Siberian purse isinglass is of moderately good quality and is in general demand. A small kind of strings in a necklace form is sometimes imported.
A very good sort of Russian isinglass comes into commerce in leaves and books, and is known by the name of Samovey leaf. It is obtained, according to the statements of Russian merchants, from the common sheath-fish (Siluris Glanis). The pieces are as large as a hand, of the thickness of pasteboard, very solid, not very flexible and of a white-yellowish color. It is inferior in quality to Astrakhan isinglass, which is one of the best kinds.
In Russia the isinglass is generally prepared by boys under the supervision of elder experts. The swimming bladder is first placed in water and left there for some days with frequent changes of the water and removal of all fatty and bloody particles. The warmer the water the more rapidly the operation is completed. The bladders are finally removed and cut longitudinally into sheets which are exposed to the sun and air, being laid out to dry, with the outer face turned down, upon boards of linden or bass wood. The inner face is pure isinglass, which, when well dried, can with care be removed from the external lamellæ. The finer sheets thus obtained are placed between cloths to protect them from the flies, and are then subjected to a heavy pressure so as to flatten them out and render them uniform. After this they are assorted and tied up in packages. The packages composed of the isinglass of the large sturgeon usually contain from ten to fifteen sheets and weigh a pound and a quarter; those of the other contain twenty-five sheets weighing a pound. Eighty of these packages are usually sewed up in a cloth bag, or sometimes inclosed in sheet lead.
The outer lamellæ of the air-bladder, after the isinglass has been removed, also contain a considerable quantity of glue which, when softened in water, is scraped off with a knife and moulded into little tablets of about the size of a silver dollar, and then dried.
2. North American or New York Isinglass. It is in thin strips several feet long but ½ to 1½ inch wide. It is less soluble than Russian isinglass, and yields frequently a dark-colored solution. It is prepared, according to Dr. J. V. C. Smith’s statements, from the air-bladder of the common hake (Gadus merluccius), which is macerated in water for a short time, cut open and subjected to pressure between iron rollers, by which it is elongated to the extent of half a yard or more. It is then carefully dried, packed and sent to market. The air-bladder of the common cod (Gadus morrhua) is prepared in a similar manner, but yields a poorer kind of isinglass.
3. East India Isinglass. It would seem that for a long time this has been exported from Calcutta to China, but has only lately attracted the attention of European dealers. It is prepared from the air-bladder of the Polynemus plebejus, and comes into commerce either in the form of leaves or purses which seem to consist of the unopened air-bladder. East Indian isinglass has a disagreeable fish odor, due very likely to careless preparation, which makes its use impossible for many purposes, and, of course, depreciates its commercial value. The oval-oblong purses are about nine inches long, three and a half inches wide, weigh about 7 ozs. and have a dark-yellow color. East India leaf isinglass, i. e., the opened and dried air-bladder, consists of yellowish-colored leaves eight to nine inches long, six to seven inches wide, and about three-tenths of an inch thick. The leaves are sometimes rolled out into long ribbons about one-tenth of an inch thick, the surface of which is covered in places with a thin film of lime.
What is known as picked East India isinglass is brought into commerce in small shreds about two to three inches long, and tapering at the extremities.
A variety of isinglass very white and pure and scarcely inferior to Samovey leaf is brought from Manila. The fish which yields it is caught on the coast of the Philippine Islands, especially at Luzon.
4. Hudson Bay Isinglass. It is brought into commerce in the purse form. Some specimens measure twelve inches in length and three and a half inches in diameter, and weigh one and a half ounces. It is of light-yellow color, nearly transparent, without odor or taste. The inner lining of the sac, which can be readily stripped off, is insoluble in water, while the remaining portion dissolves to a slightly colored jelly. We have been unable to ascertain from what species of fish this isinglass is procured.
5. Brazilian Isinglass. This is imported from Para and Maranham, and is also called Cayenne isinglass. For a long time there existed a doubt from what species of fish this isinglass was procured, but it is now settled that it is prepared from the air-bladder of Silurus Parkerii, a fish which is frequently found in the muddy waters of the rivers in the province of Grao Para, where these waters mingle with the sea.