This phosphate of ammonia and magnesia is readily formed by mixing a solution of a magnesian salt with hydrochlorate of ammonia, phosphate of soda, and a little free ammonia. It is an occasional constituent of urinary calculi, and crystallizes in beauti ful prisms from urine and other animal fluids, when they begin to putrefy. It is also frequently present in the excrements in cases of diarrhea.
The silicates of magnesia are numerous. A large number of minerals are formed either wholly or partly of them, among which may be mentioned olivine or chrysolite, talc, steatite or soapstone, meerschaum, serpentine, augite, hornblende, etc.
The haloid salts of magnesium—the chloride, iodide, and bromide—are of no special interest, except that the chloride of magnesium is, next to chloride of sodium, the most abundant of the salts existing in sea-water.
The compounds of magnesium ernployed in medicine are magnesia, its carbonate, and its sulphate.
Magnesia is presented in small doses (from 10 grains to a scruple), as an antacid, in cases of undue acidity of the stomach, heart-burn, and abnormal acidity of the urine; in larger doses (from a scruple to a dram), it produces distinct purgative effects. It
is useful, especially when combined with rhubarb and a little ginger (in the form of compound rhubarb powder or Gregory's mixture), as a purgative for children, in, acid conditions of the alimentary canal.
Carbonate of magnesia (magnesia alba) acts in the same manner as magnesia, except that it is less active, since more than half of it consists of water and carbonic acid. Dinneford's solution of magnesia, and other fluid preparations of the same nature, are made by dissolving this salt in water charged with carbonic acid. A drarn of carbonate of magnesia, the juice of one lemon, and a wine-glassful of water constitute an agree able laxative, a citrate of magnesia being thus formed.
Sulphate of magnesia is a purgative in very general use. It is much employed in febrile affections, and when the portal system is congested; but it may be used in almost any case in which a mild but efficient laxative is required. Its dose varies from 2 to 4 or 6 drams. In combination with the infusion of senna, it forms the ordinary..Nack draught. See 31AGNESIUM AND THE MAGNESIUM LIGHT.