ZOOLOGY AND BOTANY, MICROSCOPY", ETC. 271 



Theory of Hardening Carbon Steels.* — C. A. Edwards examines the 

 available data relating to the hardening of carbon steels by quenching, 

 in the light of the phase rule and the theory of alloys, and concludes 

 that the hardening is due to the retention of the solid solution of carbide 

 of iron in y-iron. The theory that the hardening is the result of the 

 retention of /3-iron is held to be untenable. The suggestion is made 

 that there is no constitutional difference between the so-called austenite 

 and martensite. and that the apparent difference is due to the twinning 

 of the y solid solution crystals, caused by the mechanical pressure 

 absorbed in suppressing the decomposition of this solution into a-iron 

 and carbide of iron. The author's views met with both support and 

 criticism in the discussion. 



Hardening of Carbon and Low-tungsten Tool-steels. f — S. N. 

 Brayshaw has submitted two varieties of steel to a lengthy series of 

 experiments, the results of which are chiefly of workshop interest. Both 

 steels contained about 1*15 p.c. carbon; one contained - 5 p.c. 

 tungsten, the other no tungsten. Heating and cooling curves, with 

 different rates of change of temperature and different maximum tempera- 

 tures, were taken ; the effect of each variable is considered. The range 

 of temperature within which the best results could be obtained in 

 hardening, was determined. The effect upon physical properties of 

 variations in temperature of the steel before quenching and of the quench- 

 ing medium was investigated, as well as the effect of length of time of 

 heating. 



Slag in Steel.} — Matweieff, continuing on the lines of his previous 

 work,§ has investigated the rnetallographical characteristics of the 

 phosphates of calcium, magnesium, manganese, and iron, and calcium 

 ferrite. All these bodies may occur in basic Bessemer steel as inter- 

 mixed slag. The compounds, either singly, or mixed with each other 

 or with oxides, were enclosed in small hollow cylinders of steel closed 

 with s'eel plugs ; the cylinders were then heated to 1300° C. After 

 cooling, transverse sections were cut and polished, so that both the 

 envelope and the juxtaposed contained matter could be examined. 

 Calcium phosphate did not melt, and had no action on the steel enve- 

 lope. The other three phosphates were reduced by the iron, and some 

 phosphide of iron was formed. As a result of this work, three new 

 etching reagents are recommended : 1. A 2 p.c. solution of ammonium 

 oxalate, which slowly attacks cementite in the cold, giving a red colora- 

 tion after 30 minutes. 2. A boiling solution of neutral sodium picrate, 

 which colours phosphide of iron after 30 minutes, leaving cementite, 

 ferrite, the solid solution of phosphide of iron in iron, and pearlite, 

 unaffected. 3. A 2 p.c. solution of ammonium carbonate ; in specimens 

 heated in this reagent for 20 minutes on a water-bath, the slags formed 

 in dephosphorizing are disintegrated, while the metallic surface is 



* Joum. Iron and Steel Inst , lxxxii. (1910) pp. 147-96 (17 figs.), 

 t Proc. Inst. Mech. Eng. (1910) 2, pp. 517-710 (62 figs.). 

 t Rev. Metallurgie, vii. (1910) pp. 848-58 (27 figs.). 

 § See this Journal, 1910, p. 794. 



