IN MANGANESE STEEL BY HEAT TREATMENT. 347 



Hardness was : Bar No. i, 26.3 ; Bar No. 7, 26.6. 



The ten bars were next heated slowly to 645° and allowed to 

 cool slowly in the furnace to room temperature. 



Hardness was: Bar No. i, 26.5; Bar No. 7, 25.9. 



All the bars were now very moderately magnetic, though in their 

 softest condition. 



The foregoing quenching temperatures were falling ones. The 

 following quenching temperature was a rising one, from the an- 

 nealed condition last described. 



Fourth quenching: The bars were heated slowly to 615° and 

 quenched. 



Hardness was now: Bar No. i, 38; Bar No. 7, 30.3. 



Notwithstanding this considerable increase of hardness, there 

 followed no appreciable generation or absorption of heat. The bars 

 remained very moderately magnetic. 



The results of the foregoing experiments make it highly prob- 

 able that no spontaneous generation or absorption of heat can be 

 brought about by quenching this manganese steel at any tempera- 

 ture, rising or falling, while in its normal, useful non-magnetic con- 

 dition. But it was thought worth while to make further experiments 

 with the steel in its magnetic condition and, incidentally, to study 

 the development of this magnetic condition during the prolonged 

 moderate heating necessary to bring it about. The latter study has 

 proved so interesting that I have pursued it to considerable length 

 and made it the titular subject of this paper. 



The apparatus employed in the following study consists, in part, 

 of a vertical cylindrical electric furnace heated by small spirals of 

 " nichrome " wire carrying alternating current regulated by a 

 rheostat. The heating spirals are so disposed as not to produce any 

 magnetic field inside or outside the furnace. Instead of the usual 

 sheet-iron casing, this furnace is cased with sheet brass slotted longi- 

 tudinally to prevent induction currents in it when the external mag- 

 netizing solenoid is excited. The furnace is surrounded by a 

 solenoid 16 inches inside, and 20 inches outside diameter, and 4 

 inches long (high), consisting of 860 turns of No. 12 insulated 

 copper wire wound in two equal coils adapted to be placed in series 

 or parallel relation by means of a suitable switch. The axes of the 



