Heating on the Magnetic Properties of Iron. 



263 



is intended to carry out experiments to find if this is so, using more 

 prolonged heating. 



In order to exhibit the character of the change in magnetic 

 property, supplementary experiments were made by the ballistic 

 method, using a ring of soft iron formed by coiling* up a long strip 

 of sheet metal. This was first annealed, and tested in the annealed 

 state. It was then baked by heating at 200 C., and cyclic curves 

 were determined in the usual way after the ring had become cold. 

 The results are stated in Table III, and are shown in the curves of 

 fig. 3. Carve 1 shows the initial state (after annealing), where 

 the value of the hysteresis is 830 ergs per cycle per cubic centimetre 

 (B = 4000). Curve 2 shows the state after nineteen hours of baking 

 at 200 C., when the hysteresis had greatly increased and had 

 reached a value of 1580 ergs. Curve 3 was taken after further 

 heating at the same temperature for four days, by which time the 

 decrease of hysteresis is very apparent, its value having diminished 

 to 1420 ergs. Permeability curves, taken by the method of reversals 

 after heating during the same periods, are given in fig. 4 and 



FIG. 4. 



6,000 



$.opo_ 



4,0 00 



5,000 



.000. 



/.OOP 



Curves. 



I 



1 



9 



.*/ 



I / 



1 f 



H 



3-0 



show the falling off and subsequent partial recovery in the 

 permeability. 



YQL, LXIII, V 



