Brazilian isinglass comes in the form of pipe, lump and honeycomb. On account of its dark color it is not in much demand for ordinary use, but is frequently employed in England for clarifying glue. When digested in water it leaves much insoluble substance behind, being in this respect also inferior to Russian isinglass.
6. German Isinglass. Under this name we may mention the mucous membrane of the sturgeon (Acipenser sturio), prepared in Hamburg. When boiled with water it leaves 16 per cent. of insoluble substance.
It is said that an excellent isinglass can be made from the scales of shad and herring, which are first freed from their silvery coating. This may furnish a useful hint to persons who are near some of the great fishery establishments of the country, at Gloucester, N. J., and Alexandria, Va., for instance, where thousands of shad are scaled and salted every year.
To give inferior qualities of isinglass a better appearance and make them more salable, they are frequently bleached with sulphurous acid.
Ichthyocolle Française. Under this name, Rohan has introduced a substitute for isinglass. The material used for its manufacture is blood fibrin, which, after washing in running water, is thoroughly kneaded and, after draining, digested at 59° F. with dilute sulphuric acid of 8° to 10° Bé. for eight days, after which the mass is freed from acid by washing in running water.
The fibrin freed from acid becomes transparent and gelatinous by treating with weak soda lye of 3° to 4° Bé. at 59° F., whereby it swells up and increases hourly in volume. After twenty-four hours it is taken from the soda lye, and after removing the free soda by washing, heated to 212° F, in a water-bath. The fibrin dissolves and becomes so thinly fluid that it can be filtered. 75 to 80 per cent. of the water is then evaporated, and the fibrin thus prepared can be used as a substitute for isinglass for fining purposes. Ichthyocolla swells more quickly in cold water than isinglass; 15 to 20 per cent. divided in water forms a thickly fluid substance, which on heating dissolves to a perfectly clear fluid. For fining beer with ichthyocolla add 2 to 10 per cent. of pure tannin, which does not injure its power of dissolving.
Isinglassine. Under this name is known an isinglass substitute prepared from the gelatinous material from calves’ feet and other sources. The material is reduced by machinery to a pliable homogeneous mass, rolled out into sheets, dried, pressed and shredded.
Chinese isinglass is identical with the Japanese Agar-Agar, and is obtained by cleansing and boiling certain species of algae found in Chinese and Japanese waters. This isinglass, or gelatine, possesses the following properties:
Placed in cold water it softens without dissolving like gelatine, and forms a structureless tubular mass which is not sticky. By boiling, it dissolves more readily than isinglass, but with greater difficulty than gelatine. A 1 to 2 per cent. solution is easily filtered through paper or linen, and when cold forms a solid jelly clear as water and without taste or odor. Jelly prepared with one-half per cent. of Chinese gelatine is more solid than one prepared with 4 per cent. of French white gelatine, retains its consistency longer, and will stand a temperature of 86° to 122° F. before becoming liquid. Used for jellies, or mixed with other foods, it does not impart to them a glue taste never wanting in bone gelatine. When decomposed by long standing, it does not acquire a disagreeable odor, while decomposed isinglass or gelatine exhales a putrid smell.
Agar-Agar contains, according to analyses: Cellulose, starch, gum, dextrine, vegetable mucus, vegetable wax, resin, chlorophyll, albumen, a peculiar acid, and several mineral substances.