RETARDATION PRODUCED BY INTERPOSED PLATES. 463 



1021. This seems to be a consequence of the diminution of the difficulty of decom- 

 posing water when its hydrogen, as in these cases, instead of being absolutely ex- 

 pelled, is transferred to the oxygen of the nitric acid, producing a secondary result at 

 the cathode (752.) ; for in accordance with the chemical views of the electric current 

 and its action already advanced (913.), the water, instead of opposing a resistance to 

 decomposition equal to the full amount of the force of mutual attraction between its 

 oxygen and hydrogen, has that force counteracted in part, and therefore diminished 

 by the attraction of the hydrogen at the cathode for the oxygen of the nitric acid 

 which surrounds it, and with which it ultimately combines instead of being rendered 

 in its free and independent state. 



1022. When a little nitric acid was put into the exciting cells, then again the cir- 

 cumstances favouring the transmission of the current were strengthened, for the iii- 

 tensity of the current itself was increased by the addition (906.). When therefore a 

 little nitric acid was added to both the exciting and the retarding cells, the current 

 of electricity passed with very considerable freedom. 



1023. When dilute muriatic acid was used, it produced and transmitted a current 

 more easily than pure dilute sulphuric acid, but could not compete with nitric acid. 

 As muriatic acid appears to decompose more freely than water (765.), and as the 

 affinity of zinc for chlorine is very powerful, it might be expected to produce a cur- 

 rent more intense than that from the use of dilute sulphuric acid ; and also to trans- 

 mit it more freely by undergoing decomposition at a lower intensity (912.). 



1024. In relation to the effect of these interpositions, it is necessary to state that 

 they do not appear to be at all dependent upon the size of the electrodes, or their 

 distance from each other in the acid, except that when a current can pass, changes 

 in these facilitate or retard its passage. For on repeating the experiment with one 

 intervening and one pair of exciting plates (1011.), fig. 20, and in place of the inter- 

 posed plate P using sometimes a mere wire, and sometimes very large plates (1008.), 

 and also changing the terminal exciting plates Z and P, so that they were sometimes 

 wires only and at others of great size, still the results were the same as those already 

 obtained. 



1025. In illustration of the effect of distance, an experiment like that described 

 with two exciting pairs and one intervening plate (1012), fig. 21, was arranged so 

 that the distance between the plates in the third cell could be increased to six or 

 eight inches, or diminished to the thickness of a piece of intervening bibulous paper. 

 Still the result was the same in both cases, the effect being no greater, sensibly, 

 when the plates were merely separated by the paper, than when a great way apart ; 

 so that the principal opposition to the current does not depend upon the quantity of 

 intervening electrolytic conductor, but on the relation of its elements to the intensity of 

 the current, or to the chemical nature of the electrodes and the surrounding fluids. 



1026. When the acid was sulphuric acid, increasing its strength in any of the cells, 

 caused no change in the effects; it did not produce a more intense current in the 



3 o2 



