331 



thought it deserved particular examination, although the quantity 

 which he could obtain was too small for accurate analysis. 



The appearance of this mineral is whiter than Peruvian platina ; 

 the grains are rougher and more angular, being evidently fragments 

 of larger masses, very little worn at their surfaces. When examined 

 by solution and precipitation, the greatest part of the grains appeared 

 to be platina nearly pure, as they are free from iron, which forms a 

 considerable part of the Peruvian ore ; and apparently free from the 

 several metals, which have within these few years been discovered 

 in that mineral ; but they contain, on the contrary, a small quantity 

 of gold, which is not contained in the grains of Peruvian platina. 



The author discovered also, among the grains of native platina, a 

 few fragments of native palladium, which he describes as resembling, 

 in the whiteness of their colour, the grains of platina, but differing 

 from them in presenting an appearance of fibres diverging from one 

 extremity. These grains are readily detected by their solubility, and 

 by the red colour of the solution : that they consisted of palladium, 

 was proved by precipitation with prussiate of mercury, or green sul- 

 phate of iron, as well as by their fusibility by assistance of sulphur. 

 It is remarked, however, that these grains are not absolutely pure, 

 but contain a very small quantity of platina, which, by its redness 

 when precipitated, seems to be contaminated by iridium. 



On a native Arseniate of Lead. By the Rev. William Gregor. Com- 

 municated by Charles Hatchett, Esq. F.R.S. Read April 13, 1809. 

 [Phil. Trans. 1809, p. 195.] 



The mineral of which this account is given was raised in a very 

 rich copper- mine called Huel- Unity, in the parish of Gwennap, having 

 been found at the depth of fifty fathoms, at the junction of two small 

 lodes or veins. This ore is mixed with some native copper, very 

 rich gray copper, and black copper ore. 



It crystallizes in the form of a hexahedral prism, terminated in 

 general by a plane, but sometimes by a taper six-sided pyramid. 

 The colour is generally a shade of yellow, but sometimes wine- 

 yellow, like the Brazilian topaz, and sometimes as dark as brown 

 sugar-candy. The hardness varies, and is sometimes sufficient to 

 scratch flint-glass. The specific gravity at 50 temperature is 6'41. 



Being exposed to heat upon a gold spoon, it melts into a brownish- 

 yellow mass, and remains unaltered in a state of ignition. But if 

 heated upon charcoal, it is rapidly decomposed, arsenical vapours 

 being extricated, while the lead is reduced to its metallic state. 



The mode of analysis adopted by the author consisted in reducing 

 the ore to a fine powder, and decomposing it by a solution of pure 

 potash, with due precaution to avoid the solution of lead by the 

 alkali along with the arsenic acid. The arseniate of potash was de- 

 composed by nitrate of lead, which gave an arseniate of lead, con- 

 sisting of known proportions, from which the quantity of arsenic acid 

 in the ore was found to be 26 - 4 per cent. 



