Royal Institution. 383 



the compound radical ; and in like manner, the electrolytic decom- 

 position of a sulphate moves the group SO* to the positive pole, 

 where it either combines with a metal or undergoes decomposition. 



One of the strongest arguments against the view that the oxygen 

 acids contain water, is afforded by the results of recent researches 

 (especially of MM. Laurent and Gerhardt) on the atomic weight of 

 acids. Those chemists have rendered more definite and exact than 

 they had been before our ideas on the distinctions between mono- 

 basic, bibasic and tribasic acids, and have clearly established that 

 the correct expression of the atom of nitric acid must be such as 

 contains half as much hydrogen as is contained in 1 atom of water 

 (inasmuch as water is bibasic, and nitric acid monobasic). Of 

 course this proportion may be as well established by doubling the 

 atomic weight of water as by halving that of hydrated nitric acid ; but 

 either way it is clear that hydrated nitric acid cannot contain water. 



Such was the position of the question, when an English chemist 

 proved that the formation of aether from alcohol (which was con- 

 sidered chemically as the hydrate of aether) does not consist in a 

 separation of two already-formed compounds, but in a substitution 

 of hydrogen by the organic radical sethyle. A similar fact M. Ger- 

 hardt has proved respecting a great number of organic acids, by 

 preparing bodies which stand to them in the same relation as aether 

 does to alcohol. 



The researches of M. Cahours had led to the discovery of a series 

 ,of bodies necessary for Gerhardt's process. These were obtained 

 by the action of pentachloride of phosphorus on various hydrated 

 organic acids, and consisted of chlorine combined with the oxygen- 

 ized radical of the acid. Thus from benzoic acid was prepared 

 the chloride of benzoile, C^ H* OCl, and the corresponding bodies 

 from cuminic, cinnamic, and various other acids. Gerhardt has 

 since made by the same process the body C® H^ OCl, which is the 

 chloride of the radical of acetic acid, called othyle. Now on bring- 

 ing any one of these chlorides in contact with the potassium salt of 

 the corresponding acid, the chemical force of combination between 

 chlorine and potassium induced the decomposition. 



These results can be most simply stated in the form adopted by 

 M. Gerhardt, the discoverer, which consists in comparing the com- 

 position of these bodies with that of water, from which they are 

 formed by the substitution of one or both atoms of hydrogen by 

 organic radicals. 



H 



Thus water being represented by the formula tjO, acetic acid is 



formed from it by the action of chloride of othyle, C® H^ OCl, which 



C^H^ O 

 forms jj O -f HCl, i. e. hydrated acetic acid and hydrochloric 



acid. If a second atom of chloride of othyle is made to act upon 



po TT3 r\ 



this acetic acid, or better upon the acetate of potash, ^ O, we 



r\q, TT3 r\ 



get, besides chloride of potassium, a compound, ^^ rrg q O, M'hich, 



