This preparation consists of one part of gum and two of water; in
preparing it, the dispenser is particularly recommended to pulverize the
gum, and never to employ that which is purchased in the state of powder,
as it is always impure and incapable of forming a pellucid and elegant
solution.[564] INCOMPATIBLE SUBSTANCES. Neither the _strong acids_ nor
_alcohol_, when considerably diluted, occasion any disturbance in it;
but _sulphuric æther_ and its _compound spirit_, _the tincture of
muriated iron_, and _sub-acetate of lead_, produce very dense
precipitates: the _acetate of lead_ only occasions decomposition, when
an alkaline salt is present in the formula; the _volatile alkali_
curdles the mucilage, and _hard calcareous waters_ render the mixture
difficult and often impracticable. In the pharmaceutical application of
this mucilage, it should be remembered that it contains in its
composition an astringent principle, which is perhaps of but trifling
consequence except in the exhibition of some very few active metallic
salts, which are certainly decomposed by it (e. g. grs. x of _nitrate of
mercury_ are decomposed by ʒij of gum arabic.[565]) It contains also
lime in combination with some vegetable acid. USES. Diluted with four
times its bulk of water, this mucilage forms a demulcent mixture of
appropriate tenacity, which affords a convenient vehicle for several
efficient remedies; the pharmaceutical use of this mucilage depends upon
the fact of its rendering expressed and essential oils, balsams, resins,
gum-resins, resinous tinctures, and fatty bodies, miscible with water,
but if a syrup be added, the union will be more perfect; the proportions
necessary for this purpose vary according to the nature of the
substances; thus, _oils_ will require about three-fourths their weight,
_Balsams_ and _Spermaceti_ an equal part, _Resins_ a double quantity,
and _Musk_ five times its weight; the following _Formulæ_ illustrate
this property, 9, 19, 22, 135.