Properties of the Alloys of Cast-iron and Aluminium. 611 



It has been stated that the Band T curves (H = a constant) 

 change to some extent after the specimen has been raised to 

 a high temperature. It was hence thought desirable to obtain 

 a set of hysteresis-loops while the alloy cooled, to see whether 

 there was any essential difference between its behaviour during 

 the processes of heating and cooling. 



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Accordingly the specimen was heated to 800° C, and 

 allowed to cool by stages down to the temperature of the 

 room. 



Double reversal throws and loops were taken at intervals 

 when the temperature was steady. 



This series of experiments lasted 26 hours, both the authors 

 being present throughout the experiments. 



The curves of double reversals will be seen to be different 

 from those obtained by successive heatings (vide fig. 3), 

 though, as will be seen later, the curves obtained from con- 

 secutive heatings and coolings approximate much more nearly 

 to one another. 



As a check on the results, the ring was unwound and then 

 re-wound with cotton-covered copper wire soaked in melted 

 paraffin, and again tested. The values obtained in the two 

 cases were found to confirm one another. 



The loops obtained are shown on Plate YI. 



The hysteresis loss was calculated in each case and curves 

 connecting the hysteresis loss and the temperature for the 

 given limits of field- strength are shown as fig. 2. 



