for Löwenthal's process, but without the gelatin, precipitated 67 per cent. of the total tannin as usually reckoned. It is obvious that it is impossible by analysis to compare the relative value of different tannins, such as those of myrobalans and gambier, or hemlock and valonia. All that analysis can reasonably be expected to do is to give the relative values of different samples of the same substance, or at the most, of materials of the same class. All other comparisons are misleading; and would be so, even if the exact percentage of each tannin could be calculated; since the commercial and practical value of different materials does not depend on the quantity of tannin only, but on the character of the leather it produces, hard or soft, dark- or light-coloured and heavy- or light-weighing. A Commission of German technical chemists, under the presidency of Dr. Councler of Eberswalde, and including Messrs. Eberz, Kathreiner, Schaun, von Schroeder, and Simand, have recently reported on methods of tannin estimation ('Bericht über die Verhandlungen der Commission zur Feststellung einer einheitlichen Methode der Gerbstoffbestimmung,' Cassel, 1885). After reviewing earlier methods, they recommend the following modifications of the Löwenthal method, for general adoption. Chemicals employed. (1) _Permanganate solution._ 10 _grm._ of the purest potash permanganate are dissolved in 6 _litres_ of distilled water. (2) _Indigo solution._ 30 _grm._ dry sulphindigotate of soda (Carminum cærul. opt., "pure Indigotin I" of Gehe & Co., Dresden), air-dry, are dissolved in 3 _litres_ of dilute sulphuric acid (1 vol. H_{2}SO_{4} to 3 vols, water), 3 _litres_ of distilled water are added, the whole is shaken till dissolved, and filtered. In each titration, 20 _c.c._ are used in 3/4 _litre_ of water, and reduce about 10·7 _c.c._ of permanganate. (3) _Hide-powder_ must be white and in a fine woolly state of division, and should yield to cold water no substance capable of reducing permanganate. Such a powder is prepared by Dr. Both of Berlin,[N] and by the Vienna Research Station. [Footnote N: Messrs. Mawson and Swan, of Newcastle, have kindly undertaken to keep these, and the other reagents mentioned in this book, in stock for the convenience of English tanners and chemists.] Mode of Titration. Instead of adding the permanganate solution drop by drop, to the mixture of indigo, water, and liquor (as described, p. 121), it is recommended to add it 1 _c.c._ at a time,[O] vigorously stirring 5-10 seconds after each addition. When the liquid has become bright green, 2-3 drops at a time are cautiously added with stirring, till the liquid is pure yellow. Either a beaker on a white tile or a white basin may be used (compare p. 121). It is advantageous in strong sunlight to shade the window with white tissue-paper.