Page:Proceedings of the Royal Society of London Vol 60.djvu/79

64 liquid air was to cause the magnet to possess a magnetic moment about 10 per cent, greater at —185° C. than at 5° 0. It will be seen, therefore, that these steels differ from the chromium steels in this respect, that whereas in the chromium steels the effect of the first cooling is to cause an increase in magnetic moment; in the case of the aluminium steels, the effect of the first cooling was to cause a decrease of magnetic moment, although much smaller relatively than in the case of the carbon steels.

Nickel Steels.—Experiments were then made with samples of nickel steel containing 094, 3‘82, 7’6-5, 19'64, and' 29 per cent, of nickel. These steels exhibited some rather interesting peculiarities. In the case of the nickel steel with 094 per cent, of nickel, the effect of the first cooling in liquid air was to cause a very small decrease in magnetic moment (see fig. 11), and the subsequent heating and cooling

F ig-, 11.—Nickel steel. Ni = 0-94 C =0*13 Si = 0 *23 Mn = 0-72 Fe = 97-98

brought the steel into a condition in which its magnetic moment, when cold, was always greater than its magnetic moment when warm, by about 10 or 11 per cent. In the case of the nickel steel with 3'82 per cent, of nickel, the effect of the changes of temperature was very similar (see fig. 12), and also in the case of the nickel steel having 7 65 per cent, of nickel the order of the changes was not very different in this respect, that the magnetic moment when cold was

Fig. 12.—Nickel steel. Ni = 3-82 C< = 0 -19 Si = 0 -20 Mn = 0-65 Fe = 95 -14

Fig. 13.—Nickel steel. Ni = 7-65 C =0-17 Si = 0-28 Mn = 0-68 Fe = 91 -22