1904.] Liquid Air Temperatures on Iron and its Alloys. 327 



The bars were then forwarded to the Royal Institution Laboratory, 

 and there tested in a small hydraulic testing machine, similar in 

 principle to that described in * Proceedings of the Eoyal Institution, 

 1894,' to which the necessary arrangements could be applied for 

 breaking the specimens while immersed in liquid air. 



The present research confirms, in a larger field, the conclusions set 

 forth in the discourse of one of the authors at the Royal Institution 

 in 1894 on the " Scientific Uses of Liquid Air," in which the results 

 of tests on metallic wires and cast metals at low temperatures were 

 discussed, The results of the present series of tests corroborate the 

 inference previously drawn, viz., that all common metals and alloys 

 increase in tenacity at low temperatures, and this whether the 

 ductility increases or decreases, and, further, that the increase of 

 tenacity is solely due to the low temperature, and persists only during 

 its continuance. 



The Results of Low Temperatures on Irons. The first specimen 

 examined in this class was Swedish charcoal iron, this material in its 

 composition most nearly approaching that of pure iron. The analysis 

 of this specimen gave C 0-045, Si 0'07, S O'OOS, P 0'004, Mn 

 trace, Fe 99 '82 per cent. This iron, after careful annealing, gave 

 20 tons per square inch tenacity and 20 per cent, elongation at 

 normal temperature ; after cooling in liquid air the tenacity rose to 

 38 tons, with substantially no elongation. Another specimen, after 

 being quenched at 950 C. and again at 600 C. in water, showed 

 similar results in liquid air. Two other specimens in the unannealed 

 condition and one after special heat treatment, showed similar 

 properties. Specimens immersed in liquid air and allowed to return to 

 the normal temperature before testing, showed almost exactly the same 

 tenacity and elongation as before cooling, showing that the 

 brittleness is entirely a function of temperature. 



Several specimens were then quenched from 600 C., 800 C.J and 

 950 C. in liquid air, and allowed to return to the normal temperature 

 before testing. It might have been expected that with this extraordinary 

 chilling a considerable hardening effect would have been noticed, but 

 singular to say, whilst the tenacity is practically the same in each case, 

 the ductility is improved rather than reduced. It may be mentioned that 

 the specimens quenched from high temperatures in liquid air remained 

 red hot in the liquid air- much longer than would have been expected. 

 In order to determine the hardness of these Swedish charcoal irons, 

 a series of tests were carried out by the Brinell ball test, which 

 showed that the .hardness is increased nearly 200 per cent, by quench- 

 ing in liquid air. The specimens, though, no doubt, much stiffer than 

 at normal temperature, could be readily filed at - 182 C. Magnetic 

 tests also showed that no marked change takes place at low temperature 

 as regards this quality. 



