1875.] President's Address.. 91 



with the determination of the differences by which they were discrimi- 

 nated from their nitrogen analogues. We have here presented to us the 

 first example of a diatomic base formed by the action of bromide of ethy- 

 line or triethyl-phosphine, in which reaction (as in the similar case of the 

 diatomic alcohols) Hofmann successfully established the formation of 

 an intermediate monatomic bromide, the reaction taking place by two 

 distinct stages. In the third of these memoirs a new class of compound 

 bases is brought before us, containing both nitrogen and phosphorus. 

 Subsequently, in a series of somewhat less elaborate memoirs, the con- 

 ception of the typical character of ammonia is greatly expanded by the 

 examination of the derivatives of two and three molecules of ammonia. 



As to the researches in reference to the colouring-matter derived from 

 coal-tar, it is only necessary to observe that his inquiries initiated and 

 rendered possible what is now a vast branch of industry. In reference 

 to rosaniline itself (the key of the system), he established the fact, long 

 unknown, that this substance was not an aniline compound at all, but 

 derived from the combination of aniline with toluidine. 

 ■ I may lastly mention, as a fitting conclusion to this series of discoveries, 

 an investigation of very wide interest, which has resulted in the con- 

 struction of the normal cyanides (a) of the monatomic hydrocarbons, 

 formed by the action of chloroform on the primary monamines, which, 

 together with water,. are resolved into formic acid and the base whence 

 they are derived; while their isomers (Class B), the nitrites, under 

 similar conditions yield ammonia and their corresponding acids. Hofmann 

 has also established the existence of a new class of cyanates (/3) of the 

 same monatomic hydrocarbons which, together with water, are resolved 

 into ammonia and their corresponding alcohols, the original class (a) 

 being resolved under the same circumstances into carbonic acid and the 

 primary monamines, as in the experiment of Wurtz before referred to, the 

 whole investigation standing in intimate connexion with Hofmann's 

 previous work. 



• To estimate the value of these results it is necessary to go through 

 the vast mass of experimental evidence from which they are deduced, 

 which constitutes a body of complete and exact information in reference 

 to one general subject not easily paralleled in the history of Chemistry. 



The Medal was received by Dr. Hofmann. 



A Eoyal Medal has been awarded to Mr. William Crookes, E.E.S., 

 for his various chemical and physical researches, more especially for his 

 discovery of Thallium, his investigation of its compounds, and determi- 

 nation of its atomic weight ; and for his discovery of the repulsion 

 referable to radiation. 



In the year 1861 Mr. Crookes communicated the discovery of a new 

 element, which he had detected by means of a green line exhibited in the 

 spectrum of certain selenium residues which he was examining for 



