( 397 ) 
however, also be determined at higher temperatures (by retardation 
in the decomposition) and points like R 1 , R 11 etc. may be thus 
established. 
Similarly, the possibility of determining points like C 11 , C 111 etc. 
is due to the retardation in the formation of R from D -f- L 
and the non-crystallisation of this salt from the solution. 
The end of the transition interval is characterised by the fact that 
the saturated solutions of R and of R -f- L are in equilibrium with 
each other; their vapour tensions are the same and, consequently, 
this point ought to be controllable by the tensimetric method (with 
the aid of Bremer-Frowein’s tensimeter). The solubilities of R, D, 
and L at 7.5° have, however, become so small that the vapour 
tensions of these solutions do not practically differ from that of pure 
water at that temperature; consequently their mutual difference at 
a somewhat lower, or somewhat higher temperature and their equality 
at that temperature itself, is difficult to demonstrate. As a matter of 
fact I have not succeeded in verifying the result in this manner. 
In the method followed by me I have carefully avoided analysing the 
liquids saturated with R D, R L or D -j- L, by means of the 
polarimeter, as to their contents in L and D. For from the commence¬ 
ment of my research I was of opinion that such a method of 
analysis gives a wrong idea as to the inner composition of the solu¬ 
tions saturated with two salts. 
A saturated (R -j- D), (R -j- L) or {D~\~ L) solution contains 
not only R and J), R and L, or D and L, but in those solu¬ 
tions it must be assumed that R- as well as D- and Z-molecuIes 
will occur. Such solutions conform, being homogeneous phases, to the 
law of the mass-action and therefore an equilibrium is formed between 
f‘- and R- molecules, which is determined not only by the tem¬ 
perature of the solutions, but also by their concentrations. This equi¬ 
librium may be expressed by R^1D+L. 
Ladenburg and Doctor have determined the (J) -J- L) solubilities 
J T pipetting off quantities of the saturated solution; these were 
len weighed and evaporated. After having ascertained in this manner 
1 e total concentration, the residue was dissolved up to a definite 
volume. After determining the angle of rotation a, the content in D 
an d in L was calculated by means of the equation a=a d + a L 
[« d ] D 'P d . S.l [« ] .p .s.l 100« 
* Too — + — ; Ts ~ = • p * + [a i ] » * {p ~ p * } 
ln [ a <i] D and represent the specific rotatory power of D 
