This test method is used to determine the proportion of the total solids which are soluble solids and that proportion which are insoluble solids in a solution of tannin extract or in the water extract from raw or spent materials prepared for tannin analysis.

The specimens are aliquots from the analytical solutions prepared from tannin extracts or the water extract solutions prepared from raw or spent materials.

The soluble solids are defined as the portion of the total solids which are dissolved in the water and pass through a filter prepared by depositing a layer of Kaolin paste onto a standard filter paper.

The insolubles are defined as the portion of the total solids which do not pass through the standard filter paper prepared with the layer of Kaolin paste.

The results of this test method are dependent on a great many variables but particularly upon:

5.5.1 The temperature conditions under which the solutions were prepared and stored and the temperature at which the current analysis is performed;

5.5.2 The uniformity and consistency of the Kaolin paste layer deposited onto the filter paper;

5.5.3 The rate of solution run-out from the pipette; etc. It is, therefore, essential that the method be followed exactly in order to obtain reproducible results both among specimens within a laboratory and for analyses between laboratories.