Symbol, Na.

SODIUM.

Atomic Weight, 23.

Valence, I.

History. As stated under the preceding element, the salts of sodium and potassium were not distinguished from each other until 1736. Those of sodium were probably the first known. Nitrum, which later came to be a name for saltpetre, was probably in earlier times applied to an impure sodium carbonate, since it effervesced on the application of vinegar. Sodium chloride, because of its presence in sea water, was known in the earliest times.

The metal sodium was discovered by Davy in 1807, in the same manner as potassium, -namely, by the electrolysis of the hydrate.

Occurrence.-Sodium, like the other alkali metals, is not found in nature in the free state; but in combination it is very widely distributed. Sodium chloride is found as rock-salt in the earth, it is a constituent of sea water, of the water of many mineral springs, and it is almost universally distributed in animal and vegetable organisms.

Sodium silicate is a constituent of albite, or soda-feldspar, and in smaller quantity in many other minerals. The nitrate, as Chili saltpetre, is found in the warm and rainless districts of Chili and Peru. Cryolite, found in large deposits in Greenland, is the double fluoride of sodium and aluminum. Sodium carbonate occurs as a natural deposit in the warm and rainless districts of many countries, notably in Egypt, India, South America, and in Wyoming and California; in the latter places, however, it is usually associated with larger quantities of sodium sulphate or borate. Smaller quantities of the sulphate and the iodide are found in sea water.

Preparation.-Sodium is produced by the electrolytic apparatus of Castner, described under potassium, Fig. 59. It is also manufactured on a large scale by a process of Castner, in which sodium hydrate and iron carbide are heated together to 800°, when sodium distils according to the following reaction:

The operation is most successful when the ingredients are very intimately mixed.

The older method of Deville is still used considerably. This

consists in heating an intimate mixture of sodium carbonate and carbon, when the following reaction occurs :

The apparatus by which this is accomplished is shown in Fig. 61. A charge for this apparatus consists of 30 kilogrammes of soda-ash, ground with 13 kilogrammes of small coal and 3 kilogrammes of chalk. This is placed in the cylinder A, which is

1.2 meters long and 0.14 meter in diameter, and the whole is brought to a white heat. There is not the same danger from explosion that there is in the preparation of metallic potassium. Much sodium is lost during the operation, the yield being about one-third of the theoretical amount present.

It has also been proposed to prepare sodium by electrolysis directly from the chloride, since both the metal and the chlorine are valuable; many suggestions have been made and a number of patents granted, but as yet the process does not appear to have become a success.

Properties. Sodium is a silver-white metal, of a waxy consistence at ordinary temperatures, but in the cold it becomes brittle and crystalline. It has a specific gravity of 0.9735 at 13.5°.

On the application of heat sodium melts at 95.6°, and at 742° it boils; under these conditions it is necessary to exclude air. The metal is so easily oxidized at ordinary temperatures that it is necessary to preserve it under petroleum. If it is melted in the atmosphere of an inert gas like nitrogen, and when it begins to solidify the liquid portion is poured out, the remainder takes the form of octohedral crystals.

The behavior of sodium towards most other elements is similar to that of potassium, but less energetic; for instance, potassium and bromine combine with explosive violence, while sodium may be warmed with it without violent action.

When thrown on water, sodium combines with the oxygen of the water, liberating hydrogen, but the action is not sufficiently energetic to inflame the latter, unless the metal be held in one position by a piece of filter paper, or the water be warmed to 60°, when the gas ignites and burns with a yellow flame. This yellow color is characteristic of sodium compounds.

Uses. Sodium is used in the preparation of a number of other metals, notably, silicon, boron, magnesium, and aluminum. It is also a valuable reducing agent in the laboratory. In some cases where its activity does not admit of its being used alone, as in aqueous solutions, it is first amalgamated with mercury.

SODIUM AND HYDROGEN.

Sodium Hydride, Na4H.-When dry hydrogen is passed over sodium at a temperature of 300° to 400° the metal absorbs 237 times its volume of the gas. The product has a silver-white color, and a metallic lustre. Its specific gravity is 0.959.

SODIUM AND HALOGENS.

The halogen compounds of sodium are :

Sodium fluoride, NaF.

Sodium chloride, NaCl.

Sodium bromide, NaBr.
Sodium iodide, NaI.

Sodium Fluoride, NaF, is prepared by neutralizing hydrofluoric acid with sodium carbonate. The compound crystallizes in anhydrous cubes. It is soluble in 25 parts of cold water, and scarcely more so in hot water. It has a tendency to form double compounds with other salts, as instanced in cryolite, the double fluoride of sodium and aluminum, AlF6NaF.

Sodium Chloride, NaCl. Sodii Chloridum, U. S. P.-Sodium chloride, or common salt, is found abundantly throughout the globe. As rock-salt it occurs in large deposits, alternating with strata of clay and gypsum, at an average depth of 100 meters. Probably the most celebrated mines are at Wieliczka, in Galicia, the deposit there being 500 miles long, 20 miles broad, and 1200 feet thick. Enormous quantities are also found in England, at Stassfurt, Germany, and in America.

Numerous salt springs also occur in many parts of the world, in which common salt is the chief constituent. These springs are especially abundant in West Virginia, Michigan, and New York, each containing a large number of these springs.

Sea water contains 3 to 4 per cent. of solid residue, threefourths to nine-tenths of which is sodium chloride, or 2.4 to 2.8 per cent. of the sea water. There is relatively more salt in that part of the ocean situated near or crossed by the equator. Many inland seas contain a greater proportion of salt than exists in the ocean. For instance, the water of the Great Salt Lake in Utah contains over 22 per cent. of saline matter, about 90 per cent. of which is sodium chloride.

Extraction. When sufficiently pure, rock-salt is mined and sent at once into commerce without further purification. If it is more inaccessible, or mixed with earthy matter, holes are drilled into the deposits, water is run in, and the saturated solution is either forced out by the water which enters, or it is pumped out. The salt is recovered by evaporating the solution in iron or lead boilers. Weaker salt solutions are first evaporated by the sun's rays. This is accomplished either in large shallow dikes lined with clay, as carried out with sea water in the south of France, or by allowing the solution to trickle down over a large pile of brushwood, as shown in Fig. 62. When the liquid has reached a concentration representing 15 to 20 per cent. of salt, it is run into open boilers and the evaporation completed.

The salt thus produced is quite impure and requires further treatment. In some cases it is spread on washed sand, and the more deliquescent salts liquefy and are absorbed; in other cases the crude salt is placed in baskets over the boilers in which the brine is concentrating, the steam rising dissolves the more soluble salts. Finally, crude salt may be purified by washing it with a saturated solution of pure salt.

When a purer compound is desired for chemical purposes, the purest commercial salt is carefully treated with barium chloride

solution so long as a precipitate is produced, by which the sodium sulphate is decomposed, barium sulphate and sodium chloride resulting; the barium sulphate is filtered out, and the warm filtrate is treated with a slight excess of sodium carbonate, this precipitates aluminum, barium, calcium, iron, and magnesium com

pounds; after filtering clear, the solution is carefully neutralized with hydrochloric acid, and evaporated to the crystallizing point.

The output of salt in the United States in 1892 amounted to 11,585,754 barrels (280 pounds being reckoned to the barrel); of this Michigan supplied 3,812,054 barrels, New York 4,400,000 barrels, other States 3,373,700 barrels.