go SCIENCE PROGRESS. 



dissolved metal. It follows, if the theory can be trusted, 

 that the molecule of a metal when in dilute solution consists 

 of one atom. There are numerous exceptions to this rule ; 

 for example, aluminium when dissolved in tin appears to 

 form diatomic molecules, and the same is true for zinc pal- 

 ladium and mercury when one of these metals is dissolved 

 in cadmium. 



But the nature of the solvent has certainly an influence, 

 over and above that attributed to it by the above formula, 

 in determining the depression ; and from what follows it 

 will be seen that the aggregation of the dissolved body into 

 more complex molecules is not the only possible explanation 

 of these abnormally small depressions. 



In a few cases the dissolved metal, instead of causing" a 

 depression in the freezing point of the solvent, produces a 

 rise. Antimony dissolved in either tin or bismuth, and 

 silver in cadmium or in zinc, produce this effect. 



In these cases of a rise in the freezing point experiment 

 has shown that the portion of the mass which solidifies first, 

 instead of being the pure solvent, is richer in the dissolved 

 metal than either the original liquid or the still fluid por- 

 tion. Van't Hoff 1 has given a theory which fully accounts 

 for this phenomenon. He shows that whenever the matter 

 which separates first contains both metals in the form of a 

 homogeneous mixture, or, as he terms it, a "solid solution," 

 there will either be a diminished depression or a rise in the 

 freezing point. It is worthy of note that in these cases we 

 observe, not the formation of a small amount of solid, but 

 a real rise in the temperature at which the mass of the 

 alloy solidifies and sets in the solid form, even when less 

 than i per cent, of the second metal has been added. 



If we exclude for the moment cases in which the two 

 metals are combining chemically, and these cases do not 

 seem to be extremely common, it follows from what has 

 been said, that a mixture of two metals in a completely 

 molten state is either homogeneous or is a mechanical 

 mixture of two conjugate liquids, each of which may be 



1 Zeitschrift fiir Physikalische Chemie, bd. v., p. 332. 



