APPENDIX B.

CHEMICAL CLASSIFICATION.

The classification of Mohs, which has been adopted in the pre-ceding part of this treatise, more clearly exhibits the affinities ofthe mineral species, than any arrangement founded on a less gene-ral view of the relations of the species, and is best adapted to con-vey a comprehensive, systematic, and intelligible idea of the Sci-ence of Mineralogy. It is; however, frequently desirable, especiallywith the chemist and metallurgist, to view minerals simply in theirchemical relations. The following chemical classification of themineral species is therefore subjoined.

Chemical arrangements may be of two kinds; 1, the general di-visions may be formed by associating compounds, containing thesame electro-negative element; 2, these divisions may depend onthe electro-positive element.

In a classification of the first kind, in which the various mineralspecies are arranged according to the electro-negative part of theirconstitution, the binary compounds would be distributed into twoclasses, according as they form acid (electro-negative) or non-acid(electro-positive) compounds, with oxygen, chlorine, iodine, sul-phur, <fcc.; and the species, produced by the union of individualsof these two classes, would constitute a third class of salts. Thesubdivisions of these classes would depend on the particular electro-negative element in the composition of each of the species. Con-sequently, we should have families of oxyds, chlorids, sulphurets,<fcc.; of oxacids, chloracids, sulphacids, &c.; of oxysalts, chloro-salts, sulphosalts, &c.

The second method of classification associates all species con-taining the same electro-positive element, or compound. Thus allthe compounds of a particular base, as potash, copper, iron, &c., arecollected into separate families.

Since the development of the electrical relations of the elementsand their compounds by Berzelius , the superiority of the former ofthese methods of classification has been very generally admitted.The electro-negative constituent is, in general, the characterizingingredient. The sulphurets of different metals are far more closelyallied than the oxyds, sulphurets, and salts, of the same metal. Yet

App.— K