ELECTROMOTIVE FORCES IN THE VOLTAIC CELL. 467 



Wherever electrostatic methods were employed, and where the elec- 

 troscope was the instrument of research, contact theorists had it all their 

 own way, and it was only by apparent effort and twisting of experiments 

 that the chemical theorists could maintain their ground. But when 

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

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

 contact could maintain a current unless heat disappeared or chemical 

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

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

 meter the contact theory was so belaboured by Faraday that it ultimatelv 

 seemed to give up the ghost, and the chemical doctrines triumphed. So 

 much so that Volta's original fact, in spite of the evidence which had been 

 accumulated, was again doubted ; and one finds in text books culled from 

 this period statements that Volta must have had wet fingers, or that he 

 rubbed the plates together, or that there was moisture in the air. Also 

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

 varnish or lacquer might produce some electricity, and so on. It was 

 pointed out moreover by De la Rive 1 how minute a trace of chemical 

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

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

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

 action, and local action is not a satisfactory producer of manageable 

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

 that chemical action need produce no electricity, instancing the burning 

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

 &c. ; a plate of zinc placed on mercury and separated is found positive, 

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

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

 quoting. 2 



into connection with a Dellman electrometer, the other with the earth. The observa- 

 tion is repeated with a Daiiiell in the connecting wire, first one way then the other. 

 Thus three equations are obtained, M/M' = kct, D + M M'=kj8,D — M/M'=kyj whence 



M ( M = B^y D ' or ~JZTaP- - p °99- An »- v °ls. lxxv. p. 88 ; lxxxii. pp. Land 45, and 

 lxxxviii. p. 465, 1851 and 1853. He gets his results much lower than later experi- 

 menters ; only h a volt for Zn/Cu, and -58 for Zn/Pt. 



1 De la Rive.— Traite d'eleetrieitS, ii. p. 776.— Ann. de CJtimie, xxxix. p. 311, 1S2S. 



- Davy : Bakerian Lecture, 1806. See Phil. Tram. 1807, p. 3D : ' As the chemical 

 attraction between two bodies seems to be destroyed by giving one of them an elec- 

 trical state different from that which it naturally possesses ... so it may be increased 

 by exalting its natural energy. Thus while zinc is incapable of combining with oxygen 

 when negatively electrified in the circuit even by a feeble power, silver easily unites 

 to it when positively electrified . . . Among the substances that combine chemically, 

 all those, the electrical energies of which are well known, exhibit opposite electrical 

 states ... In the present state of our knowledge it would be useless to attempt to 

 speculate on the remote cause of the electrical energy, or the reason why different 

 bodies after being brought into contact should be found differently electrified ; its 

 relation to chemical affinity is, however, sufficiently evident. May it not be identical 

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

 attraction of the different chemical agents by the positive and negative surfaces in the 

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

 energies of the metals with regard to each other, or the substance dissolved in the 

 water, seems to be the cause that disturbs the equilibrium, and the chemical changes 

 the cause that tends to restore the equilibrium ; and the phenomena most probably 

 depend on their joint agency.' He then gives a very voltaic account of the action of 

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

 chemical and contact theorists by pointing out how essential a part chemical action 



H H 2 



