Only one salt of this metal is used in medicine.

Alumen. - Alum. NH4A1(SO4)2.12H1O. A sulphate of ammonia and alumina, crystallised from solution in water.

Characters. - Colourless transparent octahedra, with an acid, sweetish, astringent taste. Solubility, 1 in 12 of cold, and in 4/5 th parts of boiling water. Incompatible with alkalies, lime, barytas, lead, tartrates, and tannic acid, mercury, and iron.

Impurity. - Sulphate of Iron.

Dose. - 10 to 20 gr.

From Alumen is made:

Alumen Exsiccatum. - Dried Alum.

Source. - Made by heating alum up to 400° till aqueous vapours cease to be disengaged, and powdering.

Characters. - An opaque white bulky powder, spongy masses. Has lost 47 per cent. by heating: diffl-cult of solution in water, but unites readily with it.

Action And Uses. 1. Immediate Local Action And Uses

Externally. - Alum is astringent, an effect which is fully discussed under Plumbum. The dried alum absorbs water, and is somewhat caustic if the skin be broken, for instance, over ulcers. It is used to destroy weak exuberant granulations.

Internally. - The local action of alum is appreciated in the mouth as an "astringent taste," and in the throat as,"dryness," the mucous secretions of the parts being coagulated, and the membrane constringed, especially if the parts be inflamed and swollen. Alum is therefore a remedy for sore throat, in the form of gargles or sprays, variously combined with other substances.

A similar effect is produced on the mucous membrane of the stomach and intestines, dyspepsia and constipation being the result; in large doses it is an emetic, irritant, and purgative. A teaspoonful mixed with syrup is an excellent vomit in croup. As an injection in discharges from the vagina, uterus, and urethra, it is in constant use; and also as a wash for the eyes.

2. Action In The Blood

Alum is absorbed into the blood, probably as an albuminate.

3. Specific Action And Uses

This salt is believed to possess astringent properties when it reaches the tissues, arresting haemorrhage and chronic inflammatory discharges from the mucous membranes; and is used in the treatment of haemoptysis, epistaxis, gleet, diarrhoea, and even whooping cough. Much of this is doubtful.

4. Remote Local Action And Uses

Alum is excreted by the kidneys, and may arrest haemorrhage from these organs. Part of the salt may also escape by the skin, as it proves useful in some cases of excessive sweating.