150 Mr. F. Osmond and Prof. W.'C. Roberts-Austen. 



and free metals, chemical compounds, or various alloys may fall out 

 of solution from the liquid mass, and, finally, the eutectic alloy solidi- 

 fies, but its presence, as a residual fluid facilitates the arrangement of 

 the parts which have previously solidified. 



One of the authors in collaboration with M. Werth* was prob- 

 ably the first to direct attention to the influence which these fusible 

 residues, to which the name of " cements " was given, exert on the 

 working of steel and on the mechanical properties of the finished 

 products of steel manufacture. Since then M. Andre le Cbatelierf 

 has repeatedly insisted on this point, correctly enough as a prin- 

 ciple, though perhaps with a tendency to generalise too much from 

 ideas which are, in themselves, accurate. 



It is possible to distinguish in metals and alloys both the visible 

 structure and the 'molecular structure, and between them, such 

 methods of investigation as it is possible to adopt, enable a well 

 defined line of demarcation to be traced. Attention must, therefore, 

 be directed to ascertaining to what extent the mechanical properties 

 of a given sample of metal are due to each of these kinds of struc- 

 ture, and how far to their mutual relations. This being the case, 

 the authors considered that it would be interesting to submit 

 the gold, containing 0'2 per cent, of various elements, to micro- 

 graphical examination, and, fortunately, the identical specimens 

 which were submitted to the Royal Society, eight years ago, had been 

 preserved intact, and were available for examination. 



Descriptions are then given in detail of the methods adopted in 

 preparing, polishing and etching the micro-sections of gold alloyed 

 with various impurities, photographs of which sections illustrate the 

 paper. It is difficult to give a brief abstract of the authors' conclusions, 

 but they may be stated as follows. They consider it to be certain 

 that there is no relation between either the structure, the appearance 

 of the fractures, the melting points of the alloyed elements and the 

 mechanical properties of the masses of alloyed gold. They observe 

 that every iron metallurgist who examined the photograph of the 

 micro-section of gold with potassium would form a highly favourable 

 opinion a.s to the mechanical properties of the mass it represents, 

 while it is really, from a mechanical point of view, the worst of the 

 series. On the other hand he would think that the micro-section of 

 the gold alloyed with zirconium, indicated a structure of deplorable 

 weakness, while as a matter of fact it might equally well represent 

 alloys which vary in tenacity from less than half a ton per square 

 inch to 7f tons, and are either incapable of being extended, or will 

 elongate 30 per cent. 



The authors then proceed to examine the structure of the various sec- 



* Osmond and Werth, ' Ann. des Mines,' yol. 8, 1885, p. 5. 

 t 'Inst. Mech. Engineers Proc,,' April, 1893, p. 191. 



