The mill used for grinding sumach leaves consists of a heavy, solid, circular, wooden bed, 15 feet diameter, with a depression around the edge a few inches deep and 1 foot wide, for the reception of the ground sumach from the bed, and two edge-rollers, weighing about 2500 lb. each, 5-6 feet diameter, and provided with numerous teeth of iron or wood, thickly inserted. In Europe and in some parts of the Southern States, sumach is still ground by stones revolving on a stone bed, and the sifting is often done by hand. [Illustration: FIG. 55.--Venetian Sumach (_Rhus cotinus_).] _R. cotinus_, Venetian sumach. Fr. _Arbre à perruques_; Ger. _Perrukenstrauch_ (Fig. 55). More important as a dyeing than as a tanning material, its twigs and wood, “young fustic,” containing a large proportion of a colouring matter (fisetin), which with tin and alumina mordants dyes bright yellows; and much resembles, but is not identical with the myricetin present in _R. coriaria_.[144] Its leaves, known as Turkish or Venetian sumach, contain about 17 per cent. of tannin, and are used for tanning. [144] Perkin and Allen, Trans. Chem. Soc. 1896, 1299. _R. pentaphylla_, “Tezera,” Algeria, is used by the Arabs for tanning goat-skins. _R. Thunbergii_, _Kliphout_, Cape of Good Hope. A sample of the bark analysed in the Author’s laboratory contained 28 per cent. of tanning matter. A valuable tanning material, of reddish colour. The tannin is of the catechol class. Several other species of Rhus are used in tanning. _R. semialata_ yields Chinese and Japanese galls, containing up to 70 per cent. gallotannic acid. They are caused, not by a fly, but by the attack of an aphis, as are those of the allied Pistacia.[145] The aphides pass their asexual stage inside the gall, which is large and thin-walled. A similar aphis-gall is found on the American sumach. A specimen of the leaves examined at the Yorkshire College yielded only 5 per cent. of tannin. [145] See Flückiger and Hanbury, ‘Pharmacographia.’ _Mangifera indica_, Mango, widely distributed in the Tropics. Bark and leaves rich in tannin, which gives green-blacks with iron. CORIARIACEÆ. _Coriaria myrtifolia_, French sumach (of which there are four kinds--_fauvis_, _douzère_, _redoul_ or _redon_, and _pudis_). A poisonous shrub of South of France; leaves used for tanning, and as a sumach adulterant under the name of “stinco”; contain about 15 per cent. tannin. (Cp. p. 272.) _Coriaria ruscifolia_ bark, the _tutu_ of New Zealand, contains 16-17 per cent. of tannin. Other Coriarias merit examination, and are known to contain much tannin. RUBIACEÆ. _Rubia_, Madder, allied to Galiums, which are almost the only English representatives of the family. The coffee- and cinchona-plants are foreign representatives.