222 



dealing with the problem of asymmetric synthesis in general. 



12. Till now we have dealt only with those cases in which 

 either an externally compensated mixture of both components or a 

 true racemic compound of them was present. 



However another difficulty for obtaining the two components 

 in a perfectly pure state is, besides the obstacles already mentioned, 

 this, that the two components may occasionally form together an 

 uninterrupted series of mixed-crystals, this series behaving therefore 

 as a single solid phase of continually varying composition. 



This phenomenon discovered in 1897 by Kipping and Pope x ) in 

 the case of some caw^/zor-derivates, was named -pseudo-racemism 

 Since Bakhuis Roozeboom 2 ) in 1899 published the paper in 

 which he indicated the way to discriminate with certainty the three 

 classes: racemic compounds, externally compensated mixtures, and 

 pseudo-racemic mixed-crystals, the pseudo-racemic mixtures too have 

 been the subject of some investigations 3 ) ; however it is very neces- 

 sary in this case also, that more extended and systematic researches 

 be made to further our rudimentary knowledge in many directions. 



Kipping and Pope 4 ) described the trans-7r-camphanic acid as a 

 first example of such pseudo-racemic mixtures ; the active and inac- 

 tive substances have very similar crystal-forms and appearance: 



Active: Monoclinic; a : b : c = 1,9110 : 1 : 1,4627; /3 = 695' 

 Inactive: Monoclinic; a : b : c = 1,8105 : 1: 1,4502; /3 = 6741' 



The same was the case with the active and inactive trans-campho- 

 tricarboxy lie-anhydride. They come to the conclusion that the crys- 

 tals of the inactive substance are not homogeneous, but merely com- 

 plicated intercalations of crystals of the d-and /-components; the 

 bad reflexes of the light on some facets, observed during the measure- 

 ments, their striation, etc., remind us very much of similar peculiari- 

 ties, met with in mixed-crystals, and in crystalline aggregations as, 

 for instance, are found in some aw^ys^-crystals. The angular values 

 of inactive and active crystals are very analogous; small but per- 



1) F. S. Kippingand W. J. Pope, Journ.Chem. Soc. London 71. 973.989. (1897). 



2) H. W. Bakhuis Roozeboom, Zeits. f. phys. Chemie 28. 494. (1899). 



S) J. H. Adrian!, Akad. Proefschrift, Amsterdam, (1900); Zeits. f. phys. Chemie 

 33. 453. (1900); 36. 168. (1901); Proceed. Kon. Akad. v. Wet. Amsterdam 9. 438. 

 (1900); J. Minguin and E. G. de Bollemont, Compt. rend, de 1'Acad. d. Sc.. 

 Paris 132. 1573. (1901); J. Minguin, Bull. d. 1. Soc. Chim. (3). 27.888. (1902); 

 Compt. rend. 124. 86. (1897). 



4) F. S. Kipping and W. J. Pope, Journ. Chem. Soc. London 69. 931. 

 (1896); etc. 



