ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 125 



slow cooling between 1030° and 855° C, while the hard condition and 

 duplex structure resulted from rapid cooling through this interval. 



Metallic Silicides.* — L. Baraduc-Muller, in the course of an ex- 

 tended investigation of the action of silicon carbide on metallic oxides 

 at high temperatures, and of the properties of the metallic silicides pro- 

 duced, has studied the metallography of these bodies. Two etching 

 reagents were used : (1) commercial hydrofluoric acid, to which was added 

 twice its volume of alcohol, and an amount of water depending on the 

 rapidity of action required ; addition of water increases the activity of 

 the reagent ; (2) a preparation of aqua regia and ferric chloride. The 

 method of taking cooling curves is described, and some account of the 

 microstructure of alloys of silicon with numerous metals is given. 



Impurities in Copper. f — F. Johnson summarizes the available in- 

 formation as to the effect of arsenic, lead, nickel, bismuth, cobalt, antimony, 

 tellurium, iron, tin, silver, sulphur, and oxygen occurring as impurities 

 in copper. 



Solubility of Oxygen in Molten Silver.}— F.Gr. Donnan and T.W.A. 

 Shaw find that the concentration of oxygen in molten silver is propor- 

 tional to the square root of the oxygen-pressure over a wide range of 

 pressures. From this it is inferred that the oxygen is either physically 

 dissolved as atomic oxygen, or more probably exists in the form of dis- 

 solved silver monoxide. 



Crystallography of the Iron-carbon System. § — A. Kroll has sought 

 to establish the relation existing between the crystallography and the 

 equilibrium diagram of the iron-carbon system. The main experimental 

 method employed consisted in heating polished sections in an atmosphere 

 of hydrogen or nitrogen ; the different structures resulting are identified 

 as the effects of the more or less sudden crystalline rearrangements taking 

 place at the thermal critical points. A crystallographical explanation of 

 the formation of troostite and of the precipitation of graphite is attempted. 

 Ordinary cementite appears to be hexagonal, but the carbide entering 

 into solution in y-iron is regular ; troostite is this solution-carbide 

 saturated with y-iron. 



Iron-carbon Alloys. || — H. Liitke has investigated the effect of man- 

 ganese on the concentration at the eutectic temperature (1130° C. in the 

 iron-carbon system) of the saturated solid solution of cementite in y-iron. 

 Two series of alloys, containing respectively about 5 p.c. and 10 p.c. of 

 manganese, the carbon ranging from 1*5 to 4 p.c. in each series, were 

 examined thermally and microscopically. While in both series the cooling 

 curves indicated the first appearance of eutectic at 2 * to 2 • 3 p.c. carbon, 

 the microscopical examination showed that 1 • 8 p.c. was the concentration 

 of the saturated mixed crystals. Manganese, therefore, appears to have 

 little influence on the carbon-concentration of the saturated solid solution. 



* Rev. Metallurgie, vii. (1910) pp. 657-834 (44 figs.). 



t Met. and Chem. Eng., viii. (1910) pp. 570-5 (9. figs.). 



j Journ. Soc. Chem. Ind., xxix. (1910) pp. 987-9 (1 fig.). 



§ Journ. Iron and Steel Inst., lxxxi. (1910) pp. 304-402 (33 figs.). 



|| Metallurgie, vii. (1910) pp. 268-73 (7 figs.). 



