ON THE INTENSITY NECESSARY FOR ELECTROLYZATION. 449 



resist the action of an electric current if beneath a certain intensity ? whether the 

 intensity at which the current ceased to act would be the same for all bodies ? and 

 also whether the electrolytes thus resisting decomposition would conduct the electric 

 current as a metal does, after they ceased to conduct as electrolytes, or would act as 

 perfect insulators ? 



967. It was evident from the experiments described (904. 906.) that different 

 bodies were decomposed with very different facilities, and apparently that they re- 

 quired for their decomposition currents of different intensities, resisting some, but 

 giving way to others. But it was needful, by very careful and express experiments, 

 to determine whether a current could really pass through, and yet not decompose an 

 electrolyte (910.). 



968. An arrangement (fig. 12.) was made, in which two glass vessels contained the 

 same dilute sulphuric acid, sp.gr. 1*25. The plate z was amalgamated zinc, in con- 

 nexion, by a platina wire a, with the platina plate e ; b was a platina wire connecting 

 the two platina plates P P' ; c was a platina wire connected with the platina plate F'. 

 On the plate e was placed a piece of paper moistened in solution of iodide of potas- 

 sium : the wire c was so curved that its end could be made to rest at pleasure on 

 this paper, and show, by the evolution of iodine there, whether a current was pass- 

 ing ; or, being placed in the dotted position, it formed a direct communication with 

 the platina plate e, and the electricity could pass without causing decomposition. 

 The object was to produce a current by the action of the acid on the amalgamated 

 zinc in the first vessel ; to pass it through the acid in the second vessel by platina 

 electrodes, that its power of decomposing water might, if existing, be observed ; and 

 to verify the existence of the current at pleasure, by decomposition at e, without 

 involving the continual obstruction to the current which would arise from making 

 the decomposition there constant. The experiment, being arranged, was examined, 

 the existence of a current shown by the decomposition at e, and then left with the 

 end of the wire c resting on the plate e, so as to form a constant metallic communi- 

 cation there. 



969. After several hours, the end of the wire c was replaced on the test paper at e : 

 decomposition occurred, and the proof of a passing current was therefore complete. 

 The current was very feeble compared to what it had been at the beginning of the 

 experiment, because of a peculiar state acquired by the metal surfaces in the second 

 vessel, which caused them to oppose the passing current by a force which they pos- 

 sess under these circumstances (1040.). Still it was proved, by the decomposition, that 

 this state of the plates in the second vessel was not able entirely to stop the current 

 determined in the first, and that was all that was needful to be ascertained in the 

 present inquiry. 



970. This apparatus was examined from time to time, and an electric current 

 always found circulating through it, until twelve days had elapsed, during which the 

 water in the second vessel had been constantly subject to its action. Notwithstand- 



