It may be added, that this action would naturally bring to its aid the astonishing powers of electricity and galvanism. The _forty_ metals mentioned above, may be classed scientifically into _two_ classes. 1. _The bases of the alkalis, alkaline earths, and earths._ These are twelve: potasium, sodium, and lithium; bases of the alkalis--barium, strontium, calcium, and magnesia; bases of the alkaline earths--aluminium, glucinium, yttrium, zirconium, and silicium; bases of the earths. 2. Metals, the oxides of which are neither alkalis, or earths. These are _twenty-eight_ in number, and may be set down in the following order: gold, silver, iron, copper, mercury, lead, tin, antimony, zinc, bismuth, arsenic, cobalt, platinum, nickel, manganese, tungsten, tellurium, molybdenum, uranium, titanium, chromium, columbium, palladium, rhodium, iridium, osmium, cereum, and cadmium. Not only the _first_ class of metals are _combustible_, but the _last_ also. _All_ the metals are now well known to be combustible bodies, _and may be made to burn as really as wood_.] _Gems_ are of a higher order than metals, of a more refined nature, and consist of two classes, the pellucid and semi-pellucid. Those of the first class are bright, elegant, and beautiful fossils, naturally and essentially compound, ever found in small detached masses, extremely hard, and of great lustre. Those composing the second class are stones naturally and essentially compound, not inflammable nor soluble in water, found in detached masses, and composed of crystalline matter debased by earth: however, they are but slightly debased, are of great beauty and brightness, of a moderate degree of transparency, and usually found in small masses. The knowledge of the gems depends principally on observing their hardness and color. Their _hardness_ is commonly allowed to stand in the following order: the diamond, ruby, sapphire, jacinth, emerald, amethyst, garnet, carneol, chalcedony, onyx, jasper, agate, porphyry, and marble. This difference, however, is not regular and constant, but frequently varies. In point of _color_, the diamond is valued for its transparency, the ruby for its deep red, the sapphire for its blue, the emerald for its green, the jacinth for its orange, the amethyst for its purple, the carneol for its carnation, the onyx for its tawny, the jasper, agate, and porphyry, for their vermillion, green, and variegated colors, and the garnet for its transparent blood-red.