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MAONET. 



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nnhs tod burnt with a steady and mo*t brilliant flame. Could a 

 hsapf noont be discovered (or the manufacture of magnesium, thin 

 wires of It pun into a wick might no doubt be advantageously used in 

 man; intlan * a* a source of light Magnesium cryUllise in ooto- 

 Iwdn. It act* but very slightly upon cold water, and U not rapidly 



ted by hot waur. It ignites when brought into contact with 

 hydrochloric acid; aulphuric add dissolves It alowly with evolution of 



The equivalent of magnesium U 12. 



Mugntfimm and tayyen form only the following oxide : 



Jftg-iait.rt'nnr' majnm'ii. or otidt ofmagne*i* (MgO). Prepared 

 by heating the oarboiut* to full ml heat Its denaity depend* upon that 

 of the carbonate employed ; if a light variety baa been used, then light 

 calcined magneaU nulu, but if a heavy carbonate, then Arary calcined 

 mafoesia is obtained. 



afntiis U a white powder, Tory voluminous, inodorous, and taste- 

 Usa. In the oxyhydrogon blowpipe flame it fuses to a bard opaque 

 TrrnH Moistened with water it acU upon teat paper like an alkali. 

 Magnesia ia a powerful bate, forming salts with the acids that are 

 usually very (table. 



UfdniU uf may*t*ia (MgO, HO) is precipitated in a semi-gelatinous 

 state when an alkali is added to an aqueous solution of a salt of mag- 

 nesia. It also occurs native. [MAGNESIA, in NAT. HI.ST. Div.j 



ludidi of magnoim (Kg I). Magnesia dissolves in aqueous hydri- 

 odic acid, forming a difficultly crystallisable salt On exposure to heat, 

 it gives off hydriodic acid, and magnesia is left 



Bromide of maynaium (MgBr) may be prepared in the same manner 

 as the iodide, than which it u far more stable. This salt is also found 

 in sea water, and in many salt springs. 



1/aynaium and chlorine form 



CUaridt of magnesium (Mg CD. Magnesia dissolves in hydrochloric 

 acid, fanning chloride of magnesium, but this solution cannot be eva- 

 porated to dryness without undergoing decomposition, uuleas chloride 

 of ammonium U present, when a stable double salt is formed. This 

 salt loses its chloride of ammonium when heated to redness, and the 

 fused chloride of magnesium may then be poured out on to a Blab. 

 Thus obtained, it forms a white crystalline semi-translucent solid, very 

 deliquescent, very soluble in water, and tolerably so in alcohol. It 

 quickly decomposes in contact with air, and must therefore be kept in 

 well closed bottles. 



Carbnnal4 of tnagnetia (MgO, CO,), occurs native in acicular crystals. 

 [MaoxuiTE, in NAT. HUT. Div.] It is also deposited in small pris 

 malic crystals, containing three equivalents of water of crystallisation, 

 when a solution of magnesia in carbonic acid is allowed to evaporate 

 spontaneously. 



ilaynaia alba, the common magnesia of the shops, U a mixture of 

 corionott and hydrate of magnesia (MgO, CO, + MgO, HO) in very 

 variable proportions, the carbonate however nearly always preponder- 

 ating. It is made by mixing together solutions of sulphate of magnesia 

 and carbonate of soda, the latter being in excess, collecting, well 

 washing, and drying the precipitate. It is an exceedingly light powder, 

 inodorous, and almost tasteless. Its density varies according to the 

 strength of the solutions employed, being greatest when the two salts 

 are mixed together, without the addition of water, fused in their water 

 of crystallisation, evaporated to dryness, and the sulphate of soda sub- 

 sequently washed out The heavy carbonate thus produced is, however, 

 liable to be semi-crystalline, or gritty. 



Iiic-rtonaU of magnetia (MgO, 2 CO,). This salt exists only in 

 solution, and is made by pasting carbonic acid through water in which 

 carbonate of magnesia is suspended. 



SuJpka'e of magnetia (MgO, SO, + 7 HO). This salt was originally 

 obtained in 1697, from the Epsom waters, by Dr. Qrew, and hence its 

 common name of ]ur/m taltt. It occurs in sea-water, and in many 

 mineral waters, and is largely prepared from bittirn., or the mother 

 liquor from which common salt has crystallised after sea-water has been 

 evaporated ; the first crystallisation is called tingle tptoms, and when 

 recrystaUiaed is denominated doublet. The principal source, however, 

 of sulphate of magnesia is dolomite, or maynaian limetttxu, a double 

 carbonate of lime and magnesia, [MAUNMIAN LIMESTONE, in NAT. 

 HIST. Div.] Shippings of this stone may be readily procured, aa it 

 ia in very common use for building purposes, and on acting upon it 

 with sulphuric acid, the carbonic acid is evolved, sulphates of lime and 

 magnesia are formed, and the latter is separated from the former by 

 simple solution in water, sulphate of magnesia being very soluble, 

 while sulphate of lime is almost insoluble. On evaporating the solu- 

 tion, the sulphate of magnesia crystallises out. When prepared in this 

 way, however, it frequently contains sulphate of iron, but this may, if 

 nsfssesry, be got rid of by calcining the salt The sulphate of iron is 

 then decomposed, peroxide of iron remaining while the sulphate of 

 magnesia is unaltered, and may be dissolved away from the oxide of 

 iron by waUr. 



Ou v*porating and slowly cooling a solution of sulphate of magnesia, 

 larg* four sidvd rliuuibio prisms are obtained, but by rapid cooling and 

 frequent agitation small acioular crystals are deposited, forming the 

 Mftom sate u met with in pharmaay. 



Sulphate of magnesia is colourless, transparent, and inodorous, but 

 has an extrem<ly bitter tests. Ueatod, it fuses, parts with its water 

 f f crystallisation, and finally becomes anhydrous. The crystals slowly 



effloresce in very dry air. Five parts dissolve in four of water at 86* 

 Fahr., and in still less of boiling water. Sulphate of magnesia is also 

 exceedingly soluble in hydrochloric acid, but insoluble in alcohol. 



\Urale of magnetia (MgO, NO. + 6 HO). Formed by dissolving 

 carbonate of magnesia in nitric acid, and concentrating by evaporation. 

 It then crystallises out in rhombic prisms and needles, very deliques- 

 cent, very soluble in water, and soluble also in nine times their weight 

 of alcohol. They are almost insoluble in absolute alcohol. 



Phoiphateuf magnesia and ammonia (2 MgO, Mf,<>. !'<>, + 12 HO). 

 Precipitated in a granular form, when phosphate of soda is added to 

 a solution of magnesia in chloride of ammonium, containing also 

 ammonia. By beat it is converted into bibasic phosphate, or pyro- 

 phosphate, containing 36'67 per cent of magnesia. 



'let ofmignena. Many of those occur native. See STEATITE, 

 MEERSCHAUM, and HORNBLENDE, in NAT. HIST. Div.] 



CitroU ofmagnttia (8 MgO, Ci, HO). Prepared by saturating citric 

 id Kith carbonate of magnesia. It is less bitter than most of the 

 magnesian salts. 



S/erretftnt citrate of magnetia, or granular citrate, as it is sometimes 

 called, is nothing more than a mixture of bicarbonate of soda and 

 tartaric acid, with a small but variable quantity of sulphate of magnesia : 

 sometimes it contains a little citric acid. It is made by well mixing 

 the ingredients, slightly moistening till the mass begins to swell from 

 disengagement of carbonic acid, and then rapidly drying over a water- 

 bath with constant stirring. 



Double tall* of magnetia, especially with alkaline salts, are very 

 numerous. 



Tetif for magnetia. Magnesia is characterised by its not being pre- 

 cipitated from solution by hydrosulphate or carbonate of ammonia in 

 the presence of chloride of ammonium, and by a granular precipitate 

 with phosphate of soda and with arseniate of ammonia, especially if 

 free ammonia is present 



Ettimation of magnetia. This is generally effected in the state of 

 bibasic phosphate (2 MgO, P0 t ), in the manner already mentioned 

 under phosphate of magnesia. 



MAGNET. The natural magnet, loadttont, or lodatone, is known in 

 mineralogy as magnetic iron ore. It consists of one equivalent of 

 protoxide and one equivalent of sesquioxide of iron (FeO, Fe,0,), and 

 possesses the remarkable property of attracting iron and some other 

 metals. It is said to have been found abundantly near Magnesia in 

 Lydia, from which circumstance its name may Lave been derived 

 from the Greek itaynit. The attracting power of the magnet was 

 known at a very early period, as references are mode to it by Aristotle, 

 and more particularly by Pliny, who states that ignorant people called 

 it fcrrum virum, or quick-iron. The same author appears to have been 

 acquainted with the power of the magnet to communicate pr> . 

 similar to its own to other bodies. 



The universal law, that re-action is co-existent with action, implies, 

 that iron must re-act on the magnet, and we find in fact, th.it if a piece 

 of iron be fixed, and a small magnet be suspended by on untv.i-tr.1 lim> 

 near it, the magnet will then be moved towards the iron ; thus all the 

 iron in the mass of the globe acts upon a magnet It is also known tli.it 

 electrical currents influence magnetic bodies [ELECTRO-MAGNETISM] 

 while heat has an influence on magnetic intensity. Hence it follows as 

 a mechanical consequence, that if a magnetic needle or cylinder be sus- 

 pended by its centre of gravity, so as to be free to move in any direction 

 round that point, it will not take an arbitrary position like unmag- 

 netised bodies, but must take a specific direction, namely, that which 

 represents the resultant of all the magnetic forces to which it is subject 

 Its position in a given place con be defined by two angles, the one 

 called the variation or declination, the other the i ..r dip. 



The first U the angle formed by the vertical plane in which the needle 

 lies with the plane of the meridian ; the second is the inclination of 

 the line of the needle to the plane of the horizon. The latter is avoided 

 in the compass-needle by sustaining it horizontally on a point win. h is 

 necessarily different from its centre of gravity, and the variation is then 

 the angle uiade by the direction of the in-i-<lu- with that of an exact 

 and horizontal north-and-aouth line. This property of the needle is 

 called its polarity, and is a consequence of its other properties above 

 noticed; the fact, however, escaped the notice of the Greeks and 

 Romans of antiquity, but the Chinese appear to have been acquainted 

 with it from a very remote date. The Chinese name it, according to 

 its most valuable property, trim -</(//, <>r the "directing stone." In 

 Tonkinin it is called the " stone which shows the south." In Swedish 

 it is trad-lien, or the " seeing stone ; " in Icelandic, lcid< 

 " leading stone," after the Saxon ladan, " to lead," whence the English 

 lodettonr. In a similar way is derived the term lode-itar, or "guidim; 

 star," as applied to the pole-star, and the term I nit, the " leading vein, ' 

 in a mine. Polarity is the most useful of the known properties of the 

 magnet, being of the most essential importance to the mariner, 

 the magnet is constructed in the form of the compass-needle. [COMPASS, 

 HISTORY or Tin:.] 



Dr. Gilbert, who was physician in ordinary to Queen Elizabeth, states 

 that P. Venetus brought a compass from China in 1260. Gilbert 

 bestowed much attention , n the subject of magnetism, and to some 

 extent inculcated the doctrine of gravitation, by comparing the earth 

 to a great magnet. His theory on this subject is given in a work 



