96 "On the Ufe of Chrome, &e. 
them to powder, and afterwards boiling it in a folution of the 
carbonat of potafh, and mixing with the nitrat of lead this 
folution, after its excefs in alkali has been faturated with the 
nitric acid, By this procefs red lead may be formed as 
beautiful as the natural, and perfectly free from the matrix. 
_ There is reafon to prefume that chrome, in the ftate of an 
oxyd, or in that of an acid, will be found either free or in 
combination with other fubftances; for the analyfis of the 
emerald of Peru has fhewn to me that its colouring principle 
is fupplied by the oxyd of this metal; which is a very agree- 
able prefage for the goodnefs and fixity of this colour, fince 
we know that the emerald may be expofed to the moft 
violent degree of heat without being difcoloured. 
I have found alfo that the yellowith green velvety cryftals, 
which often accompany the red lead of Siberia, are formed 
of chrome and lead, both united in the oxyd ftate. In 
certain fragments of red lead there may be {een alfo green 
eryftals, which have the fame form, the fame dimenfions, 
! and 
under the name of red /ead was difcovered by M. Pallas, in 1770, in the 
gold mine of Berefof, near Ekaterimbourg in Siberia, under the form of 
prifms with four planes, with, or without, terminating pyramids of a beau- 
tiful orange red colour, generally fixed in a quartzy matrix, to which they 
adhere fo ftrongly that it is difficult to detach them. 
From the-above mine have been procured all the fpecimens of this fub- 
ftance preferved in the cabinets of Europe, which fhews that it was for+ 
merly very abundant; but we are affured that for fome years it has become 
exceedingly fcatce, and that it is fold at prefent for its weight in gold, 
efpecially when pure and of a regular form. Specimens which do not 
poflefs a regular form, or which have been reduced to fragments, are ap- 
plied to the purtpofes of painting, in which art jt is exceedingly valuable, 
on account of its beautiful orange yellow colour, its durability in the air, 
and the facility with which it can be mixed with oil. Profeffor Pallas ex- 
preffes himfelf thus, in {peaking of this mineral, in his Travels during the 
year 1770, under the article of the gold mine of Fifchminfkoi, vol. ii. 
p. 238.“ A very remarkable kind of mineral red lead, not found in any 
other mine of the Empire or elfewhere, is dug up here. This lead ore is 
heavy, of different colours, fometimes that of cinnabar, and very tranfparent. 
s - Ir 
