180 ACTION OF I'LATINA AN1> MERCURY: 



for In the prefent examples ptatina proteds mercury agahift 



the adion of nitric acid ; whereas in palladium the mercury i^f 



not 'only aded- upon itfelf, but it conduces to the fokition of 



platina in the fame acid. I am well avv^re of this objeflion ; 



but confining myfelf to my prefent ©bjeQy I fliall wave all 



further difcwflion of it till another opportunity. In the mean 



'''-■'time> however, it may be laid down as an axiom in chemiftry, 



that the flrongeft affinities are thofe, which produce in any 



fubflance the greateft deviation from its. ufual properties. 



The compounds ' When a button of the alloy of platina and mercury as pre- 



mercu^rv^are"fub- P^'"^'^ ^J ^"7 ^^ ^''^ above methods, is ditTolved in nitro- 



jed to great va- muriatic acidi* and afterwards precipitated by green fulphale 



nations, &c. q^- [^q^^ (\^q entire '^^jantity of the alloy ufed is feldom obtained. 



A confiderable portion of platina refifts the a6tion of green 



fulphate of iron, and remains in fokition. This may be looked 



upon as the excefs of platina, and can be recovered by a plate 



of iron. Hence it appears that lefs mercury is fixed, than can 



determine the precipitation of the entire quantity of platina ; 



yet in this flate it can draw down a greater quantity of the 



latter, than when it is merely poured into a mixed folution of 



platinaj not before fo treated. Indeed the whole of thefe 



experiments tend, not only to fliow that thefe two. metals 



exercife a very powerful a6tion upon each other, but that they 



are capabhe of great variation in the ftale of (heir combination; 



and alio that fubftances potreffing different properties have 



reful ted from my attempts to combine platina withmercury. 



Inveftlgailon of This obfervation furnifhed me with a method of afcer- 



the quantity of taining, or at lead of approaching to the knowledge of, the 



fi'x"d."'^^It is^ quantity of mercury thus fixed by platina, and in combination 



l^ppofed or in- with it. The experiment, however, having been feldora 



ak)u?j7mer- attended with full fuccefs, I mention the refult with the entire 



ciiry to ^3 pla- confcioufnefs of the uncertainty to which it is (ubje6i. I ob- 



tina, with the f^rved the incrcafe of weight, which the original quantity of 

 Specific gravity .,..- r r •fii . 



16, platina iiad acquired m lome caltt»iauer. it had been treated 



with mercury, and fufcd into a button. I counted that aug- 

 mentation as the quantity of mercury fixed. I then determined 

 hownvtfch was precipitated by green fulphate of iron from a 

 fplu^ioB., of this alloy, and fuppofed it to contain the whole 

 quantity of mercury found as above. But, even if attended 

 4m iiod*i.u: with complete fuccefs, there is a chemical reafon which muft 

 -^^ ■ make us rcfufe our aflent to this ellimate. It is poffible, and 



not 



