of Bronzes from Machu Picchu, Peru. 569 



castings. A period of 60 minutes at 775° was required for 

 homogenization. This is about three times as long as the 

 corresponding period for the chill-cast specimens. On the 

 basis of this single experiment, the period of homogenization is 

 roughly proportional to the distance between branches. 



The general diffusional characteristics of these alloys are 

 shown in diagrammatic form in fig. 8. Here, the region of 

 homogeneity is shaded and the boundary curve, ab, represents 

 the time-temperature values for complete homogenization. The 

 wedge-shaped outlines represent the gradual disappearance of 

 cores from broad end to point ; the width at any marked position 

 corresponding to a given degree of homogenization, D, V, VVF, 

 etc. Along with this lettering, the corresponding grain count 

 is given in figures taken from the original data and otherwise 

 plotted in figs. 2, 3, 4, and 7. Curves, which may be con- 

 veniently called isozonal, are drawn through the temperature- 

 time points corresponding to the same degree of homogenization 

 (same zonal characteristics). It will be observed that the 

 isozonal grain count is practically constant. For example, the 

 counts along the VVF curve are 20 at 850°, 21 at 775°, 22 

 at 700°, and 21 at 625°. These experiments do not prove that 

 a definite grain count invariably corresponds to a given degree 

 of homogenization however this may be effected. They merely 

 indicate approximate parallelism of the isozonal curves and 

 the curves of grain size in bronzes of this particular character 

 and treatment. The general question is a broad one, requiring 

 for its solution a wealth of experimental data in which difficult 

 counting problems as well as difficulties in the way of 

 characterizing the degree of homogenization will be encountered. 



Metallographic Description of the Individual Objects. 



The objects are numbered according to Table I.* Drawings, 

 diagrams and photo-micrographs are assembled in figs. 9 to 97, 

 pp. 559, et seq. The weights of the objects are given in 

 Table I. A brief summary of the structural characteristics 

 and probable treatment of the objects, along with a key to the 

 illustrations and photo-micrographs and designation of the parts 

 examined, is given in Table II. f The following list of prin- 

 cipal dimensions will serve to fix the scale to which illustrations 

 and drawings have finally been adjusted: 



* See p. 531. 



f See pp. 532 to 535. 



