68 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVI.) 
results relating to the conducting power of bodies, which will be required hereafter in 
these investigations. Galena, yellow sulphuret of iron, arsenical pyrites, native sul- 
phuret of copper and iron, native gray artificial sulphuret of copper, sulphurets of 
bismuth, iron, and copper, globules of oxide of burnt iron, oxide of iron by heat or 
scale oxide, conducted the thermo current very well. Native peroxide of manga- 
nese and peroxide of lead conducted it moderately well. 
1821. The following are bodies, in some respect analogous in nature and compo- 
sition, which did not sensibly conduct this weak current when the contact surfaces 
were small. Artificial gray sulphuret of tin, blende, cinnabar, hsematite, Elba iron- 
ore, native magnetic oxide of iron, native peroxide of tin or tinstone, wolfram, fuzed 
and cooled protoxide of copper, peroxide of mercury. 
1822. Some of the foregoing substances are very remarkable in their conducting 
power. This is the case with the solution of sulphuret of potassium (1813.) and the 
nitrous acid (1816.), for the great amount of this power. The peroxide of manganese 
and lead are still more remarkable for possessing this power, because the protoxides of 
these metals do not conduct either the feeble thermo current or a far more powerful 
one from a voltaic battery. This circumstance made me especially anxious to verify 
the point with the peroxide of lead. I therefore prepared some from red-lead by the 
action of successive portions of nitric acid, then boiled the brown oxide, so obtained, 
in several portions of distilled water, for days together, until every trace of nitric acid 
and nitrate of lead had been removed; after which it was well and perfectly dried. 
Still, when a heap of it in powder, and consequently in very imperfect contact 
throughout its own mass, was pressed between two plates of platinum and so brought 
into the thermo-electric circuit (1813.), the current was found to pass readily. 
ii. Inactive conducting circles containing a jluid or electrolyte. 
1823. De la Rive has already quoted the case of potash, iron and platina*, to 
show that where there was no chemical action there was no current. My object is 
to increase the number of such cases ; to use other fluids than potash, and such as 
have good conducting power for weak currents ; to use also strong and weak solu- 
tions; and thus to accumulate the conjoint experimental and argumentative evidence 
by which the great question must finally be decided. 
1824. I first used the sulphuret of potassium as an electrolyte of good conducting 
power, but chemically inactive (1811.) when associated with iron and platinum in a 
circuit. The arrangement is given in fig. 2, where D, E represent two test-glasses 
containing the strong solution of sulphuret of potassium (1812.); and also four 
metallic plates, about 0*5 of an inch wide and two inches long in the immersed part, 
of which the three marked P, P, P were platinum, and that marked I, of clean iron : 
these were connected by iron and platinum wires, as in fig. 2., a galvanometer being 
* Philosophical Magazine, 1837, xi. 275. 
