1897.] Metallic Alloi/s and the Theory of Solution. 409 



WEEKLY EVENING MEETING, 



Friday, April 2, 1897. 

 George Matthey, Esq. E.R.S. Vice-President, in the Chair. 



Charles T. Heycock, Esq. M.A. F.R.S. 



Metallic Alloys and the Theory of Solution. 



The term alloy in its technical sense is used to indicate a solid 

 mixture of two or more metals. The earlier investigators in this 

 field, such as Matthiesen, Eiche and many others, worked mainly 

 with solid alloys, and they endeavoured to investigate the change in 

 properties of the alloy, such as conductivity for heat and electricity, 

 malleability, ductility and the like, with successive small changes in 

 composition. 



This method, although well adapted to bring out properties of 

 alloys suitable for use in the arts, has not till recently shed much 

 light on the real constitution of this interesting group of substances. 

 Chemists have neglected the subject because the ordinary processes 

 by which they attack problems fail them when dealing with alloys, 

 on account of their opacity, want of volatility and power of being 

 separated from one another by crystallisation. Another difficulty 

 arises from the fact that the resulting alloy has usually the same 

 colour as the metals from which it is produced, except in a few cases, 

 such as the rich purple alloy of gold and aluminium investigated by 

 Professor Eoberts-Austen, and the alloy of zinc and silver noticed 

 by Matthiesen and investigated by Neville and Heycock, which has 

 the property of taking a superficial rose tint when heated and 

 suddenly cooled. 



During the past twelve years considerable advance has been made 

 in the study of alloys by investigating some of their properties whilst 

 in the liquid state, such as the temperature at which solidification 

 commences; it is convenient to term this temperature the freezing 

 point. Le Chatelier, Roberts-Austen, Neville, myself and others 

 have all worked in this way. The result of this work may be very 

 briefly stated as follows. 



Solutions of metals in one another obey the same laws that regulate 

 the behaviour of solutions of such substances as sugar in water. For 

 example, if we take solutions of sugar of different concentrations, but 

 not exceeding 3 or 4 per cent., we find that within these limits the 

 lowering of the freezing point is nearly proportional to the con- 

 centration. Exactly in the same way, if we add to a quantity of 

 molten sodium (freezing point 97° C.) some gold, we find the gold 

 dissolves much in the same way that sugar dissolves in water. On 



