246 SUMMARY OF CURRENT RESEARCHES RELATING TO 



between Bessemer and open-hearth steel are ascribed to the higher per- 

 centage of nitrogen in the former. In the second (Boussingault, 1861) 

 methods of estimating nitrogen in iron are given. The third (Allen, 

 1880) gives some results of analyses. H. Le Chatelier (editorial note) 

 states that the variations in percentage of nitrogen in steel are now 

 proved to be due to the processes of manufacture. 



Overheated Steel.*— J. E. Stead and A. W. Richards distinguish 

 between overheating and burning, the former merely resulting in the 

 formation of large crystals, the latter producing incipient disintegration. 

 Three steels, containing 0*06 p.c, 0*48 p.c, and 0'44 p.c. carbon, were 

 selected for the author's researches. One-inch square bars of each were 

 subjected to (1) overheating at 1300° C, (2) reheating after (1) to 

 880°-950° C. ; (3) annealing at 850°-950° C. ; (4) sorbitic treatment 

 (0*44 p.c. steel only), which consisted of heating to 900° C, quench- 

 ing in water, and reheating to 330° C. Mechanical tests (tensile, 

 bending in various ways, and Wohler reversal of stress tests) carried out 

 on the normal steels and on each steel treated as described, indicated 

 that " overheating reduces the power of the steel to resist fatigue, that 

 reheating such steel more than restores the original good qualities of the 

 rolled bars, and that when the steel has the carbon in the sorbitic con- 

 dition its power of endurance is more than doubled. 1 ' Portions of a 

 wagon axle were also heat treated in different ways, the results of 

 mechanical tests indicating that the fatigue-resisting properties of the 

 steel could be greatly increased by suitable treatment. The authors 

 advance the hypothesis that the weakness of overheated steel is due to 

 the presence of large masses of ferrite, a constituent which has a low 

 elastic limit. The good qualities of sorbitic steel appear to be due to the 

 absence of ferrite. 



Metallography applied to Foundry Work.f — A. Sauveur recom- 

 mends a vertical photomicrographic camera. Details of manipulation 

 are given. 



The author also describes J the microstructure of cast iron. Rate of 

 cooling probably influences the size of the graphite particles in grey 

 iron. 



Corrosion of Condenser Tubes.§ — Brass condenser tubes (70 p.c. 

 copper, 30 p.c. zinc) frequently cause trouble through rapid corrosion. 

 A. H. Sexton points out that in tubes which have a short life owing to 

 this cause, the zinc has usually dissolved out much more quickly than 

 the copper. Coarse crystallisation of the brass appears to have no effect 

 on the rate of corrosion. The great variations in the rapidity of corro- 

 sion of tubes are not due to any differences in the tubes themselves, but 

 to the conditions to which the tubes are subjected in use. The deposi- 

 tion of carbon or other electro-negative bodies on the surface of the tube 

 sets up electrolytic action and leads to rapid corrosion by the sea water. 



The Thermal Transformations of Carbon Steels.|| — The experi- 

 mental work described in this paper, largely a repetition of that carried 



* Iron and Steel Mag., x. (1905) pp. 385-404 (9 figs.). 



t Tom. cit., pp. 413-19 (2 figs). 



t Op. cit., xi. (1906) pp. 119-24 (4 figs.). 



§ Eng. Mag., xxx. (1905) pp. 211-25. 



i| Journ. Iron and Steel Inst., lxviii. (1905, 2) pp. 27-83 (17 pis.). 



