.ilCTIOISr OF PLATINA A^D MERCURY. '175 



'not fenfibly a6led upon by the fame reagent. The infoUiblHty 

 'of muriate of filver might be ulledged as the caufe of ihis, if £ 

 had not tried the experiment by pouring nitrate of iiiver into 

 green muriate of iron, in which cafe all the fabftanccs were 

 prefented to each other in foiution. The refult was not re- 

 dudion, but muriate of iilver and nitrate of iron. This fa <y: 

 refts upon a mudi more extenfivc batis than mere mechanical 

 vcircumftances; and, if purfyed with the intenlfion it deferves, 

 •it would lead lis into the wideexpanfe of complicated atlinities 

 and their relations. From reafoning alone we fhou'd be dif- 

 J^ofed to think that an add, fo eafily decompofed as the nitric. 

 fWould be ftifficient to prevent the reduSion of a metal which 

 it can diflTolve. But on the one hand it can fpend its oxygen 

 upon a part of the oxide of the green fulphate of iron, while 

 on the other its affinity for oxide of filver is not jiovverfu! 

 enough to retain it, when there is another part o{: the oxide of 

 iron prefent to deprive it of oxygen. But the afiinity of 

 muriatic acid for oxide of filver, one of the ftronge/i at 

 prefent known, is fufticient to counterbalance all the other 

 forces. There are many other inft ances of liie fame kind. 



If then a foiution of green fulphate of iron be brought into Mercury in m- 

 conta6l with either foluble or infolublerauriate of mercury, no ^'^.'^ ^^,") '^J"",^": 



• r T 1 , pitated (metallic) 



redudion takes place; but it mercury, whether at the raaxi- by gr. lu.'ph. of 

 mum or the minimum of oxidizement, be diflbU^ed in nitric '^°"* 

 acid, and green fulphate of iron be added, the mercury is 

 precipitated in the metallic ftate. 



Thefe experiments are mucij ftronger examples than the Thefe i^mark- 

 former of the effeas produced by complicated affinities. They ^hl^•c'fuits"]?f ^^ 

 .ire of importance not only as objects of general confideration meily Hated, 

 but in their application to tlie prefent fubje6t. They mod ma.- 

 terially modify and are indifpenfable to the accuracy of the 

 refults I formerly ftated ; but I was not aw?ire of them at 

 the time I firft engaged in the inveftigation of this fubjeft. I 

 can alfo now explain a very material difference between fome 

 proportiorvs obferved by M. Richter and myfelf in an expe- 

 riment which that chemift had made as a repetition of one of 

 mine. 



I had poured a foiution of green fulphate of iron into a Predpitarion of 

 foiution of 100 parts of gold and 1200 of mercury, and ^^^ 1°^^ ^f(^'^l'^!^ 

 .'Obtained a precipitate confifting of 100 of gold and 774 of ot iron: repe^^^ 

 " «rcury. M R'chter repeated, as he terms it, this ejjperi- ^y ^i^hter, 



