CHEMICAL PRINCIPLES. 
358 
Metallic, ox- . 
ides, &c. 
than that of the metal which thus loses its metallic brightness. 
This pellicle is more reatlily formed, if the lead be heated to 
nearly a melting state. The surface of the metal is tarnished, 
and becomes of a deeper and deeper colour, till it at length 
api^ears almost black. But if the heat be increased so as to melt 
the lead, the pellicle in that case will break, and in a few mo- 
ments we shall find it converted into a yellow oxide of lead. 
The same result is produced, if one half of the surface of a 
piece of lead be covered with a transparent varnish, leaving the 
other half uncovered. This latter will change its colour by 
degrees ; and if, after some time, the varnish be removed, we 
may then observe the different appearance of the metallic 
and the suboxided surfiice. 
I had some hopes of obtaining this suboxide by means of the 
action of the electric pile, and in a quantity sufficient to 
enable me to analyse it. For this purpose I employed wires 
of lead as conductors in pure water. The decomposition of 
the water took place slowly. No change was perceptible in 
the positive wire, but the negative wire was by degrees 
covered with a vegetation of metallic lead. The cause of its 
production will readily appear on recollecting the observation 
of M. Gayton Morveau, that the oxide of lead is soluble in 
pure water. 
I then thought of obtaining this suboxide by the following 
method : I combined some lead with mercury, and shaking the 
amalgam in a bottle, I took aw'ay from time to time the black 
powder which was thus formed. I considered tliis powder as 
the suboxide sought for j but when I triturated it in a mortar, 
I saw that it was almost entirely reduced to a fluid amalgam. 
A very small part, however, remained in the form of a powder j 
but this powder, when rubbed against gold, amalgamat- 
ed its surface. This experiment proves that the black pow^ 
der was really nothing more than metallic molecules, wlio e 
reunion w'as prevented by a pellicle of suboxide infinitely 
small, and which was broken by the friction. If those 
oxides of lead of which we know the composition, be exact 
, multiples 
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