and free metals, chemical compounds, or various alloys may fall out of solution from the liquid mass, and, finally, the eutectic alloy solidifies, 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 probably 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 Chatelierf has repeatedly insisted on this point, correctly enough as a principle, 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 structure, 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 micrographical 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 as 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 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 Worth, ‘ Ann. des Mines,’ vol. 8, 1885, p. 5.
t ‘Inst. Mecb. Engineers Proo.,' April, 1893, p. 191.
