342 M. Arfwedson on the Decomposition of [May, 



weight of Fe S° : : Fe S :: 100 : 46-82. I had thus obtained a 

 compound of an equai number of atoms of iron and sulphur ; 

 and consequently the body contained only half as much sulphur 

 as the compound, which we have hitherto called sulphuret of iron 

 at minimo. The increase of weight in the experiment with 

 sulphuretted hydrogen gas was too great to induce us to admit 

 that the product was Fe S- ; for the weight of Fe S : Fe S' : :: 

 0-367 : 0*450 ; whereas the experiment gave 0*474. But it is 

 known from Prof. Stromeyer's experiments,* that what we com- 

 monly call sulphuret of iron in minimo — a substance which may 

 be prepared artificially, and exists also as a natural production 

 known under the name of magnetic pyrites, is not Fe S" ; but a 

 compound which may be represented by the formula Fe S 4 -f- 

 6 Fe S 2 , so that it contains more sulphur than Fe S*. The con- 

 stituents per cent, of magnetic pyrites are : 



Iron 59-85 



Sulphur 40-15 



100-00 



Jn my experiment, 0-367 Fe S were operated upon, which 

 contain 0-283 iron ; the sulphuretted hydrogen gas augmented 

 the weight to 0-474. This new compound of course contains 

 0-283 iron and 0-191 sulphur, or in 100 parts, 59-7 iron and 40-3 

 sulphur. Thus the sulphuretted hydrogen had furnished the 

 quantity of sulphur requisite to convert Fe S into magnetic 

 pyrites. 



Subsulphate of Iron. 



This salt is obtained, as is known, when a smaller quantity of 

 caustic potash is added to a solution of persulphate of iron than 

 is requisite to separate the whole of the iron. As it contains 

 only one atom acid united to two atoms of the basis, I expected 

 that the hydrogen gas would have converted it into Fe- S. But 

 contrary to expectation, sulphurous acid and sulphuretted hydro- 

 gen were disengaged during its reduction 0-709 gr. prepared in 

 the above described way, and free from water, left for residue 

 0-422 gr. But a long time elapsed before the sulphuretted 

 hydrogen gas ceased to come over, although the mass was kept 

 in a full red heat. The matter was in appearance similar to 

 metallic iron, such as it is formed when the oxide is reduced by 

 hydrogen gas. It was acted on almost as strongly by the mag- 

 net as that, and was semimalleable, but it dissolved in muriatic 

 acid with the evolution of sulphuretted hydrogen. The quantity 

 of the reduced body, compared with that of the salt employed, 

 shows that the product was a compound of four atoms iron with 

 an atom of sulphur, or that the salt lost half of its sulphur, toge- 



• Gilbert's Ann. xviii. 186. 



