120 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
peroxide is acted upon by such bodies as nitric acid. Potash and pure strong nitric 
acid boiled on peroxide of lead readily dissolved it, forming protonitrate of lead. A 
dilute nitric acid was made and divided into two portions ; one was tested by a solu- 
tion of sulphuretted hydrogen, and showed no signs of lead : the other was mingled 
with a little peroxide of lead (1822.) at common temperatures, and after an hour 
filtered and tested in the same manner, and found to contain plenty of lead. 
2044. The peroxide of lead is negative to platinum in solutions of common salt and 
potash, bodies which might be supposed to exert no chemical action on it. But 
direct experiments show that they do exert sufficient action to produce all the effects. 
A circumstance in further proof that the current in the voltaic circuit formed by 
these bodies is chemical in its origin, is the rapid depression in the force of the 
current produced, after the first moment of immersion. 
2045. The most powerful arrangement with peroxide of lead, platinum, and one fluid, 
was obtained by using a solution of the yellow sulphuret of potassium as the connecting 
fluid. A convenient mode of making such experiments was to form the peroxide into 
a fine soft paste with a little distilled water, to cover the lower extremity of a platinum 
plate uniformly with this paste, using a glass rod for the purpose, and making the coat 
only thick enough to hide the platinum well, then to dry it well, and finally, to compare 
that plate with a clean platinum plate in the electrolyte employed. Unless the pla- 
tinum plate were perfectly covered, local electrical currents (1120.) took place which 
interfered with the result. In this way, the peroxide is easily shown to be negative 
to platinum either in the solution of the sulphuret of potassium or in nitric acid. 
Red-lead gave the same results in both these fluids. 
2046. But using this sulphuretted solution, the same kind of proof in support of 
the chemical theory could be obtained from protoxides as before from the peroxides. 
Thus, some pure protoxide of lead, obtained from the nitrate by heat and fusion, was 
applied on the platinum plate (2045.), and found to be strongly negative to metallic 
platinum in the solution of sulphuret of potassium. White lead applied in the same 
manner was also found to acquire the same state. Either of these bodies when com- 
pared with platinum in dilute nitric acid was, on the contrary, very positive. 
2047- The same effect is well shown by the action of oxidized iron. If a plate of 
iron be oxidized by heat so as to give an oxide of such aggregation and condition as 
to be acted on scarcely or not at all by the solution of sulphuret, then there is little 
or no current, such an oxide being as platinum in the solution (1840.). But if it be 
oxidized by exposure to air, or by being wetted and dried ; or by being moistened 
by a little dilute nitric or sulphuric acid and then washed, first in solution of am- 
monia or potassa, and afterwards in distilled water and dried; or if it be moistened 
in solution of potassa, heated in the air, and then washed well in distilled water and 
dried ; such iron associated with platinum and put into a solution of the sulphuret 
will produce a powerful current until all the oxide is reduced, the iron during the 
whole time being negative. 
