of Bronzes from Machu Picchu, Peru. 589 



800°. The observed grain count of 10 can be duplicated in 

 ordinary bronze of approximately the same tin-content by 

 annealing for a period of some fifteen minutes at 850°, while, 

 at 775°, more than an hour is required. Separated impuri- 

 ties, such as cuprous sulphide in the present case, as a rule 

 interfere with coalescence and retard growth of grain. The 

 large quantity of sulphide shown in fig. 69 would probably 

 raise the normal annealing temperature corresponding to the 

 grain represented. The object has not been worked severely 

 enough to sensibly alter the rounded character of the sulphide 

 particles. The original casting was, therefore, similar in size 

 and shape to the finished object. Corresponding to the 

 thorough annealing treatment adopted, the metal is completely 

 homogenized. 



Object No. 9 (cf. Table I). 



The knife illustrated in fig. 17 is the only one of the 

 analyzed objects which contains no metal alloyed to the copper 

 base. Cuprous oxide ordinarily occurs in copper and this is 

 the case with the present object. The amount of oxide is 

 considerably greater than that encountered in ordinary com- 

 mercial copper of the present day, in which reduction of the 

 oxide has been effected by the operation of poling, leaving some 

 0.3-0.6 per cent of oxide in the tough pitch metal. Photo- 

 micrograph, fig. 72, represents the structure of the metal in the 

 shank just where it joins the blade. Cf. diagram of position, 

 fig. 70, a. Here, the casting structure may be recognized in 

 the dark areas of dotted appearance which represent the eutectic 

 of copper and cuprous oxide somewhat distorted out of the 

 original casting position by mechanical treatment. According 

 to a rough estimate, the eutectic constituent occupies about one 

 third of the total area of the photo-micrograph. Since this 

 constituent itself contains all of the cuprous oxide in the pro- 

 portion of three and one half per cent of oxide to ninety six 

 and one half per cent of copper, there are about one and two 

 tenths per cent of oxide in the alloy (0.33^ X 0.03% X 

 100). This is twice the quantity previously mentioned. 



That the material of the shank has been moderately worked 

 and then annealed is evident from the moderate extension of 

 the eutectic areas and the recrystallization with twin lamellae 

 shown in fig. 72. The material of the blade has been worked 

 much more extensively, as would be expected from its thinness 

 (minimum, 0.040"). This is clearly shown by the fact that 



Am. Jour. Sci. — Fourth Series, Vol. XL, No. 240.— December, 1915. 

 40 



