BRUSH— MAGNETIC SUSCEPTIBILITY. 345 



each quenching was followed by a small but distinct absorption of 

 heat. 



The phenomena above outlined appear to be new, and have 

 aroused the interest of some eminent metallurgists, among others 

 Sir Robert A. Hadfield, who kindly furnished all the specimens of 

 nickel-chromium steel employed, and to whom I am greatly indebted 

 for joining in some of the later work, and incidentally confirming 

 the most important of my findings with different apparatus of his 

 own design. 



The foregoing outline of former work is introduced here because 

 it underlies, and is closely associated with, the subject matter of the 

 present paper. 



Sir RolDert Hadfield long ago suggested that interesting results 

 might follow similar experiments with manganese alloy-steel (with 

 which his name is so intimately connected) . 



As is well known, this remarkable steel is exceedingly tough, and 

 difficult to work with machine tools though not hard ; its softest and 

 toughest condition is brought about by water-quenching at a high 

 temperature, after which it is almost completely non-magnetic; it 

 has no critical temperature, and hence cannot be hardened in the or- 

 dinary sense ; when heated a long time at a moderate temperature it 

 becomes magnetic, loses much of its tensile strength, and all its 

 toughness, and becomes brittle and considerably harder. 



For the purposes of the following experiments Sir Robert Had- 

 field sent me 19 numbered bars of his manganese steel, each 6 inches 

 long and jA inch in diameter (round), all cut from the same long 

 bar and ground to size after treatment. 



Following is his specification : 



Analysis. — C, 1.18 per cent.; Si, .14 per cent.; Mn, 12.29 P^'" 

 cent. 



Bars I to 6, As forged. Non-magnetic. 



Bars 7 to 12, Toughened by water-quenching at 995° C. Non-mag- 

 netic. 

 Bars 13 to 18, Toughened as above, then reheated to 500° and kept 



at that temperature 63 hours. Magnetic. 

 Bar 19, Treated like 13 to 18, then reheated to 995° and water- 

 quenched. Non-magnetic. 



