462 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



1016. Five pairs of zinc and platina, with two interposed platina plates, fig. 25, 

 gave a feeble current ; there was permanent deflexion at the galvanometer, and de- 

 composition 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 simi- 

 larly 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 x, both by chemical action on the solution of iodide of potassium, and by 

 the galvanometer. This current I believe to be due to electricity reduced in intensity 

 below the point requisite for the decomposition of water (970. 984.) ; for water can 

 conduct electricity of such low intensity by the same kind of power which it possesses 

 in common with metals and charcoal, though it cannot conduct electricity of higher 

 intensity without suffering decomposition, and then opposing a new force consequent 

 thereon. With an electric current under this intensity, it is probable that increasing 

 the number of interposed platina plates would not involve an increased difficulty of 

 conduction. 



1018. In order to obtain an idea of the additional interfering power of each added 

 platina plate, six voltaic pairs and four intervening platinas were arranged as in 

 fig. 27; a very feeble current then passed (985. 1017.)- When one of the platinas 

 was removed so that three intervened, a current somewhat stronger passed. With 

 two intervening platinas a still stronger current passed ; and with only One inter- 

 vening platina a very fair current was obtained. But the effect of the successive plates, 

 taken in the order of their interposition, was very different, as might be expected ; 

 for the first retarded the current more powerfully than the second, and the second 

 more than the third. 



1019. In these experiments both amalgamated and unamalgamated zinc were used, 

 but the results generally were the same. 



1020. The effects of retardation just described were altered altogether when changes 

 were made in the nature of the liquid used between the plates, either in what may be 

 called the exciting or the retarding cells. Thus, retaining the exciting force the same, 

 by still using pure dilute sulphuric acid for that purpose, if a little nitric acid were 

 added to the liquid in the retarding cells, then the transmission of the current was 

 very much facilitated. For instance, in the experiment with one pair of exciting 

 plates and one intervening plate (1011.), fig. 20, when a few drops of nitric acid were 

 added to the contents of cell ii, then the current of electricity passed with consider- 

 able strength (though it soon fell from other causes (1036. 1040.),) and the same 

 good effect was produced by the nitric acid when many interposed plates were used. 



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