395 
electrical and chemical changes. 
by the contact of the plate first plunged in, before the relative 
states produced by the metallic contact and the regular cur- 
rents occur ; and the second, to the detaching or peeling off of 
the coat of sulphuret, which has the effect of exposing a clean 
surface, and which effect is probably occasioned by the oxi- 
dation of the positive side of the plate. 
There are few electrical actions more intense than those 
produced by the operation of hydro-sulphurets on copper in 
these different circumstances ; so much so, that I have con- 
structed a Voltaic battery which decomposed water, by six 
combinations, consisting merely of thin slips of copper, of 
which one half had been exposed to the solution about a 
minute before the other half : of course, the oxidating sur- 
face was on the side of the clean or latest exposed metal. 
With lead, and alloys of tin and lead and iron, there are 
the same phenomena, but much feebler electrical action, the 
metallic surface which is first introduced being the negative 
surface; and the principles of this kind of action are pre- 
cisely the same as those of copper and hydro-sulphurets. 
Zinc, platinum, and metals which have no chemical action 
on solutions of hydro-sulphurets, produce no phenomena of 
this kind; silver and palladium, which act powerfully with 
these menstrua, produce very decided effects ; but the com- 
pounds they form in them being positive with respect to the 
pure metals, the phenomena are the reverse of those offered 
by the more oxidable metals : the surface plunged first into 
the solution is the positive surface, and it retains this relation 
in alkaline, acid, and saline solutions, presenting peculiarities 
dependent upon the change of surface, which I shall refer to 
again hereafter. 
