46*2 Introduction to the Study of Mineralogy. 



combustible substances ; the different non-metallic bodies 

 *u*ceptil>]e of combustion, such as the diamond, sulphury 

 and minerals known by the name of bitumens. Among 

 those substances some have hitherto resisted the attempts 

 made t<> analyse them ; others, treated by distillation or by 

 other means, give out several of the principles which en- 

 tered into their composition. This difference naturally in- 

 dicates the subdivision of the class in question into two 

 orders, distinguished from each other by the denominations 

 of simple and compound combustible substances. 



The metalic substances still remain, which give the 

 fourth class, subdivided into as many genera as there are 

 metals. Under each of these genera is to be ranked as a 

 species the native metal when it exists ; then the metal com- 

 bined, either with another metal, with oxygen, combustibles, 

 or acids. With respect to the orders which subdivide this 

 class, I have formed them after the example of Bergman, 

 who has borrowed their characters from circumstances which 

 determine their oxidation and reduction, by placing in the 

 first order those which are not oxidizable, but only reducible 

 by heat : in the second, those which are oxidized when 

 heated, and which, when heated more strongly, are reduced : 

 and in the third, those which are oxidizable, but not redu- 

 cible by heat *. 



* The relations which characterize the divisions and subdivisions of the 

 chemical methods being founded upon the intimate properties and upon the 

 composition of bodies, these methods will at first appear to give way to a 

 certain point to those who employ external characters, and in some measure 

 more accessible characters, in order to establish the classification. I have at- 

 tempted to supply the place of it, at least relatively to the great divisions, by 

 characters easily ascertained. To conclude : I have not thought that the 

 consideration I have mentioned can balance the advantage of presenting a 

 distribution founded upon the very essence of the substance which it em- 

 braces, and at once more symmetrica!, more satisfactory to the mind, by. 

 givin"- legitimate order to our ideas. What furnishes an additional motive 

 for supporting this preference is, that, the number of mineralogical species 

 being very inconsiderable, the instant they are once clearly circumscribed, the 

 principal object is fulfilled. For in this case we gain by a little practice such 

 a stock of knowledge, that, when a mineral presents itself for the first time, 

 nothing remains in order to determine it than to decide between two or three 

 species, successively trying the characters which distinguish, each of them, 

 until wt have removed all doubt. 



The 



