1910-11.] On Magnetism of Copper-Manganese-Tin Alloys. 91 
further has been attempted than to show the probable nature of the 
change, if any. In stating the alterations in retentivity and coercive force 
(which are in all cases comparatively small quantities) the results have 
been given in round figures, viz. 5, 10, 15, etc. The effects produced by 
the cooling to —190° C. were temporary. When room temperature was 
regained the specimens gave the same magnetisation curves as before. In 
the case of the 18 per cent, alloy there appeared to be a slight permanent 
improvement in quality, but it was exceedingly small, and did not recur on 
a further repetition of the process. This change is of still less importance, 
as it will be shown that the alloy as cast is in a comparatively unstable 
condition as regards exposure to temperature variations, and that it may 
easily be brought to a more stable and magnetically superior condition. 
Normalising . — It is well known that iron or steel bars are, as a 
rule, initially in a state of strain as a result of the casting, forging, or roll- 
ing operations which they have undergone in the process of manufacture. 
To remove such strains it is customary to heat the bar to about a dull red 
heat and cool it down somewhat slowly. The period during which the 
metal is maintained at the high temperature is very short. Such a process 
is termed “ normalising,” and is to be distinguished from “ annealing,” in 
which the maximum temperature is maintained for a much longer period. 
A further treatment is that which is referred to in magnetic testing as 
“ ageing.” In this latter process the metal is maintained for prolonged 
periods at high temperatures with a resultant deterioration in magnetic 
quality. The coercive force augments, and the hysteresis loss is thereby 
much increased. These three processes, which act in the case of iron and 
steel comparatively slowly and only at somewhat high temperatures, rapidly 
produce similar effects in the magnetic bronzes even when the temperatures 
employed are relatively low. To bring the alloys to a “ normalised ” condi- 
tion we have therefore to expose them for a very brief time to a moderately 
low heat, and thence bring them back, not too rapidly, to room temperature. 
That such treatment is a true normalising of the material and not an 
annealing or baking process involving structural modification, is shown by 
the fact that the alloys exhibit precisely the same liquid air effects before 
and after.* The critical temperature of the material is also found to be 
unaltered. Moreover, there is no appreciable change in the hysteresis, and 
it is characteristic of these alloys that anything of the nature of continued 
* The 18 per cent, tin alloy is to a slight extent an exception. The increase in suscepti- 
bility produced by cooling to - 190° C. is subsequently a little less, but the coercive force, 
critical temperature, etc., have not been altered. Here the thermal treatment seems to have 
been partly normalising and partly annealing, the alloy being very sensitive to heat effects. 
