Before oak timber is in a state to be used it is requisite that the trees should be barked, and suffered to stand uncut for three or four years, that they may become perfectly dry. The _bark_ thus obtained is extensively used in the tanning of leather; and afterwards it serves as fuel, and for making hot-beds for the growth of pines, and some other plants. The astringent properties of oak-bark render it of use for medical purposes. The _saw-dust_ of this tree, and even the _leaves_, though much inferior to the bark, have been found useful in tanning. The former of these is the principal vegetable production of this country, which is used in the dyeing of fustian. 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.