394 SUMMARY OF CURRENT RESEARCHES RELATING TO 



this carbon which the author terms troostite. The constituent con- 

 taining this separated carbon is osmondite. All the carbide of pearlite 

 or sorbite is dissolved at 850° C. ; carbide B begins to dissolve at higher 

 temperatures. The effect of reheating on quenched steels is destruction 

 of unstable equilibrium, resulting in the formation of sorbite. 



Thermomagnetic Analysis of Meteoric and Artificial Nickel-iron 

 Alloys.* — S. W. J. Smith has determined the magnetic permeability of 

 a sample cut from the Sacramento meteorite (7-8 p.c. nickel) and of an 

 artificial nickel-iron alloy (5 "8 p.c. nickel) at temperatures between 0° 

 and 850° C, under varying conditions of heating and cooling. The 

 meteorite consisted of kamacite, through which passed thin layers of 

 taenite. Taenite is assumed to be a eutectic, with about 27 p.c. nickel, 

 of (1) mixed crystals containing about 7 p.c. nickel (kamacite), and 

 (2) mixed crystals of much higher nickel content, probably not less 

 than 87 p.c. The temperature-concentration diagram, representing the 

 magnetic changes in the nickel-iron system, is held to be the equilibrium 

 diagram showing the crystallisation of these two series of mixed crystals 

 from a homogeneous solid solution. From his results the author 

 deduces a theory explanatory of the irreversibility of nickel-iron alloys. 

 Irreversibility is held to be due to supersaturation. As the homogeneous 

 solid solution is cooled, a point is reached at which it is saturated, and 

 if nuclei of the mixed crystals which should separate were present, 

 separation would commence. But the solution remains supersaturated 

 (metastable) through a temperature interval. A lower point is then 

 reached, at which the labile succeeds the metastable state. Crystallisa- 

 tion then necessarily begins. 



Alloys of Gold and Tellurium.! — T. K. Rose has determined the 

 equilibrium diagram. One compound, AuTe 2 or Au 2 Te 4 (melting point 

 452° C), and two eutectics, with 20 and GO p.c. gold respectively, occur. 



Platinum-thallium Alloy. t — Thermal, microscopic, and chemical 

 investigations of the alloys produced by dissolving platinum in molten 

 thallium, lead L. Hackspill to assert the existence of the compound 

 PtTl, the properties of which are described. It melts at 685° C, and 

 is analogous to PtPb. 



^ 



Austenite.§ — Owing to the failure of numerous attempts to produce 



austenite in pure iron-carbon alloys, E. Maurer tried to obtain this 



constituent in three steels of the following composition : — 



12 3 



Nickel 3-73 p.c. 



Manganese 



Carbon 



Silicon 



Martensite was obtained in Xos. 1 and 2 by heating at 1050° C. for 

 15 minutes, and quenching in ice water, while No. 3 yielded pure 



* Phil. Trans. Roy. Soc, Series A. ccviii. (1908) pp. 21-109 (31 figs.). 

 t Journ. Soc. Chem. Ind., xxvii. (1908) p. 229. See also Bull. Inst. Min. and 

 Metallurgy, 1908. 



X Comptes Kendus, cxlvi. (1908) pp. 820-2. § Tom. cit., pp. 822-6. 



