(asm ) 
and L, p the total concentration, /> , the content in D, p ( the content 
in L, S the sp. gr. of the solution and l the length of the tube. 
This manner of calculation, however, is not admissible; for at a 
total concentration p and a content p d for D, we have a content pi 
for L and p — p d — p for R and the equation thus becomes: 
100« 
7 7s = - p d + -Pi + KVO’ - Pj-Pi)- 
In this are known a, \a d \ D , [a^ , [aj^ , p, l and S. 
The equation contains two unknown quantities and therefore we 
cannot get an insight into the inner composition of the solutions saturated 
with (/? -j- D), (R + L ) or (Z) -f- L) by means of a poiari metric determi¬ 
nation, even when assuming that the three compounds which occur 
in the solvent do not affect each other’s rotations (which has not 
been ascertained). 
To this it may be attributed that Ladenburg and Doctor found 
the point P, that is the transition point, on the line OR, whereas I 
have reasons to conclude that the isotherm of the temperature of the 
transition point, like all others, retains its asymmetric form. 
This untrustworthy method of analysis has been applied by Findlay 
and Hickmans in their investigation of the partial racemism of the 
/-menthyl-r-mandelic ester, which must be considered as the binary 
compound of the 7-menthyl-Z-mandelic ester with the /-menthyl-/-man- 
delic ester, a fact which has been clearly shown by the authors l ) from 
the form of the melting point curve of those two esters. The partially 
racemic ester the binary system formed by possesses in this system 
a melting point curve of its own with a flat top and has, therefore, 
been partly resolved in the fused mass into the two components. 
In their second publication *) the solubility isotherms are given at 
35°, 25° and 10°. Of each isotherm only five points have been deter¬ 
mined, namely, the solubilities of D, L, R, R + D and R -f 
whilst the solutions (Z2 + D) and (R + L) have been analysed accord¬ 
ing to the above mentioned method. 
It now appears to me that their graphic representation, which I 
reproduce, shows at once the deceiving conclusions drawn from the 
polarimetric method. If we look at fig. 2 we observe that the solubility 
of the Z-acid ester decreases on addition of the /-acid ester to the 
solution at 10°, whilst it increases at 25° and 35°. 
l ) Findlay & Hickmans Journ. chem. Soc. Trans. 91, 905, (1907). 
8 ) Ibid, 95, 1386 (1909), 
