Abstract: Hide powder method is the international standard for determining tannin extracts in vegetable tannin, and the computational formula was presented as X₅=(1.2×20(m₃-m₄)+0.075)/(m₀(1-X₂))×100. In this paper, the formula was investigated for its influence on the final results with kaolin as experimental materials. The experiments indicated that the error was significantly influenced by the blank residuals of hide powder, and the fixed factor 0.075 g/L in the formula could not reduce the error. The quantity of soluble substance in the kaolin still had effect on the test results. Based on the parameter interval estimation method and subjunctive method, the new factor- g/L was obtained and the computational formula was changed to X₅=(1.2×20(m₃-m₄)+20 m₄)/(m₀(1-X₂))×100 for the non-tannins test in vegetable extracts. A series of test results presented the error was greatly reduced due to the correction coefficient for residuals of blank hide powder and soluble substance in kaolin.

Key words: hide powder, test, non-tannins, tannins, vegetable extracts, leather making