Platina and Mercury upon each other. 121 
upon a part of the oxide of the green sulphate of iron, while 
on the other its affinity for oxide of silver is not powerful 
enough to retain it, when there is another part of the oxide of 
iron present to deprive it of oxygen. But the affinity of mu- 
riatic acid for oxide of silver, one of the strongest at present 
known, is sufficient to counterbalance all the other forces. 
There are many other instances of the same kind. 
If then a solution of green sulphate of iron be brought into 
contact with either soluble or insoluble muriate of mercury, 
no reduction takes place ; but if mercury, whether at the maxi- 
mum or the minimum of oxidizement, be dissolved in nitric 
acid, and green sulphate of iron be added, the mercury is 
precipitated in the metallic state. 
These experiments are much stronger examples than the 
former of the effects produced by complicated affinities. They 
are of importance not only as objects of general consideration 
but in their application to the present subject. They most ma- 
terially modify and are indispensable to the accuracy of the 
results I formerly stated ; but I was not aware of them at 
the time I first engaged in the investigation of this subject. I 
can also now explain a very material difference between some 
proportions observed by M. Richter and myself in an expe- 
riment which that chemist had made as a repetition of one of 
mine. 
I had poured a solution of green sulphate of iron into a 
solution of 100 parts of gold and 1200 of mercury, and had 
obtained a precipitate consisting of 100 of gold and 774 of 
mercury. M. Richter repeated, as he terms it, this experi- 
ment; that is, he used 100 of gold and 300 of mercury, and 
MDCCCV. R 
