_Castanea vesca_, True or Spanish Chestnut. Fr. _Châtaignier_; Ger. _Kastanie_. Abundant in Italy, South of France and Corsica, where it forms great forests. Bark said to be nearly as strong in tannin as oak (up to 17 per cent., de Lof), but not much used in tanning. Wood only contains 3-6 per cent. tannin, but is the source of the valuable chestnut extract, first employed for dyeing, and introduced as a tanning agent by Aimé Koch. The strength of extract is of course very variable, even for the same density (see p. 339), but it usually contains from 28 to 32 per cent. of tannin. The tannin gives blue-black with iron, but is not identical with either oak-bark or gall tannins, but apparently a mixture, or possibly a methylated derivative of the latter, and identical with oakwood tannin, or so nearly so as to be indistinguishable; it may also be identical with divi tannin. Decolorised chestnut extracts, sometimes mixed with quebracho and other materials, are often sold as “oakwood” or “oak-bark” extracts. The extract gives a firm leather, with a good deal of bloom if used strong, and a more reddish tint than valonia. The extract often contains dark colouring matters, and the colour of leather tanned with it is readily darkened by traces of lime derived from calcareous waters or imperfectly delimed hides. Like all wood-extracts it tans rapidly, the colour penetrating first, and the tan following, but, according to Eitner, it does not, alone, make full or solid tannage, perhaps from want of acid-forming matters, but answers particularly well in combination with spruce-bark. It is largely used in England for sole-leather in combination with valonia, myrobalans and other materials. The higher the temperature of extraction, the more colouring matter is contained in the extract in proportion to tannin matter and the greater is its viscosity. Much colouring matter remains undissolved if the extract is dissolved in cold water, but there is, in addition, a loss of tanning power, the colouring matter being also capable of combining with hide. It has in fact been used for tanning by dissolving it in solutions of borax or alkaline salts. By improved methods of manufacture the colouring matter has been much reduced. The chestnut is an important food tree, the nuts forming a considerable part of the food of the inhabitants of Corsica and Sardinia, and even of Italy. Oaks. Almost all species of oak contain useful quantities of tannin in the bark, and probably in the wood. Most if not all oaks yield catechol-tannins with, probably, some mixture of ellagitannic acid. _Quercus robur_, Common Oak. Fr _Chêne_; Ger. _Eiche_. It is frequently separated into the two subspecies:--