354 BRUSH— GENERATION OF HEAT IN STEEL. 



half-inch round bars five inches long, like in size and number those 

 of each of the steels of the first paper, so that results obtained were 

 quantitatively comparable with the earlier ones. Each specimen was 

 first hardened by quenching at a temperature just above that of 

 decalescence as indicated by almost complete loss of magnetic sus- 

 ceptibility. 



For observing the magnetic behavior of the steel while being 

 heated or cooled in the gas furnace employed, the bundle of bars 

 was surrounded by a single turn of asbestos-insulated platinum 

 wire, the ends of which were connected with a ballistic galvanometer 

 having the usual mirror and scale. The furnace was surrounded 

 by a large coil of heavy copper wire through which a direct electric 

 current could be established and broken at will by means of a 

 switch and storage battery. Before the steel bars were placed within 

 the platinum loop inside the furnace, closure of the outer copper 

 coil circuit caused a brief electric pulse in the loop and a "kick" in 

 the galvanometer, giving a definite minimum deflection easily 

 observed with considerable precision. With the steel bars inside the 

 platinum loop the galvanometer deflection was, of course, many 

 times greater until, with rising temperature, the decalescent point 

 was approached; then the deflection fell rapidly to the minimum 

 value as above, or very near it. This simple induction apparatus 

 was found entirely reliable and satisfactory. 



Each of the nickel-chromium steels exhibited good generation of 

 heat after hardening as above. 



They were again heated, to a temperature considerably above 

 decalescence, and quenched as before. This second hardening 

 induced a greater generation of heat than the first hardening, 

 especially in the case of specimen B. 



Specimen B was slowly heated a third time, somewhat above the 

 temperature of complete loss of magnetic suscepti'bility, and allowed 

 to cool very slowly in the furnace until complete recovery of mag- 

 netic susceptibility was attained ; then it was immediately quenched. 

 A very fair generation of heat followed this treatment. This was 

 quite unexpected because it was thought that true hardening of the 

 steel could not have taken place. In the absence of suitable appa- 



