Of the boring-worms tho only varieties hitherto specially noticed are the Tender naralis and the Limnoria terebrans ; and their ravages seem to be the most dangerous when wood is exposed to them iu decidedly salt water. The Limnoria, however, occasionally attacks timber in slightly brackish water, and it would seem that both these species of worms have an antipathy to water containing eulphurctted hydrogen, or some of the vegetable and mineral acids ; for they do not attack timber driven into the sea-shore near the outlets of sewers, and they avoid timber which either contains, naturally, considerable pro portions of pyroligneous acid, or has been artificially impregnated with creosote, sublimate of mercury, sulphate of copper, &e. The supposed immunity of the green-heart timber was long attributed to the exist ence of some such quality in it ; and though it is now known that the boring-worms do attack that wood, they certainly do not destroy it with anything like the same rapidity that they destroy fir, beech, elm, or even oak. Notwithstanding the fearful nature of the ravages caused by tho boring-worms, the habits of those creatures have not been the ' roughly studied ; and it is difficult to trace tho conditions which tend the most decidedly to their multiplication. It would seem, however, that both the species are to be found in the greatest numbers in warm Latitudes ; that the Tcrcdo prefers the sea-shores from which it can derive the carbonate of lime necessary for its growth ; that the Lim noria, on the contrary, prefers the shores upon which the sands are charged with the decomposition of silicious rocks ; and that the por tions of the timber devoured by both these worms occur a little below and a little above the lines of high and low water : these worms, in fact, require both air and water. The works of Messrs. Forbes and Hanley (' History of British Mollusea '), Cailliaud (` 516moire cur les Mollusques perforantes '), ' L'Instruction Bur les boil de Marine,' published by the French Government, and a Report by a Commission of Dutch engineers and naturalists on the boring-worn, published in Amsterdam, 1860, should be consulted by all who are interested In the durability of hydraulic works, or in shipbuilding. Opinions seem to be divided as to the merits of the various schemes proposed for resisting the attacks of the worrier upon timber. Some engineers recomniend exclusively the use of eopper sheeting, or of copper nails, over the whole exposed surfaces; whilst °there recommend exclusively the use of treasons. In practice, it is found that the worms frequently make their way into timber in the intervals between the nails, and then devour the inner portions. Ten years' experience would also appear to show that when the creosote has been thoroughly Injected into the heart of a piece of timber, the worms will not attack the latter.. The injection of mineral salts, by liyau's patent (mercury) or by 31argery's patent (copper), does not seem to produce any permanently good effect ; for they are all removed in course of time by the action of seawater frequently renewed by the tido.
The system of injecting creaeote seems also to provide an efficient protection against the ravages of the white ants, which are so incal culably numerous, and so destructive to timber in tropical latitudes. It also odds greatly to the durability of timber in damp confined positions ; and resists the tendency of the timber to assume either the wet or the dry rot. Tho two last-named modes of decay are of the most serious importance to the solidity of the buildings into whose construction timber enters largely. They affect all kinds of timber, whether native grown or foreign • and though tolerably well under stood by physiologists, and by men, it is too much the case that they are unattended to in the application of these materials.
Dee !tor has already been treated of. The Wet Rol proceeds from a chemical action in the wood itself, which may either arise from the decomposition of the sap retained is it, or from the decomposition of the vegetable tissue under the influence of confined moisture : for the albuminous parts of the sap, or of the wood, commence a putrefactive process directly they meet with the conditions of heat and moisture necessary for its development. It is therefore important that all
timber should be cut at the season of the year when the trees contain least sap, and that the timber should be preserved in such positions as to allow the sap to pass away, for some considerable time before it is used in a building; this precaution is technically called seasoning. it is therefore the custom to fell timber during the winter and early spring months, because at those seasons the sap circulates with the least activity ; or the time of the year for carrying on this description of work may be said to range between October and April. In addition however to this precaution, and to a careful seasoning, it is essential to remove all the alburnum of a tree, if it should be required for use in confined situations, for the fluids it retains ferment quite as dangerously to the durability of the timbeir as does the sap itself. The architect and the shipbuilder cannot be too particular in excluding sappy timber from positions where there would not exist a free circu lation of sir, and where there is any moisture. Sappy wood, moreover, is soft, and of a feeble power of resistance. The decomposition which takes place in timber affected by druxy, or by dead knots, is of the same character as the ordinary wet rot ; that is to say, it proceeds from a chemical action in the wood.
A mode of rendering timber less combustible has been described under FergOOFIXO.
I Vorking is hI'ood.—The cutting up of timber into beams and planks is described under Sew, j and into thin layers under VENIT11- 7NO. The use of timber in building-work is illustrated in such articles as CA II l'ENTII House, HOOP, &C. ; and the use of fine woods in Ceurma and BIAIIQIIETRT. We proceed to a few manufacturing processes not hitherto described : first noticing, however, that Mr. If oltzapffel, for practical purposes, classifies woods under eighteen groups, according as they are used for ship-building, hydraulic engineer ing, house carpentry, machinery frame-work, rollers, teeth of wheels, foundry patterns, common turnery toys, best Tunbridge toys, hard wood turning, common furniture, best furniture, ornamental work, elastic work, inelastic work, carving, colour and dye-woods, and scent woods.
Timber-bending has recently occupied considerable attention. Various plans have been introduced by Meadows, Ilookey, and other inventors, for dile purpose, chiefly by the application of steam and pressure; but the moat effective seems to be that of Mr. Blanchard, of Boston. lie has established a manufactory for bending timber of various kinds and sizes, and rendering it applicable for the making of chair backs, gig-shafts, sofa-frames, horse-haes m, plough-handles, wheel felloes, arch-pleces, staircase-rails, curved mouldings, ship-timbers, &c. Oak-timber 14 feet long sad 16 inches square can be bent to a curve In one hour, and timber of 0 inches square in twenty minutes. A piece 12 feet long, 124 inches wide, and 7 inches thick, can be bent Into a perfect and penoanent semicircle. A trough is prepared, of the proper size and form for the curve ; one side of which is rendered moveable. There is a lever, turning on a central axis, and a travelling table under the lever. The tindx.r, after being steamed for some Lours, is laid on a flexible band of metal placed on the travel ling table, and is pressed and clamped down firmly to IL One end of the timber is next clamped to one end of the curved trough ; the other end butts against a block, acted on by a screw. The action of the lever then drives or forces the timber into the trough ; the two ends of the timber ere connected by a tie or chord ; the fourth side pf the trough is then put in its proper piece ; and the timber, thus clamped and bound with a ournbination of forces, is left till cold. It is now found to have acquired a permanent set, without any rending, crip pling, or loss of harshness and durability. The timber, in the first instance, is not put aiinply into a vowel full of .twain ; it is introduced into a hot closet, through which steam at low pressure passes in a continuous current.