IIT.a. ON SOLUBILITY. 803 
substances sublime, Arctowski!* came to the conclusion that in order 
to test the validity of the so-called ‘laws of solubility ’ the simplest 
case should be studied first—namely, the dissolution of a solid in a 
gas. This he considered to be a case of purely physical dissolution— 
that is to say, one in which the effect of the solvent is reduced to a 
minimum. He regarded measurements of vapour-tension of solid 
bodies as measurements of their solubility in the surrounding medium. 
It was anticipated by Tolloczko 7 that optically active solvents would 
show a preference for optically active solutes; but experiments made 
with two optically active components of a racemic mixture in equi- 
librium with water and an active solvent have shown that this is not 
the case. 
1902 The solubility of carbon monoxide in binary organic mixtures 
‘ was studied by Skirrow,1?® who observed the existence of a 
relationship between solubility and the surface tension of the liquid 
used, mixtures which exhibit a minimum surface tension—for example, 
benzene and acetic acid—being also found to exhibit a minimum 
absorption. 
1903 In the following year interesting observations regarding the 
“~"" physical state of the solvent as conditioning solubility were made 
by Centnerszwer and Teletoff.!*? These authors found that substances 
such as anthracene and anthraquinone are much more soluble in liquid 
sulphur dioxide at temperatures near its critical point than at lower 
temperatures. The solubilities measured at the critical point were 
regarded as the mean solubilities in the liquid and in the vapour of 
the solvent, and depend upon the volume of solvent used. If the 
original volume of liquid taken is large enough, the vapour phase may 
disappear on heating, in which case the solubility determined is that 
in the liquid alone. 
The work of Andreas Smits 18° showed that solutions of a solid 
in a vapour—anthraquinone in ether—can become supersaturated, and 
that the transition to the stable phase involves passing through a meta- 
stable phase—namely, a supersaturated liquid solution. 
1906 Winkler 2®2 confirmed the rule he had put forward * that the 
* change in the absorption coefficient of a gas is proportional to 
the change in the internal friction (viscosity) of the solvent. In the 
same year Christoff ?** found a relationship between the surface tension 
of a liquid and its ability to absorb gases. Curves were plotted showing 
the variation in the solubility of the gases H,, N,, O,, CH,, CO, and 
CO, in sulphuric acid of varying strength; these all showed minima 
corresponding with the maximum surface tension of the liquid. 
Further, if a number of liquids be arranged in descending order of 
magnitude of their surface tension, they are then in ascending order 
of magnitude of their power to absorb carbon monoxide. 
1907 From a study of the solubility of gases in binary mixtures 
‘ of organic liquids and the compressibility of the latter. 
Ritzel 2®4 concluded that the power of a liquid to dissolve a gas is 
intimately connected with its compressibility; in support of that con- 
clusion he cited Just’s work, which showed that the ratio of the 
* Vide Part I., R. 190. 
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