278 Proceedings of the Boyal Society of Edinburgh. [Sess. 
cycle does not differ much from that obtained at room temperature. Q and 
Q' are the magnetisation curves obtained at 15° C. and — 190° C. respectively. 
The hysteresis is now almost inappreciable, and it will be observed that the 
liquid air effect has been reversed in direction. A chilled casting tested 
without further thermal treatment gave the curves P and P', which closely 
resemble those for the quenched material. 
Effect of Baking the Alloys . — The effect of baking the alloys D and E 
at various temperatures was now investigated, it being thought possible 
that such treatment would result in an improvement of the magnetic 
quality. Various temperatures up to 500° C. were employed, but all 
resulted in a lowering of the magnetisation curve. Fig. 3 exhibits the nature 
of the results obtained. In the upper diagram is shown the effect of 
maintaining alloy D at a temperature of 260° C. The ordinates of the 
graph are the intensities of magnetisation for the fields mentioned, while 
the abscissae give the duration of the baking in hours. The continuous 
lines show the changes in the intensity of magnetisation for fields of 125 
and 30 C.G.S. units respectively, the tests being made with the specimens 
cooled down to room temperature after the baking process. The dotted 
curves are obtained with the specimen cooled to —190° C. after the baking. 
The result of this thermal treatment has therefore been (i) to lower the 
saturation intensity continuously towards a limiting value, (ii) to cause at 
first a slight increase in the susceptibility for low fields, (iii) to reduce the 
susceptibility for all fields towards a definite limiting value, (iv) to reverse 
the liquid air effect in specimens baked for more than 8 hours. The 
hysteresis was also found to increase with time towards a maximum 
value. 
The lower part of fig. 3 similarly exhibits the effect of baking alloy E 
at 210° C. The results are shown only for H = 125, as they are of the 
same nature for all fields. The alloy undergoes a steady and rapid 
deterioration in quality, and after 10 hours’ baking has almost acquired 
an equilibrium condition. The liquid air effect in this alloy is reversed 
after 2 hours’ baking at 210° C., but it will be noticed that its direction 
was originally opposite to that in alloy D. 
The effect of baking alloy B has also been investigated by the authors. 
It has been found that the best magnetic condition of the alloy is obtained 
by exposing the material for a period of 6 to 8 hours at a temperature 
of 170° C. This results in an increase of over 10 per cent, in the saturation 
value of I,* while the short duration of the baking process does not produce 
any marked increase in the hysteresis loss in taking the material through 
* Baking, however, always reduces the values of I corresponding to small fields. 
