Gum

Certain substances, as yet imperfectly understood, which issue from trees, are called gums. Their elementary composition is the same as that of amylaceous matter, but they differ from it in several of their chemical properties. Gam may be divided into three species.

1st. Gum arabic.

2d. Indigenous gum.

3d. Gum tragacanth.

Gum arabic issues in the form of a viscous solution, from certain species of acacia, and after some time the substance coagulates and dries on the tree. Large quantities are imported from Senegal.

Gum arabic is found in small round masses, having a conchoidal and vitreous fracture, and its taste is sweetish and nearly insipid. It dissolves into indefinite proportions in water, imparting to it a peculiar consistence called gummy. It dissolves slowly in cold, and rapidly in hot water.

The purest gum arabic has always a slightly yellowish tinge; but it may be made perfectly colorless by passing chlorine through a boiling solution of gum, and drying the substance.

Gum tragacanth flows from certain vegetables of the genus Astragalus, which are cultivated in the eastern part of Europe. It exudes in the shape of a very thick gummy juice, which by solidifying forms small contorted strips. This gum is the mixture of several substances. The essential principle of this gum is called bassorin; it does not dissolve in water, but it swells, and is converted into a gelatinous substance. It dissolves in alkalies.

Nitric acid converts gums into mucic acid. Gum in the fabrication of matches must be used in fine powder.

Gelatin

Common glue answers the purpose in the fabrication of matches; it is manufactured from leather scraps, tendons, horns and hoofs of animals. When heated it melts, and congeals on cooling into a remarkably coherent mass. Cold water merely softens and swells without dissolving it, while boiling water dissolves it, and forms a viscid liquid which coagulates into a more or less consistent jelly on cooling. Alcohol precipitates gelatin from its aqueous solution. Prolonged ebullition with water destroys gelatin, and it no longer coagulates. When glue is used, it is better to soak it in tepid water for 24 hours before dissolving it