270 Chemical A&ion of Metals on each other. 
light which emanates from it may be feen, if the eye itfelf 
forms a part of the experiment, by holding a piece of filver 
in the mouth, and applying a bit of tin to the ball of the eye. 
After thefe two metals are made to communicate, you fee a . 
feeble but diftin& light, which difappears at the end of a 
few feconds, becaufe the eye becomes accuftomed to this 
feeble fenfation ; but it may be renewed by drawing the 
metal over the opake cornea, and then over the tranfparent. 
The author afcribes to a convulfive fenfation that kind of 
flafh which fome perfons think they perceive * at the mo- 
ment of the contaét of thefe metals, applied one on the 
tongue, and the other under it. 
To make the oxydation of the two metals take place under 
water, the prefence of air is alfo neceflary. C. Fabbroni thinks 
that air is ufeful in this circumftance, to add to the water a 
fufficient quantity of oxygen to be taken up by the metal, as 
filver is added to gold in order to perform the operation of 
quartation. Ifa piece of filver and a piece of tin be put in 
contact in. water, inclofed in a flafk of flint-glafs hermeti- 
cally fealed, the tin is oxydated; but the oxyde of the lead of 
the flint-glafs is decompofed, and the glafs becomes black. 
Philofophers, who afcribe thefe phenomena to eleé¢tricity, - 
bring, as a proof of their opinion, that they take place when 
the metals are conne¢ted even by means of a pretty long 
chain. C, Fabbroni has determined the length of this chain ~ 
at about 18 or 20 feet. Beyond that diftance thefe pheno- 
mena are no longer fenfible; while, on the other hand, the 
electric fluid is communicated to indefinite diftances, . 
If the phenomena of the experiment of Sultzer belonged 
really to electricity, they ought to take place with all metals, 
whatever may be the relation of thefe metals to each other, 
C. Fabbroni mentions a great number of thefe combinations 
which produced no effects; and other combinations, of the 
dame metals, which produced fenfations very diftinét. Thus, 
if filver be placed on the eye, and gold on the tongue, making 
them communicate by means of copper, the fenfation is al- 
anoft nothing; but it-becomes very evident if the iron touches 
* The perception is as real as that induced by drawing the metal ovér 
the cornea of the eye. Enprr. ; 
i) the 
