275 



(trigonal), than the racemic compound (triclinic). The symmetry 

 of the active components is Z) 3 (fig. 170), while that of the racemic 

 compound is 7, the ternary and the three binary axes of the 

 dextro- and laevogyratory components being changed into a single 

 binary axis of the second order in the case of the optically inactive 

 crystals. The hemihedrism of the optically active forms is, notwith- 

 standing the enormous rotatory power, here only betrayed by 



Fig. 170. Racemic and optically active crystals of Potassium-Rhodium-Oxalate. 



the occurrence of a trigonal bipyramid; not even a single "trape- 

 zohedral" face was ever met with in these salts, as is the case 

 for instance, with dextro- and laevogyratory quartz-crystals. 



A review of the remarkable rotatory dispersion of some of these 

 complex trioxalates is given in fig. iji. 



Pope and Peachy l ) have studied the crystal- forms of the right- 

 and left-handed components of tetrahydroquinaldine-hydrochloride: 

 C 10 H 13 N, HCl -\- H 2 0', although the molecular rotation for sodium- 

 light in alcoholic solution was almost 141, and in aqueous solution 

 122, the crystals of both antipodes (rhombic) not only showed 

 no trace of hemihedrism, but the corrosion- figures on (001 j, ob- 

 tained by means of alcohol + water, were in full agreement with 

 holohedral symmetry. If, however, in the molecule: 

 CH - CH = C - CH 2 CH, 



CH CH = C NH - CH . 



(CH 3 ), 



W. J. Pope and S. J. Peachy, Journ. Chem. Soc. London, 75, 1066, (1899). 



