LECTURE XII.] HISTORY OF CHEMISTRY. 227 



proof of the correctness of the theory propounded by Kane, 

 Berzelius, and Liebig fifteen years ago." 23 



This series of investigations, carried out between 1844 and 

 1850, rehabilitated the theory of copulae. Even if it only 

 appeared to be justified by the reactions in the case of a small 

 class of substances, still it was justified for the most important 

 compounds, and for those, in particular, which had influenced 

 Berzelius in setting up his views. Experiment had shown that 

 the assumption of methyl in acetic acid, of chloride of carbon 

 in trichloracetic acid, of ethyl in alcohol, etc., had a real 

 foundation, and it soon appeared to be clear that the way 

 opened up by Kolbe and Frankland must further lead to many 

 brilliant discoveries. 



While occupied with the isolation of ethyl from ethyl iodide, 

 Frankland discovered zinc ethyl,- 4 a substance which com- 

 manded the greatest interest on account not only of its physical 

 but also of its chemical properties. After the discovery of this 

 compound, the efforts of no small number of chemists were 

 directed towards making it available for synthetical purposes ; 25 

 and even although all the hopes which were based upon it were 

 not realised, still there are few compounds which have been 

 employed in so many ways in investigations in organic chem- 

 istry. Intimately connected with the discovery of zinc ethyl 

 is the preparation of the other organo-metallic compounds. 

 We are indebted to Wohler. 26 for the discovery of tellurium 

 ethyl ; the antimony compounds were prepared by Lowig and 

 Schweizer, 27 and the tin compounds simultaneously by Frank- 

 land 2S and by Lowig ; 2U mercury ethyl was prepared by Frank- 

 land, 30 and aluminium ethyl was prepared by Cahours 31 but 



- 3 Journ. Chem. Soc. 3, 46 ; Annalen. 74, 63. 24 Journ. Chem. Soc. 

 2, 297 ; Annalen. 71, 213. 25 Pebal and Freund, ibid. 118, I ; Wurtz, 

 Comptes Rendus. 54, 387 ; Annalen. 123, 202 ; Rieth and Beilstein, ibid. 

 124, 242; 126, 241 ; Alexeyeff and Beilstein, Comptes Rendus. 58, 171 ; 

 Butlerow, Zeitschrift fiir Chemie. 7, 385 and 702 ; Fried el and Lad en burg, 

 Annalen. 142, 310; Lieben, ibid. 146, 180, etc. '- 6 Ibid. 35, in ; 84, 

 69. 27 Ibid. 75, 315. - 8 Phil. Trans. 1852, 418; Annalen. 85, 332. 

 29 Ibid. 84, 308. 30 Journ. Chem. Soc. 3, 324; Annalen. 77, 224. 



31 Ibid. 114, 227 and 354. 



