Platina and Mercury upon each other . 123 
of iron cannot be adduced as an argument to support the 
affinity of these metals, since the effect is the same, whether 
they are separate or united. 
These preliminary considerations were necessary as well 
for the rectification of my former experiments as for the pur- 
suit of my present object ; and now to return to platina. 
Exper. 1 . If a solution of highly oxidized nitrate of mercury 
be poured into a mixed solution of platina and green sulphate 
of iron, the first action which takes place passes between 
the muriatic acid of the solution of platina and the oxide of 
mercury, by which a muriate of mercury is formed, but retained 
in solution. This effect makes it advantageous to use a greater 
quantity of the solution of mercury than is merely capable of 
drawing down the given quantity of platina along with itself 
in the form of a metallic precipitate. When this precipitate is 
washed and dried, it will be found to weigh much more than 
the original quantity of platina ; and the augmentation of weight 
has no limit but those of the mercury and the green sulphate 
of iron employed. But even after nitric acid has been boiled 
for a long time and in great quantities upon this precipitate, 
until it no longer dissolves any part of it, there still re- 
mains more undissolved matter than the original weight of the 
platina used in the experiment. By exposure to heat little 
more is left in general than the original platina ; and some- 
times even a diminution may be observed ; for as the experi- 
ment is not attended with uniform success, it does not always 
happen that the whole of the platina is precipitated, but a 
portion of it will sometimes resist the action of the green sul- 
phate of iron, even when sufficient mercury has been used. 
Before the precipitate has been exposed to heat it is dissolved 
R 2 
