CAUSES OF DIMINISHED ACTIVITY OF THE BATTERY. 467 



metal be rough and irregular. In illustration of this effect, I will quote a remarkable 

 experiment. A burnished platina plate (569.) was put into hot strong sulphuric acid 

 for an instant only : it was then put into distilled water, moved about in it, taken 

 out, and wiped dry : it was put into a second portion of distilled water, moved about 

 in it, and again wiped : it was put into a third portion of distilled water, in which it 

 was moved about for nearly eight seconds ; it was then, without wiping, put into a 

 fourth portion of distilled water, where it was allowed to remain five minutes. The 

 two latter portions of water were then tested for sulphuric acid ; the third gave no 

 sensible appearance of that substance, but the fourth gave indications which were not 

 merely evident, but abundant for the circumstances under which it had been 

 introduced. The result sufficiently shows with what difficulty that portion of the 

 substance which is in contact with the metal leaves it ; and as the contact of the fluid 

 formed against the plate in the voltaic circuit must be as intimate and as perfect as 

 possible, it is easy to see how quickly and greatly it must vary from the general fluid 

 in the cells, and how influential in diminishing the force of the battery this effect 

 must be. 



1039. In the ordinary voltaic pile, the influence of this effect will occur in all va- 

 riety of degrees. The extremities of a trough of twenty pairs of plates of Wollaston's 

 construction were connected with the volta-electrometer, fig. 1 1. (71 1 .), of the Seventh 

 Series of these Researches, and after five minutes the number of bubbles of gas issuing 

 from the extremity of the tube, in consequence of the decomposition of the water, noted. 

 Without moving the plates, the acid between the copper and zinc was agitated by the 

 introduction of a feather. The bubbles were immediately evolved more rapidly, above 

 twice the number being produced in the same portion of time as before. In this in- 

 stance it is very evident that agitation by a feather must have been a very imperfect 

 mode of restoring the acid in the cells against the plates towards its first equal con- 

 dition ; and yet imperfect as the means were, they more than doubled the power of 

 the battery. The first effect of a battery which is known to be so superior to the 

 action which the battery can sustain, is almost entirely due to the favourable con- 

 dition of the acid in contact with the plates. 



1040. A second cause of diminution in the force of the voltaic battery, consequent 

 upon its own action, is that extraordinary state of the surfaces of the metals (969.) 

 which was first described, I believe, by Ritter *, to which he refers the powers of his 

 secondary piles, and which has been so well experimented upon by Marianini, and 

 also by A. De la Rive. If the apparatus, fig. 31. (1036.), be left in action for an 

 hour or two, with the wire 3 in contact with the plate p, so as to allow a free passage 

 for the current, then, though the contact be broken for ten or twelve minutes, still, 

 upon its renewal, only a feeble current will pass, not at all equal in force to what 

 might be expected. Further, if Pi and P^ be connected by a metal wire, a powerful 

 momentary current will pass from P^ to P» through the acid, and therefore in the 



* Journal de Physique, Ivii. p. 349. 



