2. (Robiquet.) Citric acid, 351⁄4 parts, is powdered and dissolved in boiling water, 105⁄8 parts; when the solution is cold, and before it crystallises, it is poured in a wide earthen vessel, kept cold by surrounding it with water; then, by means of a sieve, carbonate of magnesium, 211⁄6 parts, is distributed evenly and rapidly over the surface without stirring; when the reaction ceases the mixture is beaten rapidly as long as it retains its pasty consistence. The salt should be dried at a temperature not exceeding 70° Fahr.
3. (Effervescing; Magnesiæ citras effervescens, L.)—a. Citric acid (dried and powdered), 7 parts; heavy carbonate of magnesium, 5 parts; mix, and preserve in well-corked bottles.
b. (Ellis.) Mix powdered citric acid, 21⁄2 oz., with powdered sugar, 8 oz.; triturate to a fine powder, and drive off the water of crystallisation by the heat of a water bath; add citrate of magnesium (prepared by fusion), 4 oz., and oil of lemons, 10 drops, and mix intimately; then add bicarbonate of sodium, 3 oz., and again triturate until the whole forms a fine powder, which must be preserved in stoppered bottles. From 1 to 3 tablespoonfuls, mixed in a tumbler of water, furnishes an effervescing draught in which the undissolved portion is so nicely suspended, that it can be taken without inconvenience.
c. (Ph. Germ.) Light carbonate of magnesia, 25 oz.; citric acid, 75 oz.; distilled water, q. s.; mix into a thick paste and dry at
86° Fahr. With 14 oz. of the dried mass mix bicarbonate of soda, 13 oz.; citric acid, 6 oz.; sugar, 3 oz. Sprinkle over the mixture enough rectified spirit so as to make it sufficiently moist to be granulated by rubbing through a tinned iron sieve.
d. (Extemporaneous.) Citric acid (cryst.), 20 gr.; carbonate of magnesium, 14 gr.; mix in a tumbler of cold water, and drink the mixture whilst effervescing. A pleasant saline.
Obs. A dry white powder, sometimes sold as citrate of magnesia in the shops, is quite a different preparation to the above, and does not contain a particle of citric acid. The following formula is that of a wholesale London drug-house that does largely in this article:—
Calcined magnesia, magnesium oxide, 11⁄4 lb. (or carbonate, 2 lbs.); powdered tartaric acid, 11⁄2 lb.; bicarbonate of sodium, 1 lb.; dry each article by a gentle heat, then mix them, pass the mixture through a fine sieve in a warm dry room, and keep it in well-corked bottles. A few drops of essence of lemon and 3 lbs. of finely powdered sugar are commonly added to the above quantity. This addition renders it more agreeable.
Prop., &c. Citrate of magnesium is a mild and agreeable laxative; its secondary effects resemble those of the carbonate.—Dose. As a purgative, 1⁄2 to 1 oz. The dose of the effervescing citrate must depend on the quantity of magnesia present. A solution of this salt in water, sweetened and flavoured with lemon, forms magnesian lemonade.
Magnesium, Boro-cit′rate of. Syn. Magnesiæ boro-citras, L. Prep. (Cadet.) Boracic acid (in powder), 113 gr.; oxide of magnesium, 80 gr.; mix in a porcelain capsule, and add enough of a solution of citric acid, 260 gr., in water, 31⁄2 pints, to form a thin paste; then add the remainder of the citric solution, and gently evaporate, with constant stirring, to dryness. A cooling saline, and, in small doses, emmenagogue and lithontriptic.—Dose. As an aperient, 3 to 6 dr.