120 Mr. Chenevix on the Action of 
But if mercury be raised to its maximum of oxidizement in 
nitric acid the case is different, for no precipitation occurs till 
the green sulphate of iron is added. The most advantageous 
method for precipitating platina and mercury by green sulphate 
of iron is, I believe, the following. Mix a solution of platina 
with a solution of green sulphate of iron, both warm, and add 
to them a solution of nitrate of mercury at the maximum of 
oxidizement also warm. It is necessary to avoid excess of acid, 
salt, &c. in this as in all such cases. With due care the preci- 
pitation of both metals will then be complete. 
By comparing the experiments made with mercury and 
platina with those made with silver and platina, a striking 
resemblance will be found. This induced me to pursue the 
analogy, and to examine whether, independently of the action 
of platina, mercury had not the same property of being preci- 
pitated by green sulphate of iron as silver. Nitrate of silver is 
precipitated by green sulphate of iron, but muriate of silver is 
not sensibly acted upon by the same reagent. The insolubility 
of muriate of silver might be alleged as the cause of this, if I 
had not tried the experiment by pouring nitrate of silver into 
green muriate of iron, in which case all the substances were 
presented to each other in solution. The result was not re- 
duction, but muriate of silver and nitrate of iron. This fact 
rests upon a much more extensive basis than mere mechanical 
circumstances ; and, if pursued with the attention it deserves, 
it would lead us into the wide expanse of complicated affinities 
and their relations. From reasoning alone we should be dis- 
posed to think that an acid, so easily decomposed as the nitric, 
would be sufficient to prevent the reduction of a metal which 
it can dissolve. But on the one hand it can spend its oxygen 
