238

MAGN

magnesia. E. Magnesia. D. Magnesia alba. O. Count Pahna's■ponder. O. Henry's Magnesia is similar. Take ftj of sulphate ofmagnesia, gix of subcarbonate of potass, and three gallons of water;dissolve separately, the subcarbonate of potass in Oiij of the water;and the sulphate of magnesia in Ov of the water, and filter; thenadd the remaining water to the solution of sulphate of magnesia ;boil this, and while it is boiling mix the former solution with it,stirring them thoroughly with a spatula: then strain through linen,wash the powder repeatedly with boiling water, and dry it on bi-bulous paper in a heat of 200°. It is sometimes made up intosquares or cubes while drying. If it is made with hard water itwill contain lime.

Decomposition. There is a mutual exchange of affinities. The sul-phuric acid of the sulphate of magnesia passes over to the potass,forming sulphate of potass, which remains in solution; while thecarbonic acid and the magnesia, being thus set free, unite and formthe carbonate of magnesia, which being insoluble is precipitated, andremains on the filter; but with a deficient proportion of carbonicacid. The preparation indeed consists of both hydrate and carbonateof magnesia, containing 48 - 92 of magnesia, 38-42 of carbonic acid,and 15-76 of water.

Adulterated with water, chalk, gypsum, sulphate of potass, flour, &c.The water makes it heavier, and is the consequence of imperfectdrying. This may be known by the spec. grav. and by its not beinglight and spongy. Chalk will be precipitated by dilute sulphuricacid, in form of a dense, white, insoluble deposit, consisting ofsulphate of lime. Gypsum, by boiling it in distilled water, andadding oxalate of ammonia, which will precipitate oxalate of lime ;or muriate of barytes will precipitate sulphate of barytes. Sulphateof potass will be detected by dissolving it in dilute nitric acid, andadding nitrate of barytes, which will precipitate sulphate of barytes.Flour will be discovered by burning.

Insoluble in water and spirit of wine.

Incompatible with metallic and acidulous salts, such as the sulphates ofiron and zinc, alum, and supertartrate of potass, muriate of ammonia,lime water, acids, alkalies, and neutral salts.

Medicinally it is employed, like the preceding, as an antacid, laxative,and lithontriptic; but from its insolubility, unless it meet with anacid in the stomach or bowels, it is apt to lodge, accumulate, and tobe cemented by mucus, and become the nucleus of intestinal calculi.The dose for cardialgia and acidity,-aphtha, and the fevers attendingdentition, is 3j to 5j. In calculous affections, uric, or red gravel,when other alkaline remedies disagree, 3j to 9jss, or more, twice or