PRESIDENTIAL ADDRESS. 



553 



The third arrest at 945° is the freezing-point of the ternary eutectic, and 

 is identical with that of the corresponding long arrest of the grey iron. 



The fourth arrest at 770° is coincident with the formation 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 



Diagram showing arrest in cooling ; grey iron No. 2 on left, 

 white iron on right. 



obvious that some other compound or compounds of sulphur existed. The 

 microscope clearly revealed the presence of manganese 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 grey instead of a white fracture. In view of this conclusion 

 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 independently, 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 — sufficient to give one per cent, of manga- 

 nese, 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 cold, it broke with a grey fracture corresponding to 

 what is known as hard forge, and the combined carbon instead of being about 

 three per cent, was reduced to 0'6 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, 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 does so crystallise is to separate 

 the carbide from the iron and test it for sulphur. With thi6 object, a consider- 

 able quantity of the original Cleveland white metal was crushed to the very finest 

 powder. It was then treated with a 10 per cent, solution of hydrochloric acid in 

 water in large excess, and the action of the acid was allowed to continue until 



