35 HISTORY OF CHEMISTRY. [LECTURE XVI. 



separation between two chemically different conditions. This 

 fixed temperature he designates the transition temperature ; 

 and he demonstrates the accuracy of his idea in the cases of 

 the formation of double salts (astrakanite), of the preparation 

 of elements in allotropic modifications (sulphur), and of the 

 splitting of racemic substances (sodium ammonium racemate). 



He afterwards treated this subject in a much more detailed 

 manner in an important monograph 02 "On the Formation and 

 Decomposition of Double Salts," in which he explains the 

 theory of the matter, and describes the methods for experi- 

 mentally determining the transition temperature. 



These investigations have found very important applications 

 in relation to the deposition of salts from ocean water, 93 and in 

 explaining the splitting of racemic compounds by Pasteur's 

 methods. 



This leads us directly to the subject of stereo-chemistry, 

 which has already been discussed in Lecture XIII. (see p. 268), 

 but which has acquired so much importance of late that I must 

 return to it here. 04 



After the propounding of the theory by van 't Hoff and Le Bel, 

 it was only isolated investigations that were, in the first place, 

 carried out with a view to. testing it such, for example, as the 

 splitting by means of fungi of a series of alcohols, which 

 Le Bel succeeded in doing ; {r and the splitting of synthetic 

 coniine, 96 which was of importance inasmuch as it was the 

 preparation, for the first time, of an active base. The theory 

 was subjected to a systematic examination by Emil Fischer, in 

 carrying out his well-known syntheses in the sugar group. 9 " 



It is simply astonishing that the theory stood the test of this 

 experimentum cruets, and that the sagacity of Fischer enabled 

 him to fix the configurations of the individual hexoses 9S with- 



92 German Edition by Dr Paul, Leipzig 1897. 93 Berlin. Akad. Ber. 

 1897, 1898, 1899. 94 Compare van 't Hoff: Die Lagerung der Atome 

 im Raume, Second Edition, Braunschweig 1894. 95 Comptes Rendus. 

 87, 213 ; 89, 312 ; Bull. Soc. Chim. [3] 7, 551 ; Comptes Rendus. 92, 532. 

 9(5 Ladenburg, Berichte. 19, 2578 ; Annalen. 247, 83. 97 Berichte. 23, 

 2114; 27, 3189. 98 Ibid. 24, 1836 and 2683. 



