64 SCIENCE PROGRESS 



to observe the occurrence of the maximum in such solutions at 

 still higher temperatures. 



We thus arrive at a generalisation which appears to be of a 

 fairly comprehensive character : The T-R curves for the simple 

 tarrates exhibit maxima. In solvents which have the power of 

 raising the rotation of the dissolved active ester this maximum, 

 with an increased rotational value, occurs at tonperatures lower 

 and lower in proportion to the power of the solvent, and vice versa. 



One solvent which, when it was first examined, did not seem 

 to conform to this regularity was quinoline {J.C.S., 1909, 95, 

 32-40) ; ethyl tartrate dissolved in it gave rotations higher 

 than that of the pure ester and, on heating, the rotation dimin- 

 ished ; but the form of the curves was peculiar, being convex 

 to the point of origin of the diagram instead of concave as in the 

 other cases. Later on, however, it was observed that the T-R 

 curves for ethyl di-monochloracetyltartrate and isobutyl di- 

 trichloracetyltartrate both exhibit distinct minima in their 

 molecular rotation, the value of which for the former is + 66° 

 at a temperature of 54°, and of the latter + 88° at a temperature 

 of + 105° {J.C.S., 191 2, 101, 378, 380). In all three cases the 

 shape of the curves obtained corresponded to the part QRST in 

 Fig. I. 



Now it seems reasonable to suppose that the T-R curves 

 for ethyl tartrate and for ethyl di-trichloracetyltartrate must 

 be related to one another in some way, however remote ; and 

 inalater paper (/.C.S., 1913,108, 153) the suggestion was made 

 that just as a slight change of constitution, in passing, say, 

 from ethyl tartrate to w-propyl tartrate, causes a slight shift 

 in the T-R curve so that the maximum is moved to a lower 

 temperature but with a higher value, the much greater change 

 of constitution in passing from ethyl tartrate to ethyl di- 

 trichloracetyltartrate may have caused a much greater shift in 

 the curve in such a way that the maximum had passed entirely 

 out of the region of medium temperatures, and may have 

 brought into view not merely the descending part of the curve 

 which had previously been supposed two-limbed, but a new 

 minimum which in the homogeneous simple ester (ethyl tartrate), 

 or in tartaric acid, could only be observed at temperatures 

 impossible to attain to. In other words, that the curve, when 

 produced to the right of the maximum, would develop into one 

 showing a minimum rotation. The extended T-R curve for 

 ethyl tartrate then would have a sinuous form exhibiting both 

 a maximum and a minimum as is shown in Fig. i, DFHNSV, 

 and it would be this same minimum which is brought into view 

 when the simple ester is either converted into its di-trichlor- 

 acetyl derivative or when it is dissolved in quinoline, whence it 

 would appear that the solvent influence of quinoline is especially 



