Page:The American Cyclopædia (1879) Volume XVI.djvu/728

 704 WOOD amount of moisture, which must be removed to fit it for most uses ; when the moisture is allowed to pass off spontaneously, the opera- tion is called seasoning. Logs and beams, whether hewn or sawed, are called timber. The term lumber is applied, chiefly in the Uni- ted States, to beams, or to the material sawed into planks and boards, or made into siding, shingles, laths, &c. The sawing is usually done soon after felling, as the operation of seasoning is thereby much hastened ; while a solid stick requires several years to dry, boards will be sufficiently seasoned in a single year ; seasoning goes on most rapidly under cover, and boards are piled up with sticks between them to allow of a free circulation of air. A previous immersion in water for several months, by removing some soluble substances from the wood, causes it to dry more rapidly afterward. The loss of moisture is accompanied in most cases by shrinkage, the amount of which varies with the kind of wood ; in the redwood of California it is imperceptible, and with this no regard is paid to seasoning, while some oaks shrink as much as half an inch to the foot. For nice work, ordinary seasoning is supple- mented by kiln drying, the lumber being ex- posed in a chamber to currents of air heated to from 100 to 300 F. A patent has been taken for drying lumber on a large scale by means of superheated steam. The durability of wood, t. ., its power of resisting decay, does not appear to be associated with any other quality, as the most durable woods are found among light and heavy kinds ; woods which decay rapidly when exposed to alternate mois- ture and drynoss are often remarkably durable when kept either altogether dry or constant- ly under water. Larch, a comparatively light wood, and locust, a very heavy one, are al- most indestructible under the most unfavor- able conditions. Sap wood is generally much less durable than heart wood, even when pro- tected from the weather. (See DBT ROT, and PRESERVATION OF WOOD.) The properties of density or hardness and specific gravity bear a direct relation to one another. One of the lightest known woods is that of anona palus- tri* of Brazil, which has a specific gravity of 0'206, somewhat lighter than cork ; and per- haps the heaviest is the ironbark of Australia (eucalyptus retinifera), of which the specific gravity is 1/426. In the hard and heavy woods, the fibres are very small, the rings of annual growth exceedingly narrow, and the tissues filled with incrusting substances. Flexibility and elasticity are usually associated qualities, and are found in their greatest perfection in straight-grained woods that are free from knots; as in such woods the fibres are not inclined to interlace, they split readily ; the ash, used for oars, lancewood, valued for fishing rods, and hickory, so flexible that when split it is woven into baskets, are woods of this kind. Woods not naturally flexible are made so tem- porarily by steaming them, and are then bent to the desired shape by powerful machines. The most rigid and toughest woods are those in which the fibres interlace and cross one an- other at an oblique angle ; such woods are diffi- cult to split, and when the parts are torn asun- der the surfaces are ragged, in consequence of the breaking of the fibres ; among native woods the elm has the quality of toughness in a use- ful degree, and the hop hornbeam and tupelo are still more difficult to split ; lignum vita- is remarkably tough, and cannot be worked by splitting. The beauty of woods depends to a great extent upon other qualities than color, though that is important. Though an exoge- nous stem is practically made up of rings of growth one with another, many causes inter- fere with the regularity of this arrangement, and a longitudinal section, instead of showing a series of straight lines, presents a great diver- sity of figure and variety of light and shade. Much of the 'beauty of a wood will depend upon the manner of dividing it ; if the sawing is done somewhat obliquely, beauties are devel- oped that are not visible when an exact longi- tudinal cut is made. Much of the beauty of some woods depends upon the medullary rays, already mentioned as plates of cellular tissue running radially across the woody fibres; if the wood bo cut tangentially, only the ends of these rays will be exposed, but by cutting in the direction in which they run, a beautifully varied surface is presented, on which the me- dullary rays reflect the light in a most pleasing manner. Knots, so often a blemish in lumber for carpentry, are in some woods the cause of great beauty ; these knots may be due to that portion of a living branch which is imbedded within the trunk, or to one that in the early life of the tree has perished, and a portion of which remains within the trunk, covered by a more recent growth of wood ; either case pro- duces contorted fibres, changes in density, and difference in color, which greatly increase the beauty of the wood. The portion of a trunk where largo branches fork, the burs or gnarls produced by some trees, and the base of the trunk where it is joined by the large roots, all present irregularities of fibre, and are turned to account by the workers of ornamental wood. In sugar maple individual trees are occasion- ally found in which there is a curious contor- tion of fibre, producing upon the polished sur- face the appearance of little projections rising from within small cavities ; this is known as birdsoyo maple. Colors in woods vary from the almost pure white of the holly to the jet black of ebony; they are sometimes of uni- form tint, but frequently, as in mahogany and black walnut, there are different shades of the same color ; in rosewood, zebra wood, Amboyna wood, and others, two or more colors are con- trasted or blended. But few colored woods fade upon exposure to the light, and in most the color is deepened by time, as in mahogany and black walnut; sometimes the effect of age is produced by applying lime water to the wood