1908 ] 
Optical Rotation of Turpentine 
91 
what the reverse has taken place. A rather marked decrease in 
the levo-rotation is shown just at the middle of the year, then the 
rotation remains practically constant during the last half. In the 
case of C 3 , another type of change is represented, the levo-rotation 
decreasig up to the middle of the season and again increasing 
during the latter half. 
With the limited facts at hand, it is impossible to interpret the 
significance of these changes. That tree which shows the most 
marked variation, A a , is a healthy, vigorous tree, from which 
variations would be least expected. Nor can an explanation be 
offered for the wide variations in the optical rotation of oils from 
the same spieces. All of the trees in Series A are located within 
20 yards of each other and have, therefore, the same general con" 
ditions of climate, light and soil. Fractionation of the volatile 
oils from these show practically the same rise in boiling-point 
for the same volume of distillate. It would seem, therefore, 
that these volatile oils, consisting so largely of pinene, are mix- 
tures principally of dextro- and levo-pinene, the preponderance 
of the one or the other determining the optical rotation. 
University of North Carolina, 
Chapel Hill, N. C. 
