Graded Series of Chrome Steels at Low Temperatures. 831 



change in susceptibility brought about by the change of 

 temperature, and in the value of the field-strength for which 

 the effect reverses its sign. 



Kow, in any such examination, particular interest always 

 attaches to the observation of the effect of similar treatment 

 on the different members of a graded series, either of steels 

 or alloys, the changes in effect being directly due to the 

 changes in the content of the specimens under examination. 



I accordingly decided to examine magnetically a specially 

 prepared series of cobalt-manganese alloys, containing re- 

 spectively 5, 10, 15, 20, 25, and 30 per cent, manganese, the 

 rest of the content of the specimen being pure cobalt. The 

 proper proportions of the two elements forming the various 

 specimens were therefore weighed out, and sent to be fused 

 and cast, and a specimen of pure cobalt was obtained for 

 comparison. At this point, however, an unexpected difficulty 

 was met with, which ultimately led to the abandonment, for 

 the time being at any rate, of the investigation of this series. 

 It was found that all the ordinary methods which are 

 usually successful in fusing metals were, in the case of the 

 first specimen of the series, ineffectual. It was probable 

 that those specimens with higher percentages of manganese 

 would fuse more easily, but as it was desired to have the 

 complete series prepared by the same method, they were not 

 attempted, and as any other methods which might have been 

 tried were unlikely to give homogeneous alloys, the exam- 

 ination of this particular series had to be abandoned. I 

 therefore decided to investigate instead the magnetic proper- 

 ties at ordinary and low temperatures of a graded series of 

 chrome steels. Such a series was accordingly obtained from 

 Messrs. Armstrong, Whitworth & Co., Ltd., — a series con- 

 sisting of six specimens containing respectively 1, 405, 8, 

 12, 16, and 20 per cent, chromium. 



The specimens were supplied in the form of cylindrical 

 rods 20 cm. long and 0'9 cm. in diameter, and the conditions 

 in which they were tested were as follows : — 



1. As supplied (viz., forged and rolled) . 



2. Annealed from 900° C. 



3. Quenched from 900° C. 



In the first condition the specimen is in a state of internal 

 strain brought about by the treatment to which it has been 

 subjected in the course of preparation, and is in general far 

 from homogeneous. Each specimen in this condition was 

 tested magnetically in a Gray-Ross magnetometer, and then 

 changed end for end, and tested again. The two sets of 



