SULPHURETS. 191 



cess of sulphur is driven oft'. It has a pale yellow 

 colour, and I have sometimes obtained it in small 

 crystals it is attracted by the magnet. This 

 sulphuret may be obtained, likewise, by mixing a 

 solution of protosulphate of iron with hydrosul- 

 phuret of potash : a black precipitate falls, which 

 is a protosulphuret of iron. Its constituents are 



1 atom iron . . . 3-5 

 1 atom sulphur . . 2 



5-5 



(2.) The sesquisulphuret of iron is obtained 

 when a solution of neutral persulphate of iron is 

 precipitated by hydrosulphuret of potash, it is 

 necessary to drop the iron solution into the hy- 

 drosulphuret : if we reverse the process, the 

 powder which falls is a protosulphuret of iron. 

 The sesquisulphuret of iron is a black powder, 

 which has not been much examined. Its consti- 

 tuents are 



1 atpm iron . . 3-5 



IJ atom sulphur . . 3 



(3.) Persulphuret of iron is found native, and 

 is known by the name of iron pyrites. It is a 

 brass yellow substance, having the metallic lus- 

 tre, and usually crystallized in cubes, either 

 smooth or striated it is not the least attracted 



