Irish moss (Chondrus crispus) which grows on rocks of the American and European shores of the Atlantic Ocean, yields a jelly which has been employed as a substitute for isinglass, as a size, for thickening colors in calico printing, and in stiffening silk. In a fresh or softened state the plant is cartilaginous, of a brownish or purple, or frequently yellow or green color. After washing in water and drying in the sun it turns whitish or yellowish, and becomes somewhat translucent and of a horny appearance. It has a slight seaweed-like odor and a mucilaginous, somewhat saline taste. One part of it boiled with 20 parts of water gelatinizes on cooling.
Fish Glue.
This product, which is prepared in many localities from fishes, must not be confounded with isinglass, though the purer varieties may serve as substitutes for the latter or for gelatine.
Jennings gives the following process for the preparation of fish glue. The fishes are treated with dilute sulphuric acid until the skin can be detached. The acid water is then drained off and replaced by milk of lime to neutralize adhering sulphuric acid as well as to saponify the fat. The milk of lime is several times drained off and renewed, the mass thoroughly washed, cut up in a hollander and treated cold with solution of sodium hyposulphite, common salt and alum. After a few days the liquor is drawn off and replaced by a mixture of alum solution, dilute sulphuric acid and nitric acid in which the mass is allowed to remain for a few days. Fishes with dark skins are treated with a mixture of hydrochloric and sulphuric acids. After washing, the skin is removed and the fibres which have become detached from the bones are separated by digestion in dilute solution of mercuric chloride and alum. Adhering fatty parts are removed with warm milk of lime, the lime is neutralized with hydrochloric acid, and the mass boiled with water for the formation of glue. The resulting glue-liquor is clarified with sulphurous acid and alum, and when all the impurities have subsided, compounded with acid sodium carbonate till all the acid is neutralized. The finished solution is concentrated so that it gelatinizes on cooling and can be cut in cakes which are dried in the usual manner.
Fish scales, especially those of carps, are treated in a similar manner. The bone-earth is extracted with hydrochloric acid, the extracted material thoroughly washed, and then boiled in soft water till it can be readily stirred. The liquor is drawn off from the horny sediment, clarified with alum, evaporated, and after all the impurities have subsided, poured into moulds and treated like ordinary glue.
Considerable quantities of fish glue are produced on the Norwegian coast from waste obtained in the preparation of codfish. The fish when caught are cut open and the air-bladders removed, which are dried and brought into commerce as isinglass. The head is then cut off and the bones detached in one piece. The flesh is dried in the air, and forms the codfish of commerce. The heads and bones are first treated with hydrochloric acid or directly boiled under slight pressure in water, and the resulting liquor concentrated so that it will gelatinize.
A substitute for isinglass, also for gelatine and glue, is prepared by C. A. Sahlströhm, of Stockholm, according to his patent, from fish and fish waste by treatment with bleaching powder, potassium permanganate, and nitrous and sulphurous gases.
For this purpose the fishes, or portions of fishes, are first well washed in fresh water and then left for from three to four hours in a solution of bleaching powder (in the proportion of 2 lbs. of bleaching powder to 300 quarts of water). After washing they are treated for about 30 minutes with a solution of potassium permanganate (in the proportion of 1¾ ozs. of potassium permanganate to 250 or 300 quarts of water), and then exposed to the action of the nitrous gas, produced by heating 10 to 15 ozs. of nitric acid for every 88 lbs. of raw material. This gas may be first absorbed by water, as in the manufacture of sugar, or sulphur dioxide may be used instead of nitrous gas. The former would be obtained by burning about 7 ozs. of sulphur for every 88 lbs. of raw material.
The material, after this treatment, is washed. Those portions intended for the production of isinglass substitute are freed from their outer skins and dried and pressed at a gentle heat. The portions destined to produce gelatine or glue are, on the contrary, exposed to a temperature of from 104° to 122° F. for from ten to twelve hours, by which the material is mainly dissolved. The mass is then forced through a strainer or sieve, and the liquor allowed to gelatinize by standing for some hours. The jelly is finally dried, as is usual in the manufacture of glue or gelatine.
Whale glue is, according to Culmann, obtained in the Russian island Jeretike from the liquor remaining in the boilers after the extraction of the oil by means of superheated steam. By reason of the raw and moist atmosphere which prevails in that locality, even in summer, drying the glue is not practicable, and for this reason it is brought into commerce in the form of a compact jelly mixed with a preservative and packed in tin boxes. The commercial article contains 41.65 per cent. water. It is liquefied by placing the can in boiling water, and melts at 176° F. As shown by mechanical tests, it possesses great tenacity, and two pieces of wood glued together lengthwise cannot be separated at the joint but break alongside of it.