Circles with Sulphuret of Potassium 26 i

investigation, by the circumstance of its giving, by its action on
the metals, resulting compounds,, some of which are insoluble,
whilst others are soluble; and, of the insoluble results, some
are excellent conductors, whilst others have no conducting
power at all.

869. The experiments to be described were made generally
in the following manner. Wires of platinum, gold, palladium,
iron, lead, tin, and the other malleable metals, about one-
twentieth of an inch in diameter and six inches long, were
prepared. Two of these being connected with the ends of the
galvanometer-wires, were plunged at the same instant into the
solution of sulphuret of potassium in a test-glass, and kept there
without agitation (907), the effects at the same time being
observed. The wires were in every case carefully cleansed with
fresh fine sand-paper and a clean cloth; and were sometimes
even burnished by a glass rod, to give them a smooth surface.
Precautions were taken to avoid any difference of temperature
at the junctions of the different metals with the galvanometer
wires.

870. Tin and platinum.—When tin was associated with
platinum, gold, or, I may say, any other metal which is
chemically inactive in the solution of the sulphuret, a strong
electric current was produced, the tin being positive to the
platinum through the solution, or, in other words, the current
being from the tin through the solution to the platinum. In a
very short time this current fell greatly in power, and in ten
minutes the galvanometer-needle was nearly at o°. On then
endeavouring to transmit the antimony-bismuth thermo current
(813) through the circuit, it was found that it could not pass,
the circle having lost its conducting power. This was the
consequence of the formation on the tin of an insoluble, invest-
ing, non-conducting sulphuret of that metal; the non-con-
ducting power of the body formed is not only evident from- the
present result, but also from a former experiment (809).

871. Marianini thinks it is possible that (in the case of copper,
at least (866), and, so I presume, for all similar cases, for surely
one law or principle should govern them), the current is due
to the contact force of the sulphuret formed. But that applica-
tion is here entirely excluded; for how can a non-conducting
body form a current, either by contact or in any other way?
No such case has ever been shown, nor is it in the nature of
things; so that it cannot be the contact of the sulphuret that
here causes the current; and if not in the present, why in any, xxi. p. 219.