WRITINGS OF JAMES SMITHSON. 65 



ON A NATIVE COMPOUND OF SULPHURET OF 

 LEAD AND ARSENIC. 



From Thomson's Annals of Philosophy, Vol. XIV., 1819, p. 96. 



PARIS, May 19, 1819. 



This mineral is found in Upper Yalais, in Switzerland. 

 It is lodged in a white, granose, compound carbonate of 

 lime and magnesia. It is accompanied in this rock by reg- 

 ular crystals of yellow sulphuret of iron ; by red sulphuret 

 of arsenic ; and by some other substances. 



This compound sulphuret has a metallic aspect. It is of 

 a grey colour ; it is exceedingly brittle and soft ; its fracture 

 in some directions is perfectly vitreous ; but in at least one 

 direction, it is evidently tabular; but the size of the frag- 

 ments I had, not exceeding coarse sand, precluded research 

 with respect to crystalline construction. By trituration, 

 this ore afforded a red powder. 



At the blow-pipe, this ore melted instantly on the con- 

 tact of the point- of the flame. It smoked considerably ; 

 and a small flame was visible on the surface of the melted 

 button. On cooling, this button forced out a quantity of 

 fluid matter from its interior. During the fusion, the bead 

 occasionally swelled up, and puffs of dense smoke issued 

 from it ; due evidently to a volatile matter, which the fire 

 expelled from another less volatile. Finally, a button of a 

 more fixed, less fusible, white metallic matter, extensible 

 under the hammer, was. left, and which proved to be lead. 



Some bits of this compound sulphuret heated in a tube 

 over a candle, melted, and a red sublimate rose, which be- 

 came yellow on cooling, and looked like orpiment. 



Some of this ore, being fused with nitre, deflagrated, and 

 became a white oxide. The solution of this nitre afforded 

 a white precipitate with muriate of barytes ; and with 



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