Properties of the Alloys of Cast-Iron and Aluminium. 603 



The primary and secondary coils, which were of copper 

 wire and insulated with asbestos-paper, came next, and 

 externally a well-ins ula ted platinum wire (diam. *5 millim.) 

 was wound non-inductively round the ring. 



The specimen was heated electrically, this non-inductively 

 w r ound platinum wire being used as a heating circuit. The 

 specimen, with the surrounding coils, was parked in asbestos 

 waste and placed in a sand-bath. Experiments were made at 

 temperatures ranging from 15° C. to 800° 0. 



The conclusions arrived at from these experiments are as 

 follows : — 



(1) The hysteresis-loss at first diminishes as the temperature 

 rises. It then increases and reaches a maximum value 

 at about 550° C, which temperature is about 80° higher 

 than the temperature of maximum induction. On further 

 heating it falls off rapidly and becomes negligible at 

 about 700° U. 



(2) The magnetic properties of the specimen depend largely 

 on its previous history. 



(3) There is no essential difference between the behaviour of 



this specimen during heating and cooling* (except near 

 the temperature of minimum permeability). 



(4) An abrupt increase in the permeability takes place at 



652° C. (during heating) followed by an equally abrupt 

 diminution on further heating. 



(5) This abrupt change in the permeability is more marked 



with falling than with rising temperatures. 



(6) Continued heating and cooling diminish the permeability 

 of this specimen (probably due to disintegration) *. 



(7) The curve connecting the temperature of minimum per- 

 meability and the percentage of aluminium for the speci- 

 mens investigated is a straight line. 



(8) The microscopic examination of the specimens shows the 

 presence of crystals. 



§ II. The Magnetic Measurements. 



The first series of experiments was made with a view to 

 ascertaining in what way the hysteresis-loss between given 

 limits of the field-strength was connected with the temperature 

 of the specimen. The ballistic method of measuring the 

 induction was made use of in this set of experiments. 



The experimental arrangement w r as roughly as follows : — 



* This statement does not hold for specimens containing onlv a small 

 quantity of impurity, as will be shown in a subsequent communication. 



2 R2 



