September S, 1910] 



NATURE 



0^0 



Per 



rbon 

 carbon.. 



3-7S 



Trace 



0-6.; 



Combined 

 Graphitic 

 Manganes 

 -Silicon ... ... ... ... ... ... 0-70 



-Sulphur 010 



Phosphorus 0-23 



It was crushed to powder and treated exactly in the same 

 way as previously described for the separation of carbide. 

 The residue contained by analysis : — 



Per cent. 



Silicon 0.028 



Sulphur ... ... ... ... ... ... 0-016 



a result showing that only a minute quantity of sulphur 

 was crystallised with the carbide. Whether a different 

 result would follow if both sulphur and manganese were 

 greatly increased has yet to be determined. 



Having proved that sulphur in some undetermined state 

 of chemical combination does crystallise with carbide of 

 iron, an attempt was made to determine the maximum 

 amount of that element the carbide will retain under the 

 most favourable conditions. With this object in view, a 

 considerable quantity of very pure white iron, containing 

 only traces of silicon, sulphur, and phosphorus, and 35 

 per cent, of carbon, was melted in a plumbago crucible, 

 and when in a molten condition sticks of roll sulphur were 





y 





Fig. 3. — Iron-Catbon-Siilphur .Mloy (4*37 per cent. 



Carbon). 



White thick bands= massive carbide of iron. 



Complex structure=iron — iron-carbide-»ulphide- 



pearlite eutectic. 



forced under the surface of the metal, and afterwards the 

 mixture was briskly shaken up with the sulphur which 

 had liquefied on the surface. 



Precisely the same result was obtained as described by 

 Karsten, who had made a similar experiment. A metal 

 was produced having a white fracture and large cleavage 

 faces. The micro-structure was similar to that of hyper- 

 eutectic iron carbon alloys. Large plates of carbide cut 

 th? metal in many directions, whilst between the carbide 

 plates was located the triple carbide-sulphide-pearlite 

 eutectic, so accurately described by Mr. Donald Levy. 



The carbide plates themselves were peculiar in having 

 circular prismatic inclusions of sulphide of iron symmetric- 

 ally arranged at right angles to the sides of the plates. 

 In horizontal sections of these plates they appeared as 

 circular dots, sometimes arranged in continuous lines, 

 suggesting that the sulphide had been actually in solution 

 with the carbide w'heix the metal was liquid, that they 

 fell out of solution together, the sulphide separating and 

 segregating along the cleavages of the carbide. 



\ portion of this sulphurous material was remelted and 



NO. 2132, VOL. 84] 



treated with a second quantity of sulphur. This time, in 

 addition to sulphide of iron, a considerable quantity of 

 the soot-like substance described by Karsten floated to the 

 surface, and free graphite separated and stuck to the sides 

 of the crucible. 



The analyses of these metals are as follows : — 



Afterlhe first After the second 



addition uf treatment with 



Sulphur Sulphur 



Carbon 



.Sulphur 

 Silicon .. 



Per 



Per < 



4 "39 



I '00 



o o; 



4'37 - ■ 



about I 00 



ooj 



From which we may conclude that the maximum degree 

 to which the carbon can be concentrated by this method 

 is about 4-4 per cent. In these trials the carbide certainly 

 had sufficient opportunity to become saturated w-ith sulphur 

 in each case. Both of the metals were crushed to exceed- 

 ingly fine powder, and were treated with acid to decom- 

 pose the free sulphides. The residues were repounded 

 and treated with acid a second time, and afterwards with 

 strong potash solution, .^fter this treatment, analyses of 

 the insoluble residues indicated in one case 0-09 per cent, 

 sulphur, and in the other o-oS per cent. From this it 

 would appear that carbides 7uill not carry in solid solution 

 more than about o-i per cent, of sulphur. 



b'la. 4. — Same as Fig. 2, heat-tinted and more highly 



magnified. 

 Broad bands = massive carbide of iron with inclusion of 



sulphide of iron. 



Comple.\ structure=joinled eutectic of Fe — FesC — FeS. 



The white specks are all FeS. 



The metal containing 4-37 per cent, carbon and i per 

 cent, sulphur, even on prolonged annealing, did not become 

 graphite, a proof that the massive carbides present were 

 quite stable. 



The microscope reveals the fact that in almost all com- 

 mercial white irons containing much sulphur the greater 

 part of the sulphur is combined with either manganese or 

 iron, and that the sulphides mainly exist as independent 

 inclusions. It appears reasonable to assume that the 

 manganese sulphide is without influence on the carbon 

 condition, and that, although iron sulphide may have some 

 influence, in the way suggested by Mr. Levy, on the 

 eutectic, it is the sulphur that crystallises with the carbide 

 which is mainly responsible in preventing the separation 

 of graphite by making the carbide more stable. 



If i^ is assumed that the stability of the carbide depends 

 on the quantity of sulphur which crystallises with it, and 

 not on the total amount present in the metal carrying the 

 carbides, it is clear that a great field of research is now 

 open, the borders of which I have barely touched to co- 

 relate their stability and sulphur contents. ; 



