This test method is used to determine the moisture content of materials (raw or spent) that are to be extracted for tannin analysis. The value obtained for moisture content by this test method is used to calculate the results of the other analyses on this material to a moisture-free basis.

The specimens are obtained from the material prepared for extraction in Practice D 6405.

Tanning materials contain moisture in varying amounts, depending both on the nature of the material and on the climatic conditions, therefore sampling must be carried out as quickly as is consistent with thoroughness in order to avoid changes in moisture content.

Negative errors may occur in the moisture determination because under the conditions of this method there may be retention of moisture by certain components (for example, hydrated salts or water bound to organic structures) of the raw or spent material or because of oxidation of other components (for example, tannins) of the raw or spent material.

Positive errors may occur in the moisture determination because under the conditions of this test method there may be volatilization of certain components of the raw or spent material other than water.

It is known that other factors can also affect the quantity of volatile matter (moisture) released by the specimen. These factors include but are not limited to: particle size of the test specimen, quantity of test specimen, oven temperature, exposure time in the oven, shape of the specimen container, and type of oven (for example, gravity or mechanical convection) used.

Because of the possibility of unknown errors in this test method it is essential that the method be followed exactly in order to obtain reproducible results both among specimens within a laboratory and for analyses between laboratories.