1897.] on Metallic Alloys and the Theory of Solution. 



411 



liave been proposed. Notwithstanding that some weighty objections 

 can be urged against this theory, it is remarkable that we can by aid 

 of it predict the numerical values for the fall of the freezing point of 

 different solvents produced by the solution of other substances, 

 provided that we know the latent heat of fusion of the solvent. 



On applying the same reasoning to alloys, we find that the theory 

 holds good, as the table below shows.* We see from this table that 



Observed Depression in the Freezing Point of a Solvent Metal, caused 

 BY the Addition of One Atomic per cent, of a Second Metal. 



in no cases are the observed depressions of the freezing points greater 

 than those calculated from the theory, but in many cases they fall 

 below this quantity ; this latter fact admits of explanation. 



On the theory of Yan'tHoff it is necessary that when a solution 

 begins to freeze the pure solvent should separate out first. This 

 admits, in case of aqueous solutions, of simple proof, for if we take a 

 dilute solution of potassium permanganate and make it freeze slowly, 

 we find that pure colourless ice separates out on the walls of the vessel, 

 whilst the purple permanganate is concentrated towards the centre. 

 This experiment led Neville and myself to try if a similar state of 

 things could be shown for metallic alloys. 



We have great pleasure in bringing before the Royal Institution 

 this evening the first announcement of the results we have obtained. 

 For this purpose we took two metals, gold and sodium, the former 

 being very opaque to X-rays, whilst the latter is very transparent to 

 them. A quantity of sodium was melted in a tube, and gold dissolved 

 in it to the extent of about ten per cent. The alloy was then allowed 

 to cool extremely slowly, and sections (about ^ inch thick) were cut 

 from different parts of the solid alloy and placed between thin plates 



* For the nature of this calculation, vide Heycock & Neville, Chem. Soc. 

 Jour. vol. Ivii. p. 339. Also Neville, 'Science Progress,' October 1895. 



