58 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



vity 1*336. One of these was retained in similar acid for eight minutes after sepa- 

 ration from the battery : it then acted on mixed oxygen and hydrogen with apparently 

 undiminished vigour. Others were left in similar acid for forty hours, and some even 

 for eight days, after the electrization, and then acted as well in combining oxygen 

 and hydrogen gas as those which were used immediately after electrization. 



579. The effect of a caustic solution of potassa in preserving the platina plates was 

 tried in a similar manner. After being retained in such a solution for forty hours, 

 they acted exceedingly well on oxygen and hydrogen, and one caused such rapid con- 

 densation of the gases, that the plate became much heated, and I expected the tem- 

 perature would have risen to ignition. 



580. When similarly prepared plates (569.) had been put into distilled water for 

 forty hours, and then introduced into mixed oxygen and hydrogen, they were found 

 to act but very slowly and feebly as compared with those which had been preserved 

 in acid or alkali. When, however, the quantity of water was but small, the power 

 was very little impaired after three or four days. As the water had been retained 

 in a wooden vessel, portions of it were redistilled in glass, and this was found to 

 preserve prepared plates for a great length of time. Prepared plates were put into 

 tubes with this water and closed up ; some of them, taken out at the end of twenty- 

 four days, were found very active on mixed oxygen and hydrogen ; others, which 

 were left in the water for fifty-three days, were still found to cause the combination of 

 the gases. The tubes had been closed only by corks. 



581. The act of combination always seemed to diminish, or apparently exhaust, the 

 power of the platina plate. It is true that in most, if not all instances, the combi- 

 nation of the gases, at first insensible, gradually increased in rapidity, and sometimes 

 reached to explosion ; but when the latter did not happen, the rapidity of combi- 

 nation diminished ; and although fresh mixtures of gas were introduced into tlie 

 tubes, the combination went on more and more slowly, and at last ceased altogether. 

 The first effect of an increase in the rapidity of combination depended in part upon 

 the water flowing off from the platina plate, and allowing a better contact with the 

 gas, and in part upon the heat evolved during the progress of the combination (630.). 

 But notwithstanding the effect of these causes, diminution, and at last cessation of 

 the power, always occurred. It must not, however, be unnoticed, that the purer the 

 gases subjected to the action of the plate, the longer was its combining power re- 

 tained. With the mixture evolved at the poles of the voltaic pile in pure dilute sul- 

 phuric acid, it continued longest; and with oxygen and hydrogen, of perfect purity, it 

 probably would not be diminished at all. 



582. Different modes of treatment applied to the platina plate, after it had ceased 

 to be the positive pole of the pile, affected its power very curiously. A plate which 

 had been a positive pole in diluted sulphuric acid of specific gravity 1-336 for four or 

 five minutes, if rinsed in water and put into mixed oxygen and hydrogen, would act 

 very well, and condense perhaps one cubic inch and a half of gas in six or seven 



