1904.] Liquid Air Temperatures on Iron and its Alloy*. 335 



mitted to the low temperature test, and tested by hammer immediately 

 after being immersed. In all cases they exhibited great brittleness, 

 breaking off instantly upon being struck. Further confirmation is 

 obtained by the Brinell hardness ball test, under which test the hardness 

 number of the S.C.I, increased at - 182 C. from 90 to 266, or about 

 equal to the hardness of '80 per cent, carbon steel at normal temperature. 

 This almost seems incredible when it is remembered that the S.C.I, 

 shows by analysis 99 '88 per cent, of iron, and has only 20 to 22 tons 

 tenacity, with 25*30 per cent, elongation. 



The importance of the discovery of the toughening effect of nickel 

 upon iron at low temperatures will be seen when it is understood that 

 whilst it has been well known that nickel in certain percentages 

 produced important improvements in the qualities and properties of 

 iron and steel alloys, no microscopical or chemical research work has 

 yet proved why this came about. It seems clear that these experiments 

 go a long way towards offering a satisfactory explanation. The experi- 

 ments prove that the purest iron, as represented by the S.C.I. (con- 

 taining 99*82 per cent, iron), becomes brittle to an extraordinary degree 

 under the influence of low temperatures, whereas nickel itself, tested 

 under the same conditions, has improved rather than deteriorated, not 

 only in tenacity, which iron also does, but in ductility, in which latter 

 quality iron entirely breaks down. If nickel, therefore, is present in 

 an iron alloy containing but little carbon, or comparatively low in that 

 element, it acts as a preventive of brittleness, or is a very considerable 

 modifier of that objectionable quality. It may be interesting to state 

 that at ordinary temperatures the toughness or ductility of nickel is no 

 greater than that of iron. For example, in comparative tensile tests 

 made on nickel and pure iron, the ductility of iron was greater. 



Iron to a more or less degree, at any rate in manufacturing operations, 

 always seems to be endeavouring to wander out of the " paths " of 

 ductility and toughness, and will assume its apparently brittle nature 

 on the slightest provocation. It would appear therefore that iron, a 

 cheap and convenient metal itself, must be permeated by some element 

 that will mask or modify its properties. Until recently carbon was 

 the only element known to modify the properties of iron ; but, as will 

 be seen in this research, this element, where great toughness is required, 

 only helps to make matters worse. Fortunately for iron, however, its 

 close companion nickel acts as a preventive in keeping it from 

 wandering out of the narrow road of metallurgical rectitude, that is 

 toughness or ductility. Why this should be so cannot at present be 

 explained. Iron is a crystalline metal, whereas nickel appears to be 

 much more amorphous ; it is possible, therefore, that nickel tends to 

 prevent iron crystallizing. This action of nickel if? remarkable in 

 certain of the alloy specimens, e.g., No. 114, which is an alloy of iron, 

 carbon 1-18 per cent., nickel 24*30 per cent., and manganese 6*05 per 



