LANTHANUM-DIDYMIUM-MAGNESIUM. 49 527 cerium and potassium, which latter salt is insoluble in a solution of potassium. The oxalate (Ee¤,04, 3 H2O) has been given in doses of from 2 to 4 grains, with good effect, in some cases of obstinate vomiting, and in some forms of pyrosis. The sesquioxide of cerium has a yellowish tinge, and its salts are yellow or red. LANTHANUM (so named from λav@ávw, to lie hid) was discovered by Mosander, in 1841. It forms only one oxide, which is buff-coloured, and freely soluble in diluted nitric acid. It forms colourless, astringent salts, which give a white precipitate with the soluble oxalates. DIDYMIUM (so named from didvuoç, twin, in reference to its close association with lanthanum) also furnishes but a single oxide, which is of a dark-brown colour, when anhydrous: in the hydrated state it is insoluble in solutions of potash and ammonia; but it. absorbs carbonic acid from the air. It furnishes a sparingly soluble white oxalate, and yields rose-white double sulphates with the sulphates of potassium, sodium, and ammonium. Its solutions, when viewed through a prism by transmitted light, show a strong absorption line in the yellow, and another in the green (Part I. p. 159). Its salts are pink or violet-coloured, and are not precipitated at ordinary temperatures by sulphide of ammonium. Zinc Cadmium Magnesium Mg 24 13.76 02499 THESE metals are all volatile, and burn in air with a powerful flame when strongly heated. They furnish but one basic oxide, and yield very soluble chlorides and sulphates: the sulphide. of magnesium is to some extent soluble; those of zinc and cadmium are insoluble. These metals have a strong tendency to form basic carbonates; their corresponding salts are isomorphous. * At 62°.6. § I. MAGNESIUM: Mg"=24, or Mg=12. Sp. Gr. 1'743. (683) MAGNESIUM is usually classed with those metals the oxides of which furnish the alkaline earths, but it is much more analogous to zinc in its properties than to any other element. Magnesium is an abundant ingredient of the crust of the earth. It is found in combination in large quantities as a double carbonate with calcium, forming magnesian limestone, or dolomite. It is contained abundantly in sea-water as chloride, and in many springs as sulphate. It likewise enters more or less extensively into the formation of many rocks, and of a great variety of minerals. Preparation. 1.-Bussy obtained it in the metallic form by heating its anhydrous chloride with potassium in a porcelain or platinum crucible. When cold, the contents of the vessel were digested in cold water, by which the chloride of potassium and undecomposed chloride of magnesium were dissolved out. The metal was left as a grey powder, which could be melted into globules. 2.-Deville and Caron (Comptes rendus, xliv. 394) obtain the metal as follows:-9000 grains of pure chloride of magnesium are mixed with 1500 grains of fused chloride of sodium and 1500 of pure fluoride of calcium, both in fine powder. 1500 grains of sodium in small fragments are carefully mingled with the powder, and the whole is thrown into a clay crucible at a full red heat, and it is then instantly covered. When the mixture has become tranquil, the cover is removed, and the fused mass is stirred with an iron rod, in order to render it homogeneous throughout, and to obtain a clean surface upon the liquid. Globules of magnesium are then distinctly visible. The crucible is allowed to cool partially, and the metallic globules are united by means of the iron rod; the melted mass is then poured upon a shovel, and the magnesium, amounting to about 675 grains, is separated from the slag. The magnesium may be placed in a porcelain tray and collected into one mass by melting it in a current of hydrogen; after which it may be purified by remelting in a bath of mixed chloride of magnesium, chloride of sodium, and fluoride of calcium. It still, however, usually retains portions of carbon, silicon, and nitrogen, from which it may be purified by careful distillation in a current of hydrogen. Sonstadt has recently prepared it on a considerable scale by this method, for commercial purposes. 