Page:Collier's New Encyclopedia v. 09.djvu/463

LEFT TIMBER 401 TIMBER fibro-vascular bundles (composed of nu- merous cell forms) through which medul- lary rays radiate. In a growing tree of this class the new wood forms next the bark, and is called sap-wood (alburnum). Gradual changes occur in these annual rings or layers of new wood as they be- come older, and in time, which varies from one to many years, they get hard- ened or solidified into ripe wood or heart wood (duramen), of which all useful tim- ber consists. These changes are of a chemical and physical character, and, al- though it is the hardening of the wood of a growing tree with age that gives it its technical value, yet the change is, physiologically, an incipient process of degradation which ends in decomposition. It is only in a few kinds of trees, how- ever, that the decay of the wood is rapid. This duramen or heartwood, when prop- erly treated after felling, is generally of a lasting nature, and in the hardwoods especially is usually of a darker color than the sapwood; but in some pine woods the sapwood, soon after the tree is cut down, gets darker than the heart wood, and is of a bluish or greenish color. The properties of wood depend partly on the mode of union of the fibers, and in close proximity, and other conditions determine to a large extent the value of wood from trees of a like kind. For example, the timber of the Scotch fir (Pinus sylvestris) brought from the Bal- tic varies so much that the Swedish wood is only two-thirds the price of that v/hich comes from Danzig, while the wood of the same tree grown in Scotland is of less value than either. "With mahogany the qualities differ far more. Spanish or Cuban mahogany is of much greater value than, and sometimes twice as heavy as, Honduras or Bay mahogany from the same species of tree. Each of these va- rieties again is found to differ greatly in quality in different samples of the wood. Seasoning of Timber. — Trees, and es- pecially deciduous trees, should always be felled in winter, as in that season they contain the least amount of natural sap. They should not be allowed to remain long on the ground where they are cut down, but, as soon as possible, the logs ought to be stacked with packing pieces between them, to allow the sap freely to evaporate. They should also be covered in from the weather. When the logs are cut up into planks or boards, these are partly on the constituents, ^such as gum, usually in the first place laid horizontally, 0. .•- _--j -^- ...1.--1. •_ ^j^j^ lathes or fillets between them, and allowed to remain in this position for six months completely protected from rain. Afterward they are placed for the same length of time in a vertical position on racks and kept a little apart. Most ordinary woods require this length of time to season them properly in a natural way, though some are ready for use sooner than others. The seasoning of tirnber can be hastened by steaming or resin, tannic acid, etc., which occur in the cellular and intercellular spaces. But there is also a small proportion of nitrog- enous constituents which set up a kind of fermentation in damp wood, and es- pecially in young spongy wood, exposed to the air, and are the cause of its decay. In other circumstances, however, even in the presence of moisture, but where the access of oxygen is prevented, some kinds of wood will keep for an enormous length of time. Pieces of wood have been taken boiling it, or, in the case of planks "and out of the lignite beds of the newer geo- thin cut wood, by placing it in hot air logical formations which are scarcely dis- chambers. Natural seasoning is, how- tinguishable from sound timber recently ever, by far the best. For cabinet work cut. The timber used in the construction and the better kinds of joinery the natur- of a house or other building should be ally seasoned wood is, just before being thoroughly dried before being put in,^nd used, usually put for a week or 10 days air allowed to circulate about it. This is especially necessary with regard to joists and flooring near the surface of the ground, otherwise damp and want of ventilation will render them peculiarly liable to be attacked by dry rot. The apparent sp. gr. of wood varies from 0.383 (poplar wood) to 1.333 (lig- num vitae), and perhaps some kinds are even denser. But the sawdust of nearly all woods is heavier than water, and the actual specific gravity (i. e., of the wood apart from enclosed air) is much the same in all. The quality and the ap- parent specific gravity of timber from the same species of tree often widely tary. Soil, climate, whether they grow in a stove heated to about 120° F. The thorough seasoning of wood is of great importance, but too frequently is only partially effected. Preservation of Timber. — For the ex- ternal woodwork of buildings oil paint is usually employed, and the painting should be renewed every four or five years. "Wooden ships and boats are coated with tar or pitch. But for such purposes as pavement, sleepers, piles, etc., treatment with certain chemicals which penetrate the wood more deeply has been proposed. Three methods of doing this have been chiefly tried, and of these the impregnation with bichloride of mercury is called kyanising; when