ON THE STRUCTURE OF METALS. 
419 
the eutectic alloy solidifies, but the presence of a residual fluid facilitates the arrange¬ 
ment of the parts which have previously solidified. 
One of us, 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, could exert on the working of steel and on the mechanical properties of 
the finished products. Since then, M. Andre le ChatelterI' 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. The Reports of the 
Alloys Research Committee, organised by the Institution of Mechanical Engineers,^ 
have, by the aid of autographic curves of the cooling of alloys, brought into promi¬ 
nence a certain number of instances of liquation in the cases of copper and silver, 
copper and bismuth, gold and aluminium, copper and tin. 
Micrographs also reveal the existence of numerous constituents in a great number 
of alloys ; in an alloy of 78 per cent, of gold with 22 of aluminium for instance, grains 
of a definite compound Au Ah, of a brilliant purple colour, are separated by a fine 
network of a white alloy of very different composition^ and numerous other analogous 
examples are to be found in the work of Behrens, || of GuilleminA of Oharpy, ## 
and others. 
In short, we are led to distinguish in metals and alloys both the visible structure 
and the molecular structure, and, between these, such methods of investigation as are 
possible, 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 
such relations as are possible between them. This being the case, we 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 by one of us to the Royal Society eight years ago, had been 
preserved intact, and were available for examination. 
Gold is a metal which may readily be purified to a high degree. It does not 
oxidize in air at any temperature. The influence of occluded gases appears to be small; 
and the quantity of the added element is in each case so small as to favour the view 
that, at least, most of the impurity remains dissolved throughout the mass without 
there being liquation either of definite or indefinite compounds. We have, in fact, 
* Osmond and Werth, “ Ann. des Mines,” vol. 8, 1885, p. 5. 
t “ Proc. Inst. Mech. Engineers,” April, 1893, p. 191. 
+ Ibid., October, 1891, p. 543; April, 1893, p. 102; April, 1895, p. 238. 
§ Tliis observation was not printed, but a diagram of the section was shown at a lecture delivered 
at the Royal Institution, 1891, and has been continuously used since by one of us in class teaching’. 
|| “ Das Mikroskopiscbe Geflige der Metalle und Legierungen,” Leipzig, Voss, 1894. 
II “Commission des methodes d’essai des materiaux de construction,” T. If., p. 19. 
** “ Bull, de la Soc, d’Encouragement,” February, 1896. 
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