84 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVI.) 
the currents it can excite very evident and strong ; and it should be remembered that 
the strength of the resulting currents, as indicated by the galvanometer, depends 
jointly upon the energy (not the mere quantity) of the exciting action called into play, 
and the conductive ability of the circuit through which the current has to run. The 
value of this exciting electrolyte is increased for the present investigation, by the cir- 
cumstance 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. 
1881. 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 pre- 
pared. 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 (1919.), 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. 
1882. 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 0°. On then endeavouring to transmit 
the antimony-bismuth thermo current (1825.) through the circuit, it was found that it 
could not pass, the circle having lost its conducting power. This was the con- 
sequence of the formation on the tin of an insoluble, investing, non-conducting sui- 
phuret of that metal ; the non-conducting power of the body formed is not only evident 
from the present result, but also from a former experiment (1821.). 
1883. Marianini thinks it is possible that (in the case of copper, at least (1878.), 
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 
application 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 case ? for nothing 
happens here that does not happen in any other instance of a current produced by 
the same exciting electrolyte. 
1884. On the other hand, how beautiful a proof the result gives in confirmation of 
the chemical theory! Tin can take sulphur from the electrolyte to form a sulphuret; 
and whilst it is doing so, and in proportion to the degree in which it is doing so, it 
