MAGNETIC ALLOYS OF IRON, NICKEL, AND COBALT 453 



the induction for the annealed sample remains lower than for the 

 air-quenched sample, but as the force increases there is a tendency 

 for the two curves to approach each other. This continues with still 

 further increase in the magnetizing force and beyond 50 gauss the 

 two curves coincide. 



The permeability curves for these samples are plotted in Fig. 15, 

 illustrating the great difference in their maximum permeabilities. 

 For the annealed and the air-quenched samples, the initial perme- 



Fig. 14 — Magnetization curves for 78.5 permalloy and for Armco iron. 



abilities are 2,000 and 9,000, and the maximum permeabilities 10,000 

 and 87,000, respectively. The initial and the maximum perme- 

 abilities for the iron sample are 250 and 7,000, respectively. 



The effect of air quenching on the energy loss is illustrated in Fig. 16 

 in which hysteresis loops for a maximum flux density of 5,000 gauss 

 are plotted for the air-quenched and the annealed samples. The 

 energy loss for the rapidly cooled sample is only 35 per cent of that 

 for the annealed. 



In deciding on a rate for air quenching we selected the rate which 

 gave the highest initial permeability for the 78.5 permalloy. In Fig. 

 17 1 wish to illustrate how small changes in this rate affect the initial 



