ISINGLASS AND ITS SUBSTITUTES.
Isinglass is obtained from the air-bladder or sound, as it is sometimes
termed, of different kinds of fishes, especially of the sturgeon,
species _Acipenser_. It is used for culinary purposes, fining beer and
other liquids, for making court-plaster and stiffening silk, though a
good quality of gelatine is practically equal to it for these purposes.
A good quality of isinglass should be pure white, semi-transparent,
dry and horny in texture, and free from odor. It should dissolve in
water of 95° to 122° F., without leaving any residue, and, on cooling,
should yield an almost colorless jelly. From gelatine imitations it
is distinguished by soaking it in warm water and examining under
the microscope, when true isinglass will show a net-work of long,
curling fibres, while gelatine will be simply hyaline. Isinglass is
often imitated with the intestinal membranes of the calf and of the
sheep. This spurious article may be readily recognized because it does
not exhibit, like isinglass, a sort of shining appearance when held
before the eye and daylight, and because, although inodorous, it has
a saltish flavor. If it be torn asunder it will be observed that it
may be rent in all directions, while true isinglass cannot be divided
otherwise than in the direction of its fibres. If a piece of artificial
isinglass be macerated in water it swells, but instead of retaining
its shape as is the case with the genuine article, it becomes divided
into several pieces, forming a sort of curdy precipitate; and if
treated with boiling water, about one-third of its weight is left in an
insoluble state, and the liquor does not form a good jelly. Isinglass
is frequently adulterated with gelatine, which is inserted between the
leaves and rolled up with it. The best indication of this adulteration
is the amount of ash; isinglass yields only 0.9 per cent., while
gelatine yields 4 per cent., and adulterated isinglass 1.5 per cent. or
more.
1. _Russian isinglass._ Russia produces the best and most isinglass.
It is chiefly obtained from several varieties of sturgeon, species
_Acipenser_, which inhabit the Caspian and Black Seas, and their
tributary rivers. The _Acipenser Gueldenstaedtii_, Br. yields the
finest, best and whitest isinglass. It is known by the name of
_Patriarch_, and consists of small horseshoe-shaped pieces rolled
tightly together. It is quite scarce and expensive. When the bladder is
merely dried in sheets, it constitutes _leaf isinglass_. When several
bladders are put together and folded before they are completely dry,
they form _book isinglass_. Each bladder may also be rolled up and
folded around a few pegs in the form of a horseshoe, heart, or lyre, in
which shape it is dried. The latter is the _staple isinglass_, which,
according to its dimensions, is again divided into _long and short
staple_.
Long staple isinglass of fine quality is produced in the Oural. It is
imported in loose leaves, and at times it is twisted like ropes, this
kind being preferred, as it is inferior in quality only to Patriarch.
_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.
_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.
_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.