_Magnesium Phosphates._--By adding sodium phosphate to magnesium sulphate and allowing the mixture to stand, hexagonal needles of MgHPO4·7H2O are deposited. The _normal phosphate_, Mg3P2O8, is found in some guanos, and as the mineral wagnerite. It may be prepared by adding normal sodium phosphate to a magnesium salt and boiling the precipitate with a solution of magnesium sulphate. It is a white amorphous powder, readily soluble in acids. _Magnesium ammonium phosphate_, MgNH4PO4·6H2O, is found as the mineral struvite and in some guanos; it occurs also in urinary calculi and is formed in the putrefaction of urine. It is prepared by adding sodium phosphate to magnesium sulphate in the presence of ammonia and ammonium chloride. When heated to 100° C., it loses five molecules of water of crystallization, and at a higher temperature loses the remainder of the water and also ammonia, leaving a residue of magnesium pyrophosphate, Mg2P2O7. _Magnesium Nitrate_, Mg(NO3)2·6H2O, is a colourless, deliquescent, crystalline solid obtained by dissolving magnesium or its carbonate in nitric acid, and concentrating the solution. The crystals melt at 90° C. _Magnesium Nitride_, Mg3N2, is obtained as a greenish-yellow amorphous mass by passing a current of nitrogen or ammonia over heated magnesium (F. Briegleb and A. Geuther, _Ann._, 1862, 123, p. 228; see also W. Eidmann and L. Moeser, _Ber._, 1901, 34, p. 390). When heated in dry oxygen it becomes incandescent, forming magnesia. Water decomposes it with liberation of ammonia and formation of magnesium hydroxide. The chlorides of nickel, cobalt, chromium, iron and mercury are converted into nitrides when heated with it, whilst the chlorides of copper and platinum are reduced to the metals (A. Smits, _Rec. Pays Bas_, 1896, 15, p. 135). _Magnesium sulphide_, MgS, may be obtained, mixed with some unaltered metal and some magnesia, as a hard brown mass by heating magnesia, in sulphur vapour. It slowly decomposes in moist air. _Magnesium sulphate_, MgSO4, occurs (with IH2O) as Kieserite. A hexahydrate is also known. The salt may be obtained from Kieserite: formerly it was prepared by treating magnesite or dolomite with sulphuric acid. Entry: MAGNESIUM
EPSOM SALTS, heptohydrated magnesium sulphate, MgSO4·7H2O, the _magnesii sulphas_ of pharmacy (Ger. _Bittersalz_). It occurs dissolved in sea water and in most mineral waters, especially in those at Epsom (from which place it takes its name), Seidlitz, Saidschutz and Pullna. It also occurs in nature in fibrous excrescences, constituting the mineral epsomite or hair-salt; and as compact masses (reichardite), as in the Stassfurt mines. It is also found associated with limestone, as in the Mammoth Caves, Kentucky, and with gypsum, as at Montmartre. Epsom salts crystallizes in the orthorhombic system, being isomorphous with the corresponding zinc and nickel sulphates, and also with magnesium chromate. Occasionally monoclinic crystals are obtained by crystallizing from a strong solution. It is used in the arts for weighting cotton fabrics, as a top-dressing for clover hay in agriculture, and in dyeing. In medicine it is frequently employed as a hydragogue purgative, specially valuable in febrile diseases, in congestion of the portal system, and in the obstinate constipation of painters' colic. In the last case it is combined with potassium iodide, the two salts being exceedingly effective in causing the elimination of lead from the system. It is also very useful as a supplement to mercury, which needs a saline aperient to complete its action. The salt should be given a few hours after the mercury, e.g. in the early morning, the mercury having been given at night. It possesses the advantage of exercising but little irritant effect upon the bowels. Its nauseous bitter taste may to some extent be concealed by acidifying the solution with dilute sulphuric acid, and in some cases where full doses have failed the repeated administration of small ones has proved effectual. Entry: EPSOM
Na 75.825 NaCl 192.860 K 3.925 K2SO4 8.756 Li 0.021 Li2SO4 0.166 Mg 4.844 MgCl2 15.044 Ca 2.424 MgSO4 5.216 Cl 128.278 CaSO4 8.240 SO3 12.522 Fe2O3 + Al2O3 0.004 O in sulphate 2.494 SiO2 0.018 Fe2O3 + Al2O3 0.004 Surplus SO_3 0.051 SiO2 0.018 Bo2O3 trace Br3 faint trace Entry: C
ENSTATITE, a rock-forming mineral belonging to the group of orthorhombic pyroxenes. It is a magnesium metasilicate, MgSiO3, often with a little iron replacing the magnesium: as the iron increases in amount there is a transition to bronzite (q.v.), and with still more iron to hypersthene (q.v.). Bronzite and hypersthene were known long before enstatite, which was first described by G.A. Kenngott in 1855, and named from [Greek: enstatês], "an opponent," because the mineral is almost infusible before the blowpipe: the material he described consisted of imperfect prismatic crystals, previously thought to be scapolite, from the serpentine of Mount Zdjar near Schönberg in Moravia. Crystals suitable for goniometric measurement were later found in the meteorite which fell at Breitenbach in the Erzgebirge, Bohemia. Large crystals, a foot in length and mostly altered to steatite, were found in 1874 in the apatite veins traversing mica-schist and hornblende-schist at the apatite mine of Kjörrestad, near Brevig in southern Norway. Isolated crystals are of rare occurrence, the mineral being usually found as an essential constituent of igneous rocks; either as irregular masses in plutonic rocks (norite, peridotite, pyroxenite, &c.) and the serpentines which have resulted by their alteration, or as small idiormorphic crystals in volcanic rocks (trachyte, andesite). It is also a common constituent of meteoric stones, forming with olivine the bulk of the material: here it often forms small spherical masses, or chondrules, with an internal radiated structure. Entry: ENSTATITE
BRONZITE, a member of the pyroxene group of minerals, belonging with enstatite and hypersthene to the orthorhombic series of the group. Rather than a distinct species, it is really a ferriferous variety of enstatite, which owing to partial alteration has acquired a bronze-like sub-metallic lustre on the cleavage surfaces. Enstatite is magnesium metasilicate, MgSiO_3, with the magnesia partly replaced by small amounts (up to about 5%) of ferrous oxide; in the bronzite variety, (Mg,Fe)SiO_3, the ferrous oxide ranges from about 5 to 14%, and with still more iron there is a passage to hypersthene. The ferriferous varieties are liable to a particular kind of alteration, known as "schillerization," which results in the separation of the iron as very fine films of oxide and hydroxides along the cleavage cracks of the mineral. The cleavage surfaces therefore exhibit a metallic sheen or "schiller," which is even more pronounced in hypersthene than in bronzite. The colour of bronzite is green or brown; its specific gravity is about 3.2-3.3, varying with the amount of iron present. Like enstatite, bronzite is a constituent of many basic igneous rocks, such as norites, gabbros, and especially peridotites, and of the serpentines which have been derived from them. It also occurs in some crystalline schists. Entry: BRONZITE