540 



SCIENCE. 



[N. S. Vol. XII. No. 302. 



ance in organic chemistry was the sj'nthet- 

 ical direction, the direction requiring per- 

 severing application of a comparatively few 

 methods and ideas, while progress in other 

 directions was barred by the chemist's 

 ignorance of subjects lying outside his spe- 

 cial field. It has been but a few years that 

 even the scientific chemist has been ex- 

 pected to know much more of physics than 

 that required to comprehend his methods 

 of molecular weight determination. The 

 importance of physics in a chemical educa- 

 tion was greatly underrated, and it is, 

 therefore, not in the least surprising that 

 the significance of such studies as those re- 

 lating to mass action, reaction velocities, 

 equilibrium, electrical conductivities, op- 

 tical rotation and other provinces of modern 

 physical chemistry should have been greatly 

 underestimated or wholly ignored by the 

 organic chemist, and that he should have 

 become a man of one idea, unwilling even to 

 take the time to open his eyes to the light 

 which was beginning to be thrown on his 

 field by those whose broader education en- 

 abled them to discern the future more 

 clearly. 



It is perhaps worth while to call atten- 

 tion here to the part which isomerism has 

 played in the various steps forward which 

 organic chemistry has taken. Before 1820, 

 the different modifications of chromic oxide, 

 of silica, of the stannic acids had been dis- 

 covered, but attracted little attention. The 

 correctness of the discovery of the isomerism 

 of the silver salts of cyanic and fulminic 

 acids by Liebig and Wohler, in 1823, was 

 even at first doubted. Once established, it 

 become clear that the atoms composing 

 the molecule could not be combined in an 

 indifferent or chaotic fashion, but that, 

 as suggested by Gay-Lussac, combination 

 must take place in a definite and fixed 

 manner, diifering in the different isomers. 

 It is to this conception that we owe the 

 ' radical theory,' which assumed the pres- 



ence in the molecule of groups of atoms 

 having an independent existence and ca- 

 pable of being transferred without change 

 from one compound to another, and, in 

 short all the various theories of constitution 

 which culminated in structural chemistry 

 as represented by Kekule. We shall pres- 

 ently see how a finer kind of isomerism 

 led to the study of space chemisty, and still 

 later, how isomerism lies at the foundation 

 of the subject of tautomerism, which is of 

 such importance at the present day. 



The structural formula implies (if we 

 may disregard the view of the few more 

 cautious chemists who regard it as a re- 

 action formula only) that the atoms are in 

 each case linked together according to a 

 definite plan, but it is purely diagrammatic, 

 it says nothing about their relation in space ; 

 this maj' be fixed or nearly fixed, or it may 

 vary as the Solar System varies, the plan 

 remaining the same, but the relative posi- 

 tions of the component bodies changing en- 

 tirely from instant to instant. Up to 1860 

 scarcely a chemist concerned himself in the 

 least with the relative positions of the atoms 

 or groups in space, and it was not till 1887 

 that the chemical mind became awakened 

 to the importance of this question. A 

 few earlier chemists, it is true, as Boyle, 

 Wenzel, Wollaston, Gmelin, Laurent, had 

 suggested the possibility of the existence of 

 such definite relations, but the absence of 

 any experimental basis for such specula- 

 tions prevented their suggestions from 

 having any positive ' results. It is about 

 the year 1887, therefore, that I am inclined 

 to place the beginning of the revival of 

 organic chemistry. 



The development of the conception of 

 chemistry in space is inseparably bound 

 up with the chemical and crystallographic 

 study of tartaric and racemic acids, and 

 with Biot's discovery of the rotation of the 

 plane of polarization of light by certain dis- 

 solved organic compounds. The isomer- 



