

Chemical Affinity in terms of Electromotive Force. 185 



action the less will be the mean densities of the aurse, and 

 hence the greater will be 2(A) and the less the value of e. 

 Experiments on the Influence of dissolved Gases on the Rate of 

 Fall of the Polarization existent after rupture of the original 

 current {Subsequent Polarization). 



69. It results from the general theorem above stated (§ 61), 

 that the rate of fall of the " subsequent polarization " in any 

 given electrolytic cell (e. g. a voltameter) must be more rapid 

 when the circumstances are such as to increase the numerical 

 value of the term 2(H) than when the term is negligible ; 

 that is, the rate of fall must be a minimum (under any given 

 conditions) when the fluids surrounding the electrodes (them- 

 selves unattacked by the products of electrolysis) have no che- 

 mical or physical action on these products, and when the elec- 

 trodes have attracted and occluded as much of the products as 

 they possibly can, but must be greater when these conditions 

 are' not fulfilled ; so that in any ordinary voltameter, if the 

 fluid surrounding the — electrode contain dissolved oxygen, 

 the rate of fall must be greater than would be the case if 

 no dissolved oxygen were present to act on the hydrogen aura ; 

 whilst, cceteris paribus, the larger the electrodes within certain 

 limits, the less will probably be the effect of the oxygen dis- 

 solved in a limited amount of surrounding fluid on the hydrogen 

 aura as a whole. Experiments on the rate of fall of " subse- 

 quent polarization " have been already made by Ayrton and 

 Perry (Journ. Tel. Eng. v. p. 391, 1876), and the results ex- 

 pressed as curves ; these observers, however, did not particu- 

 larly examine the influence of varying amounts of dissolved 

 air &c. on the rate of fall. On the other hand, Helmholtz, 

 Fleming, and others have noticed that when water freed from 

 dissolved air by boiling is electrolysed, the " subsequent pola- 

 rization " diminishes less rapidly than when water containing 

 dissolved air is employed. 



The mode of observation adopted for the purpose of verify- 

 ing the above deductions from the theorem was much the same 

 as that used by Ayrton and Perry (loc. cit.). The electrodes 

 of a given voltameter were connected with an electrometer, a 

 suitable resistance being also in circuit, so that a current of 

 known strength could be passed for any required length of 

 time : to measure the current passing it was found convenient 

 to employ a method based on Ohm's law, viz. reading off the 

 difference of potential set up by the current between the ends 

 of a known resistance by means of a quadrant-electrometer. 

 This method, first, is independent of the errors (due to pos- 

 sible change of zero, horizontal magnetic component, &c.) of 

 ordinary galvanometers, which cannot conveniently be verified 



