for procuring pure Platinum. 2bl 



with the retort, a second in the same line connected with the 

 receiver, and a third on the top, into which a small glass tube 

 proceeding from a gasometer, filled with common air, is fixed. 

 The tube which joins the two balloons, should have a slight de- 

 clivity from the retort, and should dip at its end, into the water 

 of the second. The outlet of this last must be closed with a 

 Welter's tube of safety. When nitrous vapours are coming over 

 open the stop-cock of the gasometer, and transmit into the first 

 balloon, a moderate current of air. Its oxygen will immediately 

 re-acidify the nitrous gas, which will condense in the form of 

 nitric or nitrous acid, in the second receiver ; while the azote 

 will pass off. By M. Baruel's arrangement, §7 and §9, much 

 of the osmium is preserved ; which by following M. Vauquelin's 

 directions is lost sight of, and dissipated. 



In § 12, M. Baruel desires us to dilute with 5 or 6 parts of 

 water, the concentrated platinum solution. M. Vauquelin, says 

 that " ten parts of water and one of the solution in a state of 

 great concentration, appear to me to be the best proportion." 

 " Without the precaution of dilution," he observes, " it would 

 be very difficult to wash the precipitate, and it would remain 

 mixed with iron, and with the other metals, that happen to be 

 present. It is better that the whole platinum should not be pre- 

 cipitated, than that the precipitate should be impure ; because 

 the platinum remaining in solution is separated in the subsequent 

 processes." " Ammonio-muriate of platinum is not pure," he 

 subjoins, " unless it has a lemon colour, does not become brown 

 on drying, and is easily reduced to powder." 



In a subsequent part of his interesting Memoir, M. Vauque- 

 lin states, that on treating the black metallic precipitate, (ob- 

 tained by immersion of iron plates into the solution freed from 

 platinum by sal-ammoniac,) successively with cold nitric, and 

 muriatic acids, washing and drying the residuum, very acrid 

 white vapours rose, which he ascertained, by heating a portion 

 of Uie residuum in a crucible, to be a mixture of calomel and 

 muriate of copper. " The sublimate," adds he, " contained 

 likewise globules of mercury, and a black matter, which I sup- 

 pose, from the smell which it exhaled, to be osmium." The 



