KLECTfiOMOTIVE FORCES IN THE VOLTAIC (KM.. 



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Whorcvri' electrostatic methods were employed, and where the elec- 

 tvoseopo wiis the instrument of research, contact tlieorists had it all tlieir 

 own way, and it was only by apparent efl'ort and twistiiii^ of experiments 

 that the chemical theorists could maintain their pjround. But when 

 electric currents were dealt with and the galvanometer iised, then the 

 chemists had their turn, and they showed most conclusively that no mere 

 contact could maintain a current unless heat disappeared or eliemical 

 action occurred: a fact obvious enough to us to-day on the principles so 

 laboriously and finally established by Joule. By means of tlie galvano- 

 meter the contact theory was so belaboured by Faraday that it ultii-iutely 

 seemed to give np the gliost. and the chemical doctrines triiimphed. .So 

 much so that Volta's original fact, in spite of the evidence whicli liad been 

 aecumnlated, was again doubted; and one tlnds in text books cuUi'd iVom 

 this ])eriod statements that Volta nmst have had wet fingers, or that he 

 nibbed the platea together, or that there was moisture in the air. Also 

 hints are given that lilms existed on the plates, that squeezed coats of 

 varnish, or lacqner might produce some electricity, and so on. it was 

 pointed out moreover by 13e la Kive ' how minute a trace of cheniiciil 

 action could produce how much electricity, and how little electricity could 

 iilToct an electroscope. But it is to be noted that any chemical action caused 

 liy damp on the plates or moisture in the air would be of the nature of local 

 liction, and local action is not a satisfactory pi-odncer of managedblc 

 electricity. Sir Humphry Davy is veiy clear on this head. He shows 

 that chemical action need produce no electricity, in.stancing the burning 

 of iron, nitre on charcoal, potash and acid in a crucible or an electroscope, 

 (tc. ; a plate of zinc placed on mercury and separated is found positive, 

 bat if left long enough to amalgamate, the compound shows no signs of 

 electricity. Davy"s views are singularly advanced, and are worth 

 (liioting.- 



into connection with a Dollinan electrometer, the other witli the cartli. The observa- 

 tion is repeated witli a Daniell in th(! ennnectins wire, lii-st one way tlien the (.tlit^r. 

 Tims tliree ecjuiitiuius iire dbtained, M;.Ar = l<a, IH- Jl, .M' = k/3, JJ--.AI,'M' = k7 ; whenct; 



M/M'= 1), (ir -1) -Po,/,, .l/i,v. vol.s. Isxv. p. 88 ; Ixxxii. vv. 1. .ind 4", and 



Ixxxviii. p. -to.", ]8.")I iHul 18.13. He p:ets liis results much lower tlian later oxpcri- 

 iiKiiters ; only \ a volt for ZnCu. and -.IS for Zn I't. 



' IH" la Hive. — Tmiir (rilrrlririfi; ii. p. ~iH\.—Ann. ilr Ch'imii; xxxix. }). ill 1, IS28. 



- Davy : liakcvian Lecture, 180(i. See I'liil. Trtuig. 1807,'p. :i!) : ' As tlie ciumical 

 :iitr:iction l>etween two bodies seems to be destroyed by f^'iving one of them an elec- 

 trical state dilYeront from that which it naliu'aliy possesses . . . .so it may lie increased 

 liy exalt iiiir its natural eneriry. 'J'iuis while zinc is incapable of combinin<^ with oxy<ren. 

 v.luii noi.'-atively (Mecti'ilied in the circuit even by a feeble power, silver easily unites 

 111 it when positively electriiic<l . . . Aniunp; the substances that combine clu'mically, 

 :ill those, the electrical eneraies of which are well known, exhibll opjiosite electrical 

 >tatcs ... In tlie present state of our knowledp:e it would be useless to attempt to 

 ^lii'i^ilate on the remote cause of the electrical eiier<ry, or the reason why ditfercnt 

 lindies after beinu- brought into contact should be found diiTerently eloctrilied ; its 

 I'l'lation to chemical atlinity is, however, sufficiently evident. May it not be identical 

 with it, and an essential property of matter ." Page 44 : ' The great tendency of the 

 attract ion of the different chemical agents by the positive and negative surfaces in the 

 voltaic apparatus seems to be to restore the electrical equilibrium . . . The elect lical 

 •'ncrgics of the metals with regard to each otlier, or tiie substance dissolved in the 

 water, seems to be the cause that distmbs theeciuilibrium, and the chemical clLingcs 

 tlie cause that tends to restore the ecjuilibrium ; and the phenomena most pro l)ably 

 wpend on their joint agency.' He tlien gives a very voltaic account of the action of 

 the pile — much in agreement with Sir Wm. Thomson— and endeavours to reconcile 

 eliemical and contact tlieorists by pointing out how essential a part chemical action 



H H 2 



