Some of these metals are the _bases_ of the _alkalis_, _alkaline earths_, and _earths_. And as _this_ class of metals is but little known to the great mass of readers, some remarks will be acceptable: they are recommended to his special attention, as they form the base of the only satisfactory theory of _volcanos_ and _earthquakes_. The number of metals in this class are _twelve_. 1. The bases of the three alkalis, _potash_, _soda_, and _lithia_. The base of _potash_ is POTASIUM. This metal was discovered in 1807 by Sir H. Davy. Its texture is crystalline; color and lustre similar to mercury. It is solid at the ordinary temperature of the atmosphere; somewhat fluid at 70°, melts at 150°. Its affinity for oxygen is so great that it oxidizes rapidly in the air; and decomposes water instantly upon contact, emitting heat, flame, and light, as it swims on the surface of the water, being the _lighter_ substance. In these cases it oxidizes and becomes potash, by abstracting oxygen from the air and water. The base of _soda_ is SODIUM. This metal was discovered by the same chemist the same year. It has the strong metallic lustre of silver. It fuses at 200°, and evaporates at a full red heat. It decomposes both air and water, but not so rapidly as potasium. When thrown on water it effervesces strongly; and inflames with light, when thrown on boiling water. In these cases soda results, which is the _oxide of sodium. This metal is the base of common salt._ The base of _lithia_ is LITHIUM. This metal was discovered in Sweden in 1818, by Arfwedson. It is of a white color, like sodium; but oxidizes so rapidly as not to be kept in its pure metallic state. Its peculiar properties are, therefore, not so certainly known. Its alkaline quality is well ascertained, when in combination with oxygen, in which form it commonly appears. 2. The bases of the four alkaline earths, _baryta_, _strontia_, _lime_ and _magnesia_. The base of _baryta_ is BARIUM. This metal was discovered by Sir H. Davy, in 1808. It is of a dark gray color, very heavy, and attracts oxygen very strongly from the air, and from water, with effervescence, caused by the escape of hydrogen gas, and thus becomes an oxide which is the pure earth baryta, of a white color, and very heavy. Its intimate properties are not yet well known. The base of _strontia_, is STRONTIUM. This metal is very much like barium, in color, weight, and power of decomposing air and water, and thus becoming an oxide, which is the earth strontia. Yet it is satisfactorily distinguished from barium.