If tannins are boiled with dilute sulphuric or hydrochloric acids, and allowed to ferment under the influence of pectose and other natural ferments, which are always present in vegetable tanning materials, a different series of decompositions takes place. Many tannins yield glucose, or starch sugar, as one of their products, or as that of closely associated impurities. Of this more must be said later. In addition it will be found that the catechol tannins invariably yield insoluble reddish-brown bodies which have been called phlobaphenes, and which differ from the original tannins in containing one or more molecules less water, and which, in chemical language, are anhydrides of their respective tannic acids. The pyrogallol tannins, on the other hand, yield gallic acid, or ellagic acid (the deposit forming bloom) either alone or in mixture. Oak-bark and valonia give both bloom and insoluble reds, and by digestion with acids in sealed tubes also gallic acid. If the red anhydrides, which are produced from the catechol tannins, be fused with caustic potash, or in many cases, if they be simply boiled with concentrated potash solution, they are broken up still further, and from the fused mass, protocatechuic acid (which bears the same relation to catechol that gallic acid does to pyrogallol) may always be obtained. This is in many cases accompanied by phloroglucol, a phenol isomeric with pyrogallol, as may be seen by the table on p. 61, but which tastes sweet like a sugar. Cutch, gambier, mimosa, quebracho, and probably many others, are phloroglucide tannins. The tannins which do not yield phloroglucol frequently give acetic acid, and other acids of the "fatty" group, along with protocatechuic acid. We may summarise this classification in the following table:-- Tannins boiled with dilute sulphuric acid yield (frequently glucose, and) /─────────────────────^───────────────────────\ _Insoluble Reds_, which fused with potash yield _protocatechuic acid_, and,---- /────────────────────────^───────────────────────────────────\ _Phloroglucol_, as chestnut, gambier, kino, cutch, quebracho, rhatany, fustic, horse-chestnut, tormentil. _Acetic acid_, coffee, Peruvian bark, male-fern. _Reds and gallic } and ellagic acids; } Oak-bark and valonia tannins. no glucose_ } _No reds, but gallic { Galls, myrobalans, sumach, divi-divi, pomegranate and ellagic acids_ { rind. { _These are probably mixtures of two tannins which yield_ _Gallic acid only_ Digallic, or pure gallotannic acid. _Ellagic acid only_ Pure ellagitannic acid.