VI. ON SOLUBILITY. 841 
Measurements were made by Gibson and Denison *** of the strength 
of hydrogen chloride solutions necessary to cause precipitation of 
chlorides from their saturated solutions. The experimental results 
obtained led these authors to conclude that the ‘ laws of ionic dissocia- 
tion ’ very far from satisfactorily explain solubility phenomena, and this 
they considered to be due to the fact that no account is taken of hydrated 
ions and of undissociated molecules in solution. 
Mention must also be made of the study made by Forbes 41? of the 
solubility of silver chloride in the presence of many other chlorides and 
of the research of Barre*°* which showed that the sulphates of 
lanthanum and cerium are more soluble in solutions of ammonium 
sulphate than in solutions of either the sulphate of sodium or potassium. 
VI. Mutual Solubility and Distribution Coefficients. 
1996. The problems presented by the distribution of a substance 
between two solvents continued* to engage the attention of 
Jakowkin.* He studied the distribution of iodine and bromine between 
water and respectively carbon bisulphide, chloroform, &c., and found 
that the amount of halogen dissolved in the organic liquid and the amount 
dissolved in water diminish on dilution and appear to approach a limiting 
value. It was found by Tolloczko’ that when a racemic mixture dis- 
tributes itself between water and an optically active solvent no separa- 
tion of the racemate into d and | forms was observable. 
Le Chatelier ® published a continuation of his research on the mutual 
solubility of salts.+ He found that the graphs representing melting 
point and composition of melted portion, showed maxima which occur 
usually in the neighbourhood of points where the composition is that 
of a definite compound and, in certain cases, for example with lithium 
and potassium carbonates, the maximum region is reduced to a point. 
Some alloys also give curves of this nature. It was also shown 
theoretically that the composition of the melted part is different from 
that of the mixture. 
The graphs for mixtures of sodium sulphate * with certain metallic 
sulphates were found to be different from those previously obtained 
(loc. cit.); the effect of the added sulphate being to raise, or at any rate 
not to lower the melting point of the sodium sulphate. 
In a later communication by the same author,” 1897, it was stated 
that mixtures of alkali sulphates with alkaline earth or other metallic 
sulphates form a group of mixtures which do not fall into either of the 
three general classes previously enumerated. t 
Aignan and Dugas 2! examined the behaviour of benzene and acetic 
acid when mixed together in various proportions and carefully studied 
the homogeneous mixtures which form at different temperatures. 
1898 In the following year, a summary of the previous work on the 
‘ mutual solubility of liquids was given by Rothmund.*** He 
expressed the opinion that the general form of mutual-solubility graphs 
for two liquids not completely miscible is a closed curve. He also classi- 
fied a number of liquids with regard to their mutual solubility and observed 
* Vide Part I. R, 243, + Vide Part J, R, 221. = { Vide Part I. R, 221, 
