Condition of an A Hoy of nearly Pure Iron and Aluminium. 297 



It did not contain any large amount of impurity, as is shown 

 by the following analysis : — 



Aluminium 2*42 



Carbon O'lO 



Manganese 0*09 



Silicon 0-05 



Phosphorus 0*02 



Sulphur 0*03 



Iron (by difference) . . . 97'29 



This specimen was cast in the form of a disk. A ring- 

 was turned out from this disk, and was wound with primary 

 and secondary coils carefully insulated with asbestos paper. 

 The ballistic method was used for measuring the induction, 

 and the temperature was determined from the resistance of a 

 platinum wire furnished with compensating leads. The 

 specimen was heated by means of a current flowing in a 

 non-inductively wound platinum wire. By this means a 

 constant and easily adjustable source of heat was obtained. 



A detailed account of the apparatus and method of expe- 

 riment will be found elsewhere. 



The specimen, which had not been annealed, was slowly 

 heated or cooled over a considerable range of temperature, 

 and the induction was measured from time to time when the 

 temperature had become steady. It was found that no two 

 successive curves were the same. 



For a low field (H = 0'5) the permeability increased with 

 each heating. 



The curves at first showed three very distinct maxima, 

 which, however, became less and less marked with each 

 heating. 



In the first experiments it was found that the induction 

 increased slightly at first, and then very rapidly diminished, 

 having a very small value at about 300° C. 



On further heating the induction increased again up to 

 470° C. It then diminished, though not to any large extent,, 

 until the temperature reached 510° C. 



On still further heating, it increased rapidly to a tempe- 

 rature not much below that of minimum permeability, when 

 it fell off very abruptly. The curve, however, on nearing 

 the axis of no induction bent round gradually, showing, as 

 has been previously demonstrated by one of us, that these 

 specimens do not abruptly lose their magnetic properties as 

 the temperature approximates to that of minimum permeability. 

 As the heatings and coolings are continued the curves- 

 Phil. Mag. S. 6. Vol. 1. No. 3. March 1901. X 



