of Bronzes from Machu Picchu, Peru. 553 



illustrated by fig. 64, which represents spontaneous recrystal- 

 lization during hot-working. 



As the degree of deformation increases, whether by rolling, 

 drawing, hammering, etc., the curve of fragmental resolution 

 recedes in the direction of maximum resolution, a specific 

 condition for each metal or alloy beyond which further destruc- 

 tion of grain will bring about fracture. Recession in this 

 direction is indicated by the set of curves, T 2 T 5 , T X T 4 , and 

 TjTs- As maximum resolution is approached, the abscissa 

 range covered by the curve becomes narrower, since large 

 fragments give place to smaller ones and the size of the latter 

 cannot be reduced without limit. Ultimately we would reach 

 a condition of uniform resolution into fragments of minimum 

 size. It is improbable that such a condition can be realized 

 without overworking the metal to the point of manifold frac- 

 ture. Thus, the limiting curve, TjTg, is drawn to represent a 

 50 per cent resolution into fragments of minimum size. 



There is, for each metal or alloy, a minimum temperature 

 at which recrystallization will start from a condition of 

 maximum resolution into fragments of minimum size. This 

 temperature is represented by T x in the present diagram. One 

 half of the metal deformed according to the curve TjT 3 

 would recrystallize at T x . At the higher temperature, T 3 , all 

 of the metal deformed according to the curve, T X T 3 , about 85 

 per cent of the metal deformed according to T X T 4 , about 35 

 per cent of the metal deformed according to T 2 T 5 , but no part 

 of the metal deformed according to T 4 T 7 would recrystallize. 

 At T 7 , the grain of all four would be identical and would grow 

 uniformly beyond this temperature. These curves all represent 

 severe deformation, in that the percentage of coarse fragments 

 is low compared with the percentage of fine fragments. In the 

 alpha bronzes, such a condition occurs when the reduction 

 by rolling or hammering is carried beyond some 15 or 20 per 

 cent. Above 700°, provided the annealing period is not con- 

 fined to a short term of minutes, a bronze of definite composi- 

 tion will give uniform grain characteristics whatever the 

 extent of previous reduction beyond the minimum value given. 

 Hence, we may draw certain conclusions relative to heat treat- 

 ment from these grain characteristics without intimate knowl- 

 edge of the previous mechanical treatment. 



Turning now to the effect of anneal upon metal which has 

 received very light deformational treatment, it appears that 

 the curves of fragmental resolution will here assume a some- 



