Chemical Affinity in terms of Electromotive Force. 183 



Experiments on the rate of diminution of the " subsequent 

 polarization " and the circumstances influencing it are detailed 

 later on (§ 69 et segq.). 



67. When an electrolytic cell (e. g. a voltameter), the elec- 

 trodes of which are destitute of attracted films of gas or 

 occluded gases, is connected with an electromotor and a cur- 

 rent of very short duration sent through it, if the amount of 

 decomposition produced be so small that the hydrogen- and 

 oxygen-development equivalent to the quantity of electricity 

 passing are only small fractions respectively of the amount 

 requisite to saturate the electrodes, no visible development of 

 gas will ensue ; the polarization at the instant of rupture of 

 current will then be (§ 62) 



e=E 1 -2(A)xJ, 



the value of h depending on the particular amounts of con- 

 densation to which the evolved products are condensed. On 

 passing the current from the same electromotor for the same 

 time again, a slightly less amount of current will flow ; for the 

 mean counter E.M.F. set up during this second interval of 

 time will be somewhat greater than that during the first, whilst 

 the total resistance in circuit is the same, whence the current 



(which = yX>\ — p? § 57) must lessen. Similarly, on pass- 

 ing the current again and again for equal intervals of time, 

 quantities of electricity will pass in each interval, gradu- 

 ally diminishing in amount; whilst the "subsequent pola- 

 rization " continually increases, the voltameter acting as a 

 condenser, the capacity of which is simply measured by the 

 power of the electrodes to condense upon their surfaces and 

 occlude internally the products of electrolysis. On dischar- 

 ging a charged condenser by causing it to generate a regular 

 succession of currents of equal but very short duration as to 



more energetic reducing action upon various substances than ordinary 

 free hydrogen, the same result for palladium charged with occluded 

 hydrogen (so-called hydrogenium) having been previously observed by 

 Graham (Proc. Roy. Soc. xvii. p. 212, 1869). This result is not due to 

 the condensed hydrogen being capable of evolving more heat by action 

 on the substances in question than would be produced by the same 

 quantity of free gaseous hydrogen, because the reverse is the case, the 

 difference being the heat given out in condensing the hydrogen from the 

 ordinary gaseous condition to the condensed form obtaining in the par- 

 ticular cases in question. The " catalytic " action of spongy platinum 

 exemplified in Dobereiner's lamp, for instance, also illustrates this fact. 

 The effect of the condensation, therefore, is analogous to that of increased 

 temperature, causing chemical actions to take place that would not ensue 

 (at least at any measurable rate) under other conditions, i. e. less con- 

 densation or lower temperature respectively. 



