412 On the magnetic Phenomena 
a vessel which could be filled with any saline solution; and a 
similar piece of platinum pleced opposite at an inch distance ; 
the whole was then made part of a Voltaic circuit, which had 
likewise another termination by silver wires in water; and so- 
lution of salts added, till gas ceased to be liberated from the ne- 
gative silver wire. In several trials of this kind it was found 
that the whole of the surface of six inches, even with the strongest 
solutions of common salt, was insufficent to carry off the elec- 
tricity even of two pair of plates; and a strong solution of po- 
tassa carried off the electricity of three pair of plates only; 
whereas an inch of wire of platinum of 53, (as has been stated) 
carried off all the electricity of 60 pair of plates. The gas li- 
berated upon the surface of the metals when they are placed in 
fluids, renders it impossible to gain accurate results; but the 
conducting power of the best fluid conductors, it seems probable 
from these experiments, must be some hundreds of thousand 
times less than those of the worst metallic conductors. 
A piece of well-burnt compact box-wood charcoal was placed 
in the circuit, being 32, of an inch wide by =}, thick, and con- 
nected with large surfaces of platinum. It was found that one 
inch and ,%; carried off the same quantity of electricity as six 
inches of wire of platinum of 53,5. 
Vil. 1 made some experiments with the hope of ascertaining 
the exact change of ratio of the conducting powers dependent 
upon the change of the intensity and quantity of electricity ; but 
I did not succeed in gaining any other than the general result, 
that the higher the intensity of the electricity, the less difficulty 
it had in passing through bad conductors; and several remark- 
able phenomena depend upon this circumstance. 
Thus, in a battery where the quantity of the electricity is very 
great and the intensity very low, such as one composed of plates 
of zinc and copper, so arranged as to act only as single plates 
of from 20 to 30 feet of surface each, and charged by a weak 
mixture of acid and water. Charcoal made to touch only ina 
few points, is almost as much an insulating body as water, and 
cannot be ignited, nor can wires of platinum be heated when 
their diameter is less than ;!, of an inch, and their length three 
or four feet ; and a foot of platinum wire of 54, is scarcely heated 
by such a battery, whilst the same length of silver wire of the 
same diameter is made red hot; and the same lengths of thicker 
wires of platinum or iron are intensely heated. 
The heat produced where electricity of considerable intensity 
is passed through conductors, must always interfere with the ex- 
act knowledge of the changes of their conducting powers, as is 
proved by the following experiment. A battery of 20 pair of 
plates of zinc, and copper plates 10 inches by 6, was very highly 
charged 
