218 
Lead . 
mon metals. Its specific gravity is 11,35, which is not 
encreased by hammering. It is very malleable, but not 
very ductile. A wire of t 4>6 of an inch diameter sup- 
ports only 18,4 lbs. its point of fusion is 612°. It eva- 
porates in the common blast-heat of the hearth furnace. 
It combines with oxygen slowly, by means of heat. The 
oxyds appear to me to be, 1st, The greyish black dust 
that first appears on the surface of the melted lead. 2dly, 
The yellow massicot, which also is first of a dirty yellow 
and then of a greenish yellow, before it comes to be of 
a full yellow colour ; indicating, as I conjecture, various 
states of oxydation. This yellow oxyd is massicot, to 
which red lead also may be reduced, by driving off a por- 
tion of its oxygen ; though it is usually made, in the stage 
of the process that precedes the red lead. It is the oxyd 
of lead, usually supposed to be combined with acids, 
from which it may be precipitated by pure alkalies, as a 
white hydrated oxyd, from which the water may be ex- 
pelled by strong heat. This white hydrated oxyd, like mas- 
sicot, contains about 7 percent, of oxygen. Dr. Thompson 
supposes that litharge is this oxyd of lead, mixed with a 
little carbonic acid obtained from the carbonaceous mat- 
ter burnt in the refining furnaces, where litharge is made : 
but as yet, I hold all this to be probable conjecture only. 
We do not yet know the precise state of oxygenated lead 
that constitutes litharge. 3dly, Red lead, which contains 
from 10 to II per cent, of oxygen. 4thly, The brown, 
puce-coloured (flea-coloured) oxyd, containing from 13 
to 14 per cent, of oxygen. 
The puce-coloured or brown oxyd, is only made by 
the experimental chemist, by digesting nitric acid on red 
lead. The preparations of commerce among the oxyds, 
are white lead, massicot, litharge, red lead. 
