94 
Proceedings of the Royal Society of Edinburgh. [Sess. 
where the magnetisation curves of the four magnetic alloys are drawn to 
the same scale. Not only, then, are the magnetic 14-18 per cent, tin alloys 
separated from the strongly magnetic 38 per cent, alloy by comparatively 
non-magnetic alloys about 30 per cent., but there is a noteworthy dissimi- 
larity in the general magnetic properties of the two divisions. 
Effect of Baking . — Investigations were carried out with a view to 
ascertaining what thermal treatment brought the alloys into the condition 
of maximum susceptibility. The methods found most suitable vary some- 
what with the alloy, but all involve exposure for a longer period to a 
temperature at least as high as that used in the normalising process. 
Table Y. gives the treatment resulting in maximum susceptibility for a 
Table V. — Effect of Baking the Alloys. 
Alloy. 
Thermal 
Treatment. 
Percentage 
Increase in I 200 . 
Percentage Increase 
in Hysteresis Loss. 
14 
per cent. tin. 
7 hours at 200° C. 
+ 3 
+ 10 
16 
5 „ 200° 
+ 3 
+ 15 
18 
55 
6 „ 180° 
+ 2 
+ 10 
38 
55 
4 „ 180° 
+ 
+ 5 
magnetising field of 200 units. The efficiency of the procedure is indicated 
by the percentage increase in I over the value obtained in the normalised 
specimen. The last column shows the augmentation of hysteresis loss 
brought about by the process, and shows that, from a practical point of 
view, the alloys are now inferior in quality. Hence in all the subsequent 
tests described in this paper the material used was the normalised alloy, 
exhibiting as it does the most satisfactory magnetic condition. The effect 
of prolonged baking at moderate temperatures was investigated in the case 
of the alloy with 18 per cent, of tin. The change produced was very 
Table VI. — Baked 18 per cent. Tin Alloy. 
Condition. 
Percentage Change produced by 
Cooling to - 190° C. 
hr 
ho- 
boo- 
boo* 
boo* 
b. 
C.F. 
Normalised ..... 
+ 15 
+ 20 
+ 35 
+ 60 
+ 65 
+ 35 
+ 15 
Baked, 24 hours at 185° C. 
+ 5 
+ 10 
+ 20 
+ 35 
+ 37 
+ 20 
+ 10 
