OPTICALLY ACTIVE COMPOUNDS 



63 



To the first class belong water, nitrobenzene, the nitro- 

 toluenes, benzaldehyde, and other substances (J.C.S., 1908, 93, 

 1846), and it seems clear that amongst solvents generally the 

 power to raise the rotation of the dissolved ester involves also 

 a passing of the maximum in the T-R curve towards lower 

 temperatures as is shown in Fig. 3 . Thus both for one substance 

 in different solvents and for different, but related, substances 

 in the homogeneous condition a similar behaviour is observed : 



3G 



.2 

 o 



24* 



mrotohjeneB:So_ 

 — Tartrate 



40 80 A2Q 160° 



Temperature 



Fig. 3. 



the maximum in the T-R curves occurs at a lower temperature 

 the greater its rotation value — it passes gradually towards the 

 top, and to the left, of the diagram. On the other hand, when 

 a solvent such, for example, as chloroform, ethylene bromide, 

 or acetylene tetrabromide depresses the rotation of the ethyl 

 tartrate the opposite would appear to be the case, although, 

 since the maximum in homogeneous ethyl tartrate occurs at 

 the already fairly high temperature of 1 75°, it is difficult actually 



