sounds of cod-fish, or ling; or, indeed, from any other fish: and also from the skins of soles.
The best isinglass is nearly all gelatine, and contains ninety-eight parts in every 100 which are soluble in boiling water. Isinglass varies in price from 1s. 6d. to 16s. per lb. There are various modes of ascertaining its value: and we extract two modes from a paper on the subject by Mr. S. Roberts, in Dr. R. D. Thomson's Records of Science, No. 14., pp. 106, 107.[deeplink needed]
“A great variety of isinglass is offered for sale, at a range of prices from 3s. to 16s. per pound; and the relative value of each kind may be known by the following tests:—
“In the first place, isinglass should remain unchanged, by being steeped in spirit of wine or alcohol, from 50° to 60° over proof, in which gelatine (the chemical principle of isinglass) is insoluble. The alcohol, or spirit of wine, in which the isinglass has been steeped, should then be tried with a few drops of tincture of galls; if the liquor remain clear and unchanged, it is much in favour of the character of the isinglass. If, on the other hand, the tincture of galls causes a precipitate from the alcoholic liquor, the isinglass is not pure, as it contains something more than pure gelatine.
“Different samples of isinglass, which have remained unchanged in alcohol or spirit of wine,
should also be tried by the two following methods,
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