On the Chemical caufe tf Galvanifm. 30^ 



He has remarked that feveral metals, fuch as mercury, tin, and lead, preferve their metallic 

 luftre as l©ng as they are pure; but that their alloys are quickly tarniflied and oxided; and 

 that the mere contaft of two difterent metals appears to haften their oxidation. In this 

 manner the alloy employed to folder the plates of copper which cover the ohfervatory of Flo- 

 rence was foon changed into a white oxide, at the place of its clofe contact with the 

 copper, &c. He thinks, that in this cafe the metals have a mutual action on each other; 

 and that this adion, though more efficacious and perceptible when the aggregate attradlioft 

 of the metals is deftroyed by fufion, does not the lefs exift in folid metals when they touch 

 each other. 



If we attribute to a particular fluid, not galvanic, or to the eledlric matter, thofc efFedl* 

 which with the quicknefs of lightning are produced on the tongue by two metals 

 brought into contaft, it is becaufe we do not recolledl that the chemical aftion is alfo 

 exerted between bodies with the utmoft rapidity. The figns of eleiStricity which are fomc- 

 times obferved when two metals are feparated from contadt, are rather the confequence of 

 that adlion than the caufe. For we know that moft chemical operations change the elcdric 

 equilibrium of bodies, and confequently muft produce the phenomena of eleftricity. And 

 hence, without entirely excluding eleftricity from all the fads relating to galvanifm, Cit. 

 Fabioni thinks this fluid has no part in the fenfation experienced on touching the tongue 

 with the two metals. This aftion of the metals in conta(St is proved by the following ex- 

 periment :— Cit. Fabroni placed different pieces of metal in glaffes full of water ; one in each 

 glafs. In other glaffes he put two different pieces of metal, but he feparated the metals by a 

 plate of glafs. In a third fet of glaffes he alfo put two pieces of different metals ; but fo as to 

 touch each other. He did not obferve any alteraiion in the metal in the two firft fsts of 

 glaffes ; but the moft oxidable metals of the third fet became loaded with oxide, which was 

 confiderably increafed in a few days, and the metallic pieces adhered together very ftrongly. 

 The quantity of caloric difengaged during thefe combuftions is too fmall to be meafured ; but 

 we may perceive the light which proceeds from it if the eye itfelf be made an inftrument in 

 the experiment, by holding a piece of filver in the mouth, and applying a piece of tin to 

 the ball of the eye. As foon as the two metals come in contaft, a faint but dlftin(5l light ap- 

 pears, which vanifhes in a few moments, becaufe the eye accuftoms itfelf to this weak fenfation ; 

 but it might be renewed on paffing the metal firft over the opake, and then over the tranf- 

 parent cornea. The author attributes to a convulfive fenfation, the flafh of lightning which 

 fome perfons imagine they fee at the moment the two metals touch, when one is applied o« 

 the tongue and the other between the gums and upper lip. 



The prefence of air is required for the oxidation of the two metals in contact beneath the 

 water. Cit. Fabroni thinks that the air is of ufe in thefe circumftances, to add oxygen to 

 the water in fufficient quantity to be received by the metal, as filver is added to gold in the 

 parting affay. 



If a piece of filver and a piece of tin are put fo as to touch each other in water, in a vefiel 

 Vox.. III. — October 1799, Ss of 



