THE ACCOMPANYING SUBSTANCES. 15 



feem to pofTefs. Theory would certainly give a general pre- 

 ference to piatina, from its refinance both to heat and to acids ; 

 and practice willjuftify this preference, in all but a fingle in- 

 ftance. If a quantity of potafh be kept for fome time in fu- p} a tina Is pre* 

 lion, in a piatina crucible, it will be found that the crucible fcrabie } "^P* 

 has loft feveral grains of its weight. The piatina fo diflblved ^^ aBtuton 

 may be looked for in the. potafh ; and, if this be faturated it* 

 with muriatic acid, and evaporated, we (hall find the well- 

 known triple fait, formed by the combination of muriatic acid 

 with potafh and oxide of piatina. This action of potafh upon 

 piatina, does not depend upon any mechanical caufe, fuch as 

 friction, the force that determines it being purely chemical. 

 If a fait formed by potafh, or a fait formed by ammonia, be Spanifh method 



mixed with a fait of piatina, a precipitate enfues, which is a °J de . te ^ in 6 P ,a - 

 r * r r ' tina in ln gots of 



triple fait ; and it is by this method, that the Spanifh govern- gold. Thefalts 

 ment detects the piatina, in the ingots of gold lent from their of p) at »na are J 

 American poffeffions. It is therefore evident, that an affinity pj e ) Dy the falts" 

 doesexift between potafh and piatina, in a certain ftate; and of potafh. 

 I imagine it to be this affinity, which caufes the oxidizement 

 of the piatina, when potafh is kept in fufion upon that metal. 

 I muft however obferve, that my crucible was prepared by Is piatina af- 

 Janetty, in Paris, according to a method he has publifhed in fe j? e ? ty the 

 the Annates de Chimie: and that he always employs arfenic, a tains ? 

 little of which certainly remains united to the piatina. What 

 influence arfenic may have, remains to be determined. Soda Soda fcarcely 

 does not form a triple fait with the oxide of piatina ; for I have a . fts u P on P 1 ** 

 frequently kept this alkali in fufion, in a piatina crucible, for 

 a long time ; yet very little action was produced upon the 

 metal. This fact feems to corroborate my affertion, that the 

 affinity of potafh for oxide of piatina, determines the oxidize- 

 ment of the metal. 



Whenever I fufpected that piatina had been diflblved, I Muriate of tin 



could eafily detea the fmalleft portion of it. A folution of is , the f* **• 

 r i-i i r cate teft of pla- 



platina, fo dilute as to be nearly colourlefs, manifefts, in a tina. 



very fhort time, the colour of a much more concentrate folu- 

 tion, and becomes reddifh, by the addition of a folution of tin 

 in muriatic acid. This I have found to be, by many degrees, 

 the moft fenfible teft for piatina ; and it would anfvver the 

 purpofes of the Spanifh government, -much better than that 

 they ufually employ,, 



4 The 



