Isinglass, as it is generally called fish glue, is prepared from the air-bladders of the sturgeon. It is found in commerce under various forms, such as large strings, small strings, and leaves. It is always white, semi-transparent, dry, fibrous, horny, of a faint odor and insipid taste. When a very thin leaf is moved between the eye and the light of the sun, a species of chatoyance is perceived. If macerated in cold water, Isinglass swells and softens; if boiled in water, it dissolves almost without any residue and forms a solution, which, on becoming cool produces a semi-transparent jelly. There are several counterfeits, but all are easily detected.
Papier-Mache.--Pulped paper moulded into forms. It possesses great strength and is a valuable article in the manufacturing of cases for Daguerreotypes. It may be rendered partially water-proof by the addition of sulphate of iron, quicklime, and glue, or white of eggs, to the pulp; and incumbustible by the addition of borax and phosphate of soda. The papier-mache Daguerreotype cases, tea-trays, waiters, snuff-boxes, &c., are prepared by pasting or glueing sheets of paper together, and submitting them to powerful pressure, by which the composition acquires the hardness of a board when dry. Such articles are often inlaid with mother of pearl, and japanned, and are then perfectly water-proof.
Chloride of Calcium.--This is so easily manufactured that any Daguerreotypist can make it with but little difficulty. Saturate dilated muriatic acid, say three pints of water to one of acid; this should be filtered through a sponge and then allowed to stand until all the aquus solution has evaporated and the calcium crystallized. This may be improved by it being placed in a crucible; and fused with a quick fire, then poured out on a flat stone. When cold, it should be broken and put in close bottles. This is much used by Daguerreotypists as it possesses a strong affinity for water; consequently, it is a valuable auxiliary in keeping the iodine dry. It is also much used for drying gases and absorbing water from ethereal and oily liquids, in organic analyses.
Muriate of Ammonia--_sal-ammoniac._--This is used by _few_ to bleach Daguerreotype impressions, and relieve them of the "_blues_;" should, however, the plates be _well_ cleaned and the mercury at a proper temperature, there will be no need of this preparation: yet, as a number have requested, we give the following combination, knowing that all Daguerreotypists are troubled more or less with solarized impressions, they may be more particularly with the _blues_. Make a saturated solution of muriate of ammonia, in pure water, and filter through paper. This reduced with an equal quantity of water before used; when the linen or any portion of the impression is badly solarized, after removing the coating with the hyposulphite solution, thoroughly rinse the plate with water, then pour the bleaching solution over the surface of the impression in the same manner as in gilding.