ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 85 



and chromium were also present, nitrification at higher temperatures 

 caiised the formation of the nitrides of these elements, these nitrides 

 being more stable than iron-nitride. Heat-tinting was employed to 

 distinguish the constituents, since the nitrogen-containing constituents 

 oxidized more rapidly than the carbide or the ferrite. Lnmiere auto- 

 chrome photomicrographs preserved a record of the heat-tinted specimens 

 in their actual colours. 



Decarburization of Steels in Salt Baths.* — A. M. Portevin 

 describes experiments indicating the considerable extent of the decar- 

 burization of surface layers which may occur in steel objects during 

 heating in salt baths previous to hardening. When cyanides are present 

 in the salt bath, the carbon-content of a low-carbon steel may be 

 increased, that of a high-carbon steel diminished, by immersion. In 

 iron, originally carbon-free, which had become superficially carburized 

 through heating in a salt bath containing cyanides, there were observe I 

 microscopically, in the ferrite below the carburized layer, needles 

 resembling those seen in specimens of steel suspected to contain much 

 nitrogen. 



Heat-treatment of Steel Wircf — In the course of manufacture, 

 steel wire undergoes heat-treatments which vary according to the 

 composition of the steel and the purpose for which the wire is intended. 

 J. F. Tinsley describes and explains the effect of such treatments on 

 microstructure. The principal heat-treatments are : (1) annealing ; 

 (2) " patenting " ; and (3) hardening and tempering. Annealing is 

 employed to effect one or more of three results : (a) to remove cold- 

 work effects ; (b) to refine the crystalline structure ; (c) to produce some 

 desired structure such as granular pearlite. To remove cold-work effects 

 it is not necessary to heat above the critical range ; ' 600° C. is a 

 sufficiently high temperature. " Patenting " consists in heating above 

 the critical range and cooling rapidly to a temperature below the critical 

 range, as by immersion in molten lead. The structure produced is 

 sorbitic. Hardening and tempering are usually conducted as a 

 continuous operation, the wire passing from the furnace, through a 

 quenching bath of oil or water, and then through a tempering bath such 

 as molten lead. 



Theory of Hardening and Constitution of Steel 4 — In some 

 remarks introductory to a discussion of the constitution of steel, E. D. 

 Campbell states that in a steel containing 0*82 p.c. carbon, cooled from 

 1060° to 700° C. in seven hours, the carbide areas were sharply separated, 

 and were 0*2 to 0*3 mm. in size, embedded in nearly pure ferrite, the 



*|Journ. Iron and Steel. Inst., xc. (1914, 2) pp. 196-203 (2 figs.). 

 t Iron and Coal Trades Review, lxxxviii. (1914) pp. 948-50 (8 figs.). 

 t Journ. Iron and Steel Inst., xc. (1914, 2) pp. 1-16. 



