"The swimming-bladder of Acipenser Huso, Linné, and of other species of Acipenser"—(U. S. P).
Class: Pisces. Order: Sturiones.
Source and History.—Isinglass is an almost pure gelatin, being usually procured from the air-bags, sounds, or swimming-bladders of various fishes, chief among which are those furnishing Russian isinglass. These are mainly the belugo (Acipenser Huso, Linné), the sterlet (Acipenser ruthenus, Linné), the osseter (Acipenser Güldenstädti, Ratzeburg), and the sewruga, or starred sturgeon (Acipenser stellatus, Pallas). These sounds are membranous sacs situated under the spine, in the middle of the back, and above the center of gravity. In most fishes they connect with the stomach or oesophagus by the pneumatic duct; these sacs are filled with air, containing about 80 per cent of oxygen, and are composed of a firm, silvery external coat, and two thin and delicate internal coats. The sounds are removed from the fish, cut open, carefully washed, and then exposed to the air to dry; then, after being dampened to soften them, they are made into rolls about half an inch in diameter, and folded between three pegs, into the shape of a horseshoe, heart, or lyre (long and short staple), or folded in the manner book-binders fold printed sheets of paper (book isinglass), or dried in single sheets (sheet isinglass). When the sound is rolled out it is termed ribbon isinglass. The internal membrane of the sounds is thin and insoluble. Sometimes isinglass is reduced to small shreds, when it will be scarcely possible for the eye to distinguish the inferior from the finer kinds; the latter may be known by their whiteness, freedom from unpleasant fishy odor, solubility in water, and translucency of the jelly obtained on cooling from its hot solution. The above are the best forms; the sheet isinglass is superior to any; an ounce of water will dissolve 10 grains of it, leaving hardly any insoluble matter, and furnishing an excellent jelly.
There are other kinds of an inferior character, as the cake isinglass, which is in cakes or round pieces, having an unpleasant smell, and a tawny color, and which is principally used by artists. The Samovey isinglass is prepared in Russia from the Silurus glanis, but it is not so pure as those named above. Isinglass is also made in the eastern states, in this country, from the sounds of the hake (Gadus merluccius, Linné., and cod (Gadus Morrhua Linné, or Morrhua americana) and other fishes. It is in long, flat pieces, known as ribbon isinglass, is very pure, being almost wholly soluble in water, but its piscatory flavor is an objection to its use for domestic or pharmaceutical purposes. A very inferior isinglass is prepared in Brazil from the sounds of fish (lump isinglass and honey-comb isinglass), and in the East Indies (purses and leaves, P.) (Amer. Jour. Pharm., Vol. XVIII, p. 54). A variety of fish glue, apparently procured from the natatory bladder of the yellow sturgeon, but unfit for pharmaceutical purposes, has been met with in commerce in France. It swells up in water and is only partially dissolved. Isinglass prepared from the air-bags of large fishes, when unopened, is known as pipe or purse isinglass.
When American isinglass, in solution, is thinly spread on cotton cloth, previously oiled and dried, it forms a very pure article, in clear, delicate laminae, but having a piscatory smell, and is known as "transparent or refined glass." The so-called Chinese or Japanese isinglass is the vegetable product of certain algae (see Agar Agar).
Description and Chemical Composition.—"In separate sheets, sometimes rolled, of a horny or pearly appearance; whitish or yellowish, semi-transparent, iridescent, inodorous, insipid; almost entirely soluble in boiling water and in boiling diluted alcohol. A solution of isinglass in 24 parts of boiling water forms, on cooling, a transparent jelly"—(U. S. P.).