3.-Bunsen (Liebig's Annal. lxxxii. 137) prepares magnesium by the electrolytic decomposition of the chloride of magnesium; MAGNESIUM-PROPERTIES-MAGNESIA. 529 this salt he melts in a deep covered porcelain crucible divided by a vertical diaphragm of porcelain, which extends half-way down. the crucible; the electrodes are made of carbon, and are introduced through two openings in the lid, the negative electrode being notched to receive the reduced magnesium which lodges in the cavities: the crucible is brought to a red heat, and is filled with the melted chloride, which then is readily decomposed by 10 cells of the zinc carbon battery (266). The principal difficulty in this operation arises from the small density of the reduced metal, which rises to the surface of the fused salt, and is liable to reoxidation. Properties.-Magnesium is a malleable, ductile metal of the colour of silver, which takes a high polish, and preserves it nearly as well as zinc at ordinary temperatures in dry air; but in a moist atmosphere it becomes slowly oxidized. Its fracture appears sometimes to be crystalline, at other times fibrous. It has about the same degree of hardness as calc-spar. At a moderate red heat it may be melted. When ignited in dry air or in oxygen gas, it takes fire and becomes oxidized; in the form of wire it burns easily, emitting a light of dazzling brilliancy, which has lately been employed as an artificial light for photographic purposes; the magnesia which is produced exhibits no sign of fusion. Deville and Caron have shown that magnesium is nearly as volatile as zinc, and that it may be distilled by heating it strongly in a current of hydrogen. A portion of the metal is carried away in suspension by the gas, and if the latter be kindled as it issues from the apparatus, it burns with a beautiful and highly luminous flame. Magnesium is but slowly acted upon by cold water, but it is rapidly dissolved if the water be slightly acidulated. It is also freely soluble in a solution of sal ammoniac, When thrown into strong hydrochloric acid it bursts into flame; yet a mixture of concentrated sulphuric and fuming nitric acid has no action upon it unless it be heated. When heated in chlorine and in the vapour of bromine, of iodine, or of sulphur, it burns brilliantly. Magnesium unites directly with nitrogen, forming a transparent crystallized nitride (Mg,N), which is decomposed rapidly by water into magnesia and ammonia (Deville). Geuther and Briegleb obtained a greenish-yellow amorphous nitride of similar composition, by heating the metal in pure and dry nitrogen, It is immediately decomposed by water. (684) MAGNESIA (Mg0=40, or MgO=20); Sp. Gr. 36; Composition in 100 parts, Mg, 60; →, 40.-The only known oxide of magnesium is a bulky, white, tasteless, infusible, and nearly 11. M M 530 SULPHIDE, CHLORIDE, AND SULPHATE OF MAGNESIUM. insoluble powder, which when placed upon moistened turmericpaper turns it distinctly brown. It is usually procured by strongly igniting the artificial carbonate in a crucible, but it may also be obtained by ignition of the nitrate of magnesium; in this case it assumes a much denser form. Magnesia, when mixed with water, gradually combines with it, and forms a hydrate (H¿MgO2), which absorbs carbonic acid slowly from the air: no sensible elevation of temperature occurs during the process of hydration. A native hydrate of similar composition occurs in crystalline scales. (685) SULPHIDE OF MAGNESIUM (MgS=56) is but sparingly soluble in water. It may be obtained as a hydrate by precipitating a boiling solution of sulphate of magnesium with sulphide of potassium, when it falls as a white mucilaginous mass. 2 (686) CHLORIDE OF MAGNESIUM (MgCl,=95, or MgCl=47'5; Sp. Gr. 2177, cryst. with 6 H2, 1-562) is contained abundantly in sea water. It may be obtained in the anhydrous condition by dissolving I part of magnesia in hydrochloric acid, and adding 3 parts of sal ammoniac in solution, after which the mixture is evaporated to dryness; by this means a double chloride