upon the Black Wadd. 287 
the precipitation of the other matters by the Prufiian. lixivium, 
and been precipitated by the alkali added at laid. 
exp. 9. On precipitating a like folution by gradual additions 
of alkaline lixivium, and feparating the precipitates as often as 
a frefh addition of the alkali occafioned any different appearance 
from what the preceding had done ; the firft precipitate was 
white ; the next of a rufty red colour, like precipitate of iron ; 
the lad; very white, while diffufed through the liquor, and 
when fettled, but in drying turned a little brown. The firff, 
which was in a very frnall quantity, as nearly as could be 
judged by weighing the filters, about a twentieth part of the 
other two, was found to be lead ; the fecond was iron ; and 
the third manganefe, nearly in equal quantities, all pure, or 
very nearly fo, from one another. 
It appears from thefe experiments, that 22 parts of this 
mineral contain nearly two of indifloluble earth, chiefly mica- 
ceous, 1 of lead, about 9! of iron, and the fame quantity of 
manganefe. 
Specimens of the colours produced by vitrification . 
0. The mineral itfelf. 
1 . 2. 3. The fird:, fecond, and third precipitates. 
■SUSP 
Vol. LXXIIL Q q 
1 
