LESS USEFUL METALS.

The less useful metals are sodium, magnesium, aluminium, antimony, bismuth, and nickel. These are little used in a metallic state, though their compounds are of the highest importance.

95. SODIUM. This metal was discovered by Sir H. Davy, by the decomposition of soda with the galvanic current. It can be procured by reducing the carbonate in presence of carbon, and is now manufactured in considerable quantities for the preparation of other metals, especially magnesium and aluminium. Sodium is a silver-white metal, soft at ordinary temperatures, and melting at 207°; it volatilizes below a red heat, yielding a colorless vapor. The compounds of sodium are very widely diffused, being contained in every speck of dust. They exist in enormous quantities in the older rocks; but they are most readily obtained from sea-water, which contains nearly 3 per cent of sodic chloride (common salt), or from the large deposits of this substance which occur in the form of rock-salt.

96. MAGNESIUM. - This metal occurs in large quantities in combination with lime and carbonic acid, in dolomite or mountain limestone, and also in sea-water and certain mineral springs, as chloride and sulphate. The metal itself has only recently been prepared in quantity. It is best obtained by heating magnesic chloride with metallic sodium, sodic chloride and metallic magnesium being formed. This metal is of a silverwhite color, and fuses at a low red heat. It is volatile, and may be easily distilled at a bright red heat. When soft, it can be pressed into wire, and with care it may be

cast like brass; although, when strongly heated in the air, it takes fire, and burns with a dazzling white light, with the formation of its only oxide, magnesia, MgO. The light emitted by burning magnesium wire is distinguished for its richness in chemically active rays, and is therefore employed as a substitute for sunlight in photography. It is coming to be used for purposes of illumination.

97. ALUMINIUM. This metal occurs in large quantities, combined with silicon and oxygen, in felspar and all the older rocks, and also in clay, marl, slate, and in many crystalline minerals. Metallic aluminium is obtained by passing the vapor of aluminic chloride over metallic sodium. It has recently been manufactured on a large scale, both in England and France, and from its lightness (specific gravity 2.6), its tenacity, and its bright lustre, it has been used for optical purposes as well as for ornamental work. Some of its alloys, as aluminium bronze, promise to become of great value in the arts.

98. ANTIMONY.-Metallic antimony occurs native, but its chief ore is the trisulphide, Sb,Sg. The metal is easily reduced, by heating the sulphide with about half its weight of metallic iron, when ferrous sulphide and metallic antimony are formed. Antimony may also be reduced by mixing the ore with coal, and heating in a reverberatory furnace. Antimony is a bright bluishwhite metal. It is very brittle, and can readily be powdered in a mortar. It melts at about a red heat, and may be distilled at a white heat, in an atmosphere of hydrogen. Antimony undergoes no alteration in the air at ordinary temperatures, but rapidly oxidizes if exposed to air when melted; and if heated more strongly, it takes fire, and burns with a white flame, giving off dense white fumes of

oxide. Antimony is not attacked either by dilute muriatic or sulphuric acid; but nitric and nitro-muriatic acid dissolve it easily. The alloys of antimony are largely used in the arts. Of these, type-metal (an alloy of lead and antimony) is the most important; it contains from 17 to 20 per cent of the latter metal.

99. BISMUTH.—This metal is found in small quantities in the native state, but occurs more often as a sulphide; it is easily reduced to the metallic state, and then exhibits a pinkish-white color. It melts at 507°, and is volatilized at a white heat. Bismuth does not oxidize in dry air at the ordinary temperature; but if heated strongly, it burns with a blue flame, forming an oxide; it also takes fire when thrown into chlorine gas. Bismuth dissolves easily in nitric acid. The metal is chiefly used as an ingredient of fusible metal. The alloy of 2 parts of bismuth, I of lead, and 1 of tin, melts at 201°; that of 8 parts of bismuth, 5 of lead, and 3 of tin, melts at 212°. The compounds of bismuth are used in the porcelain manufacture, in medicine, and as cosmetics.

Both bismuth and antimony closely resemble arsenic in the compounds which they form. Thus we have Sb2O3, Sb2O5, and H,Sb; Bi̟2O, and Bi2O (67). Hence bismuth and antimony are now generally classed among the non-metallic elements of the nitrogen group.

5

100. NICKEL.-Nickel occurs in large quantities combined with arsenic, as kupfernickel; also together with cobalt in speiss; and it is now prepared in considerable quantities for the manufacture of German silver, an alloy of nickel, zinc, and copper. Nickel is a white, malleable, and tenacious metal; it melts at a somewhat lower temperature than iron, and is strongly magnetic, but loses this property when heated to above 600°.

101. SALTS OF SODIUM.—There are two compounds of sodium and oxygen, Na,O, sodic oxide, and Na2O2, sodic peroxide. Sodic oxide has a strong affinity for water, with which it combines to form HNaO, sodic hydrate (caustic soda). This is a white solid, very soluble in water, very caustic and alkaline, and is largely used in making soap.

Caustic soda is now manufactured on a very large scale, by boiling lime and sodic carbonate (carbonate of soda) with water, and evaporating down the clear solution. The reaction is as follows:

CaO+Na2CO+H2O = CaCO3 + 2HNaO.

102. Sodic Chloride. Sodic chloride, NaCl, is common salt. It is from this compound that nearly all the other sodic compounds are prepared.

In Southern Europe, on the shores of the Mediterranean, large quantities of salt are obtained from seawater. The water is allowed to flow into large shallow pools, called salt-pans, where it is evaporated by the agency of the air and the sun. Only pure water passes off in the form of vapor, and the solution grows more and more concentrated. After a time, the brine is pumped into large iron pans, and evaporated by artificial heat until the salt crystallizes.

In many parts of the earth there are salt lakes, often called seas. The streams flowing into them are more or less impregnated with salt, which they dissolve from the soil over which they flow. Such lakes are natural saltpans, for the water which is evaporated from them is pure, and they consequently become more and more saturated with salt, till it is finally deposited on the bottom in solid crystals. The most remarkable of these lakes is the Great Salt Lake in Utah.

Such salt lakes appear to have existed in all geological

The

ages, and by long-continued evaporation to have given rise to large masses of solid salt, called rock salt. These beds of rock salt are found in all parts of the earth. most remarkable are at Wieliczka in Poland, and at Cardona in Spain. The former is 500 miles long, 20 miles broad, and 1,200 feet deep. It has been worked for several centuries. Some of the galleries excavated in it are 30 miles long. The bed at Cardona is a "mountain of salt," 400 or 500 feet high, and the salt is of the greatest purity.

Salt is obtained from these beds sometimes by excavation and sometimes by solution. In the latter case, a hole is sometimes bored down to the bed of salt, often to the depth of 1,200 or 1,500 feet. A tube somewhat smaller than the bore is then introduced, and fresh water allowed to flow down outside the tube. This water, on reaching

the bed, becomes saturated with salt, and rises in the tube. Since, however, it is heavier than fresh water, it will not rise to a level with the latter on the outside of the tube. If the bore is 1,200 feet deep, the brine will rise within about 200 feet of the top. It must be pumped up the remaining distance. The solution is then evaporated, and solid salt obtained.

It not unfrequently happens that natural springs occur in such localities that their waters come into contact with beds of salt. Such springs are called salt springs, or brine springs. They sometimes come to the surface; but oftener they can only be reached by boring, and the brine brought to the surface by means of the pump. The water of these natural springs is usually less concentrated than that of the artificial springs described above. In England and in this country the salt produced is nearly all obtained from brine springs.

The most important salt springs of this country are in Central New York, in Virginia, and in Pennsylvania.