Isinglass is sometimes kept in thin, very fine cuttings, in which form it is more readily dissolved by boiling water. Isinglass is chiefly a very pure gelatin—that known as glutin (see Gelatin). The best kinds are white, transparent, glistening, odorless and tasteless; the poorer varieties are colored, opaque, and have either a fishy taste or smell. It is soluble in weak acidulous and alkaline liquids, and in water at 100° C. (212° F.), forming with the latter, when strained and cooled, a pure animal jelly. It is not dissolved by alcohol, ether, nor by water at 15.5° C. (60° F.), but with this latter it expands and becomes soft. Tannic acid added to its solution occasions a tough, gelatinous precipitate, tannate of gelatin. When boiled with caustic potash, or with concentrated mineral acids, it is decomposed, forming sugar of gelatin or glycocoll (amido-acetic acid), C2H3(NH2)O2, which is in large transparent crystals, very sweet, soluble in water, and forming beautifully crystallized salts with acids. John found 100 parts of the purest isinglass to consist of 70 parts of gelatin, 16 of osmazome,* 2.5 of membrane insoluble in boiling water, 4 of free organic acid salts of potassium, sodium and phosphate of calcium, and 7 parts of moisture. Mr. R. Baird (Amer. Jour. Pharm., 1888, p. 608) found the ash in three samples of Russian isinglass to vary from 0.4 to 0.6 per cent, while in two specimens of American isinglass the ash amounted to 2.17 and 2.40 per cent. Prof. W. T. Wenzell (Amer. Jour. Pharm., 1894, p. 447) recommends the use of American isinglass for the quantitative determination of tannin, in place of the hide-powder usually employed.
(* Osmazome, according to Gmelin (Handbook of Chemistry, translated by Watts, London, 1871, Vol. XXVIII, p. 271), was obtained by Thénard by exhausting flesh with water, evaporating the extract, treating the residue with alcohol, and evaporating the alcoholic liquid.)
Action, Medical Uses, and Dosage.—Isinglass is seldom used in medicine, except as a nutritive. It is used as a diet, in the form of jelly, or added to other jellies, to give them a tremulous appearance. It has proved very useful for scrofulous and consumptive patients. Ɣ I have used the following preparation in incontinence of urine, both in children and adults, in many instances, and have found it a useful as well as agreeable remedy, proving serviceable when other means had failed: Take of isinglass (long staple), 1 roll; boil it in 1 pint of water till it is dissolved, then strain, add 1 pint of sweet milk, put it again over the fire, and remove it just as ebullition commences; then sweeten with loaf sugar, and grate nutmeg upon it. When made it very much resembles custard. Of this, a tumblerful may be taken 3 or 4 times a day by an adult (K.). Isinglass is employed in the arts for various purposes, for clarifying or fining wines, beer, coffee, syrups, etc., and is a constituent of court-plaster. Three drachms form a proper jelly with a pint of water.
Cements.—An excellent, cement, called ARMENIAN or DIAMOND CEMENT, is made with isinglass, which is valuable for mending glass, china, and porcelain vessels, which are not to be exposed to heat and moisture. It is made by sprinkling water upon 2 drachms of isinglass, allowing it to stand until softened, then adding as much proof-spirit as will rather more than cover it, then dissolving with a moderate heat. Have previously prepared, a solution made by dissolving 1 drachm of gum mastic in 2 or 3 fluid drachms of alcohol. Mix the two solutions, and stir in 1 drachm of gum ammoniacum, previously reduced to a fine powder, and rubbed down with a little water. Evaporate, if necessary, on a water-bath to a proper consistence. Keep the cement thus prepared in a vial. When required for use plunge the bottle in warm water, and keep it there until the cement becomes fluid; then apply it with a stick or small hard brush to the edges of the broken vessel, previously warmed. Compress the pieces firmly together until cold, taking care to make the contact perfect, and using a very thin layer of cement. When properly applied, the cement is almost, if not quite, as strong as the glass or china itself.
A cement for stoneware may be made by softening gelatin in cold water, warming and adding recently slaked lime enough to render the mass sufficiently thick for the purpose. A thin coating of this cement is to be spread while warm over the gently heated surfaces of fracture of the articles, and dried under strong pressure.