SKETCH OF AUGUST KEKULE. 405 



will remember the enthusiasm with which the work was received. 

 For the first time, in place of the former system of organic chem- 

 istry based on the old radicals of Berzelius, a system of treatment 

 appeared which in the dress of the theory of types had the doctrine 

 of valency as its foundation, and exposed the construction as well as 

 the isomeric relations of the numerous carbon compounds with won- 

 derful clearness. The work, the first two published volumes of which 

 contained the substances designated by Kekule as the fatty com- 

 pounds, is still recognized as the prototype of many text-books that 

 followed it. 



" In 1855 Kekule put forth the second of his great theories. First 

 in the Bulletin of the Chemical Society of Paris, and afterward in 

 fuller form in Liebig's Annalen, appeared the essay, Researches 

 among the Aromatic Compounds, in which he showed that the sub- 

 stances so designated all contain six or more atoms of carbon, and 

 that they could be described as derivatives of the simplest of them, 

 benzene. He proposed two hypotheses to explain the constitution of 

 this substance, one of which, the only one afterward pursued, sup- 

 posed that the six carbon atoms are associated in a ring, and alter- 

 nately linked by one and two valencies. By replacing the hydrogen 

 atoms corresponding to each carbon atom by other elements or radi- 

 cals one could arrive at the knowledge of the constitution of a large 

 number of aromatic bodies which now figure as benzol derivatives. 

 These considerations led, however, to another question — namely, 

 whether or not the supplied places of the six hydrogen atoms are 

 chemically equivalent. The question of space relations in chemistry 

 first came up in connection with this investigation, and Kekule at 

 once endeavored to solve it. All these ideas were, however, ex- 

 pressed at first with reserve, and this essay closes with the words, ' I 

 place no more value on these views than they are worth, and I believe 

 that much labor must still be applied before such speculations can be 

 regarded as anything else than more or less elegant hypotheses; but 

 I believe, too, that at least experimental speculations of this kind must 

 be used in chemistry.' 



" In this case, again, Kekule's modest expectations have been sur- 

 passed. The wonderful results that have accrued from the benzol 

 theory are patent to all of us. We know that it was the instigation 

 to the carrying out of an innumerable multitude of researches which 

 are still pursued with undiminished industry. Rarely has a thought 

 exercised so fructifying and forwarding an influence on chemistry, 

 and so redounded to the advantage of both pure science and art. 

 Thankfulness for this gift, as you know, prompted our society to 

 honor the author of the benzol theory and the twenty-fifth year of the 

 announcement of it by a public festival; and the Kekule celebra- 



