160 E. I. Rosenblum : 



vents increases when the temperature rises, while that of optically 

 active liquids decreases. 



Guye and Astonl examined some fifty organic liquids, and found 

 that in all cases except that of amyl alcohol the rotatory power 

 diminished with rise of temperature. This exceptional case they 

 explained by the dissociation of i:)reviously associated molecules. 



The rotations of the only four terpenes which were optically 

 active were measured over a range of from 20° to 60^ by means 

 of a Ptilfrich polarimeter, fitted Avith a device for varying the 

 temperature of the tube by means of a bath, and the experimental values 

 are .shown in the accompanying table, while the molecular rotatory 

 powers - ajlAld.M.- have also been calculated and plotted against the 

 temperature. 



The rotations of d- and 1-pinene are little affected by tempera- 

 ture change, but slowly decrease as the temperature rises. That 

 of d-limonene falls 0.134O for every degree rise of temperature, 

 while phellandrene again shows its abnormal character by a marked 

 increase of rotation. 



In every one of its physical properticvS then, the curious nature 

 of this terpene, as obtained from the oil of Eucalyptus dives, is 

 expressed. It appears as if it must either be a mixture of two 

 terpenes inseparable by distillation, whose equilibrium is upset by 

 temperature change, or, as seems more probable, the molecules may 

 be associated at the lower temperatures, as in the case of amyl 

 alcohol. 



Furtlier work may shed more light on this interesting terpene. 



Rotation. 



Molecular Eotations - . - . M 



I d 



1 Conipt. Rend., 1897, 124, 194197. 

 Compt. Kend., 1897, 126, 819-821. 



