C i6 3] 
form of a purplilh grey calx, the whole of the platina. 
remaining diifolved. It appeared, on numerous re- 
petitions of this experiment, that no part of the 
platina was precipitated along with the gold, nor any 
of the gold kept fufpended with the platina. Where 
the quantity of the mixt to be affayed was very 
fmall, the precipitation was ufually performed in a 
filter, that the gold, which feparates in very minute 
molecuiae, fome of which might polfibly remain un- 
obferved in the bottom of a glafs, might be detained 
on the paper. The colourlefs forts of filtering-paper 
are preferable for this ufe to the coloured ; as thefe 
laft may be impregnated with aftringent matter, 
which would extricate fome of the ferrugineous part 
of the vitriol. The vitriol was diffolved in about 
fix times its quantity of water, and a few drops of 
oil of vitriol added, to prevent the feparation of any 
of its iron in the filter. This folution was put into 
the filter firft, the folution of gold and platina im*j 
mediately poured into it, the whole flirred together 
with a clean glafs rod, and flich part of the liquor, 
as had run thro’ before they had been duly mixed, 
poured back to the reff. The gold remaining in the 
filter was waflied with frelh parcels of water, the 
paper cautioufly rolled up, and burnt in a crucible, 
as mentioned in a former experiment. 
3. Solutions of the vitriol, recommended by Kunc- 
kel and others for precipitating gold of an uncom- 
monly high colour, made no change in the folutions 
either of gold or platina. The bluilh green did in- 
deed precipitate the gold ; not as blue vitriols, but 
by virtue of the ferrugineous matter, of which thefe 
kinds largely participate. White vitriol was like wife 
Y 2 made 
