OPTICALLY ACTIVE COMPOUNDS 65 



powerful and of much the same effect as a very considerable 

 change of constitution. The effect of change of constitution 

 therefore, or of change of solvent, would appear to be a shifting 

 of a fundamental type of sinuous curve so as to bring different 

 parts of it into the region of medium temperatures, but, of 

 course, with modifications, often very considerable, of the actual 

 values of the rotations. 



But in passing from a maximum in a curve to a minimum 

 there must be, somewhere, a point of inflection, and in fact a 

 number of points of inflection had already been noticed, par- 

 ticularly in the curves for solutions of ethyl tartrate in water 

 for all dilutions less than about 50 per cent. {J.C.S., 1904, 85, 

 1 1 29), as well as in other instances ; the curves obtained in these 

 cases being of the shape of the part HMNQ of the curve in Fig. i , 

 which shows a point of inflection at N. Presumably, therefore, 

 they correspond to this part of a general curve. Assuming, 

 then, from the evidence adduced above, that the T-R 

 curve for homogeneous ethyl tartrate, if the ester were heated 

 over a range of temperature of, say, -50° to 500°, would have the 

 form DFHNSU, shown in Fig. i, we find that solution in water 

 and nitro-benzene moves the maximum which occurs at H in 

 the homogeneous ester towards lower temperatures and higher 

 values. Solution in acetylene tetrachloride moves the maximum 

 at H in the opposite direction. Solution in water (p : 25) 

 brings into view a part of the curve HMNQ which just exhibits 

 the point of inflection at N. Solution in quinoline alters the 

 substance to such an extent that the part QRST comes into 

 view, and in a similar manner when ethyl tartrate is converted 

 into ethyl di-trichloracetyltartrate this same part of the general 

 curve comes into the region of ordinary temperatures. Sum- 

 ming up the evidence leading to this conclusion, we have there- 

 fore the following experimental facts: (i) The occurrence of 

 maximum rotations. (2) The transference of this maximum 

 in varying degrees from higher to lower temperatures or vice 

 versa in accordance with — (a) The nature of the solvents ; 

 (b) the concentration in a given solvent ; (c) change of con- 

 stitution of the active substances. (3) The occurrence of 

 minima in the T-R curves for derivatives of substances 

 themselves showing a maximum. (4) The occurrence of 

 points of inflection in T-R curves, which presumably would 

 be found to connect together a maximum and minimum if the 

 curve could be sufficiently extended, which for the most part 

 it cannot. Such a curve as this would apply to a single colour 

 of light. If other colours of light be used, it is found that 

 the T-R curves obtained for homogeneous ethyl tartrate 

 intersect one another {J.C.S., 1913, 103, 164; 1916, 109, 1145) 

 in a manner which is sufficiently represented for our present 



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