174 Mr. Coiqtihotm on the Life and Writings [MARbii, 



and insoluble salt. Alas ! how often in theory, as well as iti 

 practice, does the problem become strangely difficult of making 

 the two ends meet. How often do we find that on the insect 

 wirig of one sinall moment ride the eternal fates ! Mercury is 

 iiideed a nimble, sprightly metal, yet one cannot help assenting 

 to the observation of Proust, that in this theory there is really 

 too much stress laid on both its agility and intelligence. Here, 

 said he, we find this countless host of infinitely various and dis- 

 tinct oxides, all constituting separating nitrates, in an instant, 

 and per saltnm, as it were, abandon the staiions they had occu- 

 pied in the scale of their thousand and one oxidations, to fly to 

 the extremes of that scale, which happen also to be the posts of 

 calomel and corrosive sublimate, the only points at which they 

 will suffer the anxious investigator to come up with and secilrei 

 them ! What promptitude ! What exactness ! Really, says 

 Proust, one must concede at least to M, Berthollet, that nothing 

 can surpass the admirable evolutions and discipline of his 

 oxides ! 



It was in this manner that the controversy was concluded on 

 both sides, in the most liberal spirit, and at the same time with 

 the most lively argument and research. But before we take 

 leave of it, it is no more than due to Proust, in order to show 

 how admirably just and perspicuous was his exposition of the 

 views which the doctrine of chemical equivalents unfolds, to 

 state what he himself then wrote on the subject. Take an 

 instance of his reasoning relative to the oxidation of metals. 



The existence of an infinite number of distinct and independent 

 oxides is inconsistent with the ordinary progress of nature in 

 every thing else. In the oxidation of metals, nature follows the 

 same course as in combining oxygen with any of the combusti- 

 bles. The latter combine avowedly with definite and invariable 

 proportions of oxygen ; and the former, when placed in a situa- 

 tion favourable to their union with that substance, combine, at 

 the instant of contact, with the whole quantity of it required to 

 produce saturation at one or other of the points which in com- 

 mon terms we style the maximum or minimum of oxidation. In 

 the same manner, when a molecule of any alkali is placed iri 

 contact with an acid, it does not at first combine with less and 

 then with mo7e of the quantity necessary for saturation : on the 

 contrary, it insianlly attracts the whole proportion of acid, with 

 which, in obedience to the invariable laws of its affinities, it at 

 once forms a complete combination. The proportions in which 

 substances unite have been fixed by nature from all eternity, and 

 are as little under our controul as are those afiinities by which 

 the compounds are upheld. Election and proportion are two 

 poles around lohich the ichole system of true combinations inoariahly 

 revolves, w'lether in external nature, or in the investigations of' the 

 chemist. From their agency result the laws exerting that 



