116 Barrett, Bkown & Hadfikld — On the Electrical Conductivity and 



The most interesting fact in the above results is the small decrease in induc- 

 tion, together with the great increase of retentivity and coercive force up to a 7\ 

 tungsten steel ; the retentivity being higher in this last steel, 1294 I, than in any 

 alloy we have examined. Tungsten steel has long been used for making perma- 

 nent magnets, but the percentage of tungsten added to the steel is important. The 

 highest magnetic power attainable with the greatest retentivity evidently lies 

 between a 4 and 7 per cent, tungsten steel. 



The large hysteresis loss in 1294 I is due to the great increase in reten- 

 tivity and coercive force combined with the high induction in this specimen. The 

 steady rise in coercive force with increase of tungsten is well seen in fig. 12, 

 p. 117. 



It must be remembered that all our specimens (except a few duplicates 

 marked unannealed) had been most carefully annealed (see p. 68) before being 

 tested magnetically. Hence the coercive force and the hysteresis loss are very 

 much less than would be found in unannealed or hardened specimens. 



The next series is a small group of aluminium steels. 



Table XI. — Aluminium Steels. (Plate VII.). 



The remarkable fact is revealed that the addition of aluminium to steel but 

 sliglitly affects its magnetic induction and coercive force up to 2\ per cent. A 

 larger percentage softens the steel and the retentivity and coercive force both fall. 

 This reduction of coercive force is seen in fig. 12. The hysteresis loss, which is 

 increased by the addition of most other elements to iron, is slightly decreased in a 

 2\ per cent, aluminium steel, and considerably decreased in the 5| per cent, 

 specimen, notwithstanding the maximum induction, in a field of 45 C.G. S. units, 

 still remains very high. 



The permeability of the '2\ per cent, aluminium steel, at a magnetizing force of 

 8 C.G.S. units, is even higher than good iron : the fuller chemical analysis of 

 these steels is given in group 5, p. 83. 



*"Tlie curve, 1178 D, belongs to Table XII., aluminium-chromium steels. 



