116 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
2021. It appears to me probable that any one of the very numerous combinations 
which can be made out of the following Table, by taking one substance from each 
column and arranging them in the order in which the columns stand, would produce 
a current without metallic contact, and that some of these currents would be very 
powerful. 
Rhodium 
= i 
"Dilute nitric acid 
Gold 
o & 
Dilute sulphuric acid 
Platinum 
(Z 2 W 
?-> ^ 
Muriatic acid 
Palladium 
o « 
Iron < 
Solution of vegetable acids 
Silver 
'o r5" 
Iodide of potassium 
Nickel 
r <» 
Iodide of zinc 
Copper 
CZ3 
o o 
Solution of salt 
Lead 
Tin 
Zinc 
Cadmium 
Strong nitr 
solution 
tassium. 
_Many metallic solutions. 
2022. To these cases must be added the many in which one metal in a uniform acid 
gave currents when one side was heated (1942, &c.). Also those in which one metal 
with an acid strong and diluted gave a current (1977, &c.). 
2023. In the cases where by dilution of the acid one metal can be made either 
positive or negative to another (1996, &c.), one half of the results should be added 
to the above, except that they are too strong ; for instead of proving that chemical 
action can produce a current without contact, they go to the extent of showing a total 
disregard of it, and production of the current against the force of contact, as easily 
as with it. 
2024. That it is easy to construct batteries without metallic contact was shown by 
Sir Humphry Davy in 1801*, when he described various effective arrangements in- 
cluding only one metal. At a later period Zamboni constructed a pile in which but 
one metal and one fluid was used'f~, the only difference being extent of contact at the 
two surfaces. The following formsj which are dependent upon the mere effect of 
dilution, may be added to these. 
2025. Let a b, a b, a b, fig. 12, Plate III., represent tubes or other vessels, the parts 
at a containing strong nitric or sulphuric acid, and the parts at b dilute acid of the same 
kind ; then connect these by wires, rods, or plates of one metal only, being copper, 
iron, silver, tin, lead, or any of those metals which become positive and negative by 
difference of dilution in the acid (1979, &c.). Such an arrangement will give an 
effective battery. 
2026. If the acid used be the sulphuric, and the metal employed be iron, the current 
* Philosophical Transactions, 1801, p. 397. Also Journals of the Royal Institution, 1802, p. 51 ; and 
Nicholson’s Journal, 8vo, 1802, vol. i. p. 144. 
t Quarterly Journal of Science, viii. 177 ; or Annales de Chimie, xi. 190. (1819.) 
