─────────────────────────────────┬──────────────────┬──────────────────┐ │ │ Other Bodies │ │ Tannin │ Oxidised │ │ (as Oxalic Acid).│ (as Oxalic Acid).│ ─────────────────────────────────┼──────────────────┼──────────────────│ Spent Liquor │ O·12 │ 11·0 │ Valonia (good Smyrna). Sample 1 │ 29·1 │ 2·3 │ " " Sample 2 │ 30·7 │ 2·1 │ " " Sample 3 │ 30·5 │ 1·9 │ Hungarian Larch Extract. Sample 1│ 14·78 │ 1·95 │ " " Sample 2│ 18·08 │ 2·33 │ Chestnut-wood Extract, 25° B. │ 25·53 │ 3·68 │ Pegu Cutch │ 63·59 │ 2·45 │ ─────────────────────────────────┴──────────────────┴──────────────────┘ It is proved by experiment that kaolin removes nothing which is oxidised by permanganate, but simply facilitates the precipitation and filtration; and it is often found useful to clarify the original infusions and liquors before the first titration. On the other hand, there is no doubt that the salt and acid of Löwenthal's method precipitate of themselves a large proportion of certain tannins. In the case of cutch this amounted, in the analysis given, to 67 per cent. of the whole. There is, however, good reason to believe that this would also have been absorbed, or at least removed from solution by hide in the process of tanning. This is shown by the analysis of the spent liquor above given, which originally contained the tannins of oak bark, valonia, myrabolans, gambier, hemlock, and oak wood extracts, &c., to the extent of 10 to 15 per cent., but which was reduced by contact with hide to 0·12 per cent. That a portion had not been absorbed but decomposed is proved by the large accumulation of oxidisable impurities (equal to 11 per cent. of oxalic acid); at the same time this example shows that the method is capable of estimating a very small portion of tannin in presence of much gallic acid and other analogous substances. It is worth remark that such spent liquors become very pale in colour, and also that the filtrates, freed from tannin by precipitation, are nearly colourless, thus proving that the colouring matters present in tanning materials are of the nature of tannins, at least as regards their precipitability by hide and gelatin.