(UO BUNSEN MEMORIAL LECTURE. 



pouiuls tho tongnio l)oc()nies covered with u blaek coating, even when 

 no further evil etiects are noticeable."' 



Respecting the constitution of the radical of the cacodyl compounds, 

 various theories have from time to time been put forward. Bunsen 

 himself did not give any opinion on the point, and it was Kolbe who 

 tirst suggested the view that it was arsini'-dimethyl, As(C}I.j)o, while 

 the experiments of Frankland, and subsequently those of Cahours and 

 liiche, rendered this probable. It is, however, to the researches of 

 Adolf von Bae3'er (AnnaliMi, 1858 (107), 257) on the arsemnonomethyl 

 compounds that we owe tlie full explanation of the relation which these 

 various l)odies bear to one another. 



The cacodyl research claims our interest not onh' because, as we 

 have seen, it furnishes us with the first example of an isolable radical, 

 but also l)ecause it assisted Frankland and Kekule in more exactly 

 illustrating the term ''chemical valency." For it is not too much to 

 say that the subsequent researches of Frankland on the organo-metal- 

 lic bodies and on the so-called alcohol radicals, as well as those of the 

 French chemists, and, 1 may add, those of Baeyer, received their tirst 

 impulse from the cacodyl investigation. This indebtedness was 

 acknowledged by our late laniiMited Fellow in the graceful. and modest 

 words which appear in the dedication of the volume of his collected 

 researches: 



' ' To my friend and teacher, Robert William Bunsen, whose researches 

 on cacodyl. on the gases of the iron furnaces, and on the volcanic phe- 

 nomena of Iceland I lunc always regarded as models of investigation 

 in i)ure. ai)plied. and physical chemistry. I dedicate these pages, both 

 as a testimony of my regard and in gratitude for the teaching whereby 

 he inibucMl me with tlu> necessity for thoroughness and accuracy in all 

 scientific work. \\'ould that the}' were more worthy of such a high 

 standard." 



Thus it is seen that, although this remarkable research is the only 

 one of any importance which was carried out by Bunsen in the domain 

 of organic chemistry, it was destined to exert such an influence on the 

 later developments of that branch of the science that he may with 

 truth be regarded as one of the pioneers of modern organic chemistry. 



I now pass to an investigation of a different type, but one not less 

 important or interesting than the last. 



Up to the 3^ear 1838, when Bunsen began his investigation of the 

 composition of the gases of the iron furnaces, the mode of measuring 

 gaseous volumes and the methods adopted for the separation of the 

 several gases were faulty and inaccurate in the extreme. But during 

 the period elapsing between the above year and 1845 Bunsen had not 

 only elaborated and perfected his well-known gasometric methods, but 

 had applied these methods with signal success to the investigation of 



