ELEf"ni05I0TIYK FOIU'E.S IN THE VOLTAK! CEIJ.. 



.023 



ratnre ; 

 ! to uso 



in any 

 , or tlio 

 litVerent 

 ng only 

 naves of 



Sucli !l 



atii'Te. 



i-metallic 

 pcriments 

 'homson's 

 r perfectly 



d zinc and 

 5 the case 

 reckon up 

 Kn/air (or 

 :i't find, or 

 in the 10° 

 lU not find 

 ;m there if 

 ts ; and for 

 leir proper 



pature pro- 

 ^,u/ZnSO„ 

 licm all up. 

 bo made, 

 affect tlie 

 of series. 

 Ibe found to 

 Id antimony 

 lie alloying 

 |o mer(!ury, 

 a stulinm- 

 tremendous 

 ,e with tlu' 

 1110 it dot'^ 



tisidered tbe 



due to the 



by tlK>lici^t 



Usbelieving- 



|i of bismutli 



hese metals; 



but perhaps it is no more truo. The greater part of a contact force of this 

 kind is probably duo to a physical difference between the metals, such as 

 difference in atomic vfdocity, and has no close relation to their chemical 

 ailinities for each other. It is, however, just possible that part of a 

 metallic j unction- foi'ce is due to chemical tendency between the two metals 

 in contact. For instance, take the case of zinc and copper. Thei'o is, 

 1 suppose, an nndoubtcd aninity between them, as shown by the formation 

 of brass under proper conditions, [if chemists assume the rij^lit to demur 

 to this on the ground that the two metals mix equally well in any pro- 

 portions, one can choose any other pair of metals -say, perhaps, copper 

 and tin — for which the statement does not hold. ] Now does this affinity 

 result in any E.M.P. between tliem on making contact ? This question, 

 I apprehend, is to be answered by passing a current for a long time across 

 a copper-zinc junction and seeing if any brass does, after a long time, 

 result. Thermopiles show a curious secular deterioration with use, and 

 it may he that some alloying action goes on, though I have never heard 

 of its being noticed. But if no such alloying goes on during the passage 

 of a current, then I should say that, in whatever ways chemical atlinity 

 between two metals is able to show itself, it does not show itself as an 

 K.M.P. 



Observe, I do not for a moment question the existence of a few 

 luindred microvolts of E.M.F. at a zinc-copper junction. I only ask, is 

 this chemical, or is it physical, or is it a mixture of the two ? Statement 

 No. xxiv. is general enough to take into account the possibility of its being 

 a mixture of the two at every kind of junction. It is easy to write one of 

 them zero, if so it turns out. 



21. We have been led into a pretty wide discussion of contact force in 

 general; and, before digressing again on the question of a contact-force- 

 detcrmination of the size of atoms, it may be convenient here to quote the 

 vemidiider of my preliminary notes, which aim at summarising, in a com- 

 pact form, the main argument with respect to the immediate subject of 

 disciis.sion, viz., the seat of electromotive force in a voltaic cell, and in 

 ordinary Volta condenser experiments. 



IV. — BliJKr SUMMAliY OF THIO AU'GUMENT. 



XXV. Whei'cver a current gains or loses energy tlicrr must be a seat of 

 I'l.^I.F. ; and conversely, wherever there is a seat of E.M.F. a current must 

 lose or gain energy in passing it.' 



xxvi. A current gains no appreciable energy in crossing from copper to 

 zhic, hence there is no appreciable E.M.F. thei'e. 



xxvi When a current flows from zinc to acid the energy of the com- 

 bination which occurs is by no means accounted for by the heat there 

 srcnorated, and the balance is gained by the current; hence at a zinc acid 

 jmiction there must be a considerable E.]\I.F. (say at a maximum i'o volts). 



xxviii. A pieee of zinc immersed in acid is therefore at a lower potential 

 than tlie acid, though how mneh lower it is impossible precisely to say, 

 honause no actual chemical action occurs. [If chemical action does occnr 

 It is due to impurities, or at any rate to local currents, and is of the nature 

 of a disturbance.] 



' Xdtr (i(f(/rd Jtiinirrri/ If'^S').— My aiiowiionhns just been callod to an article by 

 ^Ii'. O. Uuaviside, in tlie L7rrtrlciitii of I'djiuary li, ISSl, in wlii(^h Lo states views 

 Very like tlioso contained in these statements. Had I known of this pajier earlier I 

 should of course liave mentioned it, but 1 did not know of it. 



