Sivut kuvina
PDF
ePub

Payne's pro

seems to act, firstly, by coagulating the albumen; secondly, by furnishing a water-proof covering to the fiber of the wood; and, thirdly, by preventing the putrefaction of the sap by its antiseptic properties.

The various processes for the preservation of timber, by the absorption of metallic salts, have all more or less failed in practice, and are now very generally abandoned. These are known by the names of the inventors, as Ryan's, MARGARY'S, BURNETT's and Payne's processes. The object sought by each of the three first of these methods was to coagulate the albumen in the capillary tubes of the timber and thus prevent or retard the putrefaction of the sap.

RYAN used chloride of mercury for this purpose, dissolving, at first, one pound of the salt in four gallons of water; but as it was found that the wood absorbed about six or seven pounds of this costly salt per load, more water was added to lessen the expense, until the solution became so weak as, in a great measure, to lose its effect. This process has, therefore, been entirely abandoned. The salt employed by MARGARY was sulphate of copper, which, being much cheaper than chloride of mercury, could be used as a stronger solution. Its efficacy, however, has proved doubtful in many cases, while in not a few instances it has failed altogether. Better than either of the preceding is Sir WILLIAM BURNETT's plan of injecting a solution of chloride of zinc, in the proportion of about one pound of the salt to four or five gallons of water. This process is still in use, and has certainly proved beneficial in a great many cases, but it cannot always be relied upon. cess consisted in the successive injection of two substances in solution; the first, a metallic or earthy solution, and the second, a decomposing fluid