ELKCTKOMOTIVE FORCES IN THE VOI/f.VIC CEI-L. 



il5 



^ed with 



complete 



sir plates 

 11. Pass 

 measure 

 the Slime 

 t one side 

 that it is 

 aur cases. 

 ich volta- 

 :. Kxnov) : 

 etweeu its 

 isily show 

 af hiiKlcv- 

 [le cells is 

 a^ — if it is 

 ttinura will 

 [1 retard it, 



ic heats of 

 )U will have 

 is energy is 

 cform. In 

 lut forward. 

 ) generation 

 has to tiiovc 

 [u opposition 

 and lihorati' 

 bit itself as 

 er less still; 

 le generated 



|at all hy tlic 

 zed and the 

 Jl energy) of 

 Iheat is tlieve 

 Is, the same 

 lent hindered 

 jombiuation- 



I as a virtual 

 in any one 

 for helinnu' 

 the combioa- 

 Iberated ; (.f;- 

 M, SO4, 1^ 

 III of heat ai 

 belling iorcf 

 this purpose, 



"Whefchev one ought to write SO., or O in these expressions I am not sure, 

 but it is not essential to decide this at present. 



Another way of regarding the matter is to say that the force ])ropclling 

 the cnrrcut is that due to the difl'erence of energies Zn,0 — M,0, but 

 that as soon as a current actually passes and hydrogen is liberated it coats 

 the cathode more or less thickly, and an extra terra must be snbtracted 

 from the above to rei)resent the opposition force of this hydrogt;n. Tho 

 efficacy of this hydrogen as a current opposcr must depend in sonic way 

 on the intensity of the current itself, since with a feeble current it will bo 

 able to dissipate itself faster than it forms, and with a strong current it 

 •\v'll thoroughly coat the plate and tho balance will escape. Suppose then 

 Ave represent the force exerted by the hydrogen as lJ.j,0/ (C) ; where 

 f (0) = 0, and/ (x )=1 or something like 1 ; then the force available for 

 urging tho current forward in any of the above cells is, in volts, 

 ,,;„„. {/n,(3-M,0-H„0/(C)}._ 



There is an obvious objection to bo taken to this last hypothesis, 

 viz., that it supposes the second metal ]\I comjiletely operative, even 

 though it be thoronghly coated with hydrogen. This is hardly reason- 

 able, and a compromise between the two preceding hypotheses is alforded 

 by one of greater generality in which the available force is symbolically 

 represented by 



Zn-M./.(C)-H,,/(C), 



where <> is a function such perhaps that ^'j(C) = ! + /(./ (C). On this 

 hypothesis the projielling E.M.P. is 



e = 40000 l^-",0-M,0-(lL,0 + M.M,0)/(C)). 



This is too much like miscellaneous guessing, and wo will make no 

 more of suclv hypotheses; but if experiment could fix an empirical formula 

 for this force in any case, we could apparently at once obtain the Joule or 

 Bouty effect,' or rather the difference of two such effects, for that case, 

 because we should have the E.M.F. experimentally observed on the one 

 hand, and that calculated from pure energy considerations on tho other ; as 



4-bUUU ' '■ ' 



where the two IJ's stand for the Bouty coeflicients at the zinc and tho 

 other metal respectively. The oidy objection is that in the cells now 

 under discussion M is coated more or less with hydi'ogen, and hence tho 

 Bouty effect obtained is nothing very easily definable. 



21. To see if the actual behaviour of such cells at all bears out a hypo- 

 thesis formed on the above plan, I have made some rough experiments on 

 the lines suggested ; that is, I passed the same current through different 

 simple cells. There are so many sources of uncertainty and of variation, 

 that it would be very difficult to get really definite and rclial)lo results. 

 Thus, for instance, the back E.^M.F. will depeiul considerably u])on how long 

 the current has been flowing, and so tho readings will differ according to 

 the time they are tai'cn. Tlie metals I usetl were zinc-zinc, zinc-coppci-, 

 ?.nd zinc-platinum ; and it was found necessary to put the cathode })lato 

 in a porous cell to avoid deposition of zinc on it. But it was now diffi- 

 cult to compare the cells easily when arranged in series, because different 

 porous pots had different resistances. I therefore ultimately decided to 

 use the same porous pot and the same anode zinc plate, and to substitute 



' Tliat is, tlie tlicrmo-eIcct;ic contact force a*^ a ii'.e'al-li juid jr.r.ct'on. S'o(» 

 !>CL'tion 0. L, L 2 



