SOLID SOLUTIONS. 127 



three liquids, ether, water, and benzene, ether and water are 

 partially miscible, benzene and water are immiscible, and 

 ether and benzene miscible in all proportions. Suppose we 

 take water as the original solvent — then on shaking it up 

 with ether we find that the latter dissolves to a certain 

 definite extent in it, i.e., possesses a certain solubility 

 in water. If now we previously dissolve benzene in the 

 ether which we shake up with the water, we find that the 

 water will now take up less ether than before. The solu- 

 bility of ether in water is thus diminished when benzene is 

 dissolved in it — and this behaviour is characteristic of all 

 such combinations of substances. 



A case of this kind where two solids play the part of the 

 ether and benzene in the previous instance has been 

 thoroughly studied by F. W. Klister. The solid hydrocarbon 

 naphthalene is, like the hydrocarbon benzene, insoluble in 

 water ; /3-naphthol, on the other hand, is, like ether, 

 sufficiently soluble in water to permit of accurate estimation. 

 But naphthalene and /3-naphthol can crystallise together in 

 any proportion so as to form a complete series of isomor- 

 phous mixtures, the melting-points of which vary according 

 to the rule given above for mixtures of antimony and tin. 

 A comparison of the amount of /3-naphthol dissolved by a 

 given quantity of water from such mixtures led to some- 

 what unexpected results. Instead of the addition of a 

 small quantity of naphthalene to /3-naphthol lowering the 

 solubility of the latter in water, it was found that mixtures 

 containing as much as 30 per cent, of naphthalene had 

 precisely the same solubility as /3-naphthol itself. As more 

 naphthalene was added the solubility increased slightly, 

 afterwards to diminish continuously to zero as the mixture 

 was made to contain more and more naphthalene. The 

 explanation of this behaviour suggested by Klister is that 

 naphthalene and /3-naphthol are capable of forming a chemi- 

 cal compound consisting of one molecule of each substance, 

 this compound being decomposable by water, an assumption 

 by no means improbable, as many similar cases have been 

 observed. If we allow further that the solubility of the 

 compound is greater than the solubility of /3-naphthol, the 



