Chemistry. — “Zrtension of the law of Braun’. By P. H. J. HOENEN 
S.J. (Communicated by Prof. Scarempmakers). 
(Communicated at the meeting of September 27, 1919). 
Through the brilliant researches which have been carried out in 
recent years in the Van ’r Horr-Laboratory, attention has again 
been directed to the so-called Braun’s law. At present this is gene- 
rally expressed by the formula 
(=), Ox as: TAV ( 
ee 
: Ow 
in whicb, for the equilibrium solid-liquid, (=) represents 
p/T 
a dar 
the pressure coefficient of the solubility, ai the temperature 
p 
coefficient, Q the differential heat of solution, AV the differential 
increase in volume. 
This law of Braun is a particular case of a general law which 
we shall proceed to develop. 
1. Let us suppose we have a solution saturated with respect to 
n solid substances. Let the quantity of solvent be one mol, and let 
the amount of the dissolved substances, which are present in the 
saturated solution at pressure p and temperature 7, be w,y,2,.... 
mols. Then in this case the following relation holds: 
Ox Q, 0a 0 y Q, Oy 
AS 2E En eA eee : oe SUA Wy == 
5 i T (Ge). G) CT ea) ma ne 
Here Q, represents the heat necessary for the solution of one mol 
of the first component in an infinitely large quantity of solvent of 
the given composition at constant pressure p and temperature 7’. 
It is therefore the differential molecular heat of solution of this 
component. QV, is the corresponding volume increase, i.e., the 
differential molecular volume increment. The other symbols require 
no farther explanation. If we are dealing with one. substance only, 
Oa” Q, On 
fs | ( a pf A V, = 0, 
Op/7 T dT), 
(2) becomes: 
