On the Structure of Metals, its Origin and Changes. 151 



tions in detail, and they conclude the first part of the paper by stating, 

 that they do not contest in any way, as their previous publications 

 abundantly prove, the importance of the part which may be played in 

 the mechanical properties of the alloys by the residues which remain 

 liquid after the main mass of the alloy has solidified, the alloys being- 

 tested either at the ordinary temperature or when heated. But, in 

 order that it may be possible for such cements to intervene and affect 

 the mechanical properties of alloys, the cements must at least have a 

 real existence. Nothing indicates that they do exist in ten out of 

 twelve of the alloys examined. The authors do not express them- 

 selves too positively on this point, for some new method of etching 

 may reveal new facts. The impurities which are sought for may 

 happen to concentrate themselves beyond the particular region which 

 has been sectioned. These are, however, gratuitous suppositions. 

 Polishing only indicates the presence of cement in two cases. The 

 little secondary crystals which are described in the paper might 

 readily be mistaken for cements, of definite or indefinite composition, 

 if they were found only in certain specimens, and then in such pro- 

 portions 'as could be accepted. But they occur everywhere, and in all 

 cases with identical appearances, forms, and dimensions; and, moreover, 

 are seen tb be collected into crystallites which pervade the whole mass. 

 These are, therefore, usually and indubitably due to the crystallization 

 of gold itself, although the alloying substances sometimes (indium and 

 probably potassium) join up the crystals in question. For the same 

 reason the dark line of the joints, traced as furrows by the etching, 

 are very rarely the empty tracks of cement which has been dissolved 

 away by aqua regia ; their formation, which it is easy to follow in all 

 its phases, directly connects them with secondary crystallization. 

 The authors are led to the belief that in the case of ten of their 

 alloys of the gold with about 0*2 per cent, of various impurities, 

 solidification of the whole mass has been directly accomplished at a 

 single time, and that the foreign bodies have remained as solidified 

 solutions, as they were fltiid solutions when the alloys were liquid, 

 the impurities being dissociated into their ions in both solid and 

 liquid. Under these conditions it is difficult to invoke, as explaining 

 the mechanical properties of the alloy, the intervention of hypotheti- 

 cal " cements " with relatively low fusing points. 



In the second part of the paper attention is directed to the fact 

 that gold alloyed with bismuth, thallium, antimony, and aluminium 

 has its structure entirely changed by annealing it in sulphuric acid 

 at about 250. The large grains of the metal become divided into a 

 multitude of little polyhedral grains. Nothing remains of the 

 original structure, and the effect closely resembles that which is 

 obtained by annealing steel castings at a bright red heat (800). It 

 is pointed out that whatever this observation may signify, the trans- 



