IV.a. ON SOLUBILITY. 807 
same for different solvents: a ‘law’ which had previously been dis- 
covered experimentally by Just.* 
1911 The solubility of radium emanation in a large number of 
’ liquids was determined by Ramstedt,*2° who found that the 
emanation is more soluble in all liquids examined, except glycerol, than 
in water; it was found to be most readily soluble in carbon bisulphide. 
As regards solubility, therefore, radium emanation is very similar to 
carbon dioxide. + 
IV. A.—Physical. 
Organic compounds of equal molecular symmetry had already been 
shown by Leidie { to be possessed of equal solubility in a given solvent. 
1896 Using a racemic mixture and an optically active solvent, 
* Tolloczko’ was able to show that both optically active com- 
ponents dissolved equally. 
The solubility of supercooled sodium thiosulphate in aqtieous alcohol 
was further studied by Parmentier,? who found that the solubility varies 
with the volume of the solvent, that the concentration of the alcohol 
above the supercooled salt varies, and that a complex condition oi 
equilibrium is established between alcohol, water, and anhydrous salt. 
These results are not in agreement with those previously recorded by 
Bruner. § 
From a study of the physical properties of optical isomerides, 
Walden? concluded that the d and 1 forms of a substance always have 
the same solubility, density, and melting-point. When the racemate 
1897 has a higher melting-point it has also a smaller solubility. 
* Kipping and Pope *® have discussed the relationship between the 
solubility of optical isomerides, racemic compounds, pseudo-racemic 
compounds, and mere mixtures. They point out that many misconcep- 
tions exist. There is no justification for the idea expressed by Walden 
(loc. cit.) that the solubility of a mixture of optical antipodes should be 
twice that of its enantiomorphous constituents. No simple relationship 
is likely to exist in that case or in the case of a racemic compound. The 
opinion was expressed that at present solubility determinations are of no 
value in distinguishing between racemic compounds and mere mixtures. 
Further evidence was obtained by Bruner ?* in support of his contention 
that the solubility of a supercooled liquid must be greater than that of 
the solid substance at the same temperature: he quoted the cases of 
hydrocinnamic acid and thymol, and some work done by Alexejeff with 
salicylic and benzoic acids. || 
1898 The conclusion arrived at by Tolloczko {1 with regard to the 
‘ solubility of optical isomerides in an optically active solvent 
was confirmed by Goldschmidt and Cooper,*® who found no difference 
between the solubility of d- and I-carvoximes in d-limonene. 
1901 The theoretical conclusion of Gibbs, that the solubility of a 
* substance depends, to some extent, upon the size of the particles 
with which the solution is in equilibrium, received experimental proof 
* Zeit. phys. Chem., 37,342. + Vide Just, this Section, 1901. { Vide FartI., R. 90. 
§ Vide Part I., R. 233. || Vide Part I., R. 118. { Vide Part II., R. 7. 
