Rotation. 
21 
1918-19.] Researches in Optical Activity. 
tartrate the curve for Hg b cuts that for Hg g at [M] == + 25° and at a 
temperature of 55° ( J.C.S . , 1916, 109, 1145, 1148), whereas in homogeneous 
isobutyl tartrate the two corresponding curves would intersect at about 
[M]= +40° and at a temperature of about — 10° ( ibid ., p. 1147). The same 
thing applies to solutions. For isobutyl tartrate dissolved in acetylene 
tetrachloride (p = 48T5) the intersection occurs at [M]=+28'5 and a 
Temperature. 
temperature of 16°, whilst for isobutyl diacetyl tartrate in o-nitrotoluene 
it takes place at [M] = +33° and a temperature of 104°. The regularity 
is probably only an approximation, but that it is a fairly close- approxima- 
tion is proved by the fact that so very many data, such as those collected 
by Pickard and Kenyon, are found to lie along the lines of Armstrong and 
Walker’s characteristic diagram, which is only possible because of the 
regularity mentioned. The points of intersection of the T-R curves are 
also the points of intersection of the lines on the characteristic diagram 
{ibid., p. 1157). A similar remark, however, does not apply to the maxima 
