removed and placed in fresh acid not saturated with 

 ga,s, as in the experiments described in § 72 ; for in the former 

 case the loss of aura produced by the passage outwards of 

 occluded gas owing to solution in the liquid will be much 

 smaller than that taking place in the latter case. That this is 

 so the following numbers show, samples of numerous similar 

 observations made^ each series of numbers being the average 

 of several fairly accordant sets of determinations. 



(I.) Platinum electrodes, exposing a surface of 27*4 square 

 centims. each, kept at a difference of potential of 1*95 volt in 



