350 Scientific Proceedings, Royal Dublin Society. 



two steels when in the form of magnets with dimension ratio 33, the 

 magnetic moments per gramme were 36 and 31. 



In order to test the effects of gradually increasing the amounts of 

 chromium in steel magnets when the magnets were all of the same 

 dimensions, thirteen specimens of steel with different amounts of chromium 

 were obtained from Sir Eobert A. Hadfield, F.R.S., which were each about 

 6 inches long and \ inch diameter. They were all turned down to 0'3 cm. 

 diameter and 10 cm. long, giving a dimension-ratio of 33, and in order to 

 get them all in the same physical state, they were individually raised to a 

 bright red heat in a gas muffle furnace at a temperature of about 900° C.,' 

 and dropped end on into 3 feet of cold water. The magnets were then 

 cleaned, weighed, and magnetized in a field of 2000 c.g.s. units by putting 

 them on the poles of a powerful electro-magnet. 



About twenty hours after being magnetized they were tested for the 

 magnetic moment per gramme by the usual magnetometric method, the east 

 and west position of Gauss ; and immediately after the first observations 

 each magnet was allowed to fall once through a height of one metre on to a 

 block of glass and again tested, and then allowed to fall three times 

 through the same vertical distance and tested once more, the percentage 

 loss due to percussion being thus obtained. The magnets were let fall in 

 every ease with the true north or south-pointing pole downwards. 



The magnets were then put into a steam chamber and annealed for 

 twenty-five hours in steam at 100° C. They were then magnetized and again 

 steamed for five hours ; and about twenty hours after the final heating, they 

 were all tested for magnetic moment and loss by percussion in the same way 

 as was done when they were glass-hard. 



The results for seven of the more important of the thirteen specimens are 

 sliown in Table I., which gives the chemical composition' — the amount of 

 iron in each being estimated by difference — the magnetic moment per 

 gramme when glass-hard and when annealed, and the last two columns gives 

 the percentage loss in the magnetic moment per gramme due to the magnets 

 falling end on four times through a height of one metre on to a thick block 

 of glass. 



^ Determined by means of a calorimeter. 



* Determined in the chemical laboratory of the Hecla Steel Works, Sheffield. 



