226 MODERN SCIENCE READER 



be assumed to be divalent, and so it is directly shown to be 

 by the formula H 2 0. Kekule soon came to the conclusion 

 that in practically all organic compounds one carbon atom 

 is combined with a quantity of other elements which is 

 equivalent to four atoms of hydrogen. This gave rise to a 

 lively controversy, the critic Kolbe especially maintaining 

 that the valency of an element may not be the same in all 

 of its compounds. Kekule 's view, however, was finally 

 accepted by all, and in 1860 chemists the world over were 

 busy determining the "structure" of organic compounds 

 a problem which has since occupied the attention of a 

 majority of them almost exclusively. The theory of types, 

 the mother of structural theory, exhibited the radicles of 

 compounds, and thus explained those cases of isomerism in 

 which compounds are different because they contain differ- 

 ent radicles. Those further cases in which the radicles 

 themselves are differently constituted it could not explain. 

 The doctrine of valency, showing the different ways in 

 which the atoms can be linked in the radicles, has furnished 

 a satisfactory solution of the problem of molecular consti- 

 tution, and has completely explained the fact that the 

 molecules of different compounds may be made up of the 

 same atoms. At first Kekule failed to appreciate the full 

 value of his own ideas. In the very memoir in which he 

 states the doctrine of valency, he advances the view that 

 this doctrine cannot by any means solve the problem of the 

 constitution of compounds; the old problem, he thought, 

 might possibly be solved some day by physical chemistry. 

 Perhaps he was not altogether wrong. For now, after half 

 a century of experience, organic chemists are beginning to 

 complain of the inadequacy of the structural theory, even 

 with its more recent development stereochemistry (q.v.) 

 and to look forward to some broader idea, that would cor- 

 relate a larger number of known phenomena and permit 

 of foreseeing a larger number of as yet unknown facts. 

 What that idea -will be, no one can tell as yet. 



GENERAL CHEMISTRY. The doctrine of valency could not 



