PRESIDENTIAL ADDRESS. 551 



Gontermann 1 found that on adding pure silicon to molten iron, the iron and 

 silicon combined with considerable rise in temperature, and I have noticed the 

 same thing even when adding it to carburised iron. 



The same authority, who has made a most careful study of the ternary alloys 

 of the iron-carbon-silicon series, has shown that the eutectic freezing-point rises 

 with the silicon from 1130° when silicon is absent, to about 1150° when it 

 reaches 10 per cent., and to 1175° when it is about 17 per cent., and that the 

 carbon in the eutectic of the alloys containing between per cent, and 10 per cent, 

 silicon, falls as the silicon rises by about 03 per cent, for each unit of silicon. 



The same author proved that the pearlite reversion-point in these alloys 

 rises with the silicon on an average of about 30° C. for each unit of silicon in 

 the alloys containing between 0° and 6 per cent, silicon. He concluded, but 

 did not actually prove, that in the region of the curve of unvarying equilibrium 

 two cementites crystallise ; one a solid solution of the carbide and silicide of 

 iron; and a second, a mixture of this with another ternary iron-silicon-carbon 

 solid solution. 



If the composition of the alloy lies between the curve of saturated silico- 

 austenite and the curve of non-varying equilibrium, saturated silico-austenite 

 primarily forms ; and following this a secondary crystallisation of a binary 

 eutectic consisting of this saturated austenite and silico-cementite. 



In the year 1901 I described certain unique idiomorphic crystals which had 

 been found in the hearth of a disused blast-furnace at Blaina. The crystals 

 were more or less oxidised on their exterior surfaces. 

 The analysis was as follows : — 



After deducting the 

 Oxygen, &c. 

 Per cent. 



Manganese 54-56 



Iron 37-71 



Carbon 391 



Silicon 3-82 



100-00 



A micro-examination proved the crystals to be quite homogeneous mixtures, or 

 solid solutions. It was difficult to assign to them any definite chemical consti- 

 tution. They may be considered as silico-carbides of manganese and iron, and, 

 as will be shown presently, bear a close relation to similar crystals which 

 primarily form during the freezing of iron-carbon-silicon alloys. 



Having briefly referred to the work of a number of authorities, I now propose 

 to describe my attempts to supplement our knowledge in this direction by a 

 purely micro-chemical research. 



In order to understand the remarks which follow, it is necessary briefly to 

 describe the changes which occur when pure iron-iron carbide alloys pass from 

 the liquid to the solid state as are indicated by the researches of Osmond, 

 Eoberts-Austen, Stansfield, and of Carpenter and Kneeling 



In the iron alloys containing less than the eutectic proportion of 4-3 per cent, 

 carbon, described as hypo-eutectic alloys, austenite octahedral crystallites of 

 the fir-tree type first fall out of solution, and these continue to grow till the 

 liquid is so impoverished of iron and enriched in carbon that when the eutectic 

 proportion of 4'3 per cent, carbon is reached, the liquid solidifies and breaks 

 up into carbide of iron and austenite. 



The hypereutectic alloys, containing more than the eutectic proportion of 

 carbon, on cooling, first yield carbide of iron crystals, and these continue to 

 grow till, by removal of the excess carbon, the eutectic proportions of iron and 

 carbon are reached. The eutectic in its turn then freezes. 



For the purpose of my research it was necessary to select pig metals, grey 

 and high in silicon and white with high sulphur. These were kindly supplied 



1 Anorganische Chemie, Bd. 59, 1908. 



