_Quebrachitannic_ acid is got from the wood of the quebracho colorado, _Quebrachia lorentzii_ (formerly _Loxopterygium_) which must not be confounded with the bark of the _Aspidospermum quebrachia_, which is valuable, not for its tannin, but for an alkaloid, aspidospermin, which is used for medical purposes. It has been pretty thoroughly investigated by P. N. Arata (Chem. Soc. Jour., xxxiv. 986 and xl. 1152). It seems, however, a little doubtful to the writer whether the substance investigated by Arata was not the anhydride of the tannin, rather than the tannin itself, as it presents many points of analogy to catechu-red and was less soluble in water than quebracho tannin appears in practice to be. According to Arata, quebrachitannic acid is a pale red amorphous mass, having an astringent taste and yielding a light cinnamon coloured powder. It is insoluble in carbon-bisulphide, turpentine oil, and benzene. Its aqueous solution gives a white precipitate with both normal and basic lead acetate, which when heated, acquires first a rose, and then a chocolate colour; with ferric chloride a green liquid is produced, which changes after a time to red and becomes black on addition of sodium acetate. It forms white precipitates with gelatin, albumen, and alkaloids. By dry distillation it yields catechol. By fusion with potash or the action of sulphuric acid, phloroglucol and protocatechuic acid, while nitric acid converts it into oxalic and picric acids. While it shows great similarity in its reactions to catechutannic acid, it differs materially in percentage composition, containing only 52·5 as compared with 62·0 per cent. of carbon. CHAPTER V. WATER AS USED IN TANNING. Water, as obtained from rivers, wells, or water companies, contains a variety of impurities which affect its use in tanning, but of which in most cases the precise influence is very imperfectly known. These may be classified into (1) merely suspended matters, such as clay and mud, and sometimes animal or vegetable organisms such as infusoria; (2) dissolved mineral matters, which consist mostly of lime and magnesia salts and which make the water hard; (3) and organic dissolved impurities, such as the brown colour of peat water and the putrefying animal matters of sewage contamination.