Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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stiasny test

A chemical test designed to determine the type of vegetable tanning agent used in tanning a leather. It consists of boiling the specimen in a solution of formaldehyde and hydrochloric acid, which causes any condensed tannins present to be completely precipitated. while any pyrogallol tans remain in solution. The test solution is obtained by extracting a fragment of the sample (a piece 4 by 4 mm) by refluxing, for 4 hours, first in a 50% aqueous solution and then equal volumes of 6N hydrochloric acid, acetone and water.

Even under the best of conditions this test is difficult to use. Since most vegetable tannins contain both pyrogallol and condensed tannins, it is frequently impossible to judge the colors and precipitates with any degree of certainty. Usually more information of a qualitative nature can be obtained by paper chromatographic separation of the tannin constituents. (291 )




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