of Bronzes from Machu Picchu, Peru. 545 



that, in the fashioning of these objects, ease of working was 

 placed above other considerations, and the composition of the 

 metal adapted to this requirement. 



Recrystallization and Growth of Grain. 



Two prominent metallographists, E. Heyn and Gr. Tammann, 

 have lately dealt with the conditions of recrystallization and 

 growth of grain in overstrained metal. E. Heyn (15) gives 

 curves representing the mean size of grain developed by anneal- 

 ing cold drawn copper wire as a function of the time at four 

 different temperatures, 500°, 700°, 900°, and 1000-1050° C. 

 Experiments were also made with soft iron wire. Owing to 

 the' transformations which occur in iron, y to (3 at 900° and 3 

 to a at 780° C. and their influence upon grain development, 

 particularly that of the former, attention need not be directed 

 to the latter experiments in considering the grain growth of 

 alpha bronzes, which are not subject to transformation. On 

 the basis of the experimental curves obtained and certain fun- 

 damental considerations, mainly of surface tension, Heyn 

 develops generalizations relative to the crystallization of cold 

 worked metal. 



It is quite evident that, in any particular case, an estimate 

 of the previous treatment to which a given alloy may have been 

 subjected by observation of its grain characteristics requires 

 systematic study of the grain structure developed in a similar 

 alloy under a variety of carefully adjusted conditions. This 

 feature of the present investigation was served by hot working, 

 cold working and annealing under varying conditions a large 

 number (150) of small bronze specimens ranging in composi- 

 tion in three stages from 92 to 96 per cent copper (92, 94, 

 and 96 per cent). It is not the intention in this paper to 

 tabulate the results of these experiments nor to describe them 

 fully. Some pertinent conclusions derived from them will be 

 made use of in the forthcoming description of the individual 

 structures of the ancient bronzes. A number of curves, figs. 

 2, 3, and 4, representing the development of grain upon 

 annealing (a) chill cast specimens, (b) chill cast and homo- 

 genized specimens, and (c) chill cast, homogenized, cold worked 

 and recrystallized (850°) specimens, respectively, all of which 

 had been reduced 25 per cent in area of section by cold ham- 

 mering, will, however, be shown, together with homogenization 

 curves to be described later. These curves are particularly 

 important in that they show the characteristic annealing proper- 



