536 G. H. Mathewson — Metallographic Description 



constituent was identified metallographically (cf. observations 

 on cuprous sulphide in copper by Heyn and Bauer (4)) in 

 every bronze examined, although sulphur was not reported in a 

 number of the analyses.* One specimen, No. 8, contains 

 nearly a per cent of iron and another, No. 4, contains about 

 the same quantity of silver. Others contain smaller percent- 

 ages of these elemnts, while small amounts of zinc were found 

 in two specimens. The rest of the bronzes contain practically 

 no metallic impurities. Two silver discs are also very pure, 

 one containing a trace of lead. 



Perhaps the most noteworthy specimen is No. 30, which 

 consists of very nearly pure tin. Other specimens were found 

 in which strips of the metal were rolled into the form of a 

 ball, presumably intended for convenience in cutting small 

 pieces to alloy with copper. This metal was not analyzed but 

 it is unquestionably tin of good quality. Probably the dis- 

 covery of these specimens constitutes the first direct proof that 

 Inca metallurgists were acquainted with tin in elementary 

 form. It is fair to infer that they used it in preparing their 

 bronzes. 



On the other hand, it is certainly true that the proportion 

 of tin present in any given case has not been chosen with par- 

 ticular regard to the use for which the object must have been 

 intended. The largest percentage of tin was found in a small 

 spatula- or spoon-shaped object (No. 2) which is particularly 

 distinguished by a perfectly executed cast figure of a humming 

 bird at the extremity of the handle. This specimen contains 

 13.45 per cent tin. Next in order, we have another artistic 

 casting representing a prostrate fisher-boy with line and fish 

 which, although worked (mildly) into a blade below the figure 

 (cf. fig. 13), could never have been intended for severe use. 

 This object contains 9.39 per cent tin. The ordinary axes and 

 knives, which would seem to require high percentages of tin 

 to give them maximum hardness and strength, carry from 3 to 

 9 per cent of this element, most of them in the neighborhood 

 of 5 per cent. One knife, No. 9, is composed of very nearly 

 pure copper. Boman (5) points out similar anomalous rela- 

 tionships in discussing a table of some 65 analyses representing 

 the compositions of various objects found in Argentina, Bolivia, 

 Peru, and Ecuador. 



* When we consider that one part by weight of sulphur yields about five 

 parts of cuprous sulphide, the constituent which appears under the micro- 

 scope as a distinct structure element, it is apparent that the micrographic 

 method may well be superior to methods of chemical analysis in detecting 

 small quantities of sulphur in bronze. 



