116 Barrett, Brown & Haprintpb—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 74 
tungsten steel; the retentivity being higher in this last steel, 12941, 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 imcrease 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, 
D> Wile 
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. 
Taste XI.—Aluminium Steels. (Plate VIL.).* 
| 
Marks. Ee var Os arp re eae | Retentivity. | Coercive force. | « for H = 8. ee aL 
Tron 0 17480 | 7120 1-66 1560 11090 
1167 D 0°75 16500 8000 2-00 1517 11620 
est 9:25 16500 7620 1:87 1620 10960 
inGy i | SSO 13410 3480 1:43 1095 6825 
The remarkable fact is revealed that the addition of aluminium to steel but 
slightly affects its magnetic induction and coercive force up to 24+ 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 
21 per cent. aluminium steel, and considerably decreased in the 53 per cent. 
specimen, notwithstanding the maximum induction, in a field of 45 C.G.S. units, 
still remains very high. 
The permeability of the 24 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 54, p. 83. 
* The curve, 1178 D, belongs to Table XIL., aluminium-chromium steels. 
