n8 Mr. Chenevix on the Action of 
by a solution of green sulphate of iron, either silver or mer- 
cury is present. 
The precipitation of a mixed solution of platina and silver 
requires no further caution than to free the salt of platina as 
much as possible from muriatic acid ; for as I observed in 
my former Paper, the effect of nitrate of silver poured into 
muriate of platina, is to produce a precipitate, not of muriate 
of silver, but of a triple muriate of platina and silver. It was 
by this experiment that I then proved the affinity of these two 
metals ; for when silver is not present, muriate of platina is 
among the most soluble salts. The best method of presenting 
the three solutions of platina, silver, and green sulphate of iron 
to each other, is first to pour the filtered solution of the last 
into the solution of platina, and then, after mixing them tho- 
roughly together, to add the solution of silver by degrees, and 
to stir them constantly. In this, as in all similar operations, 
the presence of all acids, salts, &c. excepting those necessary 
for the operation, should be avoided ; and if proper proportions 
have been used, and all circumstances attended to, the preci- 
pitation of these two metals will be very complete. 
But the precipitation by a solution of mercury requires to be 
further considered, as the state of oxidizement of this metal, 
as well as the acid in which it is dissolved, produces a consi- 
derable modification in the result. In the first place the oxide, 
at the minimum of oxidizement, dissolved in muriatic acid, is 
unfit for the experiment ; and even the red oxide dissolved in 
the same acid, or corrosive sublimate, is not the most advan- 
tageous. When a warm solution of the latter is poured into a 
mixed solution of platina and green sulphate of iron also 
