440 Sir Henry Boacoe [June 1, 



transact as well, how could he possibly find time to carry on 

 laborious experimental investigations of his own? for it must be 

 remembered that he never kept an assistant to work at his re- 

 searches for him, but did all the experimental work with his own 

 hands. Well, it is always the busy man who has most time for 

 work — or, at least who does most — and so it was with Bunsen. 

 Spending the whole day in the laboratory he was often able to 

 spare an hour or two to devote to his own work, either of devising 

 and testing some new form of apparatus, of separating the rare earth 

 metals, or of preparing and determining the crystalline form of a 

 series of salts. Then he was an early riser, and when I lived with 

 him, I know that it was his habit to rise often before dawn in the 

 summer, to complete an experiment or to edit a research. The long 

 summer holiday again was a great time for work. We often spent a 

 few weeks together in excursions in Switzerland or the Tyrol to rub 

 off the fatigues of the session, but we soon returned to Heidelberg, 

 and in those quiet days we got through much experimental work, for 

 I had the good fortune for many years to be associated with Bunsen 

 in a research on Photochemical Measurements, about which I shall 

 say a few words later on. 



Let me now glance rapidly at some of his more important in- 

 vestigations. 



The research which stamped Bunsen as a first rate experimentalist, 

 was his investigation on the cacodyl compounds, on which he laboured 

 for six years. It is remarkable as an example of how the most 

 difficult and dangerous problems of experimental chemistry can be 

 solved by a master hand. It was a frightfully difficult and dangerous 

 research, because the compounds are both poisonous and explosive. 

 In 1846 Bunsen was nearly killed and poisoned when examining the 

 properties of cacodyl cyanide. " It is remarkable," he says, " that when 

 one is exposed to the smell of these compounds the tongue becomes 

 covered with a black coating, and the smell produces giddiness and 

 even insensibility." I therefore do not propose now to illustrate 

 these properties experimentally. 



The cacodyl research claims our interest, not only because it 

 furnishes us with the first example of an isolable radicle, but also 

 because it assisted Frankland and Kekule in more exactly illus- 

 trating the term " chemical valency." For it is not too much to say 

 that the subsequent researches of Frankland on the organo-metallic 

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

 French chemists, and, I may add, those of Baeyer, received their first 

 impulse from the cacodyl investigation. This indebtedness was 

 acknowledged by one whose voice and face, once familiar to this 

 audience, we all of us now sadly miss — the late Sir Edward Frankland 

 ■ — 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 re- 

 searches on cacodyl, on the gases of the iron furnaces, and on the 



