Livro The Tannins; A Monograph on the History, Preparation, Properties, Methods of Estimation, and Uses of the Vegetable Astringents, with an Index to the Literature of the Subject Volume 2

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PREPARATION AND PURIFICATION OP THE OAK TANNINS. The first attempts at preparing a pure oak tannin were the application of the lead acetate process; that is, by extracting with water, and then precipitating the infusion with lead acetate in fractions, in which the middle portion was assumed to be pure.

This precipitate was decomposed by hydrogen sulphide, and the filtrate from lead sulphide, after agitation with ether, was evaporated to dryness. This was about the process of E c k e r t, Gr r a b o w- s k i, and 0 s e r.

Later, Johanson tried, besides this method, one in which he exhausted the bark with 85 per cent. alcohol, but concluded that the latter had no advantages as a solvent because it extracted so much resin along with the tannin.

In 1880, Et1 i resorted to a very dilute alcohol as a solvent, but extracted the tannin from the solution by agitating with acetic ether instead of precipitating with lead acetate.

Lowe about the same time employed 90 per cent. alcohol as the menstruum for extracting, and then removed the solvent by distillation under reduced pressure. The residue he poured into eight or ten volumes of water and allowed to stand.

The clear supernatant liquid he separated and saturated with common salt. This treatment separated anhydrides, which were removed by filtration, and the clear filtered liquid was then agitated with ether to remove resinous compounds and decomposition products.

After separation of ether the residual liquid was agitated with acetic ether, which removed the tannin. Experiments have also been made with commercial ether as a solvent. This consists of about three parts ether, one part alcohol, and a little water.

In addition to its slow solvent action, this menstruum is expensive, unless a substance contains ov..

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Autor(es)
EditoraRarebooksclub.com
IdiomaInglês
ISBN0217641849 9780217641845
FormatoCapa comum
Páginas28
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