207 



distilled, left a blackish brown substance, weighing 49 grains. Thia 

 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. 



On the Discovery of Palladium ; with Observations on other Substances 

 found with Platina. By William Hyde Wollaston, M.D. Sec. R.S. 

 Read July 4, 1805. [Phil. Trans. 1805, p. 316.] 



In this paper the author relates circumstantially the series of ope- 

 rations 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 platina, of making many observations that have not oc- 

 curred 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 only. 



These grains, which he considers as the proper ore of iridium mi- 

 neralized 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 these he gives a particular description, but 

 does not undertake the analysis, on account of the veiy small quan- 

 tity 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 ammo- 

 niac, and the remainder in an impure state by iron, a second metallic 

 precipitate, which he observes consists of various metals intermixed. 



