Gum

a product collecting on the stems and branches of many plants. It is formed usually by the sap which exudes and dries up. A true gum differs from a resin. It may be dissolved, or at least softened, in water, while water has little or no effect on resin. On the other hand, a resin dissolves in alcohol while a gum does not. The dried sap of the caoutchouc or rubber tree is popularly called gum elastic, but, properly speaking, it is not a gum.

Of the true gums, gum arabic is best known. It is collected in the form of tears from several plants, particularly an acacia of Arabic and southern India. A variety called gum senegal is collected in tropical Africa. It must be gathered by hand. London imports half a million dollars' worth of gum arabic annually. Mixed with sugar, honey, or glycerine to prevent cracking, it makes the best of mucilage, especially for labels. It is employed in medicine and in making confectionery. Used as a size, it imparts luster to silk and other fabrics. We buy $500,000 worth a year from the Mediterranean countries.

Gum tragacanth is collected also by hand from several low shrubs of Asia Minor. They are known locally as goat thorns. The gum occurs in flakes, or in a threadlike form to which the name of vermicelli is given. Smyrna is the chief city of export. This gum is used by the pharmacist to give firmness to pills and lozenges. It makes an excellent mucilage. It is also employed as sizing to give stiffness to crepe and calico, and by the hat maker to stiffen his felt. We import half a million dollars' worth yearly.

Chewing gum was originally resin picked from the bark of the spruce and cherry tree. The demand has so far exceeded the supply that makers now rely largely on chicle gum. It is pressed from the milky juice of a South American evergreen tree, sometimes called the sapodilla. Much of the chewing gum on the market, however, consists almost wholly of paraffine, sweetened and flavored. The ingredients are kneaded to a stiff dough, which is then passed between rollers. These rollers are set at the right distance apart to produce a sheet, and are at the same time provided with sharp ridges that cut the sheet into oblong pieces. These are then dried, wrapped in paper, and sent to market.

See Chicle