the Nature of fome Mineral Subjlances . 6 1 1 
that a fingle grain, of neutral fait in an ounce of alkaly 
may be dilcovered by this procefs, 
EXPERIMENT I. 
Two drams of the horn fiver [#] were well ground in 
a glafs mortar, with an equal quantity of fixed alkaly of 
tartar, and diftilled water enough to make the mixture of 
a foft confidence; it was then taken out of the mortar, 
and deprived of its moifture in a china cup fixed in a 
find heat. The mixture was then powdered and put 
into a common green ounce phial, and this into a cruci- 
ble, and furrounded with fand up to its neck. The cru- 
cible was fixed in a proper furnace, and a fire made round 
it, which was increafed by degrees until the phial became 
of a dull red colour, in which date it was kept for an 
hour. The crucible was then taken out of the fire, and, 
when quite cold, the phial was broken; care was taken 
to feparate the matter from the broken bits of glals. 
This matter was of a fpungy texture, and would not 
powder, but flatted in the mortar, and then fhewed its fil- 
very appearance; it was, therefore, cut into thin flices 
and digefted with four ounces of diftilled water; the fo- 
lution was poured off and filtered, and four ounces more 
of the like water added to what remained undiflole ed ; 
this alfo, after digeftion, was poured off, filtered, and 
added to the firft folution. By this means the filver Was 
deprived of all its faline part. The folution was evapo- 
rated flowly to about one-half, and then faturated with 
diftilled vinegar; this was afterwards filtered, gently 
Vol. LXVI. 4L evaporated 
