Decomposition of Iron Pyrites. 307 



heating ferric oxide with excess of sulphur, and removing the 

 excess of the latter by heating in dry hydrogen, obtained it as a 

 porous and blebby net- work of little flakes and plates, with a 

 specific gravity of 4.726, in coarse powder at 9.°8 C. 



These forms are readily soluble in dilute acids, with evolution 

 of hydrogen sulphide ; but if prepared by ignition of ferric 

 oxide in an atmosphere of hydrogen sulphide, it is found to be 

 insoluble in cold dilute hydrochloric acid. 5 



A hydrated form, Fe S, H 2 0, can be prepared, which is solu- 

 ble in dilute acids, even to some degree in carbonic and organic 

 acids. 



Iron disulphide, Fe S 2 . Wohler heated slowly an intimate 

 mixture of ferric oxide, sulphur and sal ammoniac, above the 

 temperature at which the last substance volatilizes, and obtained 

 the disulphide in small brass yellow octahedra and cubes. Ram- 

 melsberg. 6 by reduction of ferric oxide in hydrogen, and heating 

 with sulphur below ignition, obtained the disulphide. In 

 neither case is the density reported. It is not attacked by di- 

 lute acids or by cold concentrated sulphuric acid, but readily 

 decomposed and dissolved, with separation of sulphur, by nitric 

 acid, aqua regia, and boiling concentrated sulphuric acid. 7 



A third intermediate compound, iron sesquisulphide, or 

 diferric trisulphide, Fe 2 S 3 , has been formed artificially. It 

 has been prepared by Rammelsberg, by gently heating iron and 

 sulphur together, as a powdery mass of specific gravity 4.41 ; 

 also, by the action of hydrogen sulphide on ferric oxide at 

 a temperature below 100° 0. If obtained at a red heat, it 

 forms a yellow, non-magnetic, metallic mass, which has a spe- 

 cific gravity 4.4, and is decomposed by dilute sulphuric and 

 hydrochloric acids into hydrogen sulphide, ferrous sulphate, and 

 iron disulphide. 8 



Gray, bronze-colored and bronze-yellow powders have been 

 also prepared by Rammelsberg and Proust, which are magnetic, 

 possess the composition Fe 7 S 8 , and in one case a specific gravity 



5 Ebelmen, Ann. Ch. et Phys. (3), XXV, 97. 



6 Loc. cit. 



7 Berzelius, Lehrb., II, 723—725. 



8 Berzelius, loc. cit. 



