▼OL. XLVIII.] PHILOSOPHICAL TRANSACTIONS. 505' 



threw down a similar calx. It could not be judged by the eye, whether the pre- 

 cipitation was complete, the solutions of iron and platina nearly agreeing with 

 each other in colour. 



3. Copper, the precipitant of mercury and gold, readily threw down platina 

 from its solution, in form of a greyish calx, which was found on trial to retain 

 a notable quantity of the copper. The liquor remaining after the platina had 

 fallen, was of a more dusky green than solutions of pure copper, probably from 

 its retaining some of the platina. 



4. Mercury, which precipitates gold alone from aqua regia, put into a diluted 

 solution of platina, seemed in a little time to be divided, and did not run freely. 

 Soon after, it appeared covered with a greyish matter, which at first was appre- 

 hended to be a precipitate, but was found afterwards to be a part of the mer- 

 cury corroded. On applying a moderate heat, the whole of the quicksilver, the 

 quantity of which was very considerable, was dissolved, without any precipitation. 



The experiment was repeated with a larger quantity of mercury than the solu- 

 tion was capable of taking up. The platina now gradually fell down among the 

 undissolved quicksilver, in form of a dark brownish powder ; leaving the liquor 

 nearly colourless. 



5. A solution of gold mingled uniformly with a solution of platina, without 

 occasioning any turbidness or precipitation. The mixture, diluted with water, 

 and sufFerwl to stand for some time, threw up a bright golden pellicle to the 

 surface. 



Exper. g. — 1. A solution of platina, super-impregnated with as much mer- 

 cury as it was capable of taking up, on being evaporated a little, so as to dis- 

 pose it to shoot, yielded crystals not at all like those of platina, but in form of 

 spicula, externally of a yellowish hue. These, slightly washed with proof spirit, 

 became colourless. Exposed to the fire, they emitted copious white fumes, with 

 a hissing or crackling noise ; and left a very small quantity of a reddish powder. 



2. A mixture of solutions of gold and platina, being treated in the same 

 manner, ruby-coloured crystals were obtained, which appeared to be chiefly gold, 

 with very little of the platina. 



Remark. It seems therefore, that mercury and gold crystallize from their 

 solutions before platina, leaving the greatest part of that mineral dissolved. This 

 affair, particularly with regard to gold, deserves further inquiry. 



Exper. 10. — As the calces of metals, obtained by precipitation from acids, or 

 by other means, vitrify along with frit or glass, and tinge them of various 

 colours ; and as this process is recommended by some for investigating the nature 

 of unknown metallic bodies ; the following trials were made with precipitates of 

 platina. 



1 . Half an ounce of a precipitate thrown down from solution of platina by> 



VOL. X. 3 T 



