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F jg. 18.—Annealed transformer iron.
F ig . 19.—H ard transformer iron.
glass-6ard 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 respectively 1, 7*5, and 15 per cent, of tungsten in them.
Magnets were prepared of these steels, both in the glass-hard condition 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 — 186°C. was to cause a diminution of magnetic moment, and the subsequent -warming up again to 5° C., a still further 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 temperature 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 temperatures 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
