The chief qualities of timber are: - strength, the ease or difficulty with which it is split, hardness, toughness, elasticity, texture, colour and smell, weight, durability, and its capacity for shrinking and swelling. The two last mentioned qualities have already been taken up.

It is obvious that most of these qualities depend not only on the kind of tree from which the timber is obtained, but also on many incidental circumstances, such as climate and soil, the age of the tree, the season of the year when it was cut down, subsequent treatment, etc. It is therefore hardly-possible to make any general statements regarding them which shall hold good in all cases.

1. The strength of timber is shown by its power of resistance to pressure, rupture, tearing, and twisting.

The oak and the Scotch fir present the greatest resistance to pressure. The oak, the ash, the spruce fir, and next after them the Scotch fir, the larch, and the aspen, resist rupture best. In this respect the beech and the alder are not so strong. The oak and the ash, and after them the beech, the spruce fir, the Scotch fir, and the elm, present the greatest resistance to tearing.

2. The ease or difficulty with which different kinds of wood may be split. By this is meant the greater or lesser ease with which timber may be divided by a wedge-shaped tool in the direction of the length of the fibres. It is closely related to the quality of the fibres and the manner of their distribution. Wood which has grown quickly has long straight fibres, is free from knots, and is easily split. "Cross-grained " wood, the fibres of which twist and cross each other, and the wood of roots and of branches with knotty excrescences, is difficult to split. Wood from the lower part of the trunk nearest the roots is the most difficult of all to split.

When the medullary rays are large and long as in beech and oak, or numerous and fine as in needle-leaved trees, timber is easily split in radial section, but all timber is harder to split in tangential than in radial section.

The following timbers are difficult to split: - figured birch, hornbeam, elm, maple, and white-beam.

The following are easy to split: - ash, beech, alder, oak, aspen, Scotch fir, spruce fir, lime, poplar, and chestnut.

Old knotty oak, however, may present great difficulty.

3. The density or hardness of timber is shown in the resistance it offers to the tools with which it is worked. It is impossible to give definite statistics on this point, because it depends so much on circumstances, e.g., the varieties of texture in the same tree, the nature and arrangement of the fibres, the degree of moisture, the presence of resin, etc., etc.: the general rule, however, holds good, that close-grained timber with high specific gravity is hard (it being understood that comparisons are always made with seasoned wood). Seasoned timber is harder than green timber. Green heart-wood is harder than sap-wood. Resinous heart-wood is very hard, and this is also true of timber which has fine annual layers, as is shown especially in the extremely hard resinous knots often seen in planks.

The resistance which timber presents to the axe is greatest at right angles to the length of the fibres, and it decreases in proportion as the angle becomes more acute. It is least when the blade of the axe is parallel with the direction of the fibres' length, as in splitting.

Resistance to the axe and the saw.

The saw, on the other hand, works by tearing the fibres, and consequently it meets with most resistance in loose-textured timber with long tough fibres. Such timber makes the edge of the saw uneven. In close-grained timber with short fibres the saw works easily, and the edge keeps more even. Consequently, for heavy close-grained timber the saw does not require to be set so much. In certain kinds of timber moisture increases the toughness of the fibres, and on this account unseasoned timber is more difficult to saw than dry wood.

The hardness of timber is very important in all cases where it is exposed to blows, concussions, and general wear and tear.

For ordinary purposes the hardness of any piece of wood may be tested by cutting it with a knife.

The hardest timbers of all are lignum vitae and ebony. The ordinary kinds of timber may be classified as follows: Hard: hornbeam, maple, apple, pear, oak, and beech. Medium: ash, elm, white-beam, walnut, birch, lime, and chestnut.

Soft: Scotch fir, spruce fir, larch, alder, aspen, and poplar. As has, however, been indicated above, spruce fir with fine annual layers and resinous Scotch fir are often very hard, and they might thus find a place in the higher class.

4. The toughness and elasticity of timber. A piece of timber which may be bent without breaking, and which does not resume its former shape when the bending force is removed, is said to be tough; if it does resume its former shape, it is said to be elastic. Generally speaking, both these qualities co-exist in all timber, but one is usually more predominant than the other, according to the kind of wood. Thus some timbers are said to be elastic and others tough.

Unseasoned wood is tougher than dry wood, and what it gains in elasticity during seasoning it loses in toughness. Damp heat increases toughness; hence hoops and sticks are "steamed " in order that they may be bent.

As a general rule light timber is tougher than heavy timber, roots are tougher than stems; sap-wood is tougher than heart-wood, and young timber is tougher than old.

The toughest timbers are the following: - hornbeam, elm, ash, aspen, birch, juniper, hazel, osier, maple, and white-beam.

Lime, alder, beech, and the heart-wood of oak are only moderately tough.

Elasticity is increased by seasoning, and is generally great in heavy timbers. It is of great importance in the manufacture of many articles, e.g., masts, oars, wooden springs, the handles of spades, axes, hammers, etc.