Allen, A. H. Nearly all the methods worthy of detailed description are based on the precipitation of tannin by gelatin or its absorption by a gelatinous substance. Many of the methods appear very simple, but in practice offer very considerable difficulties, especially when gallic acid is present. Commercial Organic Analysis, vol. in, Pt. 1, 109.

Allen, A. H. This writer states that a German commission recommends, in permanganate titrations, the addition of the solution 1 cc at a time instead of drop by drop. The results of the "1 cc method" differ considerably from those obtained by the "drop method." The latter method was employed by Neubauer and Oser in determining the reduction coefficients; hence Allen recommends it. At the reference cited, Procter points out the source of error in the " 1 cc method." Op. cit., page 116.

Allen, A. H. A method for tea assay based on the precipitation of tannin from a hot solution by a standard solution of lead acetate, employing ammoniacal ferricyanide in ascertaining the end reaction.

Chem. News, 29, 189; also Allen's Commercial Organic Analysis, vol. III, Pt. i, 123.

Barbieri, J. Essentially the method of Carpene (vide Carpene, A., Ding, polytec. Journ., 216,452); Ber. d. chem. Ges., 9,78; also Zeitsch. f. anal. Chem., 16, 123.

Becker. A volumetric method in which a solution of tannin is run into a hot solution of methyl-violet until the color is discharged. Zeitsch. f. anal. Chem., 25, 133.

Beckman, E. A volumetric method employing a solution of ammonio-ferrous sulphate, crystallized sodium acetate, and acetic acid for the removal of the tannin. The usual permanganate titrations are made before and after the removal of the tannin. Zeitsch. f. anal. Chem., 25, 527.

Carpene, A. A volumetric method employing an ammoniacal solution of zinc acetate for the precipitation of the tannin. The precipitate is collected, washed, dissolved in dilute sulphuric acid, and titrated with permanganate of potassium. Ding, polytec. Journ., 216, 452; Zeitsch. f. anal. Chem., 15, 112.

Casali, Adolpho. A volumetric method employing a standard nickel solution. A paper soaked in ferric chloride solution containing ferrous sulphate is employed as an indicator. Annali di Chimi., 79, 65; also Chem. Ztg., 8, 1767; also Zeitsch. f. anal. Chem., 24, 272.

Cecil This author states that the presence of acetic acid, citric acid, tartaric acid, malic acid, cane sugar, dextrin, gum, fat, caffeine, or urea does not interfere in the estimation of tannin by permanganate, provided the solution is properly diluted. Zeitsch. f. anal. Chem., 7, 134.

Collin and Benoist. A volumetric method based on the precipitation of tannin by gelatin. A derivative of aniline added to the gelatin solution is used as an indicator. The tannate absorbs the coloring matter and the solution becomes colorless when the precipitation is complete. A standard tannin solution is employed in making up the gelatin solution. Mon. Scien., March, 1888, 364; Journ. Soc. of Dyers, 4, 62.

Commaille. A volumetric method employing a standard-solution of iodic acid in the presence of hydrocyanic acid. Zeitsch. f. anal. Chem., 3. 488.

Conncler and Von Schroeder. An official report on the estimation of tannins, containing recommendations in regard to methods of analysis, strength of solutions,etc. Zeitsch. f. anal. Chem., 25, 121.

Darton, N. H. Darton employed an aimnonio-sulhate of copper solution for the precipitation of tannin. Extract the tea first with cold, then with boiling water. Treat the infusion with 25 cc dilute sulphuric acid (1 part acid to 10 parts watery filter, render filtrate slightly alkaline with ammonia, and again filter. Treat 100 cc this solution with an equal volume of ammonia sulphate of copper solution (1 1/4 per cent copper salt), collect the precipitate. Titrate a known yolume of the filtrate with permanganate for non-tannins. Wash the precipitate with ammonium carhonate solution, dry and weigh or ignite, moisten with nitric acid and again ignite and weigh. Weight, CuO x 1.034= gallotannin. Journ. Am. Chem. Soc, 1882, 4.

Davy, Sir H. This is the first method devised for the estimation of tannin, and consisted in titrating with a standard gelatin or glue solution. Phil. Trans., 1803, 268.

Durieu, F. A method employing a standard calcium hypochlorite solution, under certain conditions, after the addition of ferric chloride. Arch. d. Pharm., 22, 523; Zeitsch. f. anal. Chem., 24, 273.

Eder, J. M. A method for tannin of teas based on that of Fleck (vide Wagner's Jsh., 1860, 531, or abstract in this bibliograpy). The tannin is precipitated from water solution, with copper acetate solution; the precipitate is collected, washed, and ignited, then moistened with nitric acid and again ignited. 1 gram CuO=1.3061 grams tannin. Zeitsch. f. anal. Chem., 19, 106; Ding, poly. Jour., 228, 81.

Fehling. An improvement of Davy's method, consisting in the addition of alum to the glue solution. Jsb., Liebig and Kopp, 1853, 683; Ding. poly. Journ.,130, 53.

Fleck. A method based on the precipitation of tannin by copper acetate. Wagner's Jsb., 1860, 531.

Gautier, A. A method employing carbonate of copper for the estimation of tannin in wines. Zeit. f. anal. Chem., 1878, 222; Jsb. d. Chem., 1878,1088.

Gantter, F. A permanganate method. Ten cc of the bark solution are saturated with dilute sulphuric acid, heated to boiling point, then permanganate solution is added (3.988 grams permanganate of potassium per 1,000 cc) 1 cc at a time until the color disappears slowly; boil and then add the permanganate drop by drop. When a precipitate, not dissolved by hard boiling, forms, add 1 cc permanganate and boil until the color disappears. Add oxalic acid (7.951 grams per liter) until the precipitate dissolves and the solution becomes clear, then complete the titration with permanganate. From the total permanganate, less that required by the oxalic acid, calculate the tannin. Zeitsch. f. angew. Chem., 1889, 57, 577; Jour. Anal. Chem., 4, 83.