Retardation jn-oduced by interposed Plates. 343 



its associated hydrogen, but leave such a surplus of force as, 

 passing to the second place of decomposition, should be there 

 able to effect a second separation of the elements of water. 

 Such an effect would require that the force of attraction be- 

 tween zinc and oxygen should under the circumstances be at 

 least twice as great as the force of attraction between the oxy- 

 gen and hydrogen. 



1012. When two pairs of zinc and platina exciting plates 

 were used, the current was also practically stopped by one 

 interposed platina plate: fig. 21, There was a very feeble 

 effect of a current at first, but it ceased almost immediately. 

 It will be referred to, with many other similar effects, here- 

 after (1017.)- 



1013. Three pairs of zinc and platina plates, fig. 22, were 

 able to produce a current which could pass an interposed 

 platina plate, and effect the electrolyzation of water in cell iv. 

 The current was evident, both by the continued deflexion of 

 the galvanometer, and the production of bubbles of oxygen 

 and hydrogen at the electrodes in cell iv. Hence the accu- 

 mulated surplus force of these plates of zinc, which are active 

 in decomposing water, is more than equal, when added to* 

 gether, to the force with which oxygen and hydrogen are 

 combined tin water, and is sufficient to cause the separation 

 of these elements from each other. 



1014. The three pairs of zinc and platina plates were now 

 opposed by two intervening platina plates, fig. 23. In this 

 case the current was stopped. 



1015. Four pairs of zinc and platina plates were also neu- 

 tralized by two interposed platina plates, fig. 24. 



1016. Five pairs of zinc and platina, with two interposed 

 platina plates, fig. 25, gave a feeble current ; there was per- 

 manent deflexion at the galvanometer, and decomposition in 

 the cells vi and vii. But the current was very feeble ; very much 

 less than when all the intermediate plates were removed and 

 the two extreme ones only retained ; for when they were placed 

 six inches asunder in one cell, they gave a powerful current. 

 Hence five exciting pairs, with two interposed obstructing 

 plates, do not give a current at all comparable to that of a 

 single unobstructed pair. 



1017. I have already said that a very feeble current passed 

 when the series included one interposed platina and two pairs 

 of zinc and platina plates ( 1012.). A similarly feeble current 

 passed in every case, and even when only one exciting pair 

 and four intervening platina plates were used, fig. 26, a current 

 passed which could be detected at j:, both by chemical action 

 on the solution of iodide of potassium, and by the galvano- 



