ZOOLOGY AND BOTANY, MICROSCOPY, ETC. t'>'"'0 



Application of Colour-photography to Metallography.* - - E. F. 

 Law draws attention to the unsatisfactory character of ordinary photo- 

 graphs of metal sections in which the constituents have been distinguished 

 by differential colouring. Coloured sections are obtained by heat-tinting, 

 by allowing the polished surface to tarnish by exposure to the atmo- 

 sphere, or by heating the specimen in air containing iodine, bromine, or 

 sulphuretted hydrogen. Photomicrographs of such sections in their 

 natural colours are given by the Lumiere process. A colour-photograph 

 can be taken, developed, dried, and bound as a lantern-slide in less than 

 one hour. 



Microscopic Features of Hardened Supersaturated Steels.j — E. 

 Hess heated three bars of crucible steel containing 101, 1'41, and 

 1 • 77 p.c. carbon respectively, in such a way that one end was white-hot 

 while the other end was below the critical temperature. The bars were 

 then quenched, and sections cut from each at points 1 in. apart. The 

 difference of structure between edge and centre leads the author to 

 doubt whether the real condition at high temperatures is preserved by 

 sudden cooling. Howe's theory that supersaturated steels at tempera- 

 tures above the critical range consist of austenite is held to be confirmed. 

 The austenite undergoes partial decomposition when the steel is quenched. 



Iron, Carbon, and Sulphur.J — D. M. Levy has made a very complete 

 investigation of the effect of sulphur on iron-carbon alloys. A number 

 of alloys were prepared by melting pure cast iron with sulphide of 

 iron, cooling curves were taken, and physical and chemical properties 

 and microstructure were studied. In cast-iron free from silicon and 

 manganese the saturation limit is about ' 8 p.c. sulphur ; it exists as FeS 

 (melting point above 1180° C). A certain excess of FeS may be mechani- 

 cally retained. Sulphur lowers the melting-point of cast iron. At about 

 1130° C. the sulphide separates from a solidifying alloy, as a constituent 

 of a triple austenite-cementite-sulphide eutectic. In sulphur-free cast 

 iron the cementite segregates into large masses which decompose at high 

 temperatures, giving rise to graphite : grey iron is thus produced. When 

 iron sulphide is present it forms layers and films in the eutectic. These 

 appear to prevent the coalescence of the cementite, which is a necessary 

 preliminary to its decomposition. Thus the iron is retained in the white 

 form. No evidence of any chemical union of the sulphide with the 

 carlton or carbide was obtained. The influence of sulphur in retaining 

 the carbon in the combined state appears to be purely physical or 

 mechanical. 



Constitution of Iron and Phosphorus Compounds. § — B. Saklat- 

 walla has made a thermal and microscopical investigation of the iron- 

 phosphorus system. Pure electrolytic iron was used. Much difficulty 

 was experienced in preparing a high phosphorus alloy free from im- 



* Journ. Iron and Steel Inst., lxxvi. (1908) pp. 151-4. 

 t Op. cit,, lxxvii. (1908) pp. 1-4 (30 figs.). 

 X Tom. cit., pp. 33-91 (31 figs.). 

 § Tom. cit., pp. 92-103 (10 figs.). 



