QUALITIES. _Form_, octohedral crystals, whose sides are equilateral
triangles; they are slightly efflorescent. _Taste_, sweet, rough, and
acidulous. CHEMICAL COMPOSITION. It is a triple, or sometimes a
quadruple salt, with excess of acid, consisting of sulphuric acid and
alumina, with potass, or ammonia, or frequently both of them; the nature
of the alkali however does not in the least appear to affect the
properties of alum, although it produces a crystallographic
modification; for where potass is present the summit of the crystal will
exhibit a truncation. Dr. Ure has lately produced alum with soda, and
the combination differs from common alum only in its greater degree of
solubility, a property which at once recommends it to the attention of
the pharmaceutist and physician. SOLUBILITY. A fluid-ounce of cold water
dissolves 30 grains, but if boiling four drachms; it is insoluble in
alcohol. INCOMPATIBLE SUBSTANCES. _Alkalies_ and _alkaline salts_, after
neutralizing the excess of acid, precipitate the alumine. It is also
decomposed by _carbonate_ and _muriate of ammonia_, _carbonate of
magnesia_, and _tartrate of potass_, by _lime-water_, _acetate of lead_,
and _the salts of mercury_, as well as by many vegetable and animal
substances, especially _galls_ and _kino_. It is on this account very
injudicious to combine alum with any vegetable astringent with a view to
encrease its virtues; thus the “_Pulvis Sulphatis Aluminæ compositus_”
of the Edinburgh college, is less powerful than any of the ingredients
of which it is composed; and the addition of alum to the decoction of
bark, undoubtedly diminishes its efficacy as an astringent injection.
MEDICINAL USES. Alum is internally a powerful astringent, in hæmorrhages
and inordinate fluxes, and is externally useful for repellent and
astringent lotions, gargles, and collyria. Dioscorides and Hippocrates
praised its effects as a lotion in various kinds of ulcers, and
particularly in sores of the mouth, and in spongy, swelled gums.
Van-Helmont was the first person who employed alum in uterine
hemorrhage, and the success of the practice very considerably enhanced
his reputation. _Boerhaave’s_ astringent powder for the ague consisted
of _Alum_ and _Nutmeg_ with the addition of _Armenian bole_. DOSE, gr.
x. In large doses it is liable to excite nausea, and to act upon the
bowels. Nutmeg or some aromatic should therefore be joined with it.
FORMS OF EXHIBITION. In solution, or in substance made into pills with
extract; (_Form: 53, 56_,) it is sometimes given with advantage in the
form of whey (_Alum-whey—Serum Aluminosum_) made by boiling ʒij with a
pint of milk, and then straining, the dose of which is a wine glass
full; (_Form; 54._) By briskly agitating a drachm of alum with the white
of an egg, a coagulum is formed, (_Alum curd of Riverius_; _Albumen.
Aluminosum_) which is serviceable in some species of ophthalmia, when
applied between two pieces of thin linen rag.[365] As alum is not
decomposed by sulphate of lime, hard water may be safely used for its
solution. It has the effect of retarding, and in some instances of
preventing, the acetous fermentation in vegetables; thus when added to
common _paste_ it prevents its becoming sour; animal substances, as
_glue_, are preserved by it in a similar manner. It has also the
property of clearing turbid water, wine, and spirituous liquors, for
which purpose it is extensively employed. OFFICINAL PREPARATIONS.
_Liquor Alum: co._ L. _Pulv: Alum: co._ E.
ALUMEN EXSICCATUM, L. Ustum. D. _Dried Alum._ By the action of heat alum
undergoes watery fusion, yields its water of crystallization, and loses
more than one third of its weight; if the heat be too intense, or long
continued, it is deprived of a great part of its acid. It has been
recommended in doses of a scruple, in cholic, when it has been said to
operate gently upon the bowels, and to relieve the pain: I have myself
experienced this good effect when the cholic has been produced by the
action of lead: Dr. Grashuis, a Dutch Physician, first recommended its
use in Cholica Pictonum. The preparation however is principally used as
an external application, having a degree of escharotic power, which
renders it serviceable in venereal chancres, as well as in other ulcers
having weak and spongy granulations; it is also very frequently employed
to destroy fungous excrescencies, but it should be remembered that, as
it owes such power to an excess of acid, unless it be carefully
prepared, it must be inefficient. It ought to redden syrup of violets.
ALUMEN RUPEUM. _Roche_ or _Rock Alum_. This variety was originally
brought from Roccha, formerly called Edessa, in Syria, in fragments of
about the size of an almond, covered with an efflorescence of a pale
rose colour; that however which is now sold under this name is common
English alum, artificially coloured. It is unimportant.
ALUMEN ROMANUM. _Roman Alum_ is in irregular octohedral masses, powdery
on the surface; it is the purest kind, and contains no ammonia in its
composition.