MINERALOGY. I57 
'The variety from Bifpergs Klack 
has been examined by Mr. Quift^ 
and has, by its volatilifmg under the 
muffel, in form of a white fibrous 
fublimate, induced that gentleman to 
examine the. black lead more particu- 
larly *, and he has publiflied ' fomc 
Very remarkable experiments on it in. 
the Tranfadioiis of the Academy of 
Sciences at Stockholm, for the year 
1754- 
b. Of a fteel-grained and dull texture, 
"^exturd chalyhed. It is" naturally black, 
but when rubbed it gives a dark lead 
colour. 
c. Of a fine fcaly and coarfe-grained 
texture, Text'ufd micaced granu- 
latd, Coarfe Black Lead. 
It has at the fame time a fcaly and 
a granulated appearance. 
From Gran in the province of 
Upland, and from Tavaftehuflan in 
Finland 
* Profeffor Pott has examined the black lead in covered 
VelTels, and Mr. Qnift in an open fire, from which difference 
an the method of treating it, difierent notions have arole : be<- 
caufe the black lead is nearly unalterable when expofed to 
the fire in covered vefTels, or when immediately put into a 
flrong charcoal fire, but it is almofi: wholly volatile in a cal- 
cining heat. This is the cafe with feveral others of the mi- 
neral phlogiflons ; and from this w^e may in general learn, how 
neceffary it is to examine the mineral bodies by many and 
different methods, and to endeavour to multiply the experi- 
ments more than what has been hitherto done. Pencils are 
made from the black lead , as alfo the black lead crucibles. 
SECT. 
