36G Electrical and Magnetic Properties of Pure Iron. 



When dealing with the electrical resistance of the dras- 

 tically annealed sample, it was mentioned that the micro- 

 structure was remarkably uneven. The large grains, however, 

 were the ones which seemed to exert most influence on the 

 conductivity, which was the greatest of an}^ o£ the specimens 

 tested. The magnetic results, how r ever, point in quite the 

 opposite direction. With the exception o£ the quenched and 

 tempered iron, the magnetic " hardness " of the drastically 

 annealed sample was the greatest of all ; and the conclusion 

 is inevitable that the minute crystals (despite their relatively 

 small mass) had impressed their own properties on the whole 

 sample. 



The results are of practical importance in pointing to the 

 possibility of producing by suitable annealing iron for trans- 

 formers, &c, with far lower hysteresis losses than any jet 

 obtained. 



The constant values obtained for the maximum induction 

 with varying crystal size hardly appears to be concordant 

 with the view that the high permeability of iron alloyed 

 with aluminium, silicon, or phosphorus is due to the large 

 crystals which these elements induce. As an alternative 

 suggestion, it may be noted that each of these three elements 

 is used to remove the oxygen taken up by metals during 

 melting. In the unalloyed iron it is probable that the 

 • oxygen is present partly as oxide in solid solution, a con- 

 dition which in general decreases the permeability and 

 increases the coercive force. The presence of silicon or 

 aluminium would tend to eliminate the oxide from solution ; 

 and it may be that to this fact the high permeability of the 

 alloys of these elements with iron is to be referred. 



The results here recorded were obtained in the Physical 

 Laboratories of the Department of Applied Science of the 

 University of Sheffield. The author wishes to express his 

 sincere thanks to Prof. J. 0. Arnold, D.Met, F.P.S., for 

 his interest and advice, and to Mr. E. H. Crapper, B.Eng., 

 M.I.E.E., Senior Lecturer in Electrical Engineering, for the 

 facilities offered in carrying out the electrical and magnetic 

 tests. To Professor W. M. Hicks, D.Sc, F.R.S., the author 

 is extremely indebted for his very kind criticism and 

 .help. 



