ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 351 



have microscopically examined the hardened and tempered specimens. 

 The structures observed in a steel containing 0"64 p.c. carbon, 6 "24 p.c. 

 chromium, and 17 '60 p.c. tungsten, are described as typical. After 

 cooling- in an air-blast from 1350° 0. this steel consisted of polygonal 

 austenitic crystals. After tempering at -194° and 589° C. the structure 

 was quite martensitic. After being heated to 638' C. the specimen was 

 more readily etched, and showed signs of the decomposition of the 

 martensitic structure, but the martensitic markings were not com- 

 pletely removed until a temperature between 700^ and 750° C. was 

 reached. The steel was fully annealed at 7<s4:' C, and began to harden 

 again on heating to 884° C. and cooling. The structures of steels which 

 had been overheated or partly melted showed unmistakable signs of this 

 treatment. 



Nitrog-en in Iron and Steel.* — X. Tschischewski has included with 

 other experimental work on iron and nitrogen an examination of the 

 structure of Swedish iron which had been treated in a current of 

 ammonia gas. Transverse sections of the specimens, polished and 

 etched, showed at the edge the brittle skin of iron-nitride. Under 

 this was a dark layer, etching very easily, apparently consisting of iron 

 and crystals of iron-nitride. The dark crystals became less numerous 

 towards the centre of the specimen. The changes caused by heating to 

 various temperatures and cooling rapidly or slowly are considered to 

 indicate that the iron-nitride forms a solid solution with iron on heat- 

 ing, and falls out of solution on cooling ; a eutectic structure was not 

 produced. 



Carburization of Iron in Blast-furnace Gases.t — T. H. Byrom has 



found that iron may be completely converted into carbide of iron by 

 exposure to blast-furnace gases at temperatures in the neiglibourhood of 

 500^ C. for a sufficiently long period. After a fortnight's exposure, strips 

 of electro-deposited iron were found to l)e coated with layers of carbide, 

 between which was a layer consisting of crystals of iron enclosed in inter- 

 crystalline envelopes of carbide. The formation of the carbide appears 

 to be due entirely to the action of carbon monoxide. 



Oxygen in Iron. J — "W. Austin gives a number of photomicrographs 

 of iron containing 0*24 p.c. oxygeu. The material was prepared by 

 melting iron with iron oxide in an electric-arc furnace. The highest 

 oxygen-content obtained was 0*29 p.c. The oxide occurred as an in- 

 dependent constituent, in the form of globules. A surface examined 

 after polishing, and then after heating in hydrogen at 700° C, showed 

 that the oxide was reduced by this treatment; the etching effect of the 

 hydrogen was also observed. 



Fhosphorus in Iron and Steel.§ — W. H. Hatfield has examined 

 microscopically a series of seven white irons in which the phosphorus 



* Journ. Iron and Steel Inst., xcii. (1915, 2) pp. 47-105 (21 figs.), 

 t Journ. Iron and Steel Inst., xcii. (1915, 2) pp. 106-21 (7 figs.), 

 i Journ. Iron and Steel lust., xcii. (1915, 2) pp. 157-63 (10 figs.). 

 § Journ. Iron and Steel Inst., xcii. (1915, 2) pp. 122-40 (19 figs.). 



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