198 SULPHURETS. 



Lead, 17. Sulphuret of lead. There are two sul- 



phurets of lead, both of which I have met with 

 native. 



(1.) Protosulphuret of lead is common galena, 

 a well known ore of lead. It has a bluish white 

 colour, the metallic lustre, is crystallized in 

 cubes, very heavy, and very brittle; it melts 

 easily when heated, but does not part with any 

 of its sulphur. Its constituents are 



1 atom lead . . 13 



1 atom sulphur . 2 



15 



(2.) About 20 years ago, I got a specimen of 

 galena from Sir John Sinclair, which had the 

 property of burning with a blue flame when held 

 to the flame of a candle. When distilled, it 

 gave out a quantity of sulphur. I did not sub- 

 ject it to analysis ; but, from these properties, it 

 was obviously either a sesquisulphuret or bisul- 

 phuret of lead. 



(3.) Berthier has shown that, when sulphate 

 of lead is exposed to a strong heat in a charcoal 

 crucible, it is converted into a disulphuret of 

 lead, composed of 



2 atoms lead . . 26 

 1 atom sulphur . 2 



28 



