116 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(1) escaping as gas (hardening carbon), (2) left as carbide, (3) left as free 

 carbon, denoted by Heyn as Cf. The maximum amount of carbon 

 existing in this state was found in the sample heated at 400° C. The 

 authors' main conclusions are : — (1) The transformation of marteusite into 

 pearlite by letting down a hardened steel is not continuous ; a definite, 

 well characterised intermediate phase is passed through. The name 

 " Osmondite " is proposed for this constituent. (2) Osmondite has the 

 highest solubility in dilute sulphuric acid. On solution in sulphuric 

 acid it gives the highest yield of free carbon. (8) On etching with 

 alcoholic acids, osmondite gives the darkest colour, as it is the separation 

 of this free carbon which colours the sample. (4) Quenching, rapid or 

 slow, is equivalent to perfect supercooling to pure marteusite, followed 

 by more or less tempering. The extent of the letting down depends on 

 the rate of cooling. According to the authors, the order of transition is 

 marteusite, troostite, osmondite, sorbite, pearlite. 



F. Osmond discusses this paper.* He suggests that the iron of 

 osmondite may be identical with Beilby's hard phase. He considers 

 that the properties of quenched steel may be due to all of the three 

 following causes : — (1) Retention of the carbon in the state of hardening 

 carbon ; (2) partial retention of the iron in an allotropic modification ; 

 (3) hardening by deformation caused by change in volume. Osmond 

 then gives definitions of the constituents of steel, having regard to 

 Heyn's results. 



The original papers should be consulted for a complete account of 

 the experiments leading to the remarkable conclusions here outlined. 



Iron-Carbon Alloys.f — P. Goerens discusses the equilibrium diagram 

 of the iron-carbon system, corrected by Roozeboom from the results of 

 Carpenter and Keeling. Heyn's view that all iron-carbon alloys tend to 

 decompose finally into iron and carbon, and that the presence of cementite 

 is due to supercooling, is supported by the author's experiments on three 

 alloys, A, B and C. They were prepared from Swedish iron and sugar- 

 carbon, A contained 8 • Do, B 4 • 5, C 4 • 8 p.c. carbon. They were cast 

 in thick-walled iron moulds, to give rapid solidification and cooling. 

 Microscopic examination showed that A was martensite-cementite eu- 

 tectic plus a little excess marteusite, B was practically pure eutectic, 

 C was eutectic plus a little excess cementite. In molten solutions the 

 carbon exists as carbide. A 4 • 7 p.c. alloy was cooled in a manner to 

 give incipient graphite formation. It consisted of martensite-cementite 

 eutectic with areas of excess marteusite through which ran veins of 

 graphite. The author elaborates a theory, according to which cementite 

 is formed on solidification, decomposing, if sufficient time at a high 

 temperature be allowed, yielding graphite. Remarkably clear photo- 

 micrographs support the author's conclusions. 



CiiARAGE, E. T. — The Manufacture of Tool Steel. 



English Mechanic, Ixxxiv. (1906) pp. 372-4. 



DoEBiNCKEL, F. — Alloys of Thallium with Copper and Aluminium. 



Zeitschr. Anorg. Chem., xlviii. (1906) pp. 185-90 (2 figs.). 



* Rev. M6tallm-gie, ill. (1906) pp. 621-32 (7 figs.). 

 t Tom. cit., pp. 175-86 (15 figs.). 



