222 



central rhodmm-aiom, is evidently followed by a very radical change 

 of the character of the optical rotation of the molecule, which 

 affects not only the magnitude, but also the algebraic sign of 

 the molecular rotation for a number of corresponding wave-lengths. 

 The special chemical nature of the substituents placed dissymmetric- 

 ally round the central atom therefore appears to have as much 

 intluence on the magnitude of the rotation, as the chemical nature 

 of the central metal-atom itself. 



§ 4. After many attempts we were able to obtain the crystals 

 of the optically-active salts in a measurable form. The laevogyratory 

 component set free from the c'mchonine-^dX{ of the first fractions, 

 appeared, as already mentioned, to be extremely soluble ; the solutions 

 manifested a sti-ong tendency to supersaturation. 



By this circumstance the formation of well measurable crystals 



ie severely hindered ; and, as gene- 

 lally occurs in such cases, the 

 crystals finally obtained appeared 

 to be badly formed. Because of 

 Fig. 3. Laevogijratory the vicinal facets present, most 



Potassium- Rhodium- Malonate. crystal-faces yield multiple mirror- 



images, causing the angular values to oscillate often more than 30' 

 round their mean-values. Hence it was at first thought, that triclinic 

 crystals were present here. But the repeated determinations, in con- 

 nection with the optical investigation proved to us finally, that the 

 salt crystallises monoclinically, and more especially in forms differing 

 from their mirror-images. 



The analogy of the parameters of the optically-active salt and 

 those of the racemic compound is most remarkable, as becomes 

 clear, if the directions of the a- and 6'-axes in our former determi- 

 nations are interchanged ^). 



MonocIiniC'Sphenoidical 



a: /, -.0 = 1,0637 -.1 : 1,1667. 



- /?=85°27V/. 



Forms observed: c = |001|, predominant, and mostly very lustrous; 



h' = \ÓÏO\, broad and lustrous; è = |010|, very narrow, often absent 



and always yielding good reflexes; o, = \Ml\, broad and lustrous; 



«jj = llllj, narrower than 6>,, yielding multiple reflexes; o, = |lll|, 



1) F. M. Jaeger, Proceed. R. Acad. Amsterdam, 20. 277. (1917). There the 

 ratio a':b:c' was equal to: 1,0783: 1 : 1,^309; with ^ = 86° 36'. 



