224 



If Bruni's 1 ) suspicion be right that the so-called "double-salt" 

 of d-ammonium-tartrate and l-ammonium-malate, described by Pas- 

 teur 2 ), be really a mixed-crystal, we should have here an object 

 intermediate between a pseudo-racemic mixed-crystal and a 

 partially-racemic compound, as defined by Fischer 3 ), who draws 

 attention to the fact that both salts are only antipodes with 

 respect to one half of their molecule. The corresponding d-tartaric 

 acid and l-malic acid themselves do not form such a double 

 compound or pseudo-racemic mixture. Fischer proposes to give 

 in that case a special name to the phenomenon stated above, and 

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

 very desirable to make more investigations in this direction to 

 establish the real occurrence of such "partial" pseudo-racemism 

 beyond all doubt. 



Beautiful examples of true pseudo-racemism were further found 

 by Marckwald and Nolda 4 ) in the case of active amy /-derivati- 

 ves: 1-, and 2-amyl-3-nitro-phtalic ethers; barium-act. amyl-sulphate 

 (+ 2H Z 0) ; act.amyl-carbamate; etc. Finally by Riiber 5 ) in the case 

 of dextro- and laevogyrate fi-phenyl-gly eerie acid (mpt.: 141 C.). 



As the components of such mixed-crystals in general cannot 

 be separated completely 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 6 ). 



13. 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 rotatory power completely, but there 

 are also cases where it is destroyed within a few minutes. Thus 



1) G. Bruni, in: W. Meyerhoffer, Gleichgewichte der Stereomeren,(1906), p. 62. 



2) L. Pasteur, Jahresberichte (1853), p. 417. 



3) E. Fischer, Ber. d. d. Chem. Ges. 40. 944. (1907). 



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



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



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



