The best method of preserving timber, and preventing decay from any of the above causes, is by proper seasoning, but it must be thoroughly seasoned, partial seasoning being of little avail. A coating of paint, tar, or other preparation, will help to defend the wood from injury by external causes, but will be of no service if any moisture remain in the interior, for it will only prevent its escape, and thus hasten decay. Paint is also useless, unless fresh coats be repeatedly applied, for it is as liable to decay as the timber itself, and therefore requires to be constantly renewed. If the paint be sanded over, it will be found much more durable than common painting. A very good preparation consists of linseed oil and tar put on boiling, the wood being first thoroughly heated ; this will sink into the wood, and close up all the pores. Charring the wood will be found an excellent method, and is in many respects better than some of the above. No composition should, however, be applied till the timber has been well seasoned, for to inclose the natural juices of the wood, is to render its rapid decay certain.
Description of oak there are several kinds, two of which belong to England—the common British oak, and the sessile-fruited oak. The first is found in the temperate parts of Europe, and is that which is commonly met with in the south of England. The wood lies often a reddish tinge, and the larger septa are very numerous, producing large flowers ; the grain is tolerably straight and fine, and free from knots. It splits freely, and makes good laths for plas terers and slaters ; and is decidedly the best kind of oak for joists, rafters, and firr any other purposes where still' and straight-grained wood is required. The second kind is found in the temperate parts of Europe, and in the north of England ; it is of a darker colour than the preceding, and the larger septa are fewer in number ; the grain is smooth and glossy. It is heavier, harder, and more elastic, and is apt to warp and split hi seasoning ; it is tough, and difficult to split.
The Dursault oak is a native of France and the south of England, but it is not so strong nor of so firm a texture as the above. The wood of the Austrian and American species is not very valuable ; the former being comparatively soft and the latter coarse-grained. The mountain red oak, from Canada, is useful for many purposes, but is light and spongy, and not very durable. The white oak, also from America, is more valuable, being tough and pliable, and more durable than the other species.
The colour of oak is a fine brown of various shades; that inclined to red is the most inferior kind. The transverse septa are usually large and distinct, but are smaller and less distinct in the stronger kinds of wood. The texture is alter
nately compact and porous.
Oak is particularly adapted for situations exposed to the weather, and makes the best wall-plates, ties, templets and king-posts, but is liable to twist and warp when drying.
Beech is not much used for building, and soon rots in damp situations; in dry situations it is more durable, but is liable to be injured by worms ; it is best adapted for piles and other works where it is constantly immersed in water. It is stronger and tougher than oak, but not so stiff. The colour is whitish-brown, of different shades; the texture is very uniform, and the septa smaller than in oak.
Alder has much the same qualities as beech, being very durable in water, but rotting when exposed to damp, and subject to worms in a dry state. The colour is reddish yellow of different shades, and nearly uniform ; the texture is very uniform, with larger septa of the same colour as the wood. It is soft, and works easily.
Of plane trees, that from America is very durable in water, but they are not much used flir building purposes. The colour and structure is similar to that of the beech, but in this case the septa are more numerous.
Chesnut may be used in many places as a substitute for oak, the wood is hard and compact ; when young it is tough and flexible, but when old it is brittle and often shaky. It does not shrink and swell much, and is easier to work than British oak, and contains only a small proportion of sap wood.
The wood of Chesnut is so much like that of oak, that it has frequently been mistaken for it ; it has, however, no large transverse septa, and in old wood the sap-wood is whiter, and the heart-wood browner, than in oak.
Ash is superior to any other British timber for its tough ness and elasticity ; it is tolerably durable in a dry situation, but soon rots when exposed to damp or alternate changes of wet and dry. It is too flexible for the timbers of buildings, and in old trees is of a brittle nature. The colour is oak brown, the veins being darker than in oak; in young trees, however, the colour is lighter. The texture is alternately compact and porous, the rings being strongly marked ; there are no large septa.
Elm is not much used for building ; it is very durable in water, as also when perfectly dry, but will not stand exposed to the weather. It is difficult to work, but not liable to split; it twists, shrinks, and warps much in drying. The heart wood is generally darker and redder than that of oak, and the sap-wood of a yellowish or brownish white; it is porous and eross•grained, but has no large septa.