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SCIENCE PROGRESS 



worked metals contain a proportion, perhaps small, of the 

 amorphous material and that this accounts for the form of the 

 curve DB. On this view, a specimen composed exclusively of 

 crystalline material would exhibit a strictly linear change of 

 strength with temperature, as shown by the line EC. Beyond 

 B all three curves coincide ; B is therefore the highest tempera- 

 ture at which the amorphous modification can exist. This limit 

 lies at about 650 in the case of copper, 395 in that of 

 aluminium and at 710 in that of a homogeneous alloy 

 containing 80 per cent, of copper and 20 per cent, of nickel. 



The hypothesis is ingenious but the continued existence of 

 the amorphous modification at such high temperatures is con- 

 trary to the evidence of experiments on the elasticity and 

 thermo-electric power of worked metals, which indicate lower 



Fig. 5- 



recrystallisation temperatures, about 250 for copper. The 

 sharpness of the break in the curve at B does not serve to 

 suggest that the point is merely the upper limit of a crystal- 

 lisation which sets in with great rapidity at a temperature 400 

 lower and there are other difficulties which need further 

 elucidation. 



In spite of the closeness with which the hypothesis of an 

 amorphous modification fits the facts, it has not met with 

 universal acceptance. The view also finds favour 1 that con- 

 tinued cold-working involves merely a greater and greater 

 development of slip-bands, so that the individual crystalline 

 masses which remain unchanged in form become smaller and 

 smaller but without the appearance of any new form of 

 material. 



1 O. Faust and G. Tammann, Zeitsch. physikal. C/iem. 19 10, 75, 108. 



