SULPHURET OF POTASSIUM,— VOLTAIC CIRCLES. 
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strongly to the metal, but wipes off. Accordingly if a circle be formed of antimony, 
platinum, and the solution, the antimony is positive in the electrolyte, and a powerful 
current is formed, which continues. Here then is another beautiful variation of the 
conditions under which the chemical theory can so easily account for the effects, 
whilst the theory of contacts cannot. The sulphuret produced in this case is a non- 
conductor whilst in the solid state (402.) ; it cannot therefore be that any contact of 
this sulphuret can produce the current ; in that respect it is like the sulphuret of tin 
(1882.). But that circumstance does not stop the occurrence of the chemical cur- 
rent ; for, as the sulphuret forms a porous, instead of a continuous crust, the electro- 
lyte has access to the metal and the action goes on. 
1903. Silver. — This metal associated with platinum, iron, or other metals inactive in 
this electrolyte, is strongly positive, and gives a powerful continuous current. Ac- 
cordingly, if a plate of silver, coated with sulphuret by the simple action of the 
solution, be examined, it will be found that the crust is brittle and broken, and sepa- 
rates almost spontaneously from the metal. In this respect, therefore, silver and 
copper are alike, and the action consequently continues in both cases ; but they 
differ in the sulphuret of silver being a nonconductor (434.) for these feeble currents, 
and, in that respect, this metal is analogous to antimony (1902.). 
1904. Cadmium. — Cadmium with platinum, gold, iron, &c., gives a powerful current 
in the solution of sulphuret, and the cadmium is positive. On several occasions this 
current continued for two or three hours or more ; and at such times, the cadmium 
being taken out, washed, and wiped, the sulphuret was found to separate easily in 
scales on the cloth used. 
1905. Sometimes the current would soon cease; and then the circle was found 
not to conduct the thermo current (1813.). In these cases, also, on examining the 
cadmium, the coat of sulphuret was strongly adherent, and this was more especially 
the case when prior to the experiment the cadmium, after having been cleaned, was 
burnished by a glass rod (1881.). Hence it appears that the sulphuret of this metal 
is a non-conductor, and that its contact could not have caused the current (1883.) 
in the manner Marianini supposes. All the results it supplies are in perfect harmony 
with the chemical theory and adverse to the contact theory. 
1906. Zinc. — This metal, with platinum, gold, iron, &c., and the solution of sulphuret, 
produces a very powerful current, and is positive through the solution to the other 
metal. The current was permanent. Here another beautiful change in the circum- 
stances of the general experiment occurs. Sulphuret of zinc is a non-conductor of 
electricity (1821.), like the sulphurets of tin, cadmium, and antimony; but then it is 
soluble in the solution of sulphuret of potassium ; a property easily ascertainable by 
putting a drop of solution of zinc into a portion of the electrolytic solution, and first 
stirring them a little, by which abundance of sulphuret of zinc will be formed ; and 
then stirring the whole well together, when it will be redissolved. The consequence 
of this solubility is, that the zinc when taken out of the solution is perfectly free from 
MDCCCXL. 
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