568 C. H. Mathewson — Metallographic Description 



the time factor may be disregarded and an approximate idea 

 of the temperature of anneal deduced from the grain charac- 

 teristics. Since, the degree of homogenization (as revealed by 

 etching) is also a function of the temperature and time of 

 anneal, it should be possible to obtain a graphical solution for 

 both variables through the medium of the homogenization curve 

 and the curve of grain size. Unfortunately, however, every 

 adjustment of the two variables (temperature and time) to a 

 given degree of homogenization corresponds to about the same 

 grain size, i. e., the two curves are parallel, as far as could 

 be determined by these experiments. This points to some 

 relationship between the phenomena of diffusion (homogeniza- 

 tion) and of recrystallization. Pure metals recrystallize after 

 strain-hardening and, since they are of uniform composition 

 throughout, the ordinary process of diffusion cannot occur in 

 them. Molecular movements from one sphere of attraction 

 into another do occur during recrystallization and these are not 

 incomparable with the diffusional migration of molecules, 

 particularly if we argue on the basis of a modification hypo- 

 thesis, such as that advanced by Posenhain (1. c, p. 560). 

 Apart from theory, the present experiments indicate that, in 

 the structural reorganization of the metal at elevated tempera- 

 ture, the degree of concentration adjustment is not unrelated 

 to the growth of grain. 



With respect to the past history of the Peruvian bronzes, 

 the present experiments show that a structure of the sort 

 represented by fig. 49, which is characterized by a grain count 

 of 33 and a degree of homogenization between D and F, cannot 

 be accurately placed as regards time and temperature of 

 anneal, e. g., it might have been produced by a 5-10 minute 

 period of anneal at 700°, or by a period in the neighborhood 

 of 2 hours at 625°. In any event, it is practically certain that 

 the temperature did not reach bright red in the annealing of 

 this specimen, since, under these conditions, homogenization 

 would have resulted almost immediately and the grain would 

 have grown to much greater size. Broadly speaking, small 

 grains and inhomogeneous structures are characteristic of 

 anneal at the lower temperatures. 



For comparison with the chill-cast bronzes of fine texture, a 

 single ingot (92 per cent copper) was cooled at the much 

 slower rate of 150° per minute through its freezing range. 

 This sample measured about 0.1 mm. between branches; 

 approximately three times as much as in the case of the chill- 



