1907-8.] Sensitive State in Magnetic Materials. 
615 
XXXVII. — On a Sensitive State induced in Magnetic Materials by 
Thermal Treatment. By James G. Gray, B.Sc., Lecturer on 
Physics in the University of Glasgow, and Alexander D. Ross, 
M.A., B.Sc., Assistant to the Professor of Natural Philosophy in 
the University of Glasgow. Communicated by Professor A. Gray, 
F.R.S. 
(MS. received June 23, 1908. Read July 20, 1908.) 
Part II. 
It has been shown by the authors in Part I. * of the present paper that most 
magnetic materials after having been heated to even a moderate tempera- 
ture are in a peculiar magnetic condition. The magnetic quality of a test 
specimen is then superior to that of the specimen in its normal condition, 
to which it may be reduced by the simple process of demagnetising by 
reversals. For low fields the increase in susceptibility was found to 
amount to as much as 40 per cent, in the case of some varieties of steel, 
24 per cent, in the case of cast iron, and 15 per cent, in the case of cobalt. 
Similar tests have now been carried out on specimens of nickel and of the 
Heusler alloy. It was found that in the case of the former metal the 
thermal treatment results in an increase of the susceptibility, as tested for 
a held strength of 8 c.G.S. units, of somewhat less than 2 per cent. Similar 
treatment applied to the Heusler alloy results in an increase of about 
5 per cent. 
Composition of the Steels . — Table I. exhibits the chemical composition 
of the various steels employed in the experiments described in the present 
and the previous paper. 
Table I. — Composition of the Steels employed. 
Description of 
material. 
Percentage Composition. 
Carbon. 
Man- 
ganese. 
Silicon. 
Sulphur. 
Phos- 
phorus. 
Tungsten. 
Mild steel . 
0T62 
0-218 
0-041 
0-015 
0-040 
Spindle steel 
0-896 
0-286 
0-094 
0-020 
0-043 
Steel wire . 
0-755 
0-660 
0-066 
0-017 
0-027 
Magnet steel 
0-853 
0-462 
0-072 
Trace 
0-038 
2745 
Special hard steel 
1-321 
0-339 
0T43 
0-023 
2-745 
* Proc. Roy. Soc. Edin ., vol. xxviii., part iii., p. 239 et seq. 
