BLACK LEAD. 
475 
a brush. One of the useful applications of this 
powder is to smooth the surfaces of wood-work 
which slide one over the other, such as wooden 
screws, &c. and it is said that the black lead pro- 
duces a better effect on them than either greasy or 
oily substances. 
From this mineral containing about a tenth of its 
weight of iron, some naturalists have placed it 
among the iron ores ; nevertheless it must belong 
more properly to the class of inflammables, since it 
has been observed to burn away almost entirely 
when exposed to an intense heat in an open 
vessel. 
* v . 
