of Bronzes from Machu Picchu, Peru. 567 



Three compositions were investigated, viz., bronzes contain- 

 ing 96, 94, and 92 per cent copper, respectively. Instead of 

 tabulating the large number of experimental results secured, 

 a single typical diagram is shown (fig. 8) and a general 

 summary introduced, as follows : 



(1) The time required to homogenize a given alloy at any given 

 temperature is very nearly independent of the composition within 

 this narrow range (92-96 per cent Ou). Alloys containing 96 per 

 cent copper seem to lag a little behind those containing 92 and 

 94 per cent copper. 



(2) Homogenization is complete in very few minutes (5 to 8 — 

 with preheating period of 9) at 850°, but requires a period of hours 

 (4-5) at 625°. 



(3) The curve (ab, fig. 8) showing the time required for com- 

 plete homogenization as a function of the temperature indicates 

 a rapidly decreasing temperature-rate of homogenization as 

 lower temperatures are approached. It shows that an infinitely 

 long time would be required for complete homogenization at 

 atmospheric temperatures. 



(4) The time required for homogenization at any temperature 

 is substantially the same whether the metal is annealed in the 

 unaltered cast state, or after strain hardening by cold work, i. e., 

 it is unaffected by simultaneous recrystallization of the metal. 



(5) As opposed to (4), the grain size produced by recrystalliza- 

 tion of strain-hardened metal is highly dependent upon the state 

 of homogenization. By referring to figs. 2, 3, and 4, it may be 

 seen that the two curves showing the number of grains as a func- 

 tion of the time of anneal at given temperature and composition 

 in metal which, in one case, has been cold-worked after casting only, 

 and, in the other case, has been homogenized after casting and 

 then cold- worked (e. g., the curves lettered 700°, cast, and 700°, 

 homogenized, respectively, in fig. 2) lie widely separated from 

 one another. They lie nearer together at high annealing tem- 

 peratures than at low annealing temperatures, obviously because 

 the cast metal homogenizes in the first few minutes of anneal 

 at the higher temperatures and thus becomes identical (in internal 

 composition) with the metal which had been homogenized previous 

 to cold-working. It does not appear, however, that two respective 

 curves at any temperature would ever meet, whatever the annealing 

 period. Thus, the nature of growth in the early stages of anneal- 

 ing cast metal (of zonal structure) exerts some effect on the final 

 grain size, no matter how prolonged the annealing treatment 

 may be. 



It has already been shown that the size of the recrystallized 

 grains in metal of given composition is a function of both the 

 temperature and the time of anneal. Within certain limits, 



