SODIUM. (Na,natrium.) Tho original name of natriurn for this metal Is derived from that of natron, nitron, or trona, old names of certain natural deposits of carbonate of soda which were long con founded with the true nitron or nitre (nitrate of potash). The term sodium originates from soda or sod-ash, the latter probably having allusion to the practice of burning the sods or turf of plants growing near the sea in order to obtain their ash, which is a crude carbonate of soda, known as Garilla.
Sodium, like POTASSIUM, was first isolated by Sir H. Davy. It may be prepared in a manner similar to, but with far greater facility than, the last-named element. Deville gives the following directions for obtaining it in large quantities. Intimately mix 717 parts of dried carbonate of soda with 175 parts of powdered charcoal and 108 of finely ground chalk ; knead into a stiff paste with oil : heat in a covered iron pot till the oil is all decomposed ; finally, distil, with the apparatus, arrangements, and precautions given under POTASSIUM.
Sodium has the characteristic lustrous appearance of a metal, and is of a beautiful light rose colour. It may be obtained in quadratic octohedral crystals by the method described under PorAssruar. Like potassium, it speedily tarnishes by exposure to the air, owing to its great affinity for oxygen, and this occurs more rapidly when the air is moist ; it requires for preservation the same precautions as have been mentioned with regard to potassium. It does not, like this metal, inflame when thrown upon water, but decomposes the latter with a hissing noise, the results being hydrogen and oxide of sodium, or soda, which, remaining in solution, exhibits the well-known alkaline character of that substance. When however it is placed on a moistened bad con ductor of beat, as charcoal, it decomposes water with vivid combustion. Its specific gravity is 0.972. It is a good conductor of electricity and heat ; but if too strongly heated iu the air, it burns with a yellow flame.
The equivalent of sodium is 23.
Sodium combines with all the elementary gaseous bodies, two of which combinations, namely, those with oxygen and chlorine, are of great importance and utility.
Oxygen and sodium form two compounds, protexide and peroxide of sodium; the former of these has been long known, and extensively used in various arts and manufactures. It was formerly called the
fossil or mineral alkali, to distinguish it from potash, which, as being procured by the incineration of wood, was called the vegetable alkali ; the peroxide has been discovered only since the metal was known.
Under the head of carbonate of soda we shall briefly mention the processes by which soda is procured for manufacturing purposes, stating merely at present that protoxidc of sodium, or anhydrous soda (NiO) is prepared by heating the metal in dry oxygen gas. Thus obtained, it 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 great affinity for water, dissolving readily in it, and in large quantity, and the solution has strongly marked alkaline properties.
Sodium differs remarkably from potassium in some respects ; thus, while both become first alkaline oxides, and afterwards carbonates, by exposure to the air, the carbonate of soda remains dry, while that of potash becomes fluid, owing to the absorption of water.
Sodium, as has already been noticed, is oxidised by decomposing water, and the solution of soda obtained, when evaporated to dryness, leaves hydrate of soda (NaO, HO). This is a solid white substance, greatly resembling soda in appearance and propertiei. It retains the water with such great affinity that it cannot be expelled by heat.
The hydrate is composed of one equivalent of soda and one equivalent of water.
Solution of hydrate of soda is largely used in the arts. It is made by boiling a tolerably strong solution of soda-ash or carbonate of soda with milk of lime until a portion of the filtrate ceases to effervesce on the addition of an acid. The strength of the solution is indicated by its specific gravity at 59° Fehr., as demonstrated in the following table by Zimmerman :— as potash. It is found however in albite, or cleavlandite, a con stituent of granite resembling felspar, except that it contains soda instead of potash. [Somusr, in NAT. HIST. Div.] Peroxide of Sodium (Na03 ?).—This compound is formed on mode ratty heating sodium in oxygen gas. It burns vividly, evolving much light and heat ; the peroxide resulting is of a yellowish-green colour. W'hen put into water, it is decomposed, oxygen gas being evolved, and soda, or protoxide of sodium, remaining in solution.