62 



SCIENCE PROGRESS 



It will be noticed that, roughly speaking, the maximum 

 rotation increases in value and moves towards lower tempera- 

 tures just as is the case with solutions of the tartrates. Ap- 

 parently, therefore, the comparatively slight change of composi- 

 tion in passing from, say, ethyl tartrate to n-propyl tartrate 

 brings about a corresponding, comparatively slight, shift in the 

 point of maximum rotation, in much the same way that increas- 

 ing dilution alters the position of the maximum in the T-R 

 curves for potassium-ethyl tartrate. Fig, 2. 



That this behaviour is important will appear from the con- 



Temperature 



Fig. 2. — Potassium-ethyl tartrate in water. 



sideration that maxima in curves are singular points and may 

 be taken, at least as a first approximation, to represent corre- 

 sponding conditions in the two different — but related — sub- 

 stances to which they pertain. They therefore present some 

 kind of basis upon which comparison might perhaps be 

 instituted. 



It has already been mentioned that solution in water alters 

 the position and value of the maximum rotation in ethyl 

 tartrate. It was found, later on, that some other solvents are 

 even more powerful in the same direction, whereas others, 

 again, show an opposite behaviour. 



