| Sodium compounds had been known for some time | | | | combined in a molten mixture in which the presence of |
| prior to 1807, when English chemist Sir Humphrey Davy | | | | calcium chloride lowers the melting point of the sodium |
| (1778-1829) succeeded in isolating sodium itself. The | | | | chloride by more than 30%. When an electric current is |
| element is represented by a chemical symbol (Na), | | | | passed through the mixture, sodium ions move to the |
| reflecting its Latin name ‘natrium’. In its pure | | | | cathode, where they pick up electrons to become |
| form, sodium has a bright, shiny surface, but in order to | | | | sodium atoms. At the same time, ions of chlorine |
| preserve this appearance, it must be stored in oil: | | | | migrate to the anode, losing electrons to become |
| sodium reacts quickly with oxygen, forming a white | | | | chlorine atoms. Sodium is a low-density material that |
| crust of sodium oxide. Pure sodium never occurs in | | | | floats on water, and in the Downs cell, the molten |
| nature; instead, it combines readily with other | | | | sodium rises to the top, where it is drawn off. The |
| substances to form compounds, many of which are | | | | chlorine gas is allowed to escape through a vent at the |
| among the most widely used chemicals in industry. It is | | | | top of the anode end of the cell, and the resulting |
| also highly soluble: thus whereas sodium and potassium | | | | sodium metal, that is, the elemental form of sodium, is |
| occur in crystal rocks at about the same ratio, sodium | | | | about 99.8% pure. |
| is about 30 times more abundant in sea-water than its | | | | Sodium chloride is by far the most widely known and |
| sister element. | | | | commonly used sodium compound and this in itself is a |
| Though the extraction of sodium involves the use of | | | | distinction, given the fact that so many sodium |
| a special process, the metal is plentiful in the form of | | | | compounds are a part of our daily life. Today people |
| sodium chloride, better known as table salt. In fact, the | | | | think of salt primarily as a seasoning to enhance the |
| term salt in chemistry refers generally to any | | | | taste of food, but prior to the development of |
| combination of a metal with a nonmetal. More | | | | refrigeration, it was vital as a preservative because it |
| specifically, salts are (along with water) the product of | | | | kept microbes away from otherwise perishable food |
| reactions between acids and bases. Sodium chloride is | | | | items. Salt does not merely improve the taste of food; |
| so easy to obtain, and therefore so cheap, that most | | | | it is an essential nutrient. Sodium compounds regulate |
| industries making other sodium compounds use it, | | | | transmission of signals through the nervous system, |
| simply separating out the chloride before adding other | | | | alter the permeability of membranes, and perform a |
| elements. The United States is the world's largest | | | | number of other life-preserving functions. On the other |
| producer of sodium chloride, obtained primarily from | | | | hand, too much salt can aggravate high blood |
| brine, a term used to describe any solution of sodium | | | | pressure. Thus, since the 1970s and 1980s, food |
| chloride in water. Brine comes from seawater, | | | | manufacturers have increasingly offered products low |
| subterranean wells, and desert lakes, such as the | | | | in sodium, a major selling point for health-conscious |
| Great Salt Lake in Utah. Another source of sodium | | | | consumers. |
| chloride is rock salt, created underground by the | | | | In addition to its widespread use in consumer goods, |
| evaporation of long-buried saltwater seas. Other top | | | | sodium chloride is the principal source of sodium used |
| sodium-chloride-producing nations include China, | | | | in making other sodium compounds. These include |
| Germany, Great Britain, France, India, and various | | | | sodium hydroxide, for manufacturing cellulose products |
| countries in the former Soviet Union. Salt may be | | | | such as film, rayon, soaps, and paper, and for refining |
| cheap and plentiful for the world in general, but there | | | | petroleum. In its application as a cleaning solution, |
| are places where it is a precious commodity. One | | | | sodium hydroxide is known as caustic soda or lye. |
| such place is the Sahara Desert, where salt caravans | | | | Another widely used sodium compound is sodium |
| ply a brisk trade today, much as they have since | | | | carbonate or, soda ash, applied in glass-making, paper |
| ancient times. | | | | production, textile manufacturing, and other areas, such |
| Modern methods for the production of sodium | | | | as the production of soaps and detergents. Sodium |
| represent an improvement in the technique Davy used | | | | also can be combined with carbon to produce sodium |
| in 1807, although the basic principle is the same. Though | | | | bicarbonate, or baking soda. Sodium sulfate, |
| several decades passed before electricity came into | | | | sometimes known as salt cake, is used for making |
| widespread public use, scientists had been studying its | | | | cardboard and Kraft paper. Yet another widely used |
| properties for years, and Davy applied it in a process | | | | sodium compound is sodium silicate, or "water glass," |
| called electrolysis. Electrolysis is the use of an electric | | | | used in the production of soaps, detergents, and |
| current to produce a chemical reaction, in this case, to | | | | adhesives; in water treatment; and in bleaching and |
| separate sodium from the other element or elements | | | | sizing of textiles. Still other sodium compounds used by |
| with which it is combined. Davy first fused or melted a | | | | industry and/or consumers include sodium borate, or |
| sample of sodium chloride, then electrolyzed it. Using an | | | | borax; sodium tartrate, or sal tartar; the explosive |
| electrode, a device that conducts electricity and is | | | | sodium nitrate, or Chilean salt-peter; and the food |
| used to emit or collect electric charge, he separated | | | | additive monosodium glutamate (MSG). Perhaps |
| the sodium chloride in such a way that liquid sodium | | | | ironically, there are few uses for pure metallic sodium. |
| metal collected on the cathode, or negatively charged | | | | Once applied as an "anti-knock" additive in leaded |
| end. Meanwhile, the gaseous chlorine was released | | | | gasoline, before those products were phased out for |
| through the anode, or the positively charged end. The | | | | environmental reasons, metallic sodium is now used as |
| apparatus used for sodium separation today is known | | | | a heat-exchange medium in nuclear reactors. But its |
| as the Downs cell, after its inventor, J. C. Downs. In a | | | | widest application is in the production of the many |
| Downs cell, sodium chloride and calcium chloride are | | | | other sodium compounds used around the world. |