as a Branch of Natural History, SfC. 



ancient chemists but also their analyses, are so deficient in ac- 

 curacy as to have rendered them now quite useless ; and this 

 observation is not limited to chemists of the last century ; the 

 analysis given of the Wavelite^ of the Uranite, &c. under the 

 sanction of very celebrated names, shows that an appeal can al- 

 ways be made to a more enlightened chemistry from the first 

 decisions of a less advanced chemistry. In such a case it is 

 quite natural that, when we see the minerals differing from 

 each other in important physical characters, while chemistry 

 cannot at the moment show any material difference in their 

 composition, we should, guided by strong analogies and proba*. 

 bilities, still wait for the last decision of a better informed che* 

 mistry* 



§ 42. Besides their greater certainty, the physical properties 

 or characters derive from their total independence of any ante- 

 rior or auxiliary chemical notion, a great advantage over the 

 considerations belonging to chemical composition or properties. 

 It is known that a mineral can be perfectly characterized witli^ 

 out any reference whatever to its composition, and Mohs''s whole 

 classification would be a proof, if wanted, of this assertion. Now, 

 chemistry is far from being able to boast of such an independ- 

 ence of physical considerations. In the first place, the very 

 idea of a chemical essay, either by the blowpipe or by any other 

 method, or of an analysis, implies, as a matter of course, that 

 the small portion of a physically homogeneous body, submitted 

 as pars pro toto to the essay or the analysis, is a true represen- 

 tation of the whole ; and such a notion is a strong though tacit 

 acknowledgment of the dependence which binds the chemical 

 researches to the consideration of physical properties, for it 



• That such opinions have been maintained by some of the first rate ch€>- 

 mists themselves, the following quotations will prove. ** II faut avouer qu^ 

 si la min^ralogie tire de grands avantages de la docimasie, la premiere avertit 

 i son tour le chimiste, soit par la structure du mint^ral, soit par quelque autre 

 phenomene exclusif, quil y a dans ce corps quelque chose de nouveau \ d^- 

 couvrir; et c'est ce qui est arriv^ plusieurs fois entre ces deux sciences." — 

 {Vauquelin^ Jour, des Mines, No. li. p. 192.) " Les caracteres des corps de- 

 pendent entierement de leur composition int^rieure, de maniere qu'une dif- 

 ference dans la composition en entraine toujours une dans les caracteres."— 

 {Berzelius, Nouveau Systeme de Min^ralogie, p. 6, et corrigenda, p. 311. 

 Hence, the inverse must of course be equally true, that a difference in the 

 characters mu«t be attended by a difference in composition. '' /c ;:>','i 



