28. Timber should be piled in high and dry locations only, and should be kept well up from the ground on staging and strips placed between the beams or boards, so as to allow of a thorough circulation of air around every side of the timber.

No vegetation should be allowed to grow under or around the pile, as it would create conditions favorable for the retention and germination of the spores of the fungi.

The surface of the ground should be covered with ashes or gravel, which will prevent vegetable growth and also keep the surface free from moisture.

Timber deteriorates very rapidly in quality if it becomes heated, which may arise from the material being closely piled together or from being placed in a confined situation; in either case the sap is prevented from evaporating and soon begins to ferment, and causes the fiber to show signs of decay.

The decomposition of the fiber is also caused by alternate dampness and dryness, and is forcibly illustrated by the action on fence posts, which, although sound above and below the ground line, soon give way at the parts thus affected.

29. Wounds, caused by the branches of the trees being broken off close to their roots in the stem, often result in the rotting of the knots, as well as the surrounding fibers. This rotting is caused by the decomposition of the sap which accumulates and covers the wounds, and the knots, as the roots of the branches are called, assume a spongy appearance, which is called druxy. When the druxy knots are of a brown, fox-like color, the rot usually penetrates farther into the timber and is more likely to seriously affect the healthy wood.

30. In selecting timber for building purposes, the principal points which should be carefully observed, are straight grain, freedom from large or loose knots, wind and heart shakes, and the presence of the characteristics which indicate any of the diseases and imperfections of the fiber previously described. When cut, the sawdust should not be clammy or dough-like, but granular, or meal-like, crisp, sparkling, and free from stringy fibers. The surface of the sawed material should be clean and lustrous, presenting a firm and bright appearance, and free from spongy or woolly fibers, which indicate lack of vitality. The heart wood should be sound and mature, and the sap wood, or layers next to the bark, should be entirely removed. The wood should appear uniform in texture, and when cut should smell sweet; a disagreeable smell is a sign of decay. When the wood is planed, it should have a silky, shining surface; the shavings should come off like ribbons and stand twisting around the fingers.

When the surface appears dull and chalky, and the shavings are brittle and short, it may be considered that the stock lacks much of the virtue it ought to possess. Good material should be uniform in color; when blotchy or discolored, it signifies a diseased condition, which may be due to defective development, or be caused by piling the lumber close together after it has been sawed. The black and blue streaks and patches, which often occur in lumber, are the result of close piling, which causes the sap to sour or ferment. The defective pieces should be cut out and only such portions as appear sound and perfect should be used in work where strength and durability are essential requirements.

31. Heart shakes, sometimes called star shakes, are rifts, or cracks, which radiate from the center of the tree, as shown at a, a, Fig. 5. They are common in nearly all classes of timber, and are caused by the shrinkage of the layers, incidental to loss of vitality; after the period of maturity has been passed and decline has begun, the outer rings being more active, derive their nutriment by absorbing the juices from the heart wood, thus causing a gradual but sure loss of its strength and virtue.

32. In converting timber into such sizes as are required for constructive purposes, there are several conditions governing the operation, which, if not understood, or if ignored, result in a loss of material, as well as affect the future conduct of the several pieces cut from the log.

It is seldom that the carpenter is required to use the timber in the round form given to it by nature, unless it is in the construction of rough and rustic work. Round timbers are also used in constructing pile foundations, and for props and supports when shoring buildings - the term shoring signifying a temporary disposition of timbers to afford support and rigidity to any mass or structure, but, specifically, where alterations of original conditions are being effected. They are also used for scaffolding purposes, in which both the vertical and the horizontal portions are lashed together by means of ropes.

Timber Properties Of Timber Part 4 246

Fig. 5.

Where stock of variable widths, but of equal thickness, is desired, the log would be converted into planks, as shown in Fig. 6, by a series of saw cuts, as ab, cd, ef, etc., parallel to each other, the edges of the planks being afterwards squared by cutting off the waney or beveled portions, which formed the curved surface of the tree.

Where a large number of planks of uniform width is required, the end of the log would be marked, and cut on the line shown in Fig. 7, the portions a, a, called slabs, being waste material, although sometimes used for building fences, and for siding on rustic cottages, etc.

33. The manner in which the annual rings of growth are disposed on the end section of the plank, has a great influence on its behavior, after having been cut from the log. During the process of seasoning the lumber, or the drying and hardening of its fibers by the evaporation of the natural sap, there is an ever prevalent tendency for the boards or planks to curl and warp, particularly, if the process is too rapidly enforced and special care is not taken to pile the material so as to allow free circulation of air, and at the same time have it stacked so that its weight will help to keep the boards flat.

Timber Properties Of Timber Part 4 247

Fig. 6.

Timber Properties Of Timber Part 4 248

Fig. 7.

34. The cause of this tendency to curl will be understood by reference to Fig. 8, in which is shown the end sections of two boards cut from different portions of the tree. At a it will be observed that the annual rings are nearly at right angles to the surfaces of the board, while at b they cross the surfaces obliquely and become nearly parallel to the faces. After the boards have been cut and have commenced to dry, owing to the evaporation of the sap, the sap ducts and fibers begin to contract and shrink; the form taken by the board in shrinking will be governed by the length of the annual rings on the section. In a the rings are practically of the same length, and the medullary rays being nearly parallel to the surface of the board, the faces will remain straight and true across their width, while in b the inner ring is shorter than the outer one; hence, the outer one will shrink more, causing the surface farthest from the heart of the tree to assume a concave form. This effect is further increased by the fact that the nearer the heart, the more dense and mature is the fiber, so that portions cut adjacent to it shrink less than those which are farther from it. Where a tree is twisted in its growth - that is, where the fibers seem to twist spirally around the stem in the height - it is impossible to cut boards from it which will not warp and wind, not only while they are seasoning, but also whenever affected by changes in temperature.

Timber Properties Of Timber Part 4 249

Fig. 8.

35. As has been shown, boards having the annual rings disposed as at a, are less liable to shrinkage and curling, and if the timber is rich in medullary rays, the element of beauty is also enhanced; furthermore, such boards, having only the edges of the laminations exposed, wear better and more evenly than where the leaf-like Figure of the grain is shown on the surface, as it would be in the case of the board b.