ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 253 



held to be tlie stable system resulting upon extremely slow cooling, while 

 iron-cementite is the metastable system obtained by more rapid cooling. 

 The eutectic point for the latter occurs at 4 • 2 p.c. carbon. Transition 

 from the metastable to the stable system takes place upon annealing at 

 a suitable temperature. Graphite may be formed directly from the melt 

 during solidification. The decomposition of cementite is catalytically 

 accelerated by silicon. The author examined microscopically a number 

 of pig-irons of different carbon content : his photomicrographs support 

 the above conclusions. An explanation, consistent with the theory of 

 equilibrium, of the possibility of cementing iron to a high percentage of 

 carbon by heating in contact with carbon, is given. A useful feature 

 of the paper is the bibliography appended. 



Heat Treatment of High Carbon Steels.* — W. Campbell has in- 

 vestigated the eifect of heating to different temperatures, followed by 

 slow cooling, on the mechanical properties and microstructure of six 

 steels containing (V7-2 p.c. carbon. The temperatures ranged from 

 650°-1200° C. ; the initial condition of the bars appears to have been 

 as forged to a small section. The tendency of cementite to assume a 

 globular form is noted. When a sufficiently high temperature is reached 

 (1000°- 1200° C), cementite remaining undissolved decomposes into 

 ferrite -j- graphite. Generally tenacity was found to diminish and ductility 

 to increase with increase of temperature of reheating up to Ac 1 . Little- 

 further change occurred until much higher temperatures were reached,, 

 when overheating effects were apparent. 



Constitution of the Copper-Tin Alloys.f — E. S. Shepherd and 

 E. Blough have made a careful revision of the concentration-temperature 

 diagram. The composition of the solid phases was determined by the 

 analytical method of Bancroft, lead being used as the third component.. 

 Heycock and Neville's diagram was considerably modified in certain 

 regions. The chief results are (1) the phases which can co-exist with the 

 melt are the a, (3, and y solid solutions, the compound CugSn, the e solid 

 solution, and pure tin ; (2) below 600° C. the 8 solid solution, previously 

 supposed to be CUiSn, can exist. The authors indicate the great impor- 

 tance of the time factor in establishing equilibrium relations, and the 

 impossibility of constructing diagrams solely from pyi'ometric data. 



Photographs, showing the structures characteristic of each region,, 

 will be given in a later paper. 



Influence of Chromium on the Solubility of Carbon in Iron, and 

 on Graphite Formation. J — P. Goerens and A. Stadeler regard it as 

 proved that in irou-chromium-carbon alloys part of the chromium exists- 

 as a double carbide of iron and chromium, the rest being present in solid 

 solution in the iron. The authors have prepared a series of alloys 

 saturated with carbon at 1600° C, and have determined carbon content 

 and taken cooling curves. With increasing chromium content, more 

 carbon is required for saturation, the alloy with 62 p.c. chromium con- 

 taining 9-2 p.c. carbon. The alloys with 0-10*4 p.c chromium have a. 



* Journ. Amer. Chem. Soc, xxviii. (1906) pp. 1304-22 (29 figs.). 

 t Journ. Phys. Chem , x. (1906) pp. 630-53 (6 figs.). 

 X Metallurgie, iv. (1907) pp. 18-24 (17 figs.). 



