EI.ECTUOJrOTIVE FOllCES IN THE VOLTAIC CELL. 



501 



E.M.I". 



metal and au electrolyte such as water and dilute acid, is small.' [Ayrtoii 

 and Perry, Clifton, Pellat, and probably Sir Wm. Thomson.] 



;on?cvi'C(.\ 



or with- 



junction 



o or from 



im of tluv 

 ly electro- 

 nergics d 



10. is cqna) 

 )ing on pti- 

 spcnded ir. 



its amoiini 



icrgy tliei'c 



is held by 



icnt is dm 



'UOUGII 



contact, av! 

 ton, Pellat. 

 entials ('.''• 

 oncerned m 



|r betsveen a 



|,n. Thomson t.. 

 itedatsecuon. 



a ciuc; 



,.,v,. close up tf'- 



IsTstency i» "".' 

 l,v>-thutt\ii;ri;i- 



.r thccontviin. 



t-ors oHii^ l^f^'' 

 thev Nvoro t >«- 

 Ibat til.- 



[o£ lliomw^'"" 

 Ixi is also tm-- 

 Uii tUo inei^li""- 



lie conduclor i- 

 ; ,„oro natural, 

 tntial by v.;a^'^'- 

 IM.K.ataP'i- 

 L;lectiicity. ''; 

 L, but uotlun;- 



13. Before proceeding to the statements embodying my own views, it 

 uill be more interesting if I try to explain in a fuller and more connected 

 manner what they ure.- 



Let us regard the air as a dielectric bath of oxygen, in which metals 

 fvro immersed, and picture a piece of zinc surrounded by oxygen molecules 

 which are straining at it, and endeavouring to combine with it. They 

 r.iay indeed partially succeed ; but suppose they do not, wo have hero a 

 .strung potential chemical action or chomical strain, which must probably 

 be accompanied by some physical phenomenon. Now remember that 

 oxygen is an electi'o-negativo element ; and without endeavouring to 

 examine too precisely wliat signification is involved in that statement, it 

 will be not out of accord with orthodox views if we assume that it means 

 that at least any dissociated oxygen atoms are negatively charged, each 

 with the ohnracteristic charge of a free dyad atom. Granting something 

 oqnivoient to this, without pressing tho form of expression too closely, we 

 perceive that tho strain of the oxygen towards the zinc will result in 

 what I mctapho .'ically call a .slackening up, or attempted compression, of 

 the negative electricity in it, i.e. to a rise of negative po'^ential. We n-ay 

 therefore say chat zinc is at a lowt v potential than the air surrounding it, 

 and that thr, step of potential in crossing the boundary from zinc to air 

 'i.^ closely connected with the chemical ailinity between zinc and oxygen. 

 Observe that this step of potential does not obviously nor .probably depend 

 on the amount of oxygen present. It is possible that a few million 

 molecules may be as etl'ective as a large number. Note also that tho step 

 of potential is by no means caused by actual oxidation : in so far as the 

 r.inc surface is tarnished by oxidation the strain will be diminished and 

 the step of potential become less. 



Nothing is said here about the possible effect of the nitrogen, because 

 it is simplest in the first instance to ignoi'o it, though whether experiment 

 will justify this simplicity or not, I do not yet know. 



We may go further and assert that if in general tho chemical aflBnity 

 of two substances can be measured by their energies of combination, then 

 the step of potential in tho present case may perhaps bo calculable from 

 the heat of combustion of zinc. 



And one may justify this assertion thus. Let au atom of oxygen 

 combine with an atom of zinc ; it will generate an amount of heat h, and 

 its characteristic charge, (j, will be given up to the zinc and will thereby 

 fall down the step of potential, r, which separates the zinc from the air. 

 Xow if 1V0 snpi)oso that the heat h iV iJic ivprcteniatiri' and equivalent 



(if the fall of encnji/ 7 v, it follows of course that /• = ' ■. 



ilake the hypothesis and see what comes of it. 



' Tho experiments sup])ose(l to establish this really prove only that there is very 

 little (lillVrenee between the air and the water in wliieii a metal is partially imni(!rsc<l. 

 1 do not quite know how to understand, on Sir Wm. Tin >son"s plan, the potential of 

 a niutal whicli is half in one medium and half in aiioth .. 



■ Tlie reason I set tlumi fortli at leiijrth is l)eeau.«e 1 lia:l no time at tho meetin.L, 

 both to open tluMlisciission an<l also to properly express my own ideas, and Sir Wm. 

 fliomson w;is kind ciiou^ili to tell me to write out the jiapev completely, and to 

 I'xplaiu ilic position I took up fully. This, therefore, I lla^c endeavourctl to do. 



v^l 



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