Quantitative Analysis of Tannin.

Practical Magazine 19, 1876

(Chemistry applied to the Arts, Manufactures, &c.
Dyeing, Calico Printing, Bleaching, Tanning, and Allied Subjects.)

M. A. CARPENI proposed in 1875 to make a quantitative analysis of the tannic acid in wines and other substances which contain tannin, by means of acetate of zinc dissolved in an excess of ammoniac. This method does not always give constant results, and hence M. Barbieri has sought to modify it thus:

To the solution containing tannic acid is added an excess of an ammoniacal solution of acetate of zinc. The liquor is heated to boiling with the precipitate obtained, and is evaporated to nearly a third of its volume. After cooling it is filtered, the precipitate being washed in boiling water, and dissolved in diluted sulphuric acid. Some insoluble substances are separated by the filter, and the filtrated liquor is quantitatively analyzed with chameleon mineral or manganiate of potash. The precipitated tannic acid remains adhering to the glass. It is washed by decanting to detach it, and the solution is transferred with the sulphuric acid into a precipitation vessel.

The results are satisfactory and consistent with each other. An extract of chestnut treated by Hammer's method gave 48,9 per cent, of tannin, by Barbieri's it gave 49,6.

Technologiste, May 20, 1876.

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