SODIUM (symb. Na, equiv. 23, spec. gray. 0.972) is one of the metals of the alkalies— its oxide being soda. It properties closely resemble those of the allied metal,potassinm. It is of a bluish-white color, is somewhat more volatile than potassium, and further dif fers from that metal in having a higher fusing-point (about 20S'), a greater specific gravity, and in not catching fire when dropped in water (unless the water is heated), although like potassium under similar conditions, it partially decomposes it and liberates hydrogen; and at the same time communicates a strung alkaline reaction to the solution. If, however, a piece of unsized paper is placed on the surface of cold water, and the sodium be placed on the paper, the metal takes fire, and burns with a deep yellow flame. Strictly speaking it is the liberated hydrogen rather than the metal which burns, the yellow tint (which is characteristic of the sodium compounds) being due to a little sodium volatilized by the beat, mixing and burning with the hydrogen. When heated in the air, it burns with its characteristic yellow flame, and is converted into soda. When exposed in vacuo to a red heat it assumes the form of vapor, and admits of distil lation. Like potassium, it must be kept immersed in naphtha, so as to exclude the oxidizing action of the air. As a reducing agent, it is little inferior to potassium, and as its combining power is loWer, and it is obtained much more cheaply, it may usually be advantageously substituted for potasSimn in reducing operations. Sodium does not occur in the metallic form in nature, but its compounds are very widely distributed. It is found by far the most abundantly in the form of chloride of sodium (or common salt), but it likewise occurs as albite or soda-feldspar, cryolite (the double fluoride of sodium and aluminium, and the principal source from whence aluminium is procured), borax (the biborate of soda), trona (the sesquicarbonate of soda), and Chili saltpeter (nitrate of soda).
The methods of obtaining sodium are similar to those already described for obtain ing potassium. The following procedure recommended by Deville is regarded as the best for obtaining it in large quantity, Intimately mix 717 parts of dried carbonate of soda with 175 parts of finely powdered charcoal and 108 parts of finely ground chalk, knead them into a stiff paste with oil, heat them in a covered iron pot till the oil is decomposed, and finally distil them in art iron retort with the precautions which are noticed in deseribtng the preparation of potassium (q.v.). The object of adding the
chalk is to prevent tho separation of the charcoal from the carbonate of soda when the latter fuses. This mixture ought to yield nearly one-third of its weight of sodium.
With regard to the history of sodium, it is sufficient to observe that Duhamel, is 1736, discovered that potash and soda (now known to be the oxides of potassium and sodium) were distinct bodies. Sir H. Davy first obtained the metal sodium, in 1807. The symbol of this metal, Na, is the abbreviation of natriant, which is derived from nation, one of the old names of native carbonate of soda.
Sodium combines with all the elementary gaseous bodies, and two of these combina tions—viz., those with oxygen and chlorine, are of extreme importance and value.
With oxygen, sodium forms two compounds—viz., an oxide (Na0) and a peroxide The latter being of no practical value, may be passed over without notice. The oxide (soda) was formerly known as fossil or mineral alkali, to distinguish it from potash, which, from the source from which it was procured, was termed vegetable alkali. Anhydrous soda (Nal)) is procured by burning the metal in dry air; it is of a yellowish white color, powerfully attracts moisture, and retains the water so firmly that it cannot be expelled by heat. Hydrated or caustic soda (NaO,IIo) closely resembles, both in its properties and in the mode of procuring it, the corresponding potash compound. It is, however. not so fusible as the latter, and is gradually converted, by exposure to the air, into carbonate of soda, which is also an infusible salt in its anhydrous state. Solution of hydrate of soda (or soda lye) is largely employed in the arts. It is prepared by boil ing a tolerably strong solution of carbonate of soda in milk of lime until a portion of the filtrate ceases to effervesce on the addition of an acid. _ The solid hydrate has a specific gravity of 2.13. and the quantity of anhydrous soda in any solution may be pretty closely approximated to by determining the specific gravity of the fluid at a temperature of 59°. Tables for this purpose have been constructed by Dalton (quoted in Miller's Inorganic Chemistry, 2d ed. p. 37), and by Zimmerman (reprinted in the article " Sodium" in Knight's English Cyelopadia), Many of the combinations of the oxide of sodium (soda) with acids—constituting soda salts—are of great importance. Carbonic acid forms three salts with soda—viz., a normal carbonate, a sesqui-carbonate, and a bicarbonate of soda.