544. The classification of metals is one of the most difficult, because no natural arrangement of them has been as yet attempted, and their signification is also so mysterious that we can only get at it, by clinging fast to the laws of development. Thus assuming, that they likewise arrange themselves according to the elements, classes and orders of the earths, we have at once the _Elemental metals_. The earth-metals are without doubt the difficultly fusible, ignoble or oxydized, such as iron with its congeners. Then the air-metals present themselves with their peculiar character of volatility, as Arsenic with its congeners. These being once rendered solid, the easily fusible but non-volatile will correspond to water, such as Lead with its congeners. The noble metals consequently as Gold, Silver, &c., must doubtless be regarded as fire-metals. Having once separated these 4 groups, the _Class-metals_ admit of being more readily brought into their place. There is one metal, which subjected to moisture is readily converted into a salt, namely copper. This is consequently the representative of the salts among the metals. Ore-metals are, without doubt, those resembling iron, which do not, however, occur in an oxydized condition and are therefore noble Irons. Of this kind are Platinum with its retinue. Between Copper and Platinum nothing else can be introduced but Nickel and Cobalt, as they are likewise difficultly fusible and tolerably noble. They are thus the Inflammable metals. After all these separations a great group is still left of the earth-metals or the difficultly fusible and ignoble. They divide therefore without doubt according to the 4 earths. If now iron approximates the argillaceous-earths, so will those metals whose oxydes are distinguished by a striking colour be regarded as talc-metals. Of this kind are Titanium, Chromium, Uranium, which crystallize moreover into spiculæ like hornblende, or into lamellæ like mica. These again being separated the silicious and calcareous-metals remain for investigation. The former are those which scarcely admit of being reduced; the latter, on the contrary, those which approximate to the noble, difficultly fusible metals, namely to platinum. It can hardly be doubted that Tantalum is the silicious-metal. For the calcareous-metals Sulphuret of Molybdenum is left, to which Osmium seems to approximate. We have accordingly the following genetic arrangement: A.--_Earth-Metals._ (Difficultly fusible and ignoble.) 1. Silicious-Metals Tantalium. 2. Argillaceous-Metals Wolfram, Cerium, Manganese, Iron. 3. Talcose-Metals Titanium, Chromium, Uranium, Vanadium. 4. Calcareous-Metals Molybdenum, Osmium. B.--_Class-Metals._ (Difficultly fusible and noble.) 5. Salt-Metals Copper. 6. Inflammable-Metals Nickel, Cobalt. 7. Ore-Metals Platinum, Palladium, Iridium, Rhodium. C.--_Element-Metals._ (Easily fusible or noble.)