70 MOLECULAR WEIGHT AND POLYMERISM 



3. SOLID SoLUTioxs 1 . 



There seems a prospect of extending the theory of 

 solutions which allows of determining molecular weight in 

 solution, to homogeneous solid mixtures. This possibility 

 is conveyed by the expression ' solid solution ' for such 

 homogeneous mixtures. 



According to the data which are at present available for 

 testing this assumption, it seems necessary to distinguish 

 between amorphous 'solid solutions/ such as e.g. the glasses 

 which are homogeneous mixtures of silicates, and isomor- 

 phous mixtures/ The latter are further removed from 

 solutions just on account of their crystalline structure, 

 whilst for the glasses there is a continuous series of states 

 connecting the solid and liquid conditions that almost 

 excludes any limit to the applicability of the laws of 

 solution. Only the equilibrium reached by diffusion takes 

 more and more time to reach on account of the increasing 

 viscosity, and consequently the difficult problem in the 

 8tudy of such solid solutions lies in the establishment of 

 the necessary equilibrium. 



Qualitatively these solid solutions, both crystalline and 

 amorphous, have much in common with liquid solutions, 

 but on the quantitative side of the problem it is necessary 

 first to keep to amorphous, or occasionally crystalline solid 

 solutions, whilst isomorphous mixtures in the narrower 

 senses will be discussed in the third division under molecular 

 structure. 



First, a few leading traits of a qualitative character may 

 })e touched upon l . 



A. Qualitative Considerations. 



As regards qualitative features, first come the experi- 

 ments on the lowering of vapour pressure of solids when 



1 Bodlander, Neues Jahrbuchf. Mineralogiej Geologiej Palaontologie, 1898. 



2 Van 't Hoff, Zeitschr. f. Phys. Chem. 5. 322. 



