118 PKOCEEDINGS OF THE SOCIETY. 



REPOET ON THE COLLECTION OF ME^JWLLUBGIdAL 

 SPECIMENS RECENTLY PRESENTED TO THE 

 SOCIETY BY DR. J. E. STEAD, F.R.S. 



By F. Ian (t. Rawlins. 



At the Meeting of this Society held in November 1919, Dr. .). F. 

 Stead, F.R.S., who was present, asked me to announce that he would be 

 willing to contribute a number of metallurgical microscope specimens to 

 our collection, of which the first instalment was given bv Sir Robert 

 Hadfield, Bart. 



Dr. Stead's valuable gift has now come into the Society's possession, 

 and, in accordance with the wish of the Council, it is proposed to exhibit 

 it at this meeting and to describe its outstanding features. 



A catalogue on the lines of that already issued will shortly be 

 available for the use of Fellows who wish to examine the collection. 

 IMeanwhile, it is pleasant to say that the specimens are of unique 

 interest, as being the actual material upon which Dr. Stead conducted 

 his classical researches on Blast Furnace Bears and the iron-carbon- 

 phosphorus system of alloys. 



The collection consists of eighteen micro- sections. A number of 

 these require polishing and etching, so that some delay may ensue before 

 they are ready, but those that do not require such treatment are on 

 view to-night. The method of differentiating the structure is that 

 known as heat-tinting. The piece of material is immersed in a small 

 bath of molten-lead, with the polished face upwards, just lying in the 

 liquid surface. The different constituents present oxidize at different 

 rates, forming, for a given temperature, characteristically coloured films. 

 The process can be stopped at any desired moment by removing the 

 specimen from the lead, and plunging it into mercury. As a method 

 of showing up the structure it is very perfect and beautiful, no 

 depressions or alteration of level of the surface beiug produced, such 

 as necessarilv occur with etching re-agents. It mav be pointed out 

 that the examination of such sections microscopically is attended with 

 some difficulty, as the light incident upon such a surface must be truly 

 normal, otherwise there is loss of illumination and also flare due to the 

 complete absence of minute shadows such as occur with etched slides. 



Before proceeding to a brief resume of the structures it might be 

 well to mention that the behaviour of phosphorus in iron and its alloys is 

 complicated, but in general it is as follows : In carbonless iron, a binary 

 eutectic Fe-^P (61 p.c.) and a saturated solution of FcgP in iron (;)9 p.c.) 

 occurs, but when carbon is present a ternary eutectic containing FcyP, 

 FcgC, and ferrite with small amounts of phosphorus in solution manifests 

 itself. This ternary eutectic is characteristic of white and mottled cast- 

 iron, but the binary eutectic (" Steadite ") is found in grey cast-irons, 

 even if the metal contains less than 1*7 p.c. C. 



