(Acipenser _Huso & Ruthenus_. _The great and small Sturgeon._)
_Isinglass._ _Fish Glue._
The following kinds, imported from St. Petersburg, are found in the
market. _Short Staple_; _Long Staple_; _Book_; and _Leaf_. _Picking the
Staple_, as it is called, is a peculiar art practised by persons in this
town, who gain a very good livelihood by it; they engage to return the
same weight of isinglass in shreds, as they receive in _Staple_; this in
itself secures very fair profit, for by damping the isinglass in order
to pick it, it gains considerable weight; these persons moreover are in
the habit of adulterating it with pieces of bladder, and the dried skin
of soles; such frauds however are easily detected by their insolubility,
for pure isinglass will dissolve entirely, and yield a clear and
transparent jelly; a single grain will produce, with an ounce of water,
a solution of considerable thickness; it is also soluble in acids and
alkalies; and although insoluble in alcohol, yet it is not precipitated
by it from its watery solutions, unless when added in a very
considerable quantity; it is coagulated by the infusions and decoctions
of vegetable astringents; _carbonate of potass_ likewise throws down a
precipitate. 100 parts of good isinglass consist of 98 of gelatine, and
2 of the phosphates of soda and lime. Its solutions soon putrefy. USES.
It is now rarely used except as a nutrient; its mechanical application
in fining wines and turbid liquors is well known, and its mode of
operation is equally obvious, for by forming a skin, or fine network,
which gradually precipitates, it acts just like a filtre, with this
difference, that in this case the filtre passes through the liquor,
instead of the liquor through the filtre.