88 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVI.) 
it falls, does not come to a close as in the former cases, and for these simple reasons; 
that the sulphuret formed is not compact but porous, and does not adhere to the 
copper, but separates from it in scales. lienee results a continued renewal of the 
chemical action between the metal and electrolyte, and a continuance of the current. 
If after awhile the copper plate be taken out and washed, and dried, even the wiping 
will remove part of the sulphuret in scales, and the nail separates the rest with facility. 
Or if a copper plate be left in abundance of the solution of sulphuret, the chemical 
action continues, and the. coat of sulphuret of copper becomes thicker and thicker. 
1898. If, as Marianini has shown*, a copper plate which has been dipped in the 
solution of sulphuret, be removed before the coat formed is so thick as to break up 
from the metal beneath, and be washed and dried, and then replaced, in association 
with platinum or iron, in the solution, it will at the first be neutral, or, as is often 
the case, negative (1827. 1838.) to the other metal, a result quite in opposition to 
the idea, that the mere presence of the sulphuret on it could have caused the former 
powerful current and positive state of the copper (1897- 1878.). A further proof that 
it is not the mere presence, but the formatioji, of the sulphuret which causes the cur- 
rent, is, that, if the plate be left long enough for the solution to penetrate the investing 
crust of sulphuret of copper and come into activity on the metal beneath, then the 
plate becomes active, and a current is produced. 
1 899. I made some sulphuret of copper, by igniting thick copper wire in a Florence 
flask or crucible in abundance of vapour of sulphur. The body produced is in an 
excellent form for these experiments, and a good conductor ; but it is not without 
action on the sulphuretted solution, from which it can take more sulphur, and the 
consequence is, that it is positive to platinum or iron in such a solution. If such sul- 
phuret of copper be left long in the solution, and then be washed and dried, it will 
generally acquire the final state of sulphuration, either in parts or altogether, and 
also be inactive, as the sulphuret formed on the copper was before (1898.); i. e. when 
its chemical action is exhausted, it ceases to produce a current. 
1900. Native gray sulphuret of copper has the same relation to the electrolyte: it 
takes sulphur from it and is raised to a higher state of combination ; and, as it is also 
a conductor (1820.), it produces a current, being itself positive so long as the action 
continues. 
1901. But when the copper is fully sulphuretted, then all these actions cease; though 
the sulphuret be a conductor, the contacts still remain, and the circle can carry with 
facility a feeble thermo current. This is not only shown by the quiescent cases just 
mentioned (1898.), but also by the utter inactivity of platinum and compact yellow 
copper pyrites, when conjoined by this electrolyte, as shown in a former part of this 
paper (1840.) 
1902. Antimony . — This metal, being put alone into a solution of sulphuret of po- 
tassium, is acted on, and a sulphuret of antimony formed, which does not adhere 
* Memorie della Societa Italians in Modena, 1837, xxi. 224. 
