gto Dr. Wollaston on the Discovery of Palladium . 
of platina precipitated by sal ammoniac; but it was observable 
that the precipitate now obtained was not of so pale a yellow as 
the preceding. Nevertheless the impurity was in so small quan- 
tity, that the platina reduced from it by heat did not differ 
discernibly from that obtained from the purest yellow preci- 
pitate. 
At this time I found it advantageous to neutralize the solution 
with soda, and to employ a solution of green sulphate of iron 
for the precipitation of the gold, of which, I believe, a portion 
may always be obtained from the mixed ore ; but I have ob- 
served in experiments upon any quantities of mere grains of 
crude platina carefully selected, that the smallest portion of 
gold could not be detected as a constituent part of the ore 
itself. 
Bars of iron were subsequently employed as before for re- 
covering the platina that remained dissolved, together with 
those substances which I have since found to accompany it. 
The precipitate thus obtained, which I distinguish by the 
name of the second metallic precipitate, was to appearance of 
a blacker colour than the former, and was a finer powder. 
As I was not at first prepared to expect any new bodies, I 
proceeded to treat the second precipitate, as the former, by so- 
lution and precipitation. But I soon observed appearances 
which I could not explain by supposition of the presence of any 
known bodies, and was led to form conjectures of future disco- 
veries, which subsequent inquiry has fully confirmed. 
When I attempted to dissolve this second metallic precipitate 
in nitro-muriatic acid, I was surprised to find that a part of it 
resisted the action of that solvent, notwithstanding any varia- 
tions in the relative proportions or strength of the acids 
