LECTURE VII.] HISTORY OF CHEMISTRY. 12) 



nauseating smell, by distilling potassium acetate with arsenious 

 anhydride. 53 This liquid took fire spontaneously in air, and 

 it was known to contain arsenic and to be poisonous. These 

 properties appear to have deterred chemists from the study of 

 it, for, with the exception of a few unimportant experiments by 

 Thenard, they had not occupied themselves with it at all for 

 seventy years, and had been content to mention it in text-books 

 as Cadet's liquid. Dumas had then endeavoured, by distilla- 

 tion, to separate a pure compound from the crude product, 

 which was contaminated, amongst other things, with elementary 

 arsenic. According to his analyses, it is represented by the 

 formula C 8 H 12 As 2 [C = 6, As = 75]. 54 Bunsen's first results 

 appeared to confirm this, 55 while later experiments eventually 

 fixed it as C 4 H 12 AsoO [C = 1 2]. 56 Bunsen called the substance 

 cacodyl oxide, and assumed the existence in it of the radical 

 CjH 12 As 2 . He succeeded in preparing the chloride, bromide, 

 iodide, cyanide, and fluoride by treatment with the corre- 

 sponding acids ; the action of barium hydrosulphide produced 

 the sulphide ; by oxidation Bunsen obtained cacodylic acid, 

 C 4 H] 2 As2.O 3 + H 2 O ; finally, he found it possible to isolate the 

 radical cacodyl by decomposing the chloride by means of zinc, 

 and, naturally, this assisted very materially in procuring recog- 

 nition for his mode of regarding the matter. We can understand 

 how keenly interest must have been aroused on hearing of the 

 isolation of an organic radical containing a metal, and possessed, 

 besides, of the extremely remarkable property of spontaneous 

 inflammability. 



I have intentionally introduced here the account of this 

 important research of Bunsen's (the completion of which falls 

 at a later date) in order to be able to make clear the idea of a 

 radical as it now gradually came to be conceived. This idea 

 is essentially different from what was formerly understood by 

 the term, and the new conception was brought to the front by 



53 Mem. de Math, et de Phys. des savants etrangers. 3, 633. 

 54 Dumas, Traite. Organic Part, I, 135; compare Annalen. 27, 148. 

 53 Annalen. 24, 271. 56 Ibid. 31, 175 ; 37, i ; 42, 14 ; 46, i. 



