232 



to call it partial pseudo-racemism. However, here also it appears 

 very desirable to make more investigations in this direction to 

 establish beyond all doubt the real occurrence of such "partial" 

 pseudo-racemism, and its true significance. 



Beautiful examples of true pseudo-racemism were further found 

 by Marckwald and Nolda x ) in the case of active amy /-derivati- 

 ves: 1-, and 2-amyl-3-nitro-phtalic ethers', barium-act. amy Isulphate 

 (+ 2H 2 0)', act.amyl-carbamate', etc. Finally by Riiber 2 ) in the case 

 of dextro- and laevogyratory (3-phenyl-glyceric acid (mpt. : 141C.). 



As the components of such mixed-crystals cannot be in general 

 completely separated by repeated crystallisations, at least if 

 the number of these be not infinitely great, or in practice: exceedingly 

 great, a separation will certainly not be reached in our case, 

 where the solubilities of both components are equal. Therefore, 

 pseudo-racemism may also be mentioned amongst the serious obstacles 

 eventually met with in the fission of racemoids into their optically 

 active components 3 ). 



13. Autoracemisation. 



A phenomenon often observed in working with optically active 

 substances is, that the rotatory power of such a solution, especially 

 if it be heated to a higher temperature, gets gradually smaller 

 and smaller until finally it has become inactive. The velocity 

 of this change can vary within wide limits : there are solutions which 

 even on boiling preserve their full rotatory power, but there are 

 also cases where it is destroyed within a few minutes. Thus, Wer- 

 ner 4 ) observed that tris-a-dipyridyl-ferro-salts of the type: 



lose half of their original and very high rotatory power in about half 

 an hour ; in the case of the carbonato-diethylenediamine-cobalti-salts 5 ) : 



(C0 3 ) 



(Eine) 2 



it diminishes in about eight days and at room- temperature, to 

 half its original value, while at 90 C. it is destroyed completely in 

 a very short time. Also the complex chromi-trioxalates 6 ) : 



J ) W. Marckwald and E. Nolda, Ber. d. d. Chem. Ges., 42, 1583, (1909). 



2 ) C. N. Riiber, Ber. d. d. chem. Ges., 48, 823, (1915). 



3 ) W. J. Pope and J. Read, Journ. Chem. Soc. London, 97, 987, (1910). 



4 ) A. Werner, Ber. d. d. Chem. Ges., 45, 434, (1912). 



5) A. Werner and MacCutcheon, Ber. d. d. Chem. Ges., 45, 3283, (1912). 



6) A. Werner, Ber. d. d. Chem. Ges., 45, 3065, (1912). 



