on the Magnetic Properties of Iron. 27 



These results are shown graphically in figs. 12 and 13: the 

 scale of magnetic force for each curve is so chosen that the 

 point giving the maximum permeability in each case occurs 

 at the same distance along the horizontal axis. 



It has been seen from the corresponding curves for each of 

 the preceding specimens that the permeability at any stage of 

 the process of magnetization has, in a general way, increased 

 with the temperature. 



This, however, is not the case with the aluminium alloy. 



Keferring to fig. 12, it will be seen that for magnetic forces 

 above about 04 c.G.s. the specimen is much more susceptible 

 to magnetization at a temperature of 360° 0. than it is when 

 the temperature has risen to 489° C. 



It is also seen that at these particular temperatures the 

 successive stages of the magnetizing process are brought on 

 with practically the same magnetic forces. This is also the 

 case for temperatures of 632° C. and 660° C. 



Corresponding curves for higher temperatures are shown in 



fi g' 13 ' 



As the temperature is raised beyond 632° 0. the permea- 

 bility for weak magnetic forces rapidly increases, and reaches 

 a value of about 17250, the maximum obtainable with a force 

 of about 0*125 C.G.s., at a temperature of 686° C. 



The values of the permeability at different temperatures 

 under a magnetic force of 0*127 c.G.s. were: — 



Temp in l l&0 21go g60 o 428 o 4390 5270 5090 63 2° 660° 686° 

 cleg. C. J 



It 381 490 599 735 1035 1689 3977 5790 10696 17250 



Plotting these results, we get a curve very similar to that 

 obtained for iron with the corresponding critical force of 

 0'172 c.G.s., shown in fig. 4 (p. 9). 



As the magnetizing force is reduced beyond this critical 

 value, the maximum permeability obtained in each case 

 decreases. 



It will be seen that the magnetic force giving the maximum 

 obtainable permeability for the aluminium alloy is smaller 

 than the corresponding force for the iron specimen. 



At a temperature of 695° C. the alloy is practically non- 

 magnetic. It was found, however, that the effects of previous 

 magnetization were not entirely got rid of by heating the ring 

 beyond this temperature. 



Observations were taken with different magnetizing forces 

 as the ring cooled. The magnetic quality returns as rapidly 

 as it disappeared at a temperature slightly below the critical 

 point, and for each magnetizing force the permeability reaches 

 the same maximum value as that obtained during; heating. 



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