1875.] President's Address. 89 



to the President for his Address, and that he be requested to allow it to 

 be printed." 



I now proceed to the presentation of the Medals. 



The Copley Medal has been awarded to Professor August "Wilhelm 

 Hofmann, F.R.S., of Berlin, for his numerous contributions to the 

 science of Chemistry, and especially for his Researches on the Deriva- 

 tives of Ammonia. 



. The researches of Dr. A. W. Hofmann, from first to last, are related 

 by a strict logical connexion, from which (although in various side-paths 

 he has made truly interesting discoveries) he has never essentially deviated. 

 Indeed these researches may be considered as constituting one great and 

 prolonged research on the organic bases theoretically and experimentally 

 considered. It is not, however, to be imagined that because, to a certain 

 extent, limited in its range, this work is of a special or technical order. 

 The subject covers a large area, and is calculated to lead the investigator 

 to the consideration of the most important chemical problems. 



The memoirs of Dr. Hofmann in reference to the organic bases fall 

 under several heads : — (1) The researches on Aniline and the organic 

 bases contained in Coal-tar. These researches are mainly included in the 

 period between 1843 and 1850. (2) The investigations on the molecular 

 constitution of the organic bases derived by the substitution of the 

 Alcohol radicals in the molecule of Ammonia (1850-51). (3) The 

 Phosphorus bases and the Diatomic ammonias (1857-60). (4) The 

 investigations on Eosaniline and the various Colouring-matters derived 

 from Coal-tar (1860-70). 



In the course of the Aniline investigations Hofmann made an im- 

 portant contribution to the Unitary theory of Chemistry. Dumas had 

 shown that the essential chemical properties of acetic acid were not 

 altered by the substitution in the acid-molecule of chlorine for hydrogen; 

 but no organic base had yet been discovered derived from another base 

 by a similar process. Pritsche, indeed, had made a bromine- derivation 

 of aniline, in which three atoms of hydrogen were replaced by bromine ; 

 but the substance thus formed was a neutral (not basic) body. It 

 occurred to Hofmann that the substitution had here gone too far, and 

 that for this reason the basic properties of aniline had disappeared. 

 Consequently, by an ingenious process (devised for the experiment), the 

 treatment of chlorisatin by the hydrate of potash, he prepared mono- 

 chloraniline — aniline, that is, in which one atom of hydrogen was re- 

 placed by chlorine. This body was a base, like aniline itself. Hofmann 

 established its basic character by the preparation of many of its salts 

 (Liebig's ' Annalen/ vol. liii. p. 1, 1845). 



At the date when Hof mann's paper on the molecular constitution of the 

 volatile organic bases was presented to the Royal Society (December 

 1849), Wurtz had just prepared, by a striking experiment, the primary 



