Circles with Protosulphuret of Potassium 269

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 redis-
solved. The consequence of this solubility is, that the zinc
when taken out of the solution is perfectly free from investing
sulphuret of zinc. Hence, therefore, a very sufficient reason,
on the chemical theory, why the action should go on. But
how can the theory of contact refer the current to any contact
of the metallic sulphuret, when that sulphuret is, in the first
place, a non-conductor, and, in the next, is dissolved and
carried off into the solution at the moment of its formation?

895. Thus all the phenomena with this admirable electrolyte
(868), whether they be those which are related to it as an active
(867) or as a passive (813, etc.) body, confirm the chemical
theory, and oppose that of contact. With tin and cadmium
it gives an impermeable non-conducting body; with lead and
bismuth it gives an impermeable conducting body; with
antimony and silver it produces a permeable non-conducting
body; with copper a permeable conducting body; and with
zinc a soluble non-conducting body. The chemical action
and its resulting current are perfectly consistent with all these
variations. But try to explain them by the theory of contact,
and, as far as I can perceive, that can only be done by twisting
the theory about and making it still more tortuous than before;
special assumptions being necessary to account for the effects
which, under it, become so many special cases.

896. Solution of protosulphuret of potassium, or bihydro-
sulphuret of potassa.—I used a solution of this kind as the
electrolyte in a few cases. The results generally were in ac-
cordance with those already given, but I did not think it neces-
sary to pursue them at length. The solution was made by
passing sulphuretted hydrogen gas for twenty-four hours
through a strong solution of pure caustic potassa.

897. Iron and platinum with this solution formed a circle
in which the iron was first negative, then gradually became
neutral, and finally acquired a positive state. The solution
first acted as the yellow sulphuret in reducing the investing
oxide (1037), and then, apparently, directly on the iron, dis-
solving the sulphuret formed. Nickel was positive to platinum
from the first, and continued so though producing only a weak
current. When weak chemical action was substituted for
metallic contact at x, fig. 65 (819), a powerful current passed.pact "nickel; and if porous,