_Tragacanth Mucilage._
Tragacanth is, strictly speaking, not soluble in water, but imbibes a
large portion of it and swells into a considerable bulk, forming a soft
but not a liquid mucilage; on the farther addition of water, a fluid
solution may be obtained by agitation, and the liquor is turbid; but on
standing, the mucilage subsides, the limpid water on the surface
retaining a little of the gum;[566] it differs from all gums in giving a
thick consistence to a larger quantity of water, its power in this
respect being to that of gum arabic as twenty to one; one part converts
twenty of hot water into a stiff mucilage. Tragacanth is not increased,
but actually diminished in solubility by the addition of any other gum,
it accordingly separates from water with much greater facility when gum
arabic is present. This preparation, according to the Edinburgh college,
consists of one part of gum and eight of water; the resulting mucilage
is stiff, and is principally employed for making _troches_. The Dublin
preparation contains four times that quantity of water.