Page:Proceedings of the Royal Society of London Vol 1.djvu/227

Rh distilled, left a blackish brown substance, weighing 49 grains. This substance appeared, by experiments made upon it, to be a variety of the artiﬁcial tanning matter, much resembling that obtained from re- sinous bodies by means of sulphuric acid; but it is remarkable, that when a small quantity of nitric acid was added to an aqueous so- lution of the substance obtained from camphor, and, after evaporation to dryness, the residuum was dissolved in water, a reddish brown liquid was formed, which acted in a manner exactly similar to the tanning substance obtained from carbonaceous substances by nitric acid.

In this paper the author relates circumstantially the series of operations by which he was led to the original discovery of palladium; and as he had an opportunity during the solution of a considerable quantity of platiua, of making many observations that have not occurred to others, he "undertakes. on the present occasion, to mention those which are most worthy of notice.

He remarks, that the gold which is usually found with platina is a constituent part of the ore of platina itself, when the grains are carefully selected.

The metals iridium and osmium, on the contrary, which were ex- tracted by Mr. Tennant from the black powder that remains after solution of the ore of platina, Dr. Wollaston observes, are not only to be found in that powder which is extricated by solution from the interior of the grains of crude platina, but there exist also other grains originally distinct from those of platina, and consisting of these metals ouly.

These grains, which he considers as the proper ore of iridium mineralized by osmium, are harder than those of platina, are more brittle under the hammer, and when broken appear to be laminated.

The speciﬁc gravity of these grains, he says, is very remarkable, being greater than that of the ore of platina, which in his experiments has not exceeded 17'7, while that of the former is 'as much as 19'5. It would naturally be supposed that such a density might arise from the presence of a large quantity of platina in them; but the author did not succeed in obtaining any platina from these grains.

Among the various substances that may be separated from the ore of platina by washing, he notices also certain minute crystals of the colour of the ruby. Of thesc he gives a particular description, but does not undertake the analysis, on account of the very small quantity which he could obtain.

The author next proceeds to the solution of platina, from which he ﬁrst precipitates the greater part of the platina pure, by Sal ammoniac, and the remainder in an impure state by iron, a second metallic precipitate, which he observes consists of various metals intermixed.