12 Dr. J. G. Gray on the Magnetic Properties of a 



general features to those which were Burnished by the speci- 

 mens containing lower percentages of manganese. For all 

 the field-strengths employed the susceptibility is greater at 

 — 190° 0. than at room-temperature. 



The effect of quenching was in both cases to diminish 

 greatly the susceptibility for all fields, and in these specimens 

 the improvement brought about in the magnetic quality of 

 the quenched material by cooling to —190° 0. was compara- 

 tively slight. 



Complete hysteresis curves for the specimens containing 

 15 per cent, and 20 per cent, manganese in the annealed and 

 quenched conditions are shown in PL T. figs. 10 and 11. 

 It will be seen that in these alloys the hysteresis Is much 

 greater at —190° (J. than at room-temperature. The curves 

 show that the coercive force is small for both materials. 



It is interesting to contrast the behaviour of these manga- 

 nese-nickel alloys with that exhibited by the manganese- and 

 nickel-steels. The effect of alloying iron with manganese is 

 to mask to a great extent the magnetic properties of the 

 iron. Specimens of manganese-steel containing less than 

 12 per cent, of manganese are magnetic, but much less so 

 than would be expected from the amount of iron present. 

 Manganese-steel containing 9 per cent, of manganese is 

 slightly magnetic, and if the percentage of manganese i- 

 greater than 12 the resulting material is practically non- 

 magnetic. The magnetic manganese-steels are transformed 

 in magnetic quality by cooling to the temperature of Liquid 

 air. If a specimen containing 6 per cent, of manganese, for 

 example, is examined in the annealed condition (1) at room- 

 temperature, (2) at —1^0° C.j and (3) at room-temperature 

 following upon cooling to — 190° C., and the magnetization 

 curves yielded by the three sets of tests plotted, it will be 

 found that the curve corresponding to (.'0 will lie everywhere 

 above that corresponding to (2), and that the curve cor- 

 responding to (2) lies everywhere above that corresponding 

 to(l). 



The behaviour of the nickel-steels is very similar to that 

 of the manganese-steels. The magnetic' quality of iron is 

 greatly reduced by the addition o( nickel, and the alloys 

 are transformed by Cooling to the temperature o\' liquid 



air. 



The effeel of alloying nicked with manganese is to diminish 

 the susceptibility of the nickel, but the alloy- are distinctly 

 magnetic, even when the percentage of manganese is "• ,) . 

 These alloys are not transformed by cooling to —190 C. 



It hafl already been pointed out that on BopkinSOn'fl 



