96 
Proceedings of the Royal Society of Edinburgh. [Sess. 
tures between the normal room temperature and the critical temperature. 
In all cases the alloys showed less susceptibility, retentivity, and coercive 
force at these higher temperatures. This was perhaps to be anticipated 
from the enhanced susceptibility found in bars cooled in liquid air. In 
carrying out these investigations the normalised specimen was placed in 
an electric furnace within the solenoid, raised to the desired temperature, 
submitted to the action of an alternating field of intensity gradually 
diminishing to zero (being thereby rendered devoid of previous magnetic 
history), and put through a hysteresis cycle. The current in the electric 
furnace was then altered so as to give a new higher temperature, and the 
process was repeated. Table VII. gives the results obtained in these tests. 
[The 30 and 48 per cent, tin alloys being so feebly magnetic were not 
tested.] The values obtained in the tests at —190° C. have been included 
in the table, and in this way the variation of magnetic quality over the 
whole range of over 400° C. is shown. It will be observed that the 
susceptibility of the 38 per cent, tin alloy is fairly constant through the 
wide variation of temperature from —190° up to about 180° C., but that it 
very rapidly falls off after this point has been reached. The magnetism of the 
other alloys diminishes much more evenly with increase of temperature. 
Critical Temperatures . — In the course of the furnace tests the critical 
temperatures of the alloys were ascertained and are set out in Table VIII. 
Table VIII. — Critical Temperature. 
Alloy. 
Critical 
Temperature. 
14 per 
cent, tin .... 
275° C. 
16 
.... 
270° 
18 
?? .... 
255° 
38 
55 V 
225° 
The temperatures of transformation from the magnetic to the non-magnetic 
state and vice versa were found to be practical identical in all cases. Table 
VIII. shows that the variation of critical temperature with composition is 
much smaller in the case of these ternary alloys than in the copper- 
manganese-aluminium system.* 
Tests at various Temperatures while Cooling. — After the determination 
of the critical temperatures, the specimen was gradually brought back to 
room temperature, tests being carried out again at different stages during 
* F. Heusler and F. Richarz, ZeM anorg. Chem., Ixi., 265 (1901) ; and A. D. Ross and 
R. C. Gray, Proc. Roy. Phil . Soc. Glasg ., lv., 94 (1909). 
