Retarding Effects of interposed Plates. 341 



be obtained at the expense of three or four equivalents of a 

 very common body, namely, zinc : and practice seems thus 

 far to justify the expectation. In this point of view I think it 

 very likely that plates of platina or silver may be used instead 

 of plates of copper with advantage, and that then the evil 

 arising occasionally from solution of the copper, and its pre- 

 cipitation on the zinc, (by which the electro-motive power of 

 the zinc is so much injured,) will be avoided (1047.)- 



f iv. On the Resistance of an Electrolyte to Electrolytic Action^ 

 and on Interpositions, 



1007. I have already illustrated, in the simplest possible 

 form of experiment (891. 910.), the resistance established at 

 the place of decomposition to the force active at the exciting 

 place. I purpose examining the effects of this resistance more 

 generally; but it is rather with reference to their practical inter- 

 ference with the action and phaenomena of the voltaic battery, 

 than with any intention at this time to offer a strict and phi- 

 losophical account of their nature. Their general and prin- 

 cipal cause is the resistance of the chemical affinities to be 

 overcome; but there are numerous other circumstances which 

 have a joint influence with these forces (10S4. 1040. &c.), 

 each of which would require a minute examination before a 

 correct account of the whole could be given. 



1008. As it will be convenient to describe the experiments 

 in a form different to that in which they were made, both 

 forms shall first be explained. Plates of platina, copper, zinc, 

 and other metals, about three quarters of an inch wide and 

 three inches long, were associated together in pairs by means of 

 platina wires to which they were soldered, (Plate I.) fig. 16, the 

 plates of one pair being either alike or different, as might be 

 required. These were arranged in glasses, fig. 17, so as to 

 form Volta's crown of cups. The acid or fluid in the cups 

 never covered the whole of any plate : and occasionally small 

 glass rods were put into the cups, between the plates, to pre- 

 vent their contact. Single plates were used to terminate the 

 series and complete the connexion with a galvanometer, or 

 with a decomposing apparatus (899. 968. &c.), or both. Now 

 if fig. 18 be examined and compared with fig. 19, the latter 

 may be admitted as representing the former in its simplest 

 condition; for the cups i, ii, and iii of the former, with their 

 contents, are represented by the cells i, ii, and iii of the latter, 

 and the metal plates Z and P of the former by the similar 

 plates represented Z and P in the latter. The only difference, 

 in fact, between the apparatus, fig. 18, and the trough repre- 

 sented fig. 19, is that twice the quantity of surface of contact 



