LECTURE XVI.] HISTORY OF CHEMISTRY. 353 



in the case of nitrogenous organic compounds that was proved 

 by these investigations. Le Bel 116 and Ladenburg 117 en- 

 deavoured to prove that asymmetric nitrogen can further pro- 

 duce or influence optical activity. The investigations of both 

 have, however, been attacked, 118 but they have been able to 

 establish the accuracy of their results. 119 



Another subject that was much discussed was the signi- 

 ficance of racemism, about which a clear understanding only 

 became possible upon the introduction of the conception of 

 the transition temperature, and upon the recognition of the 

 analogy between racemic substances and double salts. The 

 most important method of splitting racemic substances that 

 by means of optically active substances remained a standing 

 enigma as long as the existence of partially racemic substances 

 was denied. 120 Every difficulty was removed, however, after 

 Ladenburg had shown that such substances do without doubt 

 exist, 121 and after a transition temperature had been recognised 

 in their case also. 122 



Furthermore, the much debated question as to how a truly 

 racemic substance (inactive by intra-molecular compensation) 

 can be distinguished from the mixture of the active components, 

 may now be looked upon as practically settled. 123 



It is beyond doubt that the founding and development 

 of stereo-chemistry (a name which originated with Victor 

 Meyer 124 ) is the most important thing that has been accom- 

 plished in organic chemistry during the last two decades. 

 Stereo-chemistry possesses a significance for this period similar 

 to that which the foundation and introduction of the theory of 



116 Comptes Rendus. 112, 724. m Berlin. Akad. Ber. 1892, 1067; 



Eerichte. 26, 854 ; 27, 853 and 859. 118 Marckwald and Droste- 



Huelshoff, Ibid. 32, 560 ; Wolffenstein, Ibid. 29, 1956. 119 Comptes 

 Rendus. 129, 548 ; Berichte. 29, 2706. 1>2 E. Fischer, Berichte. 27, 

 3226 ; Landolt, Das Optische Drehungsvermogen, Second Edition, 

 Braunschweig, 1898, 85. 121 Ladenburg and Herz, Berichte. 31, 937 ; 

 Ladenburg and Doctor, Ibid. 31, 1969. l ~ 2 Ladenburg and Doctor, 



Ibid. 32, 50. 123 Roozeboom, Z, physik. Chem. 28, 494 ; Ladenburg, 

 Journ. Chem. Soc. 75, 465. m Berichte. 23, 568. 



Z 