of magnesium and ammonium is formed (H,NCI,MgCl2), which may be evaporated without loss of acid, whilst the solution of mere chloride of magnesium is partially decomposed during evaporation : when the double salt is ignited in a covered crucible, the sal ammoniac is expelled, and pure chloride of magnesium remains. At a red heat it fuses to a transparent liquid, which forms a silky-looking mass of confused crystals on cooling. Chloride of magnesium is deliquescent, and gives out heat whilst undergoing solution in water; by evaporation at a low temperature it may be obtained in crystalline needles with 6 H2. It is soluble in alcohol: it forms double chlorides with the chlorides of the metals of the alkalies. If heated strongly in a current of dry ammoniacal gas, the chloride of magnesium is volatilized, and a white sublimate of (MgCl2, 4 H,N) is obtained (Clark).. (687) SULPHATE OF MAGNESIUM (MgSO, 7 H,O=120+ 126, or MgO,SO„HO . 6 HO = 60 + 63); Sp. Gr. anhydrous, 2.706, cryst. 1·660; Composition in 100 parts, dry, MgO, 33'33 ; SO3, 66.67; cryst. MgO, 16:26; SO3, 32'52; H2O, 5122.-This is the most important salt of magnesium. It is made in very large quantities from sea water, either by precipitating the magnesia by means of lime, and then dissolving it in sulphuric acid; or by first crystallizing out the greater part of the common salt, after which, on evaporation, crystals of the sulphate are obtained. SULPHATE, NITRATE, AND CARBONATE OF MAGNESIUM. 531 Native carbonate of magnesium is also sometimes acted upon with diluted sulphuric acid, and the salt obtained by evaporation. The sulphate is also procured in considerable quantities from magnesian limestone: the rock is burned, slaked, and largely washed with water to remove part of the lime; it is then treated with sulphuric acid, and the sulphate of magnesium is separated from the sparingly soluble sulphate of calcium by solution and recrystallization. It is also obtained in considerable quantity from the mother-liquors of the alum works. Sulphate of magnesium is a Its trivial name of Epsom common ingredient in mineral waters. salts is derived from the circumstance of its being abundantly contained in many springs in the neighbourhood of Epsom, from the waters of which it was at one time obtained. Sulphate of magnesium is soluble in 3 times its weight of water at 60°, and 1 at 212°. Its solution has a bitter, disgusting taste. It crystallizes readily in right rhombic prisms, which are slightly efflorescent: when heated moderately, they lose their water of crystallization; if the heat be intense and long continued, a part of the acid also escapes. If crystallized from a hot solution, oblique rhombic prisms, with 6 H,→ are deposited, and the ordinary crystals, when heated to 125°, become opaque and lose 1 H2O. Crystallized sulphate of magnesium loses 6 of its 7 atoms of water at a temperature below 300°, but it retains 1 atom even at 400°. This last atom may be displaced by an equivalent of an anhydrous salt, such as sulphate of potassium, with which it forms a double salt, possessed of the same crystalline form as sulphate of magnesium (MgSOK,SO. 6 H2O) of sp. gr. 2076. Sulphate of ammonium forms with the sulphate of magnesium a similar double salt. 4 3 = (688) NITRATE OF MAGNESIUM (Mg 2 NO ̧ . 6 H ̧Ð 148 + 108; Sp. Gr. 1'464) is deliquescent, and soluble in alcohol; it crystallizes with difficulty. (689) CARBONATE OF MAGNESIUM (Mg0,=84, or MgO,CO2=42; Sp. Gr. 3.056) occurs native as a white, hard, amorphous mineral, called magnesite. It is procured artificially by precipitating a boiling solution of a salt of magnesium with carbonate of potassium, and dissolving the precipitate in carbonic acid water; as the gas escapes, the salt is deposited as a terhydrate, in transparent hexagonal prisms (MgCO ̧ . 3 H2O): by exposure to air the crystals effloresce and are converted into a protohydrate (Mg¤Ð ̧. H2O). The anhydrous carbonate may be obtained by introducing a test-tube containing a solution of sulphate of magnesium into a strong glass tube containing a solution of carbonate 3 2 |