214 Mr. J. R Ashworth. Methods of making Magnets 



magnetised at the air temperature; No. 7 was made red hot and 

 allowed to cool whilst in the magnetic field. No. 8, a specimen of 

 cobalt steel, was kindly supplied by Mr. Hadfield, and is probably 

 unique. All of these and the first example of nickel steel, No. 9 on 

 the list, are Sheffield steels. 



Attention was then directed chiefly to three classes : Nickel steels, 

 cast irons, and steel pianoforte wires. 



Nickel Steels. — The first of these, No. 9, is a crucible steel from 

 Sheffield, containing 3 per cent, of nickel and about 045 per cent, of 

 carbon. The next two are from Scotland. They contain 2'4 per 

 cent, of nickel and 0"19 per cent, of carbon. Nos. 12, 13, and 14 are 

 also from Scotland, and contain 3 per cent, and 27 per cent, of nickel. 

 They were kindly supplied by Mr. Riley, of the Glasgow Iron and 

 Steel Company. The behaviour of the last three was remarkable, as 

 when hardened they exhibited a small, negative coefficient. On 

 heating and cooling they continuously lost magnetism for the first 

 three alternations ; at the fourth and fifth heating and cooling there 

 was hardly any change of intensity ; afterwards a small increase of 

 intensity with rise of temperature and decrease with fall of tem- 

 perature regularly took place. In the specimen containing 3 per 

 cent, of nickel these operations caused a total loss of no less than 50 

 per cent, of the original magnetic intensity. This same piece was 

 then annealed and magnetised ; the coefficient was now positive, the 

 intensity rather higher, and the total loss 30 per cent. On re- 

 hardening the events first described were reproduced, the negative 

 coefficient and large total loss being almost exactly as before. It is 

 very likely that by carefully adjusting the degree of hardness in this 

 kind of steel a zero coefficient could be obtained. 



The 27 per cent, nickel alloys, after hardening in cold water, became 

 almost non-magnetic, as discovered by Dr. John Hopkinson,* and it 

 was only in this state that they were tested. No. 13 was magnetised 

 at the air temperature; No. 14 at —16°. All the other examples of 

 nickel steels had positive coefficients. 



Cast Irons. — Specimens of grey cast iron, as used for general castings 

 made at different times and of different blends of pig irons behaved 

 very similarly. Magnetised as supplied they did not take a high 

 intensity, lost permanently 30 to 40 per cent, of their magnetism, 

 and had a large temperature coefficient. When hardened their 

 magnetic properties were very different ; the intensity was then com- 

 parable with that of tungsten steel, the total loss only about 15 per 

 cent., and the temperature coefficient as low as, or lower than, the 

 best examples of hardened steels. In three different kinds of care- 

 fully hardened cast-iron magnets it was from 0*00016 to 0'00018 per 

 degree centigrade. The average value for steel magnets of a similar 

 * Hopkinson, ' Koy. Soc. Proc.,' vol. 48, p. 61. 



