IRON. 349 



phuric acid, they combine with 1 grain of oxy- 

 gen. Now, by this solution, the iron is convert- 

 ed into protoxide ; consequently, protoxide of 

 iron is composed of 



Iron . 3-5 



Oxygen . 1 



4-5 



1 being the atomic weight of an atom of oxy- 

 gen, 3'5 must be the weight of an atom of iron ; 

 and the atomic weight of protoxide of iron is 

 obviously 4%5. 



4. Iron and sulphur unite together in two Sulphuret 

 proportions, forming the protosulphuret and per- f n ana - 

 sulphuret of iron. The former is called by mi- 

 neralogists magnetic pyrites, because, when in 

 powder, it is attracted by the magnet. The lat- 

 ter is called cubic pyrites, because it usually 

 crystallizes in cubes. The protosulphuret of iron 

 may be formed artificially, by mixing together 

 iron filings and sulphur, and exposing the mix- 

 ture for some time to a red heat, in a well cover- 

 ed crucible. The mixture fuses, and the excess 

 of sulphur is gradually driven off, and protosul- 

 phuret of iron remains. This sulphuret, when 

 in crystals, has a yellow colour, the metallic 

 lustre, and a specific gravity of about 4i. 



When it is reduced to powder, and digested 

 for a sufficient length of time in nitric acid, the 



