WRITINQS OF JAMES SMITHSON. 66 



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 Valais, 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 cour 

 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 

 6 



