Quercus. N. F. IV (U. S. VIII). Oak. White Oak Bark.
Quercus. N. F. IV (U. S. VIII). Oak. White Oak Bark. Stone Oak. Scarce de Chene, Fr. Cod. Cortex Quercus, P. G. Eichenrinde, G. Quercia, Corteccia de quercia. It.—"The dried bark of the trunk and branches of Quercus alba Linné (Fam. Fagacecae), deprived of the periderm." N. F.
There are about sixty-five species of oak found in the United States. Many of these are applied to important practical purposes. Quercus Robur, or European oak, has a very wide distribution. It is the common British oak, constitutes a large part of the European forests, and has spread itself over almost the whole northern section of Asia and along the northern coast of Africa. There are two distinct varieties of it, one, pedunculata, with sessile or shortly stalked leaves and the acorns on long peduncles; the other, sessiflora, with the leafstalks more or less elongated and the acorns either sessile or provided with a very short peduncle. The dried bark of the smaller branches of this tree were formerly recognized by the Br. Pharmacopoeia under the name of Quercus Cortex.
Of all the American species, the white oak approaches the nearest, in the character of its foliage and the properties of its wood and bark, to Q. pedunculata, of Great Britain. Its trunk and large branches are covered with a whitish bark, which serves to distinguish it from most of the other species. The leaves are regular and obliquely divided into oblong, obtuse, entire lobes, which are often narrowed at their base. When full grown, they are smooth and light green on their upper surface, and glaucous beneath. Some of the dried leaves remain on the tree during the whole winter. The acorns are large ovoid or ellipoidal, contained in rough, shallow, grayish cups, and supported singly or in pairs upon peduncles nearly 2.5 cm. in length.
The white oak abounds from Ontario to Maine and Minnesota, and extends southward. It is the most highly valued for its timber of all the American oaks, except the live oak, Q. virginiana Mill. (Q. virens Ait.), which is preferred in ship building. The bark is sometimes used for tanning, but the barks of the red and Spanish oaks are preferred. All parts of the tree, with the exception of the epidermis, are more or less astringent, but this property predominates in the fruit and bark.
White oak bark, deprived of its epidermis, is of a light-brown color, of a coarse, fibrous texture, and not easily pulverized. It occurs "in nearly flat pieces, from 2 to 10 mm. in thickness; externally light brown, becoming darker with age, rough-fibrous; fracture uneven, coarsely fibrous. Odor distinct; taste strongly astringent; not tingeing the saliva yellow when chewed. Quercus yields not more than 7 per cent. of ash." N. F. IV. The medicinal value of oak bark depends on the presence of a considerable proportion of tannin. The proportion of this ingredient varies with the size and age of the tree, the part from which the bark is derived, and even the season when it is gathered. It is most abundant in the young bark, and the English oak is said to yield four times as much in spring as in winter. H. Davy found the inner bark most abundant in tannin, the middle portion or cellular integument much less so, and the epidermis almost wholly destitute as well of this principle as of extractive. Kraemer examined the tannin of white oak bark (A. J. P., 1890, p. 236) and assigned to it the formula C29H27O13, which was later confirmed by Trimble (Tannins). The tannin yields upon sublimation a principle resembling pyrocatechin and upon fusion with potassium hydrate a phenol similar to protocatechinic acid. Dilute solutions of white oak tannin are colored olive-brown with ferric chloride T.S. and possess a slight fluorescence.
The tannic acid of the oak barks is known as quercitannic acid, and has, according to Lowe (Zeit. An,. Chem., 20, p. 208), two forms, one soluble in water, of the formula C28H28O14, and the other difficultly soluble, C28H24O12. Both are changed by the loss of water into oak red, C28H22O11. Neither is a glucoside. Gerber discovered in European oak bark a peculiar bitter principle upon which he conferred the name of quercin. This quercin Husemann considers to have been only impure quercite (or oak sugar).
Quercus velutina Lam., or black oak, is one of our largest trees, frequently attaining the height of eighty or ninety feet. Its trunk is covered with a deeply furrowed bark, of a black or dark brown color. The leaves are ovate-oblong, pubescent, slightly sinuated with oblong, aculeate lobes. The fructification is biennial. The acorn is globose, flattened at top, and placed in a saucer-shaped cup.
Black oak bark has a more bitter taste than that of the other species, and may be distinguished also by staining the saliva yellow when it is chewed. Its cellular integument contains a coloring principle, capable of being extracted by boiling water, to which it imparts a brownish-yellow color, which is deepened by alkalies and rendered brighter by acids. Under the name of quercitron, large quantities of this bark, deprived of its epidermis and reduced to coarse powder, are sent from the United States to Europe, where it is used for dyeing wool and silk of a yellow color. The coloring principle is called quercitrin. Herzig (J. Chem. S., 1893, 413) found that its composition is expressed by the formula C21H22O12 + 2H2O, and this is confirmed by Rudolph. (Ph. Post, 1893, 529.) The reaction for its decomposition is C21H22O12 + H2O == C15H10O7 + C6H10O6, the products being quercetin and isodulcite in equal molecules.
Quercitrin forms yellowish crystals, which, pulverized, yield a citron-yellow powder. It is neutral in reaction, is odorless, and in. the dry condition tasteless, but in hot aqueous or alcoholic solution has a bitter taste. It fuses at 160° to 200° C. (320°-392° F.) to a resinous mass. It is almost insoluble in cold water, sparingly soluble in hot water, and easily soluble in alcohol and alkaline solution. Besides this principle, the bark contains much quercitannic acid; but it is less used in tanning than the other barks, in consequence of the color which it imparts to the leather, and it was dropped from the U. S. P., 1890, on account of its decoction staining so decidedly.
Quercitrin has been found in various other plants, as in the leaves of Ruta graveolens, and the flower buds of Capparis spinosa, Sophora japonica, and Aesculus Hippocastanum, or horse chestnut. (Chem. Gaz., May 2, 1859, p. 161.) As this principle is capable of assuming various colors under various chemical influences, the idea has been advanced that it might be the coloring principle of flowers.
Acorns, besides the bitter and astringent principles of the bark, contain a peculiar saccharine matter (quercite), which is insusceptible of the vinous fermentation. (J. P. C., 3e ser., xx, 335.) They are sometimes used as a tonic or astringent, and a decoction made from roasted acorns has been long employed in Germany as a remedy in scrofula. Before roasting they should be deprived of their shells, and the cotyledons, according to Dausse, should lose, during the process, 28 per cent. of their weight. (Ph. Cb., Oct. 9, 1850, p. 687.) From half an ounce to an ounce may be prepared and taken like coffee at breakfast (Richter).
The National Formulary IV admitted quercus mainly in order to provide a process for the fluid-extract, Fluidextractum Quercus, N. F., which was formerly in the U. S. VIII; it is made with a menstruum of five volumes of alcohol, four volumes of water and one volume of glycerin, followed by diluted alcohol. The medical value of oak-bark depends solely upon its tannin. Because of its cheapness it is often used where an external astringent wash is desired. Thus it is employed as an injection in leucorrhea and hemorrhoids, as a wash for flabby ulcers and similar purposes.