148 IIELMHOLTZ ON THE CONSERVATION OF FORCE. 



contact with the platinum ; so that thus regarded an element of 

 Grove or of Bunsen would become a circuit formed between zinc 

 and nitrous acid, and those constructed with chromic acid 

 circuits between zinc and oxide of chromium. 



The batteries with polarization may be divided into two classes, 

 such as excite polarization, but which cause no chemical de- 

 composition, and such as give rise to both. To the former, 

 which produce an inconstant and quickly disappearing current, 

 belong the simple circuit of Faraday*, with combinations formed 

 of solutions of caustic potash, sulphuret of potassium, and nitrous 

 acid ; further, those of the more strongly negative metals in com- 

 mon acids, when the positive are not able to decompose the 

 acid ; for example, copper with silver, gold, platinum, coal in 

 sulphuric acid, and so forth ; of the compound circuits, all those 

 in which decomposition cells are introduced, the polarization of 

 which overpowers the electromotive force of the other elements. 

 Exact quantitative experiments on the intensity of these circuits 

 have, up to the present time, on account of the great variability 

 of the currents, not been carried out. In general the intensity 

 of these currents seems to depend upon the nature of the im- 

 mersed metal; their duration increases with the magnitude of the 

 surfaces and with the diminution of the intensity of the current ; 

 they can be renewed, even after they have almost disappeared, 

 by moving the metal in the fluid or in the air, by which the po- 

 larization of the plate against which hydrogen has been liberated 

 is annulled. To such actions the residual currents, which exhibit 

 themselves on fine galvanometric instruments, are probably due. 

 The entire process is therefore an establishing of an electric 

 equilibrium of the particles of the fluid and of the metals ; the 

 particles of fluid appear sometimes to undergo a modification of 

 arrangement ; and on the other side chemical changes occur, in 

 many cases, at the metallic surfaces f. In compound circuits, 

 where the polarization of plates originally alike is caused by the 

 action of currents from other elements, we can obtain the lost 

 force of the primitive current in the form of a secondary current, 

 by removing the exciting elements, and causing the polarized 



•Experimental Researches in Electricity, 16th series; Phil. Trans. 184. 

 p. 1 ; and Pogg. Ann. vol. lii. p. 163 and .547. 

 t Ohm, in Pogg. Ann. vol. Ixiii. p. 389. 



