INACTIVE CONDUCTING VOLTAIC CIRCLES, — NITROUS ACID. 
73 
the circuit is given in section at fig. 3, where H represents a piece of galena to be 
compared with the platinum P. 
1840. In this way galena, compact yellow copper pyrites, yellow iron pyrites, and 
globules of oxide of burnt iron, were compared with platinum, (the solution of sul- 
phuret of potassium being the electrolyte used in the circuit,) and with the same re- 
sults as were before obtained with metals (1829. 1833.). 
1841. Experiments hereafter to be described gave arrangements in which, with the 
same electrolyte, sulphuret of lead was compared with gold, palladium, iron, nickel, 
and bismuth (1885. 1886.) ; also sulphuret of bismuth with platinum, gold, palladium, 
iron, nickel, lead, and sulphuret of lead (1894.), and always with the same result. 
Where no chemical action occurred there no current was formed; although the cir- 
cuit remained an excellent conductor, and the contact existed by which, it is assumed 
in the contact theory, such a current should be produced. 
1842. Instead of the strong solution, a dilute solution of the yellow sulphuret of 
potassium, consisting of one volume of strong solution (1812.) and ten volumes 
of water, was used. Plates of platinum and iron were arranged in this fluid as 
before (1824.); at first the iron was negative (2049.), but in ten minutes it was 
neutral, and the needle at 0 o# . Then a weak chemical current excited at x (1831.) 
easily passed ; and even a thermo current (1830.) was able to show its effects at 
the needle. Thus a strong or a weak solution of this electrolyte showed the same 
phenomena. By diluting the solution still further, a fluid could be obtained in which 
the iron was, after the first effect, permanently but feebly positive. On allowing time, 
however, it was found that in all such cases black sulphuret formed here and there 
on the iron. Rusted iron was negative to platinum (2049.) in this very weak solution, 
which by direct chemical action could render metallic iron positive. 
1843. In all the preceding experiments the electrolyte used has been the sulphuret 
of potassium solution ; but I now changed this for another, very different in its 
nature, namely, the green nitrous acid (1816.), which has already been shown to be 
an excellent conductor of electricity. Iron and platinum were the metals employed, 
both being in the form of wires. The vessel in which they were immersed was a 
tube like that formerly described (1815.) ; in other respects the arrangement was the 
same in principle as those already used (1824. 1836.). The first effect was the pro- 
duction of a current, the iron being positive in the acid to the platina ; but this quickly 
ceased , and the galvanometer-needle came to 0°. In this state, however, the circuit 
could not in all things be compared with the one having the solution of sulphuret of 
* Care was taken in these and the former similar cases to discharge the platinum surface of any reacting force 
it might acquire from the action of the previous current, by separating it from the other metals, and touching 
it in the liquid for an instant with another platinum plate. 
MDCCCXL. L 
