preparation of the metal; 1,000 parts of carnallite are fused with 100 parts of fluor spar and 100 parts of sodium. The metal resembles silver in appearance; it is malleable, ductile, and fuses at a dull red heat, and can be distilled like zinc. It does not change under water or in dry air, but in damp air it soon oxidizes. It consumes with a brilliant white flame when heated to redness, or when thrown into hydrochloric acid. It burns brilliantly in chlorine or in the vapors of bromine, iodine, sulphur, &c. It was proposed by Bunsen to employ this metal in the form of fine wire for illuminating purposes. He found that it might be lighted by the flame of an alcohol lamp, and in burning gave a perfectly steady and very intense light. A wire of an inch in di

and citrate. The oxide and carbonate are frequently used in indigestion, to neutralize an excess of acid in the stomach or to act as gentle laxatives, which they do after combining with any acid. If when administered they do not meet with an acid in the alimentary canal, and consequently do not cause a laxative action, it is desirable to follow their administration with that of lemonade or a similar acid. The simple oxide of magnesia differs from the carbonate in affording by its combination no carbonic acid. Magnesia freshly prepared has been recommended as an antidote in arsenical poisoning, but is less efficient than the hydrated oxide of iron. These substances are used in pharmacy in the preparation of aromatic waters, the fineness of the powders serving to divide minutely the vola-ameter burns at the rate of about three feet in tile oil with which they are impregnated, and thus present to the menstruum a much larger surface than could be obtained by simple admixture. The sulphate and citrate are considerably used as cathartics. The former is an exceedingly efficient member of the class, and acts without undue violence. It produces copious and rather watery discharges. It is occasionally combined with other more drastic purgatives, to mitigate their violence. If these salts fail to act as cathartics, which may happen if they are administered in small and repeated doses, they are absorbed and pass out of the system through the kidneys. The effervescent preparations, both solid and liquid, known as citrate of magnesia and popularly used as laxatives, usually contain, in addition, citrate or tartrate of sodium or potassium. The average dose of sulphate of magnesia is an ounce. It acts best when it is freely diluted with water, and should be given on an empty stomach. In cases of nausea, it will often be retained when other cathartics are rejected. It is best suited to inflammatory conditions of the system, and is contraindicated by debility and prostration. A solution of the citrate of magnesia resembles lemonade in taste.-Magnesia in combination with silica enters largely into the composition of many rocks and minerals, such as serpentine, steatite or soapstone, asbestus, meerschaum, augite, hornblende, and olivine.

MAGNESIUM, the metallic base of magnesia; symbol, Mg.; chemical equivalent, 12; specific gravity, 174; hardness, that of calcareous spar. Davy proved its existence; but Bussy in 1830 first obtained it in sufficient quantity to test its properties. He decomposed the chloride of magnesium by transmitting through it when heated the vapors of potassium. Since the discovery of large deposits of the double chloride of potassium and magnesium, known as carnallite, in the the salt mines of Stassfurt, it has been proposed to use this mineral in the

a minute, and gives a light equal to that of 74 stearine candles of five to the pound. The weight of such a wire three feet long is about two grains. Bunsen proposed to have the wire wound upon bobbins and furnished at a regular rate to the lamp. Should the metal be procurable at a considerably reduced cost, as may very likely follow an increased demand for it. it may then prove an excellent method of furnishing light for domestic purposes, and more particularly for lighthouses and uses requiring a great intensity of light. It is now used in magic lanterns and for photographing in places inaccessible to the light of day. For the latter application it is especially adapted by reason of the extraordinary power of the photo-chemical property of its light. The alloy of silicon with magnesium, when decomposed by hydrochloric acid, evolves a hydride of silicon, which is a spontaneously combustible gas. Metallic magnesium precipitates nearly all metals from their neutral solutions.

MAGNET (from Gr. λίθος Μαγνήτης, the Magnesian stone), the name applied to a mass of steel or iron, or of natural iron ore, that has the property of attracting to itself otherwise inert iron. Magnets probably first became known to the Aryan races through the discovery of natural magnets by the Greeks in the Thessalian district of Magnesia. The various phenomena presented in experiments with magnets have given rise to the modern branches of physical science known as magnetism, terrestrial magnetism, electro-magnetism, and magneto-electricity, which are treated under their own names. Natural iron magnets are exceedingly rare, but a magnetic iron ore is found in large quantities in Sweden and in the states of New York and New Jersey. The important property that a freely supported magnetic bar possesses of turning steadfastly toward the poles of the earth under the influence of terrestrial magnetism is treated of in the article on that subject. (See also COMPASS.)

END OF VOLUME TENTH.