460 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



•ff 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 gene- 

 rally ; but it is rather with reference to their practical interference with the action 

 and phenomena of the voltaic battery, than with any intention at this time to offer a 

 strict and philosophical account of their nature. Their general and principal 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 (1034. 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, 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 occa- 

 sionally small glass rods were put into the cups, between the plates, to prevent 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 maybe admitted as repre- 

 senting 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 

 represented fig. 19, is that twice the quantity of surface of contact between the metal 

 and acid is allowed in the first to what would occur in the second. 



1009. When the extreme plates of the arrangement just described, fig. 18, are con- 

 nected metallically through the galvanometer g, then the whole represents a battery 

 consisting of two pairs of zinc and platina plates urging a current forward, which has, 

 however, to decompose water unassisted by any direct chemical affinity before it can 

 be transmitted across the cell iii, and therefore before it can circulate. This decom- 

 position of water, which is opposed to the passage of the current, may as a matter of 

 convenience be considered as taking place either against the surfaces of the two pla- 

 tina plates which constitute the electrodes in the cell iii, or against the two surfaces 

 of that platina plate which separates the cells ii and iii, fig. 19, from each other. It 

 is evident that if that plate were away, the battery would consist of two pairs of plates 

 and two cells, arranged in the most favourable position for the production of a current. 

 The platina plate therefore, which being introduced as at x, has oxygen evolved at one 



