LECTURE XT.] HISTORY OF CHEMISTRY. 2OQ 



oxygen, the radical C 2 H 5 , ethyl, being converted by oxidation 

 into C 2 H 3 O, othyl. Acetic acid is now regarded as water in 

 which one atom of hydrogen is replaced by othyl. The 

 formula C 6 H 12 O 3 fixed upon for acetone by Kane, 39 did not 

 appear to be in harmony with this ; it had, however, already 

 been halved, and Williamson endeavoured to explain the for- 

 mation of the substance during the distillation of the acetates, 

 by means of the following equation : 



C 2 H 3 C 2 H 3 _ CO . K0 C 2 H 3 

 K K K f CH 3 ' 



According to him, the potassium peroxide is replaced during 

 the reaction by methyl derived from the othyl. Here, also, he 

 checks his opinion by applying the method already mentioned. 

 He distils mixtures of acetates and valerianates and obtains 

 mixed ketones : 



C 2 H 8 C 5 H 9 Q COKO Q C.H.O 

 K K K f CH 3 ' 



Williamson concludes this paper, which did a great deal to 

 advance chemistry, with the words : " The method here em- 

 ployed of stating the rational constitution of bodies by com- 

 parison with water, seems to me to be susceptible of great 

 extension ; and I have no hesitation in saying that its introduc- 

 tion will be of service in simplifying our ideas, by establishing 

 a uniform standard of comparison by which bodies may be 

 judged of." 



The " terme de comparaison " which Laurent had already 

 sought for in vain, had now been found. Substances were to 

 be conceived as formed from water in accordance with the pro- 

 posal, which Williamson makes in 1851 in his famous paper 

 upon salts, 40 to regard this substance as the type for all com- 

 pounds. His method of fixing molecular weights is a purely 

 chemical one ; he regards compounds as formed from water by 

 the replacement of one or of two atoms of hydrogen. Inas- 

 much as he tests all his views by means of facts already known, 

 as well as by means of new experiments, these views obtain, I 



ya Annalen. 22, 278. 40 Journ. Chem. Soc. 4, 350. 



O 



