Generally speaking, sodium salts closely resemble the corre sponding potassium salts, and their methods of preparation are usually the same. For sodium salts not mentioned below reference should be made to articles wherein the acid is treated, unless otherwise indicated.
Sodium combines directly with the halogens to form salts which are soluble in water and crystallize in the cubic system. The fluoride, NaF, is sparingly soluble in water (r part in 25). For the chloride see SALT. The bromide and iodide crystallize from hot solutions in anhydrous cubes ; from solutions at ordinary tempera tures in monoclinic prisms with ; and at low temperatures with The iodide differs from the other haloid salts in sep arating from solution in alcohols with "alcohol of crystallization." Sodium sulphide, obtained by saturating a caustic soda solution with sulphuretted hydrogen and adding an equivalent of alkali, is employed in the manufacture of soluble soda glass. Sodium sulphite, which is employed as an antichlor, is prepared (with by saturating a solution of sodium carbo nate with sulphur dioxide, adding another equivalent of carbonate And crystallizing. The anhydrous salt may be prepared by heating a saturated solution of the hydrated salt. The acid sulphite, or probably (i.e., metabisulphite) when solid, obtained by saturating a cold solution of the carbonate with sul phur dioxide and precipitating by alcohol, is employed for steriliz ing beer casks. Sodium sulphate, Na2SO4, known in the hydrated condition (with 1 as Glauber's salt, is manufactured in large quantities for conversion into the carbonate or soda. (See ALKALI MANUFACTURE.) For many years sodium was not known to form an alum (q.v.), but if a supersaturated solution of so dium and aluminium sulphates is allowed to crystallise below 20° C, the alum is obtained, higher temperatures giving monoclinic crystals. The acid sulphate, NaHSO4, also known as bisulphate of soda, is obtained as large asymmetric prisms by crystallizing a solution of equivalent quan tities of the normal sulphate and sulphuric acid above 50°.
The manufacture of sodium carbonate, commonly called soda, is treated under ALKALI MANUFACTURE. The anhydrous salt is a colourless powder or porous mass, having an alkaline taste and reaction. It melts at 852°. On solution in water, heat is evolved and hydrates forMed. Common washing soda or soda-crystals is the decahydrate, which appears as large clear monoclinic crystals. On exposure, it loses water and gives the monohydrate, a white powder sold as "crystal car bonate"; this substance, which is also formed on heating the deca hydrate to crystallizes in the rhombic system. Both these hydrates occur in the mineral kingdom, the former as natron and the latter as thermonatrite. The heptahydrate, is
obtained by crystallizing a warm saturated solution in a vacuum; it appears to be dimorphous. The acid carbonate or bicarbonate of soda, is produced in the ammonia-soda process for alkali manufacture. Another acid carbonate, is the mineral trona or urao. We may here notice the "percarbo nates," obtained by acting with gaseous or solid carbon dioxide on or at low temperatures. For sodium nitrite see NITROGEN ; for sodium nitrate see SALTPETRE ; for the cyanide see PRUSSIC ACID ; and for the borate see BORAX.
Of the sodium silicates the most important is the mixture known as soluble soda glass formed by calcining a mixture of white sand, soda-ash and charcoal, or by dissolving silica in hot caustic soda under pressure. It is a colourless transparent glass mass, which dissolves in boiling water to form a thick liquid. It is employed in certain printing processes, as a cement for artificial stone and for mending glass, porcelain, etc., and also for making the so-called silicated soaps. (See SOAP.) Sodium silicates con taining excess of silica in solution are useful adhesives.
Sodium is most distinctly recognized by the yellow coloration which volatile salts impart to a Bunsen flame, or, better, by its emission spectrum which has a line (double), the Fraunhofer D line, in the yellow (the wave-lengths are 5896 and 589o). It is estimated as sulphate by evaporation of its solutions with concen trated sulphuric acid, or as the sparingly soluble triple nitrite, Pharmacology.—The metal sodium is not used in medicine, but many of its salts are employed. Besides liquor sodii ethylatis the following salts and preparations are used in the British Pharma copoeia. (I) Sodii carbonis, known as washing soda which on heating yields sodii carbonis exsiccatus; sodii bicarbonas, from which is made trochiscus sodii bicarbonatis. Sodii phosphas. From sodium phosphate are made sodii phosphas effervescens and sodii hypophosphis. (See PHOSPHORUS.) (3) Sodii sulphas (Glauber's salt), with its sub-preparation sodii sulphas efferves cens. (4) Soda tartarata (Rochelle salt), a tartrate of sodium and potassium, from which is made pulvis sodae tartaratae effer vescens, known as Seidlitz powder. (5) Sodii citro-tartras effer vescens, a mixture of sugar, sodium bicarbonate, citric and tar taric acids. (6) Sodii chloridum, common salt. (7) Sodii sulPhis. For sodii bromidum, iodidum and salicylatum see BROMINE, IODINE and SALICYLIC ACID respectively. For sodii arsenas and cacodylate see ARSENIC. Sapo durus (hard soap) is a compound of sodium with olive oil, and sapo animalis (curd soap) is chiefly sodium stearate.