Magnesia.—Light magnesia. A white, very light and very fine powder, slowly absorbing carbonic acid from the air, odorless, having an earthy but no saline taste, and a faintly alkaline reaction when moistened with water. It is almost insoluble in water, or in alcohol, etc. Dose, 3 ss— 3 ij, or more.

Magnesia Ponderosa

Heavy magnesia. A white, dense, and very fine powder, corresponding in all other properties to the above. Dose, 3 ss— 3 ij-

Magnesii Carbonas

Magnesium carbonate. Light, white, friable masses, or a light, white powder, odorless and tasteless, insoluble in alcohol, and almost insoluble in water. Dose, 3 ss— 3 ij

Mistura Magnesiae et Asafoetidae

Mixture of magnesia and asa-foetida. (Carbonate of magnesium, five parts; tincture of asafoetida, seven parts; tincture of opium, one part; sugar, ten parts; and sufficient distilled water to make up one hundred parts. Dewees's formula.) Dose, one fourth to one tea-spoonful.

Actions and Uses

A mild antacid laxative. In the stomach it neutralizes any free acid it meets with, and the resulting salt has a laxative action. It is used to correct acidity, the carbonate being preferred when there is an irritable state of the stomach, because the carbonic acid, which is set free by the action of the stomach acid, is a local sedative and anodyne. If magnesia does not enter into combination with the stomach acid, no laxative effect is produced. Under these circumstances a solution of citric acid or lemonade, taken after the magnesia, will cause it to act. Magnesia is a useful antacid and laxative in sick-headache, especially when accompanied by acidity and constipation. It has been employed also in gouty affections, and in lithiasis (uric acid); but it is much inferior to the potash salts in these affections. In the intestinal indigestion of infants, attended with flatulence, magnesia is much prescribed in conjunction with carminatives. Dewees's formula for flatulent colic and diarrhoea in infants has been made official, and is given above as Mistura Magnesiae et Asafoetidae. The carminative of Dalby is similar in composition: Rx Magnesii carbonat, Эij; ol. menth. pip., gt. j; ol. myrist., gtt. ij; ol. anisi, gtt. iij; tinct. castor., gtt. xxx; tinct. asafaetid., gtt. xv; tinct. ol. hedeomae, gtt. xv; tinct. cardam. comp., gtt. xxx; aquae menthae pip., oz ij. M. Sig.: A tea-spoonful, as necessary.

Magnesia is frequently combined with other purgatives because of its antacid property. The following is Meigs's formula, gelsemium having been substituted for henbane: Rx Magnesii carb., 3 ss; magnesii sulphat., 3 iij; spts. ammoniae aromat., 3 j; tinct. rhei, oz ss; tinct. gelsemii, 3 ss; aquae menthae pip., oz iv. M. Sig.: A table-spoonful two or three times a day.

It is unsafe to use magnesia in large quantity for lengthened periods, owing to the fact that it may form intestinal concretions — a hydrate of magnesia. Instances of this kind have been reported.

Freshly-precipitated hydrate of magnesia is an antidote to arsenious acid in solution, but it is not so effective as the hydrated sesquioxide of iron.