The Physiomedical Dispensatory by William Cook, M.D., 1869    


I.  Calcined Magnesia:  This is prepared by putting carbonate of magnesia into an earthen crucible, with a partly open lid, and subjecting it to a dull-red heat till the carbonic acid is expelled, which commonly requires about two hours.  The product is a very light and bulky powder, pure white, without taste or smell. It is very sparingly soluble in cold water, and still less so in boiling water.  It is mildly alkaline, and combines with the acids without effervescence.  The sulphate of magnesia (epsom salts) exists abundantly in some localities, and in many German and some American springs; and is the source from which the various forms of magnesia are mostly prepared.

II.  Carbonate of Magnesia:  Dissolve ten ounces of sulphate of magnesia, and twelve ounces of carbonate of soda, each in a pint of boiling distilled water.  Mix the two solutions, and evaporate to perfect dryness on a sand-bath at a heat below the boiling point.   Digest the residue in a quart of pure water, wash thoroughly on a muslin filter, and dry at a temperature below the boiling point.   This is almost identical with calcined magnesia in appearance and properties, but effervesces when mixed with the acids.

Properties and Uses:  These two preparations of magnesia are among the mildest of all the alkalies, neutralizing acidity of the stomach, not proving corrosive if used in excess, and acting as a mild laxative.   They are particularly used in heartburn, in rheumatic and gouty persons whose urine is charged with an excess of uric acid, and in renal difficulties where an alkali is indicated.   They are far more acceptable to the stomach and  bowels than any of the preparations of soda or potassa; but their insolubility renders them less convenient of exhibition.   The carbonate, yielding its carbonic acid gas in contact with the acid of  the stomach, is liable to occasion flatulence, whence the calcined  article is to be preferred; but as this is liable to absorb carbonic acid from the air, and slowly to become a carbonate, it should he freshly prepared.  Both varieties are used to neutralize acids in case of poisoning.   Dose as a laxative, five to ten grains for infants, and fifteen to thirty grains for adults;  as  an antacid, five  to ten  grains.   The  powder may conveniently be mixed with milk.  It is often compounded with rhubarb, and used for  the diarrhea of children.   The carbonate may be mixed with twice its own weight of cream of tartar, (bitartrate of potassa,) flavored with a little oil of cinnamon, and from five to ten grains  given in sirup.  It forms an effervescing compound which often allays excessive vomiting; and by repetition every four hours proves laxative.  Both forms of this article absorb the essential oils readily, and render them capable of suspension in water by  trituration–for which purpose they are much used in the preparation of Medicated Waters.

Citrate of Magnesia is a fashionable laxative at the present  time.  It is prepared by dissolving 450 grains of citric acid in  four ounces of distilled water, and into this dissolving 120 grains  of calcined magnesia.   This solution is filtered, and poured into a strong twelve-ounce bottle with two fluid ounces of the sirup of citric acid.   The bottle is then nearly filled with water, forty grains of bicarbonate of potassa added, and the bottle quickly  corked and the cork tied down.  It forms an effervescing solution of citrate of magnesia and potassa, the excess of free carbonic acid remaining in the water.  From half to the whole of the contents of this bottle are needed as a dose; the cathartic action is brisk and often griping; it is too much like epsom salts to be a commendable purge, and has nothing but its pleasantness to recommend it.

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