128 SCIENCE PROGRESS. 



results are satisfactorily accounted for. The diminution 

 of solubility when much naphthalene is present is the 

 normal depression of the solubility of the compound by 

 the addition of excess of naphthalene. The solubility 

 greater than that of pure naphthol is the solubility of the 

 compound naphtholnaphthalene. The constant solubility 

 (equal to that of /3-naphthol) observed when there is little 

 naphthalene in the mixture is the solubility of /3-naphthol, 

 for the naphthalene in the mixture is in the form of the 

 compound naphtholnaphthalene, which is decomposed at 

 the surface by water into naphthalene and /3-naphthol, 

 which exist now alongside of each other and not in the 

 intimate union of a crystalline isomorphous mixture. 



In connection with the results of these experiments 

 Klister is inclined to make a distinction between crystalline 

 isomorphous mixtures and solid solutions proper, because in 

 the former there is practically no diffusion owing to what 

 may be termed the rigidity of the crystalline structure. 

 He admits, however, that no absolutely sharp line can be 

 drawn, as there are various intermediate degrees in which 

 diffusion may take place. A reference to the examples of 

 diffusion in solids previously cited in this paper will show 

 that they all occur in amorphous bodies without any regular 

 structure. 



A point of considerable interest in the theory of solid 

 solutions is that it affords us the possibility of determining 

 molecular weights of the dissolved substances, and since in 

 isomorphous mixtures we usually attribute similarity of 

 molecular structure to the two components, we can also in 

 this case form an estimate of the molecular weight of the 

 solid solvent. From his experiments on the amount of /3- 

 naphthol dissolved by water from mixtures of that substance 

 with naphthalene, Kiister was able to calculate with a high 

 degree of probability the molecular weight of each of these 

 substances in the solid state. In the first place he found 

 that with mixtures containing excess of naphthalene the 

 ratio of the square root of the concentration of /3-naphthol 

 in the solid mixture to the concentration in the aqueous 

 solution saturated by that mixture was very nearly constant, 



