Magnetic PermeabiUttj of various Alloys of Iron. 



113 



There is, however, this difference ; the first flexure in the magnetic properties of 

 the curve appears to take place at about 4 per cent., whereas the first flexure in 

 the mechanical properties takes place a little under 8 per cent. ; the second flexure 

 occurs at about 24. and 20 per cent, respectively. Tliis is better seen by referring 

 to the hysteresis loss in Table VII. These slight differences, probably due to 

 differences in heat treatment, will doubtless be cleared up by further experiments, 

 when a more complete set of these nickel steels has been prepared for the deter- 

 mination of their magnetic properties. 



The effect on the magnetic and mechanical properties produced by the prior 

 heat treatment, to which these steels have been subjected, is most marked, 

 especially in certain jDcrcentages of nickel.* This is well seen from Table VI. 

 The specimens containing 12-7 and 12-1 per cent, of nickel were only slightly 

 magnetic in the unannealed condition, in a field of 45, whereas they were fairly 

 magnetic when annealed. In much stronger fields, however, their magnetisation 

 in both physical states rises considerably, and soon much exceeds that of the 

 higher nickel steels, which are saturated in lower fields. The permeability and 

 the hysteresis loss of several of the nickel steels is shown on the next Table. 



Table ^ll.—NicM Steels. 



* This subject, as is well known, was first investigated by tlie late Dr. HopMnson, wbo discovered 

 that steels containing from 4i per cent, of nickel and upwards could exist in a stable magnetisable or non- 

 magnetisable state, according to the prior temperature to which they had been subjected. Dr. Hopkinson 

 also found that nickel steels, up to 4^ per cent., were capable of higher magnetisation than wrought iron, 

 in fields of from 30 to 50 C. G. S, units : see Proc. Eoyal Society for 1889 and 1890. 



