502 PHILOSOPHICAL TRANSACTIONS. [aNNO 1754. 



the solution began afresh ; the vapour, which now came over, appeared pale, 

 compared with the first. The cohobation was repeated 4 times, the distilled 

 liquor proving paler and paler every time. At length, both the fumes and action 

 ceased, though the fire was raised, and a considerable part of the platina remained 

 undissolved. The solution was therefore poured off, some more of the men- 

 struum added, the distillation and cohobation renewed, and this occasionally 

 repeated, till the whole was taken up, excepting a little blackish matter, of which 

 hereafter. The quantity of strong aqua regia, employed for dissolving the oz. of 

 platina, was 5 oz. ; but the last parcels appeared from their yellow colour not to 

 be fully saturated, and on trial were found to take up near 50 grs. of fresh platina. 

 Remark. It appeared, that by this method of managing the process, 1 part 

 of platina was soluble in about 4i of aqua regia : but that when the digestion 

 was performed in open vessels in the common manner, and the fumes, which 

 arise copiously during all metallic solutions, suffered to exhale, more than half 

 as much again of the menstruum was requisite. This process might therefore 

 possibly be applicable to advantage, in making solutions of metals in the way of 

 business. 



Examination of Solution of Platina. 



Exper. ] . — As the vitriolic acid carries down metallic bodies, gold not ex- 

 cepted, from their solutions in other menstrua ; this acid was mixed with solu- 

 tions of platina. 



1. When the solution of platina was previously diluted with water; the addition 

 of dephlegmated spirit of vitriol occasioned no precipitation, or change of colour, 

 though a large quantity of the acid was, at different times, dropped in, and the 

 mixture suffered to stand for several days. 



2. Dephlegmated spirit of vitriol, added to an undiluted solution of platina, 

 immediately rendered it turbid, and threw down a dusky-coloured precipitate. 

 The precipitate was not re-dissolved on the affusion of water ; nor was the pre- 

 cipitation prevented by adding water immediately after the acid had been 

 dropped in. 



Exper. 2. — Solutions of platina, evaporated by a gentle warmth, to a proper 

 pitch, and then set to shoot, yielded crystals, of a dark, almost opaqvie, red 

 colour, in form of leaves, like flowers of benzoin, but thicker. The crystals, 

 washed with proof spirit, became somewhat paler, but still remained of a high 

 colour, resembling the deeper chives of saffron. Exposed to the fire, they seemed 

 to melt, emitted white fumes, and at length fell into a dusky ash-coloured calx. 



Exper. 3. — Solutions of platina, dropped on hot marble, immediately cor- 

 roded it ; but did not, like solutions of gold and some other metals, communi- 

 cate any colour. Nor did they give any stain to the skin, to feathers, ivory, or 

 other like animal substances, which liquors containing gold tinge purple. 



