60 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



the platina, to determine whether the positive pole onli/ could confer it (567.)? or 

 whether, notwithstanding the numerous contrary cases, the negative pole might not 

 have the power when such circumstances as could interfere with or prevent the action 

 were avoided. Three plates were therefore rendered negative for four minutes in di- 

 luted sulphuric acid of specific gravity 1-336, washed in distilled water, and put into 

 mixed oxygen and hydrogen. JH of them acted, though not so strongly as they would 

 have done if they had been rendered positive. Each combined about a cubical inch 

 and a quarter of the gases in twenty-five minutes. On every repetition of the experi- 

 ment the same result was obtained ; and when the plates were retained in distilled 

 water for ten or twelve minutes, before being introduced into the gas (582.), the 

 action was very much quickened. 



589. But when there was any metallic or other substance present in the acid, which 

 could be precipitated on the negative plate, then that plate ceased to act upon the 

 mixed oxygen and hydrogen. 



590. These experiments led to the expectation that the power of causing oxygen 

 and hydrogen to combine, which could be conferred upon any piece of platina by 

 making it the positive pole of a voltaic pile, was not essentially dependent upon the 

 action of the pile, or upon any structure or arrangement of parts it might receive 

 whilst in association with it, but belonged to the platina at all times, and was always 

 effective when the surface was perfectly clean. And though, when made the positive 

 pole of the pile in acids, the circumstances might well be considered as those which 

 would cleanse the surface of the platina in the most eflfectual manner, it did not seem 

 impossible that ordinary operations should produce the same result, although in a less 

 eminent degree. 



591. Accordingly, a platina plate (569.) was cleaned by being rubbed with a cork, 

 a little water, and some coal-fire ashes upon a glass plate : being washed, it was put 

 into mixed oxygen and hydrogen, and was found to act at first slowly, and then 

 more rapidly. In an hour, a cubical inch and a half had disappeared. 



592. Other plates were cleaned with ordinary sand-paper and water; others with 

 whitening and water ; others with emery and water ; others, again, with black oxide 

 of manganese and water ; and others with a piece of charcoal and water. All of these 

 acted in tubes of oxygen and hydrogen, causing combination of the gases. The action 

 was by no means so powerful as that produced by plates having been in communi- 

 cation with the battery ; but from one to two cubical inches of the gases disappeared, 

 in periods extending from twenty-five to eighty or ninety minutes. 



593. Upon cleaning the plates with a cork, ground emery, and dilute sulphuric 

 acid, they were found to act still better. In order to simplify the conditions, the cork 

 was dismissed, and a piece of platina foil used instead ; still the eflfect took place. 

 Then the acid was dismissed, and a solution of potassa used, but the eflfect occurred 

 as before. 



594. These results are abundantly suflficient to show that the mere mechanical 



