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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