188. M. Boucherie, to whose able researches on this subject reference has been made, noticing the slowness with which aqueous solutions were imbibed by wood, when simply immersed in them, conceived the ingenious idea of rendering the vital action of the sap-vessels subservient to a thorough impregnation of every part of the trunk where there was this vitality. To effect this, he first immersed the butt end of a freshly-felled tree in a liquid, and found that it was diffused throughout all parts of the tree, in a few days, by the action in question. But, finding it difficult to manage trees of some size when felled, M. Boucherie next attempted to saturate them before felling; for which purpose he bored an auger-hole through the trunk, and made a saw-cut from the auger-hole outwards, on each side, to within a few inches of the exterior, leaving enough of the fibres untouched to support the tree. One end of the auger-hole was then stopped, as well as all of the saw-cut on the exterior, and the liquid was introduced by a tube inserted into the open end of the auger-hole. This method was found equally efficacious with the first, and more convenient.

189. After examining the action of the various neutral salts on the soluble matter contained in wood, M. Boucherie was led to try the impure pyrolignite of iron, both from its chemical composition and its cheapness. The results of this experiment were perfectly satisfactory. The pyrolignite of iron, in the proportion of one fiftieth in weight of the green wood, was found not only to preserve the wood from decay, but to harden it to a very high degree.

190. Observing that the pliability and elasticity of wood depended, in a great measure, on the moisture contained in it, M. Boucherie next directed his attention to the means of improving these properties. For this purpose, he tried solutions of various deliquescent salts, which were found to answer the end proposed. Among these solutions, he gives the preference to that of chloride of calcium, which also, when concentrated, renders the wood incombustible. He also recommends for like purposes the mother water of salt-marshes, as cheaper than the solution of the chloride of calcium. Timber prepared in this way is not only improved in elasticity and pliability, but is prevented from warping and cracking; the timber, however, is subject to greater variations in weight than when seasoned naturally.

191. M. Boucherie is of opinion that the earthy chlorides will also act as preservatives, but to ensure this he recommends that they be mixed with one fifth of pyrolignite of iron.

192. From other experiments of M. Boucherie, it appears that the sap may be expelled from any freshly-felled timber by the pressure of a liquid, and the timber be impregnated as thoroughly

as by the preceding processes. To effect this, the piece to be saturated is placed in an upright position, so that the sap may flow readily from the lower end; a water-tight bag, containing the liquid, is affixed to the upper extremity which is surmounted by the liquid, the pressure from which expels the sap, and fills the sap-vessels with the liquid. The process is complete when the liquid is found to issue in a pure state from the lower end of the stick.

193. Either of the above processes may be applied in impregnating timber with coloring matter for ornamental purposes. The plan recommended by M. Boucherie, consists in introducing separately the solutions by the chemical union of which the color is to be formed.

194. The effect of time on the durability of timber, prepared by any of the various chemical processes which have just been detailed, remains to be seen; although results of the most satisfactory nature may be looked for, considering the severe tests to which most of them have been submitted, by exposure in situations peculiarly favorable to the destruction of ligneous sub

stances.

195. The durability of timber, when not prepared by any of the above-mentioned processes, varies greatly under different circumstances of exposure. If placed in a sheltered position, and exposed to a free circulation of air, timber will last for centuries, without showing any sensible changes in its physical properties. An equal, if not superior, durability is observed when it is immersed in fresh water, or embedded in thick walls, or under ground, so as to be beyond the influence of atmospheric changes.

196. In salt water, however, particularly in warm climates, timber is rapidly destroyed by the two animals already noticed: the one, the limnoria terebrans, attacking, it is said, only stationary wood, while the attacks of the other, the teredo navalis, are general. Various means have been tried to guard against the ravages of these destructive agents; that of sheathing exposed timber with copper, or with a coating of hydraulic cement, affixed to the wood by studding it thickly over with broad-headed nails to give a hold to the cement, has met with full success; but the oxidation of the metal, and the liability to accident of the cement, limit their efficacy to cases where they can be renewed. The chemical processes for preserving timber from decay, do not appear to guard them in salt water. A process, however, of preserving timber by impregnating it with coal tar, patented in this country by Professor Renwick, appears, from careful experiments, also to be efficacious against the attack of the ship-worm. A coating of Jeffery's marine glue, when impregnated with some

of the insoluble mineral poisons destructive to animal life, is said to subserve the same end.

197. The best seasoned timber will not withstand the effects of exposure to the weather for a much greater period than twentyfive years, unless it is protected by a coating of paint or pitch, or of oil laid on hot, when the timber is partly charred over a light blaze. These substances themselves, being of a perishable nature, require to be renewed, from time to time, and will, therefore, be serviceable only in situations which admit of their renewal. They are, moreover, more hurtful than serviceable, to unseasoned timber, as by closing the pores of the exterior surface, they prevent the moisture from escaping from within, and, therefore, promote one of the chief causes of decay.

198. The forests of our own country produce a great variety of the best timber for every purpose, and supply abundantly both our own and foreign markets. The following genera are in most

common use.

199. Oak. About forty-four species of this tree are enumerated by botanists, as found in our forests, and those of Mexico. The most of them afford a good building material, except the varieties of red oak, the timber of which is weak, and decays rapidly.

The White Oak, (Quercus Alba,) so named from the color of its bark, is among the most valuable of the species, and is in very general use, but is mostly reserved for naval constructions; its trunk, which is large, serving for heavy frame-work, and the roots and larger branches affording the best compass timber. The wood is strong and durable, and of a slightly reddish tinge; it is not suitable for boards, as it shrinks about in seasoning, and is very subject to warp and crack.

This tree is found most abundantly in the Middle States. It is seldom seen, in comparison with other forest trees, in the Eastern and Southern States, or in the rich valleys of the Western States.

The

Post Oak, (Quercus Obtusiloba.) This tree seldom attains a greater diameter than about fifteen inches, and, on this account, is mostly used for posts, from which use it takes its name. wood has a yellowish hue, and close grain; is said to exceed white oak in strength and durability; and is, therefore, an excellent building material for the lighter kinds of frame-work. This tree is found most abundantly in the forests of Maryland and Virginia, and is there frequently called Box White Oak, and Iron Oak. It also grows in the forests of the Southern and Western States, but is rarely seen farther north than the mouth of the Hudson River.

Chesnut White Oak, (Quercus Prinus Palustris.) The tim

ber of this tree is strong and durable, but inferior to the two preceding species. The tree is abundant from North Carolina to Florida.

Rock Chesnut Oak, (Quercus Prinus Monticola.) The timber of this tree is mostly in use for naval constructions, for which it is esteemed inferior only to the white oak. The tree is found in the Middle States, and as far north as Vermont.

Live Oak, (Quercus Virens.) The wood of this tree is of a yellowish tinge; it is heavy, compact, and of a fine grain; it is stronger and more durable than any other species, and, on this account, it is considered invaluable for the purposes of shipbuilding, for which it is exclusively reserved.

The live oak is not found farther north than the neighborhood of Norfolk, Virginia, nor farther inland, than from fifteen to twenty miles from the seacoast. It is found in abundance along the coast south, and in the adjacent islands as far as the mouth of the Mississippi.

200. Pine. This very interesting genus is considered inferior only to the oak, from the excellent timber afforded by nearly all of its species. It is regarded as a most valuable building material, owing to its strength and durability, the straightness of its fibre, the ease with which it is wrought, and its applicability to all the purposes of constructions in wood.

Yellow Pine, (Pinus Mitis.) The heart-wood of this tree is fine-grained, moderately resinous, strong, and durable; but the sap-wood is very inferior, decaying rapidly on exposure to the weather. The timber is in very general use for frame-work, &c.

This tree is found throughout our country, but in the greatest abundance in the Middle States. In the Southern States, it is known as Spruce Pine and Short-leaved Pine.

Long-leaved Pine, or Southern Pine, (Pinus Australis.) This tree has but little sap-wood: and the resinous matter is uniformly distributed throughout the heart-wood, which presents a fine compact grain, having more hardness, strength, and durability, than any other species of the pine, owing to which qualities the timber is in very great demand.

The tree is first met with near Norfolk, Virginia, and from this point south, it is abundantly found.

White Pine, or Northern Pine, (Pinus Strobus.) This tree takes its name from the color of its wood, which is white, soft, light, straight-grained, and durable. It is inferior in strength to the species just described, and has, moreover, the defect of swelling in damp weather. Its timber is, however, in great demand as a good building material, being almost the only kind in use in the Eastern and Northern States, for the frame-wark and joinery of houses, &c.

The finest specimens of this tree grow in the forests of Maine. It is found in great abundance between the 43d and 47th parallels, N. L.

201. Among the forest trees in less general use than the oak and pine, the Locust, the Chesnut, the Red Cedar, and the Larch, hold the first place for hardness, strength, and durability. They are chiefly used for the frame-work of vessels. The chesnut, the locust, and the cedar, are preferred to all other trees for posts.

202. The Black, or Double Spruce, (Abies Nigra,) also affords an excellent material, its timber being strong, durable, and light.

203. The Juniper or White Cedar, and the Cypress, are very celebrated for affording a material, which is very light, and of great durability, when exposed to the weather; owing to these qualities, it is almost exclusively used for shingles and other exterior coverings. These two trees are found, in great abundance, in the swamps of the Southern States.

METALS.

204. The metals in most common use in constructions are Iron, Copper, Zinc, Tin, and Lead.

IRON.

205. This metal is very extensively used for the purposes of the engineer and architect, both in the state of Cast Iron, and Wrought Iron.

206. Cast Iron is one of the most valuable building materials, owing to its great strength, hardness, and durability, and the ease with which it can be cast, or moulded, into the best forms, for the purposes to which it is to be applied.

207. Cast iron is divided into two principal varieties, the Gray cast iron, and White cast iron. There exists a very marked difference between the properties of these two varieties. are, besides, many intermediate varieties, which partake more or less of the properties of these two, as they approach, in their external appearances, nearer to the one or the other.

208. Gray cast iron, when of a good quality, is slightly malleable in a cold state, and will yield readily to the action of the file, when the hard outside coating is removed. This variety is also sometimes termed soft gray cast iron; it is softer and tougher than the white iron. When broken, the surface of the fracture presents a granular structure; the color is gray; and the lustre is what is termed metallic, resembling small brilliant particles of lead strewed over the surface.

209. White cast iron is very hard and brittle; when recently