October 12, 1900.] 



8GIENGE. 



545 



tors, and has gone over to the camp of the 

 natural philosophers of unhappy memory, 

 which but a thin ' medium ' separates from 

 the spiritualists." 



Upon this criticism van't Hoff" remarks, 

 in a later work,* "But ten years have 

 passed — Kolbe is dead, and by a strange 

 freak of fate it is Wislicenus who has suc- 

 ceeded him in the University of Leipzig," 

 to which we may add, that after twenty-five 

 years, the Utrecht horse doctor has become 

 professor in the University of Berlin, and 

 the chemical world has united in doing him 

 honor upon the twenty-fifth anniversary 

 of his doctorate. 



Time is wanting to do more than allude 

 to the interesting ' tension theory ' of von 

 Baeyer, dating 1885, which, by adopting 

 van't Hoff's conception of the tetrahedral 

 arrangement of the carbon valences, and 

 assuming that these tend to maintain their 

 relative positions with considerable force, 

 like elastic springs, offered an explanation 

 of the relative stability of the polymethy- 

 lene rings and the instability of the poly- 

 acetylene compounds. 



The first strong impulse to the study of 

 the space relation of carbon compounds was 

 given by Johannes Wislicenus in 1887, by 

 his paper on ' The Spatial Arrangement of 

 the Atoms in Organic Molecules, and its 

 Determination in G-eometrically Isomeric 

 Unsaturated Compounds. 'f In this paper 

 the subject was treated essentially as it had 

 been twelve years before by van't Hoff, but 

 with important extensions, covering the 

 lactones and anhydrides. After the ap- 

 pearance of this epoch-making work, stereo- 

 chemistry was no longer a scientific curios- 

 ity ; it at once became the fashion, and has 

 so remained ever since. Many specula- 



* Dix aniKjes dana I'histoire d'une th^orie, p. 21. 



t Ueber die raiimliohe Auordnung der Atome nnd 

 ihre Bestimmung in geometrisch-isomeren -angesiit- 

 tigten Verbindungen. Abhand. d. K. Sachs. Gesell- 

 sch. d. Wiss. Bd. 24. 



tlons have appeared, but few have obtained 

 much foothold, and the stereochemistry of 

 to-day, so far as it concerns carbon, is es- 

 sentially that of van't Hofif, Le Bel and 

 "Wislicenus. The classical researches of 

 von Baeyer on the hexahydrophthalic acids 

 are based essentially on extensions of the 

 theory of the geometrical isomerism of 

 bodies of the ethylenic type and have con- 

 tributed not a little to its confirmation. 

 The preparation of stereoisomers of both 

 types is now a matter of almost daily oc- 

 currence. 



Unquestionably the greatest achievements 

 of stereochemistry are to be found in Emil 

 Fischer's magnificent researches on the 

 sugars. If to explain old facts and to lead 

 to the discovery of new ones be any test of 

 the truth of an hypothesis, then the appli- 

 cability of the theory of the asymmetric 

 carbon atom to the carbohydrates affords a 

 very strong presumption in its favor. The 

 stereochemistry of the sugars might by 

 itself form the subject of many lectures. 

 Not only were the relations of the already 

 known sugars satisfactorily explained, but 

 the synthesis of whole new groups was ef- 

 fected, the configuration of each of which 

 was determined. 



Pasteur discovered the three chief meth- 

 ods which are still used for separating an 

 optically inactive mixture into its active 

 components, namely, (1) separating by se- 

 lection the two kinds of hemihedral crys- 

 tals corresponding to the dextro- and Isevo- 

 rotatory forms, (2) separation by means 

 of alkaloid salts, the alkaloids being them- 

 selves optically active and forming with 

 the two constituents of the racemic mix- 

 ture two salts which are not enantiomor- 

 phic and therefore differing chemically and 

 physically, one being less soluble than the 

 other and (3) separating by means of fer- 

 mentation, the fermenting organisms fre- 

 quently showing a tendency to destroy one 

 of the forms while leaving the other un- 



