IN MANGANESE STEEL BY HEAT TREATMENT. 



349 



magnetic by heating, were subsequently substituted for the charcoal 

 iron. 



In the following experiments galvanometer deflection, less that 

 amount due to the platinum loop alone, is taken as the measure of 

 magnetic susceptibility, and the susceptibility of the Swedish iron 

 is used as a standard and assigned a value of lOO. All other values 

 are reduced to and expressed in terms of this standard. 



As a preparatory measure, the ten bars of manganese steel were 

 brought to their softest and toughest condition by quenching at 

 1000°. 



Hardness was: Bar No. i, 26.7; Bar No. 7, 25.8. 



All the bars were quite free from any trace of magnetism. 



The bars were next placed within the platinum loop in the elec- 

 tric furnace and heated 170 hours to a temperature fluctuating be- 

 tween 505° and 525°. The growth of magnetic susceptibility is 

 plotted in the curve shown in Fig. i. There is no doubt that the 



40 



a 

 Cu 20 



C/3 



40 60 80 



Hours of Heating 



Fig. I. 



100 120 



505° 525° C 



140 



160 



curve would have been smoother if the temperature had remained 

 constant. It was intended to use about 515° temperature, and it 

 was held near that value by the rheostat during the first few hours 

 Subsequent fluctuations were due to variations of voltage in the 



