556 TRANSACTIONS OF SECTION B. 



When fractionally dissolving the powdered metal in acid, it was the iron 

 and associated silicon of the pearlite which passed into solution, and the carbide 

 and phosphide which remained insoluble, and as these contained only 0-12 per 

 cent silicon, or about 0-06 per cent, on 100 parts of the original metal, it is 

 evident that the pearlite must have contained 1-89-0-06 = 1-83 per cent, of the 



silicon, or on 100 parts of it 100 * V 8 - = 4'3 per cent., and that about 97 per cent. 



42'5 

 of the total silicon had crystallised with the austenite. 



A little reflection will lead to the conclusion that if the carbon in the Cleve- 

 land white iron were to be gradually increased, the proportion of primary 

 austenite crystallites would decrease, there would be less and less of them 

 to carry the silicon, and this element would be concentrated in the diminishing 

 solid austenite. It also follows that if the carbon were to be so increased that 

 no primary austenite would form, the silicon would have to crystallise in some 

 other constituent. 



In the example, referred to above, of the chilled casting, the carbides con- 

 tained only 0-028 per cent, silicon, or - 016 per cent, on the original metal. In this 

 case, therefore, about 98 per cent, had crystallised with the primary austenite. 



The question as to what amount of silicon will crystallise with the austenite 

 so as to saturate it is probably variable with other variables. To determine 

 this by chemical analysis would involve an exceedingly tedious research. 



It is probable that as it increases, and as the austenite approaches more and 

 more nearly to the saturation point, a gradually increasing proportion of the 

 silicon will crystallise with the carbides. 



It is well known that molten low silicon grey irons, in the absence of any 

 appreciable quantity of sulphur, gives a white fracture when slightly chilled. 

 Irons with above five per cent silicon, when similarly treated, are supposed not 

 to behave in the same manner ; and this is quite true when any ordinary method 

 of chilling is adopted. For instance, when the liquid silicious glazed metal 

 No. 1 was run into water, the chilled iron contained graphite ; but when a 

 large drop was suddenly pressed into a sheet as thin as paper between cold 

 plates of iron, the chilled metal was quite white and no graphite could be 

 detected on dissolving it in nitric acid. The metal so chilled was difficult to 

 dissolve in acid, and the silica produced, instead of forming a gelatinous bulky 

 residue, remained in a close dense condition — indeed the thin chilled sheet, 

 after all soluble matter had been removed, remained a rigid sheet of dense 

 coherent silica, whereas the same metal allowed to cool slowly from the liquid 

 state in a sand mould yielded to acid gelatinous silica. 



The different behaviour to acid treatment of the chilled as contrasted with 

 that of the slowly-cooled metal indicates that the condition of the silicon in 

 rapidly chilled metal is different from its condition in the same metal slowly- 

 cooled. 



In 1895 Mr. T. W. Hogg, of Newburn Steel Works, published an account 

 of a very interesting observation, in which he showed the difference in the 

 silicon solubility in different parts of the same pig iron — a portion of which 

 was white and a portion grey. The iron referred to contained : — 



White part. Grey part. 



Per cent. . Per cent. 



Combined carbon . . . 3'88 1 . _., 0-98 i ..-_ 



Graphitic carbon . . . (M5 J i6i 3-68 J* 00 



Silicon 0-65 0-85 



Manganese .... 1-63 1-60 



He determined the solubility in dilute acid of the silicon in each portion, and 

 found that the silicon soluble in hydrochloric acid was, in the grey part= about 

 81 per cent, and in the white part = about 48 per cent. 



He found also that the silica left on treating the two varieties of metal in 

 acid differed in character — that from the white portion was dense, whilst that 

 from the grey metal was much more voluminous. The white metal contained 

 the eutectic proportion of carbon, and therefore it could not contain any 

 austenite crystallites ; indeed with the silicon 0'60 per cent, also present it must 

 be regarded as a hypereutectic alloy, and on that account we are forced to eon^ 

 elude that the silicon must have crystallised with the carbide. 



