44 HISTORY OF CHEMISTRY. [LECTURE III. 



Still the struggle is not on this account at an end. Even yet 

 Berthollet will not recognise the difference between mixtures 

 and compounds which had been advanced by Proust. For 

 both of these conceptions he demands sharp definitions. 37 



Now, as a matter of fact, Proust cannot furnish these defi- 

 nitions ; still he shows how mixtures can be distinguished from 

 compounds in special cases, and in doing so, he succeeds in 

 disproving a great many of Berthollet's statements. Obviously I 

 cannot follow this matter in all its details, and I shall, therefore, 

 only show by a single example Proust's mode of adducing his 

 proofs. Berthollet had previously asserted that, by treating 

 mercury with nitric acid, a series of oxides was obtained, in 

 which the proportion of oxygen increased steadily from a defi- 

 nite minimum. 38 Further, he had observed that these oxides, 

 on treatment with hydrochloric acid, were converted into two 

 chlorides, and had assumed that it was the insolubility of mer- 

 curous chloride which caused the oxides to betake themselves 

 from the stage of oxidation at which they stood to the two end 

 stations. 39 Proust considers that too much intelligence is, on 

 this assumption, attributed to the oxides. He shows that in the 

 dry way also, only two chlorides are formed, and that these cor- 

 respond to the only two oxygen compounds, of mercury into 

 which Berthollet's mixtures can be separated. 



Thus this controvers} 7 , which began in 1801, continues until 

 1807, but, about this time, the interest that the scientific world 

 had at first taken in the two opponents diminishes consider- 

 ably. The authority of Berthollet had made it possible that, 

 in consequence of his attack, a doctrine which had previously 

 been regarded as accurate a priori, should appear doubtful "to 

 many. But the researches of Proust on the one hand, and 

 those of Klaproth and Vauquelin on the other, had restored 

 confidence in that doctrine. Berthollet's rejoinders began to 

 lose their effects. He was forced to admit the existence, in 

 ever widening classes of substances, of compounds with con- 



37 Journ. de Phys. 60, 347. 3S Arm. Chim. 38, 119. 39 Proust, Jourru 

 de Phys. 59, 335. 



