52 Experiments on Plalina^ 



cipitates of the moft nitric folutions. In a word, the refuU 

 of folutions of platina in nitro-muriatic acid is, ao in that of 

 gold, a pure and fimple muriate of platina. To what has 

 been faid I fliall add, that the difference between one kind 

 of crude platina and another may be known bv that obferved 

 in the colour of their folutions. Black platina grains, for 

 exayiple, diflfolved in the fame quantity of acid as the white, 

 give a colour much redder. 



XI. Solution of crude Platina 071 a large Scale. 



The phenomena obferved in the folution of this mineral, 

 when large quantities are employed, do not ditler from 

 thofe eflecled by fmall quantities. In the tirft of thefe opera- 

 tions, however, there are fome eife6ls more ftriking, which 

 I iliall here point out. 



When the iiitro-muriatic acid, aided by a moderate heat, 

 begins to attack platina, the firft bubbles of gas become co- 

 vered with a yellow powder, which retains them at the fur- 

 face of the liquor. Thefe globules float in every dire6lion, 

 and at length adhere to the fides of the retort, or vanifh, to 

 give place to others. Thefe phaenomena being common to 

 many fulphurous metals, we are authorized to believe that 

 this arifes from the fulphur which envelops thefe bubbles of 

 gas. This powder, when thus depofiled on the fides of the 

 retort, is foon diffipated; becaufe, being very minute, and 

 in fmall quantity, it is fpeedily fubjetted to the aflion of 

 agents which tend to convert it into fulphuric acid. 



But to return to the black powder ; in proportion as the fo- 

 lution advances, this powder is feen forming itfelf, increafing, 

 and alfuming, with the remainder of the platina, a leaden co- 

 lour, fimilar, as already faid, to that of pulverized galena. 

 It is then proper to lay afide this refiduum, on which the 

 folvent has only a very weak aftion, which cannot be con- 

 tinued but by repeated ebullition, and adding a large quan- 

 tity of new acids. This folution, when poured on a new 

 quantity of mineral, acts with a great deal of force; which 

 proves that this refiduum, though it llill holds abundance of 

 metal, refills the adion of the folvent much more than fredi 

 grains. 



This powder has been remarked, but not examined, bv 

 thofe who have operated on platina. To obtain it feparately, 

 the refiduum mult be waflicd in a great deal of water; it 

 mull be agitated a great deal, and decanted very fpeedily, 

 becaufe its gravity is very little different from the mineral 

 which remains to be diflblved. What has not been carried 

 oti' by decantatioHj when moiftcned, and rubbed between the 



fingersj 



