Mineral Sulphides of Irorb. 213 



enz's description completely, but they were not ferrous sulphide. 

 The first, formed at 850° from soft iron wire, had a specific 

 gravity at 25° of 4*739, corresponding to a specific volume (4°) 

 of 0-2116. The second, formed at 950°, had a sp. gr. of 4*748, 

 corresponding to a specific volume of 0*2112. Making no 

 allowance for the impurities in the iron, we calculate from 

 these numbers (see p. 198) 1*1 per cent and 0*9 per cent of dis- 

 solved sulphur respectively. The diffusion of sulphur into the 

 iron is evidently too slow here to give a homogeneous product. 

 An examination of these crystals under the microscope, 

 for which the authors are indebted to Dr. F. E. Wright, 

 showed that they were either hexagonal' or pseudohexagonal, 

 but they were not adapted to measurement on the goniometer. 



Efforts to prepare ferrous sulphide in the wet way were no 

 more successful. Weinschenk* claims to have formed it by 

 the action of hydrogen sulphide on a solution of ferrous 

 chloride in sealed tubes. The product consisted of microscopic 

 hexagonal plates, which Weinschenk states did not lose sulphur 

 when heated to redness in hydrogen and therefore were fer- 

 rous sulphide. His experimental work is doubtless in error, 

 for Habermehl,f many years earlier, had shown that pyrrhotite 

 under these conditions loses sulphur continuously and gradually 

 approaches pure iron. 



Weinschenk's work was repeated by us. Pure ferrous 

 chloride was prepared repeatedly with much care, dissolved in 

 an aqueous solution of carbon dioxide and subjected to the action 

 of hydrogen sulphide, made in several ways (by the action of 

 the water on sodium thiosulphate ; and by the action of dilute 

 sulphuric acid on ammonium thiocyanate). In no case was pure 

 ferrous sulphide obtained. Free sulphur, either from secondary 

 reactions or perhaps from the dissociation of hydrogen sulphide, 

 even at 200°, always appeared to give pyrrhotite. After our 

 further experience in heating pyrrhotite in vacuo, we state with 

 confidence that pure ferrous sulphide has doubtless never been 

 made. 



Mineralogically, troilite has no claim to a separate mineral 

 species any more than have pyrrhotites of different composi- 

 tion ; it is simply the end member of the series of solid solu- 

 tions. This is abundantly attested by the synthetic evidence 

 submitted in the foregoing pages. It may also be noted by 

 way of further evidence that the specific gravity of natural 

 troilite or rather the specific volume calculated from it, agrees 

 tolerably well with the extrapolated value in fig. 7, and the best 

 crystallographies work on troilite, imperfect though the 

 material was, indicates that it is hexagonal, as it should be. 



* Zs. Krvst., xvii, 499, 1890. f Loc. cit, 



X Linck,"Ber., xxxii, 895, 1899. 



