238 head* 
pit coal, in about 48 hours it becomes red lead 9 and is 
taken out for use. 
The colour of the red lead admits some variety, which 
is occasioned by the different degrees of heat. If the heat 
is too small, instead of red it is yellow or orange coloured ; 
if it is too great, the red colour is changed into a dirty 
white, between these two extremes it is subject to some 
diversity of shades of red, which cannot be well noticed 
or described, except by those who are engaged in the 
making of it. 
It has been asserted, that the reverberation of the flame 
and smoke upon the surface of the lead, is not a neces- 
sary circumstance in giving it a red colour, but that it 
will acquire this colour by a long calcination without 
coming into contact with the flame. The truth of this 
assertion I think may be doubted. I have more than 
once calcined lead for above 60 hours, without suffering 
the flame of the fire to touch it during any part of the pro- 
cess, but by this method I could never obtain any thing 
better than a dirty red, resembling the red of brickdust, 
which is very different from the colour of red lead ; and 
even this dirty red was changed into a yellow colour, by 
augmenting the degree of heat with which the lead had 
been calcined. The method of making red lead is very 
well understood in England and Holland, but not in 
France ; and the French workmen are of opinion that it 
cannot be made by the flame of wood fires.* 
During the making of red lead, part of it is volatilized, 
there rises up from it a vapour, which attaches itself to the 
roof of the furnace, and forms solid lumps. These lumps 
are of a yellowish white colour mixed with pale green 
and some reddish streaks, wherein are frequently small 
red crystals, resembling such as may be artificially form- 
* Mem. de PAcad. des Seien. 1770. Elemens de Mineral, par 
M. Sage. Vol. 2. p. 248. 
