SODIUM, This metal is the base of the alkalies soda, natron, and the fossil alkali, in which substances it is combined with oxygen, forming the protoxide of the metal. It was discovered by Sir H. Davy in 1807. The properties of sodium are such as to prevent its occurrence in nature, except in combination, on account of its intense affinity for oxygen. Immense quantities Occur combined with chlorine, forming common salt ; and a con siderable quantity is met with in the state of oxide, or soda, combined with carbonic acid ; these are its principal sources. [Sodium] has a colour and lustre resembling those of silver. It remains a soft solid at 32°, so that small portions may be welded together by pressure; itbecomes much softer at 122°, fuses at about 100°, and by a white heat is volatilised. Like potassium, it speedily tarnishes by ex posure to the air, owing to its great affinity for oxygen, and this occurs more rapidly when the air is moist. When thrown on water it decomposes it with a hissing noise, the results being hydrogen and oxide of sodium, or soda. When however it is placed on a moistened bad conductor of heat, as charcoal, it decom poses water with a vivid combustion. Its specific gravity is 0.072, so that although it is considerably more dense than potassium, it is yet less so than water. It is a good conductor of electricity and heat ; but if too strongly heated in the air, it burns with a yellow flame.
Sodium and oxygen combine to form pure soda, which is a gray solid, resembling potash in appearance, but it is less fusible and volatile. It is extremely acrid to the taste, and is very caustic. It has a great affinity for water, dis solving readily in it, and in largo quantity, and the solution has strongly marked alkaline properties. Sodium and chlorine form the valuable substance common salt, formerly called Muriate of Soda, and now Chloride of Sodium. Of all natural soluble salts this occurs in the greatest quantity. It is met with solid, constituting rock-salt, in solution in salt springs and in the ocean, and in small quantity in almost all spring and river water. [SALT.] Nitrate of Soda is used largely in making nitric. acid and sulphuric acid. The Carbonate of Soda is noticed under SODA. MANUEACTURE. The Sulphate of Soda, formerly called Glauber's 'Salt, is readily soluble in water, and the solution by evaporation yields colourless transparent prismatic crystals. It has a very bitter taste ; it effloresces when exposed to the air, by losing water of crystal lisation.
Borax, Rochelle Salt and many other useful substances, as well as soda alum, are prepared from some of the compounds of Sodium.