LECTURE XIII.] HISTORY OF CHEMISTRY. 255 



r O OH r O OH 

 H 2 C 2 /H N/O-OH 



I N tc N \c 



pH 2 p^2 



^0 OH U OH 



Glycol. Oxalic acid. Hydrocyanic acid. Cyanic acid. 



We here meet, for the first time, with constitutional for- 

 mulae in the present sense of the term with symbols called 

 forth in consequence of the recognition of the atomicity of the 

 elements. In connection with these formulae it must be 

 remarked that the views as to alcohol and acetic acid repre- 

 sented by them, concide with those of Kolbe, 12 and that the 

 only differences are in the manner of writing them. 



These two papers of Kekule and of Couper constitute the 

 foundations of our views respecting the structure of com- 

 pounds. As a consequence of them, organic chemistry took 

 an altogether new direction, and they may be regarded as the 

 most important advances of our science, on the speculative 

 side, in recent times. Adopting the doctrine of the quadri- 

 valence of carbon, the endeavours put forth since that time 

 have been largely directed towards arriving at conceptions 

 regarding the mutual relations of the combining atoms ; and 

 I have now to deal with this portion of the historical develop- 

 ment of chemistry. 



In these considerations respecting constitution, besides the 

 hypothesis as to the nature of carbon, numerous series of 

 experimental data were required ; and in view of the fact that 

 the accumulation of the latter was only very incomplete, the 

 labours of years were frequently necessary in order to render 

 possible any application of the principles stated above, to the 

 determination of rational formulae in the cases of certain 

 classes of substances. Even up to the present we have not 

 succeeded in completely solving this problem, as there are 

 many compounds still which we cannot arrange in the system. 

 What is most important, however, has been accomplished. 

 We are satisfied that the doctrine of atomicity can be employed 



12 Compare pp. 235-236, 



