OPTICALLY ACTIVE COMPOUNDS 



6i 



similar behaviour is found in solutions of sodium and potassium 

 tartrates as well as of potassium-methyl tartrate, potassium- 

 ethyl tartrate, and potassium-w-propyl tartrate, which all exhibit 

 a maximum^ in their T-R' curves for certain concentrations ; 

 and that the position of this maximum varied with the concen- 

 tration, passing gradually to a higher value and occurring at a 

 lower temperature as the concentration diminished. Fig. 2 

 shows this in the case of potassium-ethyl tartrate. {J.C.S., 

 1904, 85, 1117-1125.) It thus appeared that the graph repre- 

 senting the relationship of temperature and rotation might be 

 two-limbed, as DFHNOP in Fig. i, and this at once reconciled 

 what had at first {J.C.S., 1901 , 79, 1 71-1 73) been regarded as very 

 contradictory behaviour, namely, that although the rotation 

 of homogeneous ethyl tartrate increases on heating, that of a 



Temperature 



P\ 



Fig. I. 



dilute aqueous solution diminishes ; for if the extended T-R 

 curve be two-limbed with a maximum, then the curve for the 

 homogeneous ester might represent one limb, the ascending one 

 approaching a maximum, whilst that for a dilute solution would 

 represent the other, the descending limb of the curve, the 

 maximum having already been passed at a fairly low tempera- 

 ture. The existence of a maximum was then observed in other 

 cases, having the value and occurring at the temperatures shown 

 in the following table : 



{J.C.S., 1913,103, 149.) 



^ The occurrence of a minimum is, of course, exactly the same kind of 

 phenomenon as the occurrence of a maximum. 

 2 Temperature— Rotation. 



