Difference between molecular rotations for green and violet. 
28 Proceedings of the Royal Society of Edinburgh. [Sess. 
with that of the dibenzoyl derivative of a homologous ester, the agree- 
ment is on the whole very satisfactory, and it may therefore be concluded 
that the curves in fig. 1 represent the influence of temperature-change 
upon the derivatives of tartaric acid generally ; that on extending the 
The diagram is for green and violet, the reference colour being green. 
Fig. 4. — Characteristic diagram for ethyl tartrate (homogeneous and in ethylene bromide, p — 9’84), 
and for isobutyl dibenzoyltartrate (homogeneous and in ethylene bromide, p — 9’ 20). 
diagram towards the left a very deep minimum is reached in the neigh- 
bourhood of low temperatures. 
A slightly different way in which the connection between m>butyl 
dibenzoyltartrate and the ethyl tartrate curves might be shown, is as 
follows : — It is reasonable to suppose that if this relationship exists, the 
dispersion coefficient should remain constant with varying circumstances, 
and should be the same for both esters. But it has been shown in a 
