Myrica Gale, Sweet Gale, or bog-myrtle.
Myrica (Comptonia) asplenifolia, U.S.A.; “Sweet Fern.” Covers millions of acres in Michigan. Yields 40 per cent. of “extract.” Leaves 4-5 per cent., roots 4-6 per cent. tannin, according to season (Trimble). Has been much talked of, but in Prof. Trimble’s opinion is not likely to prove of much importance.
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gunpowder-charcoal, and it is possible the bark might be obtained from powder-factories, if the use of gunpowder is not superseded by nitro-compounds.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]).