ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 791 



from either liquid or solid solution in iron. The metastable iron-carbide 

 always tends to decompose into carbon and iron. The effect of foreign 

 elements upon the diagram is considered. 



Effect of Low Temperature on Iron-carbon Alloys.* — C. W. Wag- 

 goner has determined the magnetic permeability and the magnetic 

 hysteresis of seven iron-carbon alloys containing - 6 to 1-37 p.c. 

 carbon, and of iron containing 0'06 p.c. carbon, at liquid air tempera- 

 ture and at 20° C. The mean coefficient of linear expansion was deter- 

 mined from room temperature to liquid air temperature, and was found 

 to decrease with increase of carbon. 



Cementation by Gases.f — J. 0. Olsen and J. S. Weissenbach have 

 determined the depth and intensity of cementation of iron rods heated 

 in illuminating gas, methane, carbon monoxide, and acetylene. In one 

 series of experiments ammonia gas was added to the gaseous cementation 

 medium, and was found to facilitate the absorption of carbon by the 

 steel except in the case of carbon monoxide. Of the three pure gases, 

 carbon monoxide is the most efficient in cementation. 



Heat Treatment of Special Steels. 1; — L. Guillet classifies alloy- 

 steels, and gives some generalizations as to their treatment. In nickel- 

 and silicon-steels, the carbide goes into solution less readily than in 

 other steels, while annealing at high temperatures appears to have a 

 much less injurious effect than in the case of carbon steels. Other 

 special steels are more sensitive to such annealing. The quenching of 

 polyhedric steels at 1000° C, so frequently practised, appears to be 

 highly injurious. The author has found in steels so treated a coarse 

 network resembling that observed in " burnt " steels. 



Thermal Treatment of Cemented Steel. § — L. Guillet recommends 

 the double quenching of cemented articles, the first from a high tem- 

 perature (up to 1000° C.) to restore the structure and qualities of the 

 body of the steel, the second quenching from 750° C, or thereabouts, to 

 harden, and produce a fine structure in, the carbonized layer on the 

 surface. The tempering of hardened cemented steel at about 200° C. 

 has been found to improve its qualities. 



Artificial Reproduction of Widmanstatten Figures. || — X. Belaiew 

 has obtained meteorite-like structures in medium carbon steels by heating 

 the molten metal to a high temperature and cooling it very slowly. The 

 Widmanstatten structure was sufficiently coarse to be perceived by the 

 unaided eye. The author attempts a theoretical explanation of the 

 formation of this structure in meteorites, which are natural iron-nickel 

 alloys. 



"Strain-disease" in Steel. % — After referring to Cohen's investiga- 

 tion of the effect of cold-working upon tin, G, Charpy points out that 

 the growth of the ferrite grains in annealing is much more rapid in steel 



* Physical Review, xxviii. (1909) pp. 393-404 (6 figs.). 



t American Machinist, xxxii. (1909) pt. 2, pp. 156-8 (1 fig!). 



X Rev. Metallurgie, vii. (1910) pp. 489-95. 



§ Tom. cit., pp. 501-9 (16 figs.). || Tom. cit., pp. 510-21 (15 figs.). 



^ Tom. cit., pp. 655-6. 



