Magnesium, Oxide of. MgO. Syn. Oxide of Magnesium, Calcined Magnesia, Magnesia (B. P., Ph. L.).
Prep. 1. (B. P.) Magnesium carbonate, heated in a crucible until all the carbonic anhydride is driven off.
Prop., &c. White heavy powder, scarcely soluble in water, but readily soluble in acids without effervescence. Its solution in hydrochloric acid, neutralised by a mixed solution of ammonia and ammonium chloride, gives a copious crystalline precipitate when sodium phosphate is added to it. See next preparation.
Magnesia levis (B. P.) Syn. Light magnesia. Prep. (B. P.) 1. Light carbonate of magnesium heated in a Cornish crucible until all the carbonic anhydride is driven off.
A bulky white powder, differing from the
magnesia (B. P.) only in its density, the volume occupied by the same weight being 31⁄2 to 1.
The properties of the two varieties of magnesium oxide are identical, and are used in medicine as antacids, laxatives, and antilithics, and much used in dyspepsia, heartburn, &c.—Dose, 10 to 20 gr. as an antacid and 20 to 60 gr. as a purgative.
Magnesium, Phos′phate of. MgHPO4.6Aq. Syn. Magnesiæ phosphas, L. Prep. From the mixed solutions of phosphate of sodium and sulphate of magnesium, allowed to stand for some time. Small, colourless, prismatic crystals, which, according to Graham, are soluble in about 1000 parts of cold water. Phosphate of magnesium exists in the grains of the cereals, and in considerable quantity in beer. It is also found in guano.
Magnesium and Ammo′′nium, Phosphate of. MgNH4.PO4, 6 Aq. Syn. Ammonio-phosphate of magnesia; Magnesiæ et ammoniæ phosphas, L. This compound falls as a white crystalline precipitate whenever ammonia or carbonate of ammonium is added, in excess, to a solution of a salt of magnesium which has been previously mixed with a soluble phosphate, as that of soda. It subsides immediately from concentrated solutions, but only after some time from very dilute ones.
Prop., &c. Ammonio-phosphate of magnesium is very slightly soluble in pure water; when heated, it is resolved into pyrophosphate of magnesium, and is vitrified at a strong red heat. It is found in wheaten bran, guano, potatoes, &c., and occasionally forms one of the varieties of urinary calculi.