( 76 ) 
The temperatures at which this change took place were however 
unknown. They were therefore determined. 
Change from regular to monosymmetric crystals. 
100%, d or ¢.112°.6 
907, , » 110°.6 
Rode Cedo 
50%,» » » 109°4 
These values are shown by the line CDE, which is completely 
symmetrical and has a minimum of temperature at the transition point 
of the inactive mixture. Since here again only one curve is obtained 
for all the transition temperatures we must conclude that the regular 
mixed crystals change into monosymmetric mixed crystals. 
When the change takes place with falling temperature it may 
be much delayed; in the other direction however it is very sharp. 
With the microscope it may be observed clearly, with the thermo- 
meter with great difficulty, and very distinctly by means of the 
dilatometer. With the non-racemic mixed-crystals it is possible that 
the transition takes place through some interval of temperature. In 
any case this is very small. 
3. A further change takes place in the monosymmetric mixed 
crystals when they are cooled still more. Pope has observed this, 
only in the inactive mixtures, and ascribed it to the formation of 
a racemic compound (which may be obtained from a solution of the 
inactive mixture at the ordinary temperature). In that case the con- 
version of the mixed crystals into the compound should theoretically 
occur in other mixtures also hut at lower temperatures. 
This has been shown to be the case. 
Conversion of mixed crystals into a compound. 
ord or 4 21035 
ore 
60, , 
n 7 
and 0/ 
10°/, nnen 
These points are indicated by the line FGH which has a maxi- 
mum at 50 °/5. 
| 
