PEESIDENTIAL ADDRESS. 555 



elusions of sulphide of iron symmetrically 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 when the metal was liquid, that they 

 fell out of solution together, the sulphide separating and segregating along the 

 cleavages of the carbide. 



A portion of this sulphurous material was remelted and 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 : — ■ 



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 with sulphur in each case. 

 Both of the metals were crushed to exceedingly fine powder, and were treated 

 with acid to decompose the free sulphides. The residues were repounded and 

 treated with acid a second time, and afterwards with strong potash solution. 

 After this treatment, analyses of the insoluble residues indicated, in one case 

 009 per cent, sulphur, and in the other 008 per cent. From, this it would appear 

 that carbides will not crystallise with '.nore than about O'l per cent, of sulphur. 



The metal containing 4"37 per cent, carbon and 1 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 commercial 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 influ- 

 ence 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 it 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. 



The microscope does not show in what constituent the silicon crystallises. 

 It is known that in grey irons it is associated with the ferrite and pearlite. 

 but grey iron is the final result of the decomposition of carbide of iron and 

 possibly silico-carbides, which primarily form during solidification, and although 

 the silicon in the decomposed product may be entirely associated with the 

 iron it is no proof that initially some of it may not have crystallised with the 

 carbides. 



In the white Cleveland iron, previously referred to. it is probable that the 

 several constituents are present in the following proportions : — 



Per cent. 



Silico-pearlite, the residue of the or 



hcdral crystallites . 

 Iron carbide in plates 

 Iron, phospho-carbide eutectic 

 Manganese sulphide . 

 Iron sulphide . 



iginal austenite octa- 



42-50 



3366 



23-10 



0-38 



0-36 



100-00 



