a variety of gelatine, sometimes called ichthyocolla, or fish-glue (from ἰχθύς, a fish, and κόλλα, glue), prepared from the air-bag, swimming-bladder, or sound of various fishes. The Russian and Siberian isinglass is most esteemed; it is chiefly obtained from sturgeons, a family of cartilaginous fishes of the genus Acipenser. The swimming-bladder is cut up, washed, and then exposed to the air, with the inner silvery membrane upwards. When dry, this membrane is removed by beating and rubbing; the sound is then prepared in various ways. For forming what is called leaf isinglass it is merely dried; for long and short staple, it is twisted between three pegs into the shape of a horse-shoe, harp, or lyre; for book isinglass, it is folded like the sheets of a book; for ribbon isinglass, it is rolled out. The swimming-bladder of A. sturio of the Caspian Sea furnishes leaf isinglass of three qualities, known as fine-firsts, firsts, and seconds. A. gueldenstadtei of the Caspian and Black Seas and their tributary rivers, furnishes cercare from its roe or ovary, whilst the swimming-bladder yields staple and leaf isinglass. The varieties of staple are Patriarch Astrakhan, and Astrakhan firsts, seconds, and thirds. The varieties of leaf are also firsts, seconds, and thirds,—the firsts forming the finest leaf known in commerce. A. rufinus and A. stellatus also yield isinglass. There is a kind known as Samoey leaf, from Tanganrood, but this is inferior; there is also the siame leaf, said to be obtained from a small fish, and kroka isinglass, which is made into small membranous disks. Isinglass is also procured from Silurus glanis. For purse, pipe, and lump isinglass, the swimming-bladder is dried unopened, and the variety known as Siberian purse, of moderately good quality, is greatly in demand.

Brazilian isinglass is obtained from Para and Maranhao, but the fishes which produce it have not been named. For the variety known as pipe-Brazil, the swimming-bladders are dried unopened, and made into pipes 10 or 12 inches long, and from 2 to 2½ inches broad, and are sometimes distended with air. Lump isinglass is formed by placing two swimming-bladders side by side, and for honey-comb isinglass, the largest lump isinglass is split open. There are also varieties of isinglass from New York, from Hudson's Bay, and from the East Indies. In Moldavia a variety is prepared from the skin, stomach, intestines, and swimming-bladder of the sturgeon. These are cut small, steeped in cold water, and simmered. The jelly thus produced is spread out into thin layers, and dried into a kind of parchment, which, on being softened with water, is rolled into cylinders, or extended into plates, and forms an inferior isinglass. Cod sounds are also used for a similar purpose. The patent gelatine prepared from glue-pieces or cuttings of hides, &c., after the manner of glue, is also used as a substitute for isinglass. A solid gelatine in thin plates and strings, is prepared from bones, and is chiefly of French manufacture.

Isinglass is prepared for sale by being picked and cut. This was formerly done by hand, but is now effected by steam machinery; the thin filaments thus produced should be whitish in colour, dry, semitransparent, nearly tasteless, and quite devoid of smell. Isinglass differs from glue, in being tough, fibrous, and elastic, instead of brittle. On boiling, it should completely dissolve, and on cooling, should form a white jelly, soluble in weak acids, but separable from them by alkalies. With milk and sugar it is used as a diet for invalids, and it is also used in the preparation of blancmange, jellies, and creams, and for enriching soups, and sauces. For the reasons given under Gelatine, isinglass is no longer considered to be highly nutritive; it is even less digestible than the flesh or muscular part of animals. The great consumer of isinglass is the brewer, who uses it as a fining material, for which purpose lump isinglass is chiefly used. This is deeper in colour, and inferior in solubility to the better varieties. On mixing it with the liquor to be fined, it partly combines with some of those matters which render the liquor cloudy, and entangles in its meshes those which are mechanically suspended, the whole then rising to the surface can be removed, and the liquor be left clear. Wine, coffee, and other liquids are also clarified by isinglass, but sole-skins and hartshorn shavings are often used as substitutes for it. Isinglass forms the adhesive material in court-plaster, for which purpose a solution of isinglass, mixed with tincture of benzoin, is brushed over black sarsenet. Isinglass dissolved in spirits of wine or common gin, and gently simmered by placing the bottle in a vessel of boiling water for about an hour, forms diamond cement, or white field-glass; gum ammoniac is sometimes added. Panes of isinglass, instead of glue, are used in France instead of horn, for lanterns, and also for lamp-shades, &c.

ISIS. See EGYPT.