504 



XATURE 



[Sfi'temiier 8, igi; 



White Iron. 



The micro-structure and analysis help more fully to 

 explain the arrests on cooling this alloy. 



The first arrest, at 1144° C, is where the primary 

 austenite crystallises with the silicon, as will be shown 

 presently. 



The second arrest is where the primary cementite plates 

 freeze. 



The third arrest, at 945°, is the freezing point of the 

 ternary eutectic, and is identical with that of the corre- 

 sponding long arrest of the grey iron. 



The fourth arrest, at 77°, is coincident with the forma- 

 tion of pearlite. 



Bearing in mind that the manganese in the white iron 

 - was insufficient to combine with the whole of the sulphur 

 present to form manganese sulphide, it is obvious that 

 some other compound or compounds of sulphur e.xisted. 

 The microscope clearly revealed the presence of mangancLie 

 sulphide and traces of free iron sulphide. 



The carbide plates were quite free from striations of 

 sulphide, such as had been noticed by Mr. Levy in the 

 eutectic of high sulphur irons. 



But for the sulphur present, the silicon would have been 

 sufficient to effect a decomposition of the carbides, and 

 the metal in absence of the sulphur would have given a 



I I.,- 1.'- CkMUiri Wliile Iron 



White = massive plales of FejC, 



Dark — pearlite, the decomposed aust 



White and hall'-tone=ternary Ke— C— P 



grey instead of a white fracture. In view of this con- 

 clusion, it appeared to be probable that if manganese were 

 to be melted with the metal, it would combine with the 

 sulphur associated with iron, &c., and crystallise as MnS, 

 previous to the solidification of the carbide, or independ- 

 ently, and that the metal would then become grey on 

 cooling. 



In order to test this, a portion of the metal was melted 

 in a clay pot with a little pure manganese, free from 

 carbon — suflicient to give i per cent, of manganese, which 

 was more than sufficient to combine with the whole of the 

 sulphur. As soon as the mass was melted it was at once 

 poured into a sand mould and allowed to set. When 

 <;old, it broke with a grey fracture corresponding to what 

 is known as hard forge, and the coinbined carbon, instead 

 of being about 3 per cent., was reduced to o-6 per cent., 

 a result proving the correctness of the hypothesis. 



It is well known that when manganese or chromium 

 and some other metals are present in large quantities in 

 pig irons, these metals, as carbides, crystallise with the 

 carbide of iron, forming double carbides, and these are 

 much more stable than the massive pure iron carbide. 

 It appeared reasonable to believe that if sulphide of iron, 



NO. 2132, VOL. 84] 



or some iron-sulpho-carbon compound, were to crystallise 

 with the carbides it would have a similar effect. 



Remembering that the conclusions on this question, as 

 to whether sulphur does or does not crystallise with the 

 carbides, are conflicting, it is evident that the only possible 

 way to find out whether sulphur docs so crystallise is to 

 separate the carbide from the iron and test it for sulphur. 

 With this object, a considerable quantity of the original 

 Cleveland white metal was crushed to the vgry finest 

 powder. It was then treated with a 10 per cent, soluiion 

 of hydrochloric acid in water in large e.\cess, and the 

 action of the acid was allowed to continue until evolution 

 of gas ceased. The insoluble matters, consisting mainly 

 of carbides and phosphides, were filtered off, washed anil 

 dried, and were ground down in an agate mortar to a 

 still finer powder, so as to liberate any mechanically 

 entangled sulphides. The powder so dealt with was again 

 treated with acid as before, after which the residue was 

 filtered off, thoroughly washed with water, was trans- 

 ferred to a separate vessel, and was boiled with strong 

 caustic-potash to dissolve any decomposition products. 



The residue was again filtered off, was washed and 

 dried, and submitted to analysis. The residue when dried 

 weighed about 45 per cent, of the original metal, and 

 contained as follows : — 



100 -00 



A second trial was made with the same metal ; but, in 

 this case, repounding and acid treatinent were repeated 

 three times, so as to eliminate the possibility of mechanical 

 inclusion of sulphide or iron. The sulphur found in the 

 remaining carbides was o.i per cent. 



.As the manganese in this metal was not sufficient to 

 form manganese sulphide with the sulphur, it seemed 

 desirable to determine whether or not, when the man- 

 ganese is in sutTicient quantity, sulphur would crystallise 

 with the carbide. For this purpose the white chilled part 

 of a crushing roll was experimented upon. The centre 

 part was open grey iron, and contained 3'i per cent, of 

 the carbon as graphite. 



The white chilled portion contained : — 



