4 o6 POPULAR SCIENCE MONTHLY. 



tion, which took place in this house on the 11th of March, 1890, is 

 memorable to all for the brilliant and witty speech with which the 

 master responded to the many addresses made to him. It is preserved 

 in our reports (Berichte 23, 1892), and the repeated reading of it 

 always affords rich enjoyment." 



Kekule assumed his last position, as professor at the University 

 of Bonn, in the fall of 1867. He there devoted his attention for a 

 period to the erection of a new institute building, but it was not 

 long before numerous works began again to appear — some of them 

 by himself alone, like the important investigation of the condensa- 

 tion products of aldehyde; and others in co-operation with his many 

 students. The continuation of his Lehrbuch was taken in hand at 

 the same time. In 1867 he gratified his fellow-chemists by the pub- 

 lication of the first volume of his Chemistry of the Benzol Deriva- 

 tives. This was followed from 1880 to 1887 by single numbers, 

 prepared with the help of co-workers, of the second and third 

 volumes. 



Prof. F. R. Japp, in the Kekule memorial lecture before the 

 Chemical Society of London, speaking of Kekule's residence in that 

 city, September, 1897, said that he always acknowledged the influ- 

 ence which Liebig and Odling and Williamson, with whom he be- 

 came acquainted in London, exercised on the formation of his 

 opinions. Kekule's theories, Professor Japp said, were based on Ger- 

 hardt's type theory; on Williamson's theory of polyvalent radicals, 

 which by their power of linking together other radicals render pos- 

 sible the existence of multiple types; and Odling's theory of mixed 

 types, which was a deduction from Williamson's theory. Less con- 

 sciously, perhaps, his opinions were influenced by E. Frankland's 

 theory of the valency of elementary atoms, and by Kolbe's specula- 

 tion on the constitution of organic compounds. Kekule gathered 

 together the various ideas which he found scattered throughout the 

 writings of his predecessors, added to them, and welded the whole 

 into the consistent system which forms our present theory of chem- 

 ical structure. In 1857, in the course of a memoir on the constitution 

 of fulminic acid, he gave a tabular arrangement of compounds for- 

 mulated on the type of marsh gas, this being the earliest statement, 

 though put forward only in an imperfect form, of the tetravalency of 

 carbon. In the same year he published an important theoretical 

 paper On the So-called Conjugated Compounds and the Theory of 

 Polyatomic Radicals, which contains a complete system of multiple 

 types and mixed types. In 1858 the celebrated paper, On the Con- 

 stitution and Metamorphoses of Chemical Compounds, and on the 

 Chemical Nature of Carbon, appeared. It embodies the fully de- 

 veloped doctrine of the tetravalency of carbon, together with 



