Magnetised Iron, $c. 9 cooled to Temperature of Liquid Air. 69 



ICC 



loo 



FlG. 19. Hard transformer iron. 



glass-hard carbon steel (see fig. 19), the changes in magnetic moment 

 being relatively about the same percentage for the same temperature 

 change : that is to say, the magnet had a moment of about 10 per 

 cent, greater at -185 C. than at 5 C. 



A series of tungsten steels were then examined, having respec- 

 tively 1, 7'5, and 15 per cent, of tungsten in them. 



Magnets were prepared of these steels, both in the glass-hard con- 

 dition and in a carefully annealed condition. These steels were found 

 to resemble the simple carbon steels in that the first effect of cooling 

 the magnet to 186C. was to cause a diminution of magnetic 

 moment, and the subsequent warming up again to 5 C., a still fur- 

 ther decrease in magnetic moment. From that time forth cooling 

 the magnet always caused an increase of magnetic moment. The 

 effect of increasing the percentage of tungsten was to cause a 

 decrease in the variation of the magnetic moment over a given tem- 

 perature range. That is to say, the hardened 15 per cent, tungsten 

 steel temporarily lost magnetic moment to the extent of about 6 per 

 cent, by heating up from 185 C. to 5 C. when once the initial 

 condition had been passed. The 7'5 per cent, tungsten steel lost 

 moment to the extent of about 10 per cent., and the 1 per cent, tungsten 

 steel lost moment to the extent of about 12 per cent, when the tempera- 

 tures rose between the same limits. As regards these tungsten steels, 

 softening the steel caused the magnetic moment to decrease by a 

 greater percentage when heated up from 185 C. to 5 C. than was 

 found to be the case when the steel was in its hard condition. A 

 sample of manganese steel containing 12 per cent, of manganese was 

 rendered magnetic by heating for 24 hours to a dull red heat. A 

 small magnet prepared from this steel was found capable of retaining 



