328 Sir J. Dewar and Mr. R A. Hadfield. Effect of [Nov. 24' 



In order to determine whether there is a critical point where the 

 abnormal rise in tenacity and loss of ductility occurred, four 

 specimens were tested at + 18 C., - 80 C., - 100 C., and - 193 C. 

 respectively. The results clearly show that there is no critical point, 

 i.e., gradual decrease in temperature is accompanied by gradual increase 

 in tenacity. 



Other irons tested were L.S.S. Swedish iron, English Bowling, and 

 Cooke iron, all showing increase in tenacity and corresponding decrease 

 in ductility upon quenching in liquid air. 



The next class are Iron-Carbon Alloys. This class is of special 

 interest and importance, as upon the various percentages of carbon 

 present in steel depend chiefly its physical properties. The specimens 

 first dealt with are those in which manganese is absent, or present in 

 only very small quantities. Test No. 74 (C (H4, Si 0-08, Mn 0-07 per 

 cent.) represents very mild or soft steel ; it enables a comparison to be 

 drawn between the Swedish charcoal iron previously described and soft 

 steel. In the case of this specimen the tenacity was nearly trebled, 

 but it is apparently more ductile than Swedish charcoal iron. A 

 specimen containing (C 078 per cent.) showed a considerable rise in 

 tenacity in liquid air, the ductility being reduced to practically nil. 

 A specimen of the same material was also submitted to the liquid air 

 temperature, and allowed to return to normal temperature before 

 testing; it showed a similar result to the original specimen not so 

 treated. It may, therefore, be said that the effect produced by liquid 

 air is of a physical and temporary character. 



Other specimens, viz., Nos. 115 (C O83, Mn 0'25 per cent.), 

 9 (C 0-85, Mn 0-32 per cent.), 10 (C 1'09, Mn 0'32 per cent.), 

 13 (C 1'23, Mn 0'14 per cent.) showed the usual behaviour at 

 liquid air temperature. Specimens of No. 115 (C 0'83 per cent.) 

 were then quenched in liquid air from 700 C. and 750 C. respec- 

 tively, and tested at normal temperature. As with the Swedish 

 charcoal iron, the quenching from these comparatively high points 

 has not produced the effect that might be expected ; in fact, instead 

 of the ductility being reduced, it is now quite considerable, viz., 

 13 per cent, from the 700 C. and 8 per cent, from the 750 C. 

 Specimens of No. 13 (C 1'23 per cent.) also showed the same singular 

 effects after quenching from 700 C. and 750 C. in liquid air. It is 

 certainly most remarkable that a specimen containing 1J per cent. C., 

 suddenly lowered 930 C., is so little injured as regards ductility. If 

 these specimens had been quenched from the same condition in ordinary 

 water or oil, they would have been unfileable and of extraordinary 

 hardness. These specimens were as magnetic at - 182 C. as at normal 

 temperature, and readily fileable. 



In connection with this series, specimens were also taken of various 

 iron-carbon alloys in which the Mn percentage was higher than in 



