Graded Series of Nickel-Manganese Alloys. 3 



series which was non-magnetic at room-temperature in the 

 annealed condition. 



The low temperatures employed by Hopkinson in his expe- 

 riments were obtained by means of carbonic-acid snow. It has 

 since been found that i£ a nickel-steel specimen is tested in the 

 annealed condition at room-temperature, and again at the 

 temperature of liquid air, a considerable improvement in its 

 magnetic quality is brought about by the cooling. If the 

 specimen is allowed to warm to room-temperature a further 

 improvement takes place in the magnetic quality. Thus, so 

 far as its magnetic properties are concerned, the material has 

 been transformed in the process of cooling. Reannealing 

 from 900° C. results in the specimen being restored to its 

 original condition of inferior magnetic quality. 



Nickel-steel is not the only iron alloy which exhibits this 

 remarkable absence of magnetic quality. The material 

 known as Hadfield's " manganese-steel," which is iron alloyed 

 with 12 per cent, manganese, is practically non-magnetic 

 under ordinary conditions. Its permeability is about 1*4, 

 and is practically constant in strong and weak magnetic 

 fields. A specimen of this material exhibits no residual 

 magnetism, even after having been exposed to a very powerful 

 magnetizing force. 



Heusler* in 1903 made the interesting discovery that alloys 

 of copper, manganese, and aluminium are strongly magnetic. 

 By properly adjusting the amounts of the component metals 

 present an alloy is obtained, the magnetic susceptibility of 

 which is comparable with that of cast iron. In Hopkinson's 

 nickel-steel containing 25 per cent, nickel we have an 

 example of an alloy composed of two magnetic metals, which 

 is itself non-magnetic at room-temperature in the annealed 

 condition. Heusler's alloy, on the other hand, which is 

 strongly magnetic, is composed entirely of non-magnetic 

 metals. 



The important part played by nickel in Hopkinson's 

 nickel-steels, and by manganese in the Heusler alloys and 

 in Hadfield's manganese-steels, led the writer to believe that 

 it would be of interest to investigate the magnetic properties 

 of a series of alloys composed of nickel and manganese in 

 varying proportions. A set of specimens was accordingly 

 cast in the form of cylindrical rods, each about 21 cm. long, 

 and having a diameter of 0'9 cm. The series was built up 

 as follows : 5 per cent. Mn, 95 per cent. Ni ; 10 per cent. Mn, 

 90 per cent. Ni ; and so on up to 30 per cent. Mn, 70 per 

 cent. Ni. On account of the fact that hot manganese absorbs 

 * Verh. d. deutsch. Phys. Ges. r. p. 219 (1903). 



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