the chemical Production and Agency of Electricity. 42 9 
posing water ; and we can have no reason to suppose that the 
contact of the silver produces any new power, but that it serves 
merely as a conductor of electricity, and thereby occasions the 
formation of hydrogen gas. 
In the 3d experiment also, the iron by itself has the power of 
precipitating copper, by means, I presume, of electricity evolved 
during its solution ; and here likewise the silver, by conducting 
that electricity, acquires the power of precipitating the copper 
in its metallic state. 
The explanation here given receives additional confirmation 
from comparative experiments which I have made with common 
electricity ; for it will be seen, that the same transfer of chemical 
power, and the same apparent reversion of the usual order of 
chemical affinities in the precipitation of copper by silver, may 
be effected by a common electrical machine. 
The machine with which the following experiments were 
conducted, consists of a cylinder 7 inches in diameter, with a 
conductor on each side, 16 inches long, and g\ inches diame*- 
ter, each furnished with a sliding electrometer, to regulate the 
strength of the spark received from them. 
Exper. 4. Having a wire of fine silver, T — • of an inch in dia- 
meter, I coated the middle of it, for 2 or 3 inches, with sealing- 
wax, and, by cutting through in the middle of the wax, exposed 
a section of the wire. The two coated extremities of the wire, 
thus divided, were immersed in a solution of sulphate of copper, 
placed in an electric circuit between the two conductors ; and 
sparks, taken at ~ of an inch distance, were passed by means 
of them through the solution. After 100 turns of the machine, 
the wire which communicated with (what is called) the nega- 
tive conductor, had a precipitate formed on its surface, which. 
