Useful Knowledge: Volume 2. Vegetables / Or, a familiar account of the various productions of nature

by William Bingley

On the leaves and buds of the oak certain excrescences are formed, in consequence of the puncture of insects, as the lodgment for their eggs and a habitation for their future young. These are termed galls, and if, when arrived at a certain state, they are infused in a weak solution of vitriol, they impart to it a purple or violet tinge; and, after the whole colouring matter is extracted, this becomes perfectly black. Considerable quantities of galls are used in dyeing, and for other purposes.

Acorns, or the seeds of the oak, possess an astringent quality, and have a bitter taste, both of which may be extracted by steeping them, for some time, in cold water, or by boiling them. After this simple process, they are not an unpalatable fruit. With the ancient Britons they were an article in great request, and even constituted an important part of their food; and there can be little doubt that, carefully prepared, dried, and reduced to powder, they might, in times of scarcity, be adopted as a substitute for bread-corn. By pressure an oil is obtained from them which may be used for lamps; and a kind of coffee is prepared from them in some parts of the Continent.

The branches of the oak, as well as those of several other kinds of trees, are burned for the formation of charcoal; and it is a remarkable circumstance that the properties of charcoal, from whatever wood it may be made, are nearly the same. One of the most remarkable of these is, that it is not liable to decay by age. Hence it was customary, with the ancients, to char or burn the outside of stakes, or other wood, which were to be driven into the ground, or placed in water. Charcoal may be preserved without injury for an almost indefinite length of time; and, in the ancient tombs of the inhabitants of northern nations, entire pieces of charcoal are at this day frequently discovered.

Besides the great use of charcoal in the composition of gunpowder, and to artists and manufacturers of different kinds, it has lately been employed, with considerable success, in correcting the rancid and disagreeable smell of train oil, so as to render it fit to be burned in chamber lamps; and several manufactories of this oil have been established in the neighbourhood of London. Newly-made charcoal, if rolled up in clothes which have contracted a disagreeable odour, will effectually destroy it; and if boiled with meat beginning to putrefy will take away the taint.

This substance is used by artists in the polishing of brass and copper-plates, for the drawing of outlines, and numerous other purposes. When purified, it forms perhaps the best tooth-powder that is known. The mode of purifying it is to reduce it to powder, wash it repeatedly with water, and then dry it by means of a strong heat in close vessels. This heat expels the foreign contents with which it is impregnated; but however intense, if the vessels are closed, it in no respects alters the quality of the charcoal. The vapour of burning charcoal is extremely pernicious; and persons exposed to it in confined rooms are liable to be suffocated in a very short time. The best remedy is immediately to take them into the strongest draught of cold air that can be obtained, to loosen all their garments, and apply volatile spirits to their nostrils.

238. CORK is the external bark of a species of oak (Quercus suber) which grows in Spain, Portugal, and other southern parts of Europe, and is distinguished by the fungous texture of its bark; and by its leaves being evergreen, oblong, somewhat oval, downy underneath, and waved.

The principal supply of the cork that is consumed in Europe, is obtained from Catalonia in Spain; and the culture and the preparation of it yield to the inhabitants of that province near 250,000l. per annum.

In the collecting of cork, it is customary to slit it with a knife, at certain distances, in a perpendicular direction from the top of the trees to the bottom; and to make two incisions across, one near the top and the other near the bottom of the trunk. For the purpose of stripping off the bark, a curved knife with a handle at each end is used. Sometimes it is stripped in pieces the whole length, and sometimes in shorter pieces, cross cuts being made at certain intervals. In some instances the perpendicular and transverse incisions are made, and the cork is left upon the trees until, by the growth of the new bark beneath, it becomes sufficiently loose to be removed by the hand.

After the pieces are detached they are soaked in water; and, when nearly dry, are placed over a fire of coals, which blackens their external surface. By the latter operation they are rendered smooth, and all the smaller blemishes are thereby concealed: the larger holes and cracks are filled up by the artful introduction of soot and dirt. The pieces are next loaded with weights to make them even; and lastly they are dried, stacked, or packed in bales for exportation.

Many of the uses of cork were well known to the ancients. Its elasticity renders it peculiarly serviceable for the stopping of vessels of different kinds; and thus preventing either the liquids therein contained from running out, or the external air from passing in. The use of cork for stopping glass bottles is generally considered to have been introduced about the fifteenth century. The practice of employing this substance for jackets to assist in swimming is very ancient; and it has lately been applied in various ways towards the preservation of life, when endangered by shipwreck. The floats of nets used for fishing are frequently made of cork: pieces fastened together make buoys, which, by floating on the surface of the water, afford direction for vessels in harbours, rivers, and other places. In some parts of Spain it is customary to line the walls of houses with cork, which not only renders them warm, but prevents the admission of moisture. The ancient Egyptians sometimes made coffins of it. On account of its lightness, cork is used for false legs; and, from its being impervious by water, it is sometimes placed betwixt the soles of shoes to keep out moisture. When burned, it constitutes that light black substance known by the name of Spanish black.