GLIICOSIDE. A name applied to a number of organic substances occurring abundantly in plants. Chemically they are compounds of va rious sugars (usually grape-sugar) with organic acids, and they readily split up into their con stituents under the action of acids, alkalies, or certain ferments. Thus, amygdalin, C.II,NO„, a glucoside found in bitter almonds and other vege table products, is decomposed by the ferment named emulsion into dextrose (a sugar), ben zaldehyde, and hydrocyanic acid. (See ALMONDS, VOLATILE OIL OF.) Again, myronic acid, a glucoside found in black mustard, is decomposed by baryta water, or by the action of the ferment named myrosin, into glucose, allyl, mal yield the better glue. Fish glue is made from the skin, scales, and muscular tissue of some of the larger fish, and is, of course, a very dif ferent product from true isinglass (q.v.). In its adhesive powers it resembles hide glue, but it retains an offensive odor. The raw material of most glue-factories is chiefly composed of the waste from slaughter-houses and from leather manufactories—the trimmings of hides and bones, and scraps of leather or pieces of old leather which was cured by some other process than tanning. Glue, however, cannot be made from material in which the slightest trace of tannic acid remains.
The accompanying statistics regarding the manufacture of glue in the United States are taken from the United States Census of 1900: iso-sulphocyanate, and acid potassium sulphate. Another well-known glucoside is quercitrin, C.H.O., which occurs in the bark of the Quercus tinetoria and is used as a yellow dye. The glucoside convolculin which is found in jalap-roots, acts as a strong purgative. The tannins are glucosides of aromatic acids. Many of the glucosides have been reproduced artificial ly, and, their chemical constitution being fairly well known, have been distributed among the sev eral classes of carbon compounds to which they naturally belong. Those glucosides, however, whose constitution is as yet unknown, or but imperfectly known, are still generally grouped together.
GLUE (from OF. glu, bird-lime, from Lat. gins, glue; connected with Gk. 7Xotor, gloios, glue, Eng. clay). An inferior grade of gelatin, prepared, on account of its adhesive qualities, for use in the arts and industries, and particularly in the various branches of wood-working. A preparation of glue or other gelatinous material for glazing the surface of a textile fabric, paper, or other material is known as 'size' With the develop ment of the textile, paper, and allied industries, the use of glue as sizing has enormously in creased the demand for this article and its consequent commercial importance. The best glue-making material is the corium or true skin of the animal, that portion. lying beneath the epidermis and inner layer of fat, which is also used for the manufacture of leather. The glue extracted from the bones of animals is inferior in adhesive qualities. The softer bones of an ani The method of glue manufacture varies with the character of the material employed. In mak ing glue from hide, the scraps are first limed, to facilitate the removal of adhering hair, flesh, and fat, as in the manufacture of leather (q.v.). This
process requires from ten to forty days, after which the skins are washed and dried. Instead of lime, caustic soda or sulphurous acid is some times used for cleansing the glue stock. The pre pared stock is converted into glue by the appli cation of heat. By an older method, the pieces are placed in flat-bottomed copper boilers, which have a perforated false bottom placed a little above the true one, to prevent the burning of the materials. The whole is kept at a gentle boiling heat until the gelatinous part has boiled out, and the mass of the material has sunk down into the fluid. The boiler is at first filled with soft water for two-thirds of its depth. The boiling is sus tained until, by repeated trials of small quan tities, the operator knows the fluid to be of the right consistency, when it is drawn off to the congealing-boxes ; a fresh lot of material is often added to the residue left in the boiler, and the process is repeated. Recently, the use of steam, either indirectly in closed pipes or directly in perforated pipes, or else blown under high pressure directly into the closed vessel contain ing the mixture, has been found to expedite the process and improve the quality of the glue. After boiling, the glue is allowed to settle, or is strained through linen bags to free it from im purities. The waste thus recovered, consisting of fat, hair, and other matter, is utilized in the manufacture of fertilizers, while the glue itself is subjected to a process of drying. Drying is likely to prove a troublesome process, requiring great care, as the glue readily spoils at this stage. Until recently, drying was accomplished in the open air, but the more recent practice is to place the glue in specially prepared drying where the temperature and humidity can be carefully regulated. The glue is dried in shallow wooden molds. Thence it is removed to a smooth-topped table, whose surface has been moistened to prevent sticking, and here it is cut, by means of wires, into pieces of the desired shape and size. Fish glue is made by a similar process.
Bone glue is extracted by boiling the bones, which have been previously treated with a solu tion of hydrochloric acid, to remove the calcium phosphate. The powdered bones are kept in a solution of dilute hydrochloric acid for several days. They are then allowed to stand in lime water for a few hours, after which the gelatin is extracted by means of boiling water or steam, as in the preparation of hide glue. The calcium phosphate recovered from the bones is used as fertilizing material, and the fat is also utilized.
Liquid glue is prepared from a solution of dried glue by the action of nitric or acetic acid, which checks its tendency to gelatinize without diminishing its adhesive qualities. An excellent liquid glue may be made by mixing four parts of transparent gelatin, four parts of strong vinegar, one part of alcohol, and a small amount of alum.