[ 349 J 



XXIX. 



CHEOME STEEL PERMANENT MAGNETS. 



By W. brown, B.Sc, 

 Professor of Applied Physios, Royal College of Science for Ireland. 



[Read Feeruaky 22. Ordered for publication March 8. Published April 21, 1910.] 



The magnetic properties of chrome steel were — as far as I know — first 

 investigated by Dr. Hopkinson' in 1885, by means of his yoke-and-bar 

 method ; the two specimens tested contained (1) Or = 0'621, = 0'532, and 

 (2) Cr = 1-195, C = 0-687. 



If we take the density^ of the samples when in the hard state to be 

 7'76, and divide the residual induction obtained by Hopkinson by 47r 

 times the density, we find the magnetic moment per gramme of the two 

 specimens to be about 88 and 81 respectively. 



In 1898 Mme. Curie,^ in her paper on the magnetic properties of 

 tempered steels, gives the residual intensities for three chrome steels obtained 

 with bars of square section 20 cm. long and one centimetre in the side. 

 Taking the bar which has the chemical composition Or = 2'48, C = 0*5, and 

 assuming the density to be 7'76, we get magnetic moment per gramme of 

 about 59. If, however, we take the value of the residual intensity which 

 was obtained when the sample was in the form of a, ring, the magnetic 

 moment per gramme is then 82, which result is more comparable with that 

 of Hopkinson, whose method of testing was also a closed circuit one. 



In 1900 Barrett, Brown, and Hadfield* published amongst other physical 

 properties the results of magnetic tests of two chrome steels containing 3'25 

 and 9'5 per cent, of chromium. The tests were made on rods of dimension 

 ratio 200 ; and from the residual induction then obtained, and taking the 

 densities^ of the materials as 7'765 and 7'703, the magnetic moments per 

 gramme come out 87 and 109 respectively. In a recent test* of the same 



' Phil. Trans. Roy. Society 1885, vol. clxxvi., part 2, p. 463. 



^ Scient. Trans. Eoy. Dublin Soc, vol. ix., p. 67. 



' Bull, de la Societe d' Encouragement, pp. 36-76. 



* Scient. Trans. Eoy. Dublin Soc, vol. vii., p. 119. 



= Ibid., vol. xi., p. 67. 



^ Ibid., vol. xii., p. 318. 



SCIENT. PEOC. B.D.S., VOL. XU., NO. XXIX. 3 L 



