SOLUBILITY AND POLARITY 
WM. KUNERTH 
Since the phenomenon of solubility is one of such common oc- 
currence and universal familiarity, it is no wonder that a great 
many attempts have been made to learn the cause of it. The mole- 
cular weight of solute and solvent, the dielectric constants, the size 
of the molecules concerned, the surface tensions of the components, 
adsorption, the vapor pressure above the solution, the magnitude of 
Van der Waal’s a and b for the components, their internal pres- 
sures as determined by a great many different methods - — all these 
and many other avenues of approach have been used, only to be 
discarded again because they did not lead to a solution of the 
problem. Combinations of some of these factors also have been 
investigated in the hope that solubility might be found to depend 
jointly on several of these characteristics. 
In 1885, Van’t Hoff determined the relation existing between 
osmotic pressure and the amount of solute in solution. About the 
same time Arrhenius established a relation between electrolytic 
dissociation and the conductivity of an electrolyte. Two years 
later Raoult conducted a series of experiments which led him to 
establish what is known as Raoult’s Law for vapor pressure, there- 
by connecting the amount of solute in solution with the lowering 
of the vapor pressure above a solution as more and more solute is 
added. Since that time many efforts have been made with this 
work as basis, to determine the cause of solubility. What pro- 
perty of the molecule is brought into play as it dissolves among 
other molecules? What forces are brought to bear upon solute 
and solvent in the act of solution? Are these forces always the 
same? And what has molecular structure to do with the process 
of solution? 
INTERNAL PRESSURE 
The method of attack upon which most stress has been laid in 
recent years is that of Dr. Hildebrand 1 who has relied on internal 
pressure as the main factor in the determination of solubility, 
stating that when two components have equal or nearly equal in- 
1 Hildebrand, Jour, of Amer. Chem. Society, Vol. 38, p. 1452 (1916). 
