Graded Series of Nickel-Manganese Alloys. 13 



theory we should expect to find the susceptibility of a mag- 

 netic material diminished for low fields and increased for 

 high fields by cooling to the temperature of liquid air, pro- 

 vided that the material is not transformed. This is charac- 

 teristic of iron, nickel, cobalt, and the carbon steels. It is 

 shown in a very marked degree by these nickel-manganese 

 alloys. The magnetization curves corresponding to room- 

 temperature and —190° C. cross for values of the magne- 

 tizing force which are small compared with those required to 

 bring about crossing of the curves for iron, nickel, and cobalt, 

 and the increase in susceptibility brought about by the 

 cooling is enormously greater than is the case for these 

 metals. 



Summary. 



1. Specimens of pure nickel and of nickel-manganese 



alloys containing 5 per cent., 10 per cent., , 30 per 



cent. Mn respectively were tested at room-temperature and 

 at —190° C. (when immersed in boiling liquid air) in the 

 conditions brought about by 



(1) the process of casting ; 



(2) annealing at 900° 0.; 



(3) quenching at 900° C. 



2. In pure nickel the effect of cooling to —190° C. is to 

 diminish the susceptibility for low fields and to increase it 

 for high fields; the value of H for which the magnetization 

 curves corresponding to 15° 0. and — 190° C, respectively, 

 cross is greater than 200 c.G.s. units. 



3. The effect of adding manganese to nickel is to diminish 

 the susceptibility of the nickel. The resulting material 

 behaves normally, in that a magnetization curve correspond- 

 ing to —190° C. lies initially below and finally above that 

 corresponding to 15° C. This is characteristic of the material 

 in all three conditions. 



4. For the nickel-manganese alloy containing 5 per cent. Mn 

 in the annealed condition magnetization curves for 15 Q C. 

 and -190° 0. cross for H = 45 c.G.s. units. For H = 200 

 C.G.S. units the values of the intensity of magnetization at 

 the two temperatures are 316 and 350 c.G.s. units respec- 

 tively. Quenching this material enhanced its susceptibility 

 for low fields. For this condition of the metal crossing of 

 the I-H curves took place for a value of the magnetizing 

 force of 20 c.G.s. units. 



5. The behaviour of the alloy of nickel with manganese 

 containing 10 per cent. Mn was very similar to that exhibited 



