_Myrica nagi_ (Hind. _Kaiphal_), India, contains 13-27 per cent. of tannin in the bark, and a colouring matter, myricetin, identical with that of sumach.[137] Leather tanned with it is of a somewhat reddish colour which is much brightened by sumaching, and converted into a pale yellow by treatment with alum. It promises to be a valuable tanning material. [137] Perkin and Hummel, Trans. Chem. Soc., 1896, p. 1287. BETULACEÆ. _Alnus glutinosa_, Common Alder. Fr. _Aulne_; Ger. _Erle_. Contains 16-20 per cent. iron-green tannin, with much red colouring matter; old barks as low as 10 per cent. Colour develops during and after tannage. Used alone it gives a red, hard and brittle leather, but with galls, valonia, etc. it produces a satisfactory tannage. Its principal use is to furnish gunpowder-charcoal, and it is possible the bark might be obtained from powder-factories, if the use of gunpowder is not superseded by nitro-compounds. (Von Höhnel.) _Alnus maritima_, _Hannoki_, Japan; and _A. firma_, _Minibari_. Fruits (_yashi_) contain 25 per cent. tanning matter (iron-blueing), and little colouring matter. Used in Japan for dyeing and tanning. _A. nepalensis_ and _A. nitida_ used in India. Several other species of _Alnus_ contain tannin. _Betula alba_, White or Common Birch. Fr. _Bouleau blanc_; Ger. _Birke_. Inner bark used in Scotland (in conjunction with larch for tanning sheep-skins), Norway, Russia, etc. It contains only 2-5 per cent. of iron-greening tannin, and much fermentable sugar. By far the most important use of birch bark in tanning is to produce the birch-bark tar used to give scent and insect-resisting power to “Russia” leather (_Youft_; Ger. _Juchten_). The outside bark consists of thin layers of cork, often white with a crystalline deposit of betulin, which when distilled yields the odorous oil. The distillation is a dry one, and tarry products accompany the true oil, and at first give a strong empyreumatic smell to the leather, which it loses by keeping, while the true “Russia” odour remains. This “ageing” may be hastened by hanging the leather in a hot stove. If the oil is distilled in a current of steam, or with petroleum ether, the tarry matter passes over, while the matter giving the true odour remains in the retort (p. 372). _Betula lenta_, American Black Birch. The bark and twigs distilled with water yield an essential oil, which is almost pure salicylate of methyl, and largely substituted for oil of wintergreen (_Gaultheria procumbens_), with which it is chemically identical. Used for perfumery, and as a rheumatism remedy. Often erroneously spoken of as the source of “Russia” oil. A mixture of a trace of wintergreen oil with sandal-wood oil considerably resembles the “Russia” scent (p. 373). CUPULIFERÆ.