(1) Known amongst mechanics as gum dragon and gum drag. It comes in irregular-shaped fragments, varying in size from that of a small pea to a hazel nut or larger. It is yellowish-white, and sometimes translucent like horn. It is hard and tough, and very difficult to reduce to powder unless when exposed to a freezing temperature, or when thoroughly dried and ground in a heated mill or mortar. When so treated, however, it is possible to produce a very fine white powder. When thrown into water, it absorbs that liquid, and swells up and forms a paste which is largely used by shoemakers, and by manufacturers of lozenges, as it gives great toughness to the mass of sugar and other ingredients. If sufficient water be used, and the soft mass be heated or mixed up, it forms a uniform, soft, adhesive paste. If allowed to settle, however, part of the gum separates from the water, and is deposited. Boiling water dissolves the gum more perfectly at first, but even when so treated, it separates afterwards. According to Planche, a mixture of gum tragacanth and gum arabic forms, with water, a thinner mucilage than the same quantity of either of these gums alone. (2) Equal parts of tragacanth powder and powdered gum arabic, moistened, according to requirements at the time, with dilute acetic acid, or, if the colour will not be of any importance, with ordinary vinegar.
This forms a very strong mucilage which keeps well.