651 
actually found, and there thus appeared to exist a very close 
agreement between the equilibria of a solid with a liquid phase on 
one side, and two solid phases on the other side. 
Already a few years after these publications Fock ') undertook 
an investigation on the partition of a third substance between mixed 
crystals and solutions, but there was not found a constant value 
for the coefficient of partition in a single case. If, therefore, this 
investigation had not been open to criticism, the conclusion might 
have been drawn from it, that the law of partition cannot be 
applied here. 
Fock’s results did not carry conviction, however; 1. because he 
omitted to examine the equilibria in which the substance to which 
he wanted to apply the law of partition was present in small concen- 
trations; 2. as he underrated the difficulties to obtain a homogeneous 
mixed crystal phase. 
BeLiatr and Lusanna’*) and also RoramunD tried to determine the 
molecular size of the dissolved substance from the lowering of the 
transition point of KNO, by the application of Van ’r Horr’s well- 
known formula for the lowering of the freezing point, in which 
the heat of transition was then substituted for Q. 
RorHMUND *), however, soon saw, that this formula is not valid 
when mixed crystals are deposited, and for this case arrived at the 
formula: 
Ree 
Gs IG ree TROUT. Seat EY 
in which: 
M, = mol. weight of a solvent. 
x, == eoncentration of the first phase. 
Lp = Dn Seconde 
This formula is valid, and follows immediately from VAN DER 
Waars’s general equation for two-phase coexistence : 
dv | dn ’ 
Uo 2 (v,— @,) dp = In. ne, %,) |az == 
dx, /P.T. da, / P.T. 
era) ae 
ve vy de, Pae 
When the considered mixed crystals contain very little of the 
1) Z. f. phys. Chem. 12, 657 (1893) 
Z. f. Kryst. 28, 336 (1897). 
2) Atti de Reale Instituto Veneto [7] 26, 995 (1891). 
3) Z. f. phys. Chem. 24, 705 (1897). 
