346 BRUSH— DEVELOPMENT OF MAGNETIC SUSCEPTIBILITY 



I carefully tested one bar of each description for scleroscope 

 hardness, with following results : 

 Bar No. i (as forged). Hardness 37.3. 

 Bar No. 7 (toughened). Hardness 28.5. 

 Bar No. 15 (toughened, reheated). Hardness 51.6. 

 Bar No. 19 (toughened, reheated, retoughened). Hardness 39. 



Each of the above hardness numbers (and those to follow) is 

 the mean of at least ten consistent measurements made on the care- 

 fully ground, horizontal end surface of the bar, a fresh spot being 

 used for each measurement. 



I subsequently heated bar No. 13 to 1074° and cooled (annealed) 

 in the furnace. Its hardness, which presumably had been about 51.6 

 like its companion No. 15, was then 28.8, and it was non-magnetic; 

 seeming to show that quenching at high temperature, and annealing 

 from a still higher temperature, gives the same hardness and non- 

 magnetic condition whatever previous treatment may have been. 

 The hardness of bar No. 19 seems to contradict this conclusion, in 

 respect of hardness, but it was quenched at a very considerably 

 lower temperature. 



In the following experiments ten of the 6-inch bars of manganese 

 steel were used, so as to approximately equal in weight the twelve 

 5-inch bars of other steels employed in former experiments. 



First quenching: Bars i to 5 and 7 to 11 (10 in all) were heated 

 in an electric muffle furnace to 1013° C. and quenched in water. 

 This treatment was followed by no appreciable generation or absorp- 

 tion of heat when tested in the calorimeter employed in former ex- 

 periments and described in the earlier papers referred to. 



Hardness was now: Bar No. i, 30; Bar No. 7, 28.3, showing 

 that the first lot " as forged " and the second lot " toughened " were 

 brought to substantially the same " toughened " condition. 



Second quenching: The ten bars were again heated to 1013°, 

 allowed to cool in the furnace to 800° and quenched. Again there 

 followed no appreciable generation or absorption of heat. 



Hardness was now: Bar No. i, 27.6; Bar No. 7, 26.3. 



Third quenching: The bars were heated to 818°, allowed to 

 cool in the furnace to 607°, and quenched. There was no subse- 

 quent generation or absorption of heat. 



