extract is now manufactured on an enormous scale in Slavonia, and is used both by sole- and dressing-leather tanners, chiefly to increase the strength of the layer liquors. The extract is also used to increase the weight of leather after tannage by mopping on the flesh-side. All the best oakwood extract manufacturers contract to sell on analysis and colour estimation, and good Slavonian oakwood extract generally contains 26-28 per cent. of tanning matter, giving a tintometer measurement of 4-5° red, and 20-25° yellow, when a solution containing ¹⁄₂ per cent. of tanning matter is measured in a 1 cm. cell. For particulars of the manufacture of concentrated extracts see p. 337. [Illustration: FIG. 46.--Cork Oak (_Quercus suber_).] _Q. cerris_, Turkey Oak. Ger. _Zerreiche_. Common in southern Europe, a fine tree, but bark inferior to _Q. robur_. Fig. 45. _Q. pubescens._ Fr. _Chêne velu_; Ger. _Weiss-_ or _Schwarzeiche_. In mountain districts and scattered in Southern Europe, about equal to _Q. robur_. _Q. ilex_, Evergreen Oak. Fr. _Chêne vert_, _Chêne yeuse_; Ger. _Grüneiche_, _Steineiche_; Span. and Ital. _Encina_. South Europe, Algeria. Said to be somewhat stronger in tannin than common oak, yielding 5-11 per cent. of a rather darker coloured tannin, but well adapted to sole-leather. Good bark is smooth outside, without fissures, short in fracture. _Q. Suber_, Cork Oak. F. _Chêne liège_; Ital. _Sughero_, _Suvero_. (Figs. 46, 47.) The outer bark is cork; the interior bark contains 12-15 per cent. of tannin which is redder than that of ordinary oak. Trees at first produce an irregular cork, sold as “virgin cork” for ferneries, etc. After this is stripped, later growths are more uniform, and fit for use; tanning bark is only obtained when the tree is cut down. Bark is rough but pale-coloured on both sides and about 1 cm. thick; interior like ordinary oak, but more strongly furrowed. Produced chiefly on Mediterranean coasts, and formerly largely used in Ireland. [Illustration: FIG. 47.--Section of Cork Oak, showing cork, inner bark and wood.] _Q. pseudosuber_, African Oak. Fr. _Chêne faux liège_. Algeria. Not stronger than English oak, but with more colouring matter, hence strikes quickly through leather. Bark very thick. _Q. Mirbecki._ Fr. _Chêne Zeen_. Algeria. Rapid growth. Bark contains 8 per cent. of tannin. _Q. Tozæ._ Fr. _Chêne tauzin_. Pyrenees and S. France. Bark contains 14 per cent. of tannin. _Q. coccifera_, Kermes Oak. Fr. _Kermes_, _Garouille_ (Fig. 48). South Europe and Algeria. Root bark is called “rusque” or “garouille”; averages 10-18 per cent. tannin, but trunk bark does not exceed 11 per cent. This tree is the food of the kermes insect, used for dyeing scarlet before the introduction of cochineal. Garouille is principally used in the south of France, giving a firm sole-leather of a disagreeable odour and dark brown colour. [Illustration: FIG. 48.--Kermes Oak (_Quercus coccifera_).]