234 
MR. J. C. 4Y. HUMFREY OX THE EFFECTS OF STRAIN 
jected to a certain amount of compression wlien the specimen was re-straightened 
after being bent. A trial was, therefore, made to see if any splitting up of the 
orientation could be produced by tension alone. A crystal was strained in tension 
in the small machine mentioned on p. 230, the stress being applied until local con¬ 
traction and fracture occurred. The two halves were then re-etched and examined, 
and it was found that the greater part of the specimen was unchanged, hut near the 
fracture, where, due to the local drawing out and transverse contraction, the strain 
must have been specially severe, a splitting up had occurred similar to that in the 
bent specimen described above. That is to say, in place of the original uniform 
orientation covering its whole surface, numerous joatches with various orientations 
appeared. 
Ewing and Eosenhain liave already drawn attention to the jirogressive growth 
of crystals which occurs after a specimen of lead or other metal has been severely 
strained, especially wdien the specimen is moderately warmed. On the suggestion 
of Professor Ewing, the autlior next tried the effect of cooking these large strained 
crystals, that is to say, subjecting them to prolonged exposure to moderate tem- 
jieratures. Tlie first specimen tried was one similar to that shown in figs. 10 and 11. 
It had been strained liy bending between the fingers and then re-straightening. After 
etching it was found that a certain area in the centre had re-crystallised, the 
specimen showing a similar appearance to figs. 10 and 11. It was then cooked for 
some hours at a temiierature of about 100° C. and then re-etched. After this treat¬ 
ment the area re-crystallised was far greater than before. This was especially 
striking upon the tension side, where, as in fig. 11, only a few isolated patches had 
existed before cooking; afterwards, however, a large area vus found to have 
changed, the patches with new orientations being quite contiguous, though of rather 
larger individual size than upon the compression side. That such a growth of new 
orientations was in some way due to the straining of tlie siiecimen was clearly 
proved by roasting an unstrained specimen. In this no change was produced, but 
after straining and again cooking the specimen was found upon re-etching to have 
to a great extent re-crystallised. It was also found that it was not necessary for 
the specimen to show any signs of re-crystallisation before annealing, hut that so 
long as a certain amount of strain had been given, whether upon re-etching after 
this strain the orientation showed any signs of alteration or not, yet after cooking 
at 100° C. the re-crystallisation either continued or was started. Specimens were 
strained both by bending and tension, and in both cases a further re-crystallisation 
occurred after heating. It lias been mentioned above that, when a specimen had 
been strained in tension, only a small area near the fracture showed any signs of 
alteration vdien re-etched, but it was found that if such a strained specimen was 
afterwards heated, the whole orientation could he changed. In studying this effect 
it was indeed found to be far more convenient to strain the specimens in tension, as 
the amount of strain to which they were sulijected could be more easily regulated. 
