582 G. H. Mathewson — Metallographic Description 



contrasty etching with acidified ferric chloride. One of these, 

 fig. 51, shows the structure of the pin and the change of struc- 

 ture which occurs on passing through the pin into the adjacent 

 metal, while the other, fig. 52, shows the structure at the base 

 of the hemispherical depression just below the pin. The 

 latter is typical of the crystallization at large. 



The present alloy contains a low percentage of tin (2.11) 

 and a high enough percentage of silver (0.81) to give it a 

 ternary aspect. Without special knowledge of the ternary 

 relationships involved, it is not possible to fix the identity of 

 a bright secondary constituent which was observed in the loca- 

 tion commonly held by the a X § complex. This constituent 

 is not of eutectoid appearance, nor may it be positively identi- 

 fied as the sulphide constituent usually found in these bronzes, 

 although similar in many respects. It is barely distinguishable 

 between the lobes of some of the grains in fig. 52 (in the form 

 of bright points). The somewhat deeper etching in fig. 51 has 

 obscured this structural feature at the present magnification. 

 It may be observed, in this connection, that sulphur was not 

 reported in the analysis of the present object (cf. Table I). 

 For present purposes it is not essential that the nature of this 

 structure-element be ascertained and no further experiments 

 were devoted to this question. Far more important is the fact 

 that it occurs with well-marked characteristics both in the pin 

 and in the body of the object, whereby we may affirm that both 

 parts are composed of the same metal. 



While the structure of the pin is distinctly different from 

 the structure of the adjacent metal, in that twinned elements 

 abound in the former but are entirely lacking in the latter, the 

 transition from one to the other is gradual and continuous ; 

 no mechanical union, welded or soldered joint, or duplex 

 casting could furnish the degree of continuity revealed in fig. 

 51. There is no doubt that the pin was cast along with the 

 rest of the metal, i. e., the object was completely formed in 

 one casting operation. In the tabulated summary of metal- 

 lographic results, it is suggested that congenital twinning may 

 have occurred in this object. The comparatively small volume 

 of metal comprising the pin probably solidified first and realized 

 an appreciable fraction of its total shrinkage by the time it 

 was gripped by the adjacent metal. Subsequent contraction of 

 the latter might then have overstrained it at a temperature 

 favorable to recrystallization. This is purely a provisional 

 explanation. The facts and conditions pertaining to congenital 



