Cork. Suber. Liege, Fr. Kork, G.—The great use made of this substance in pharmacy and the arts justifies a brief notice of it. It is chiefly produced by Quercus Suber L. (Fam. Cupuliferae), but is obtained also from the Q. occidentalis F. Gay. It consists of the exterior layers of the bark beneath the epidermis, which acquire in these species an extraordinary development, becoming thick, and of that peculiar spongy consistence which characterizes cork. The tree begins to yield cork when fifteen or sixteen years old, and every six or eight years—the interval requisite for the renewal of the suberose layers by the living portions of the bark beneath—furnishes a fresh supply, even for a century and a half, before it perishes. There are four constituent layers of the bark: the epidermis, the cork, the cellular envelope, and the bast which lies upon the wood. Each of these increases year by year; but the cork thus naturally produced is not valued. The commercial product is the result of an artificial injury to the bark. The exterior layers are removed, and the bast exposed. In the interior of this, at a variable distance from the surface, a layer of the proper cork is now formed, apparently by a change in the substance of the bast, the outer portions of which perish, while annually a new layer is added to the cork already existing, until it acquires a thickness which will justify its removal. Incisions are made in such a way that the cork is removed in large concave plates, which are then flattened under pressure, and dried. At present cork comes into commerce from Portugal, Spain, France, Italy, Tunis, Algeria, and Morocco. About one million of quartels of it are said to be produced annually. The value of the cork imported into the United States in 1914 was $3,851,794:, and in 1915 $2,761,895.
A cork has recently come into the United States commerce from Nicaragua. It has been found by E. F. D. Baker to be obtained from the roots of the Anona, a tree closely resembling in appearance the ordinary cottonwood of the United States.
In selecting cork for use, those parts should be preferred which are soft and of uniform consistence, and in the choice of the larger plates those should be selected which are thick, flexible, elastic, finely porous, and of a reddish color. Boiling hot alcohol extracts from rasped cork tissue some 10 per cent. of soluble principles. From the hot alcohol solution a substance crystallizes which was first noticed by Ghevreui under the name of cerin. According to Kugler (Dissertation on Suberin, Halle, 1884), besides cellulose and lignocellulose, cork contains two constituents, cerin, to which he gives the formula C20H32O, and suberin, which is a fat, and contains stearic acid and phellonic acid, C22H42O3. This constituent, suberin, prevents the penetration of liquid into the cork, and is only extracted by alcoholic alkali solutions. When treated with nitric acid, cork yields a peculiar acid, which has been denominated suberic acid. This is a dibasic acid homologous with oxalic acid, and has the formula C3H14O4. It is formed by the oxidation of many other substances, such as the oils from linseed, castor bean, cocoa, nut, almond, spermaceti, etc.
Stanislaus Martin has called attention in France to the use of refuse corks in Paris, where they are collected by the scavengers, and sold to persons whose business it is to revive them, recutting such as are of unsuitable shape, filling up the interstices with mastic, and covering them over with some powder which may give them a fresh appearance. Corks are sometimes bleached with sulphurous acid, and the odor of hydrogen sulphide has been noticed in prescriptions which have been compounded, when such corks have been used in the dispensing bottle. (P. J., 1881, 1080.) Mohr has found that old corks may be regenerated by allowing them to soak for twenty-four hours in hot water, washing well several times, allowing to stand for a few hours in a mixture of one part of hydrochloric acid and fifteen parts of hot water, and finally washing well in pure water. (See also A. J. P., 1875, 467.) It is easy to conceive that a cork at one time used to enclose arsenical or other deadly solution may become saturated with the poison, and afterwards impart enough of it to another liquid, if not to produce dangerous effects on the health, at least to give to tests evidence of its presence, and thus lead to serious suspicions. No cork, therefore, which has been used in a bottle containing a poisonous substance should be employed a second time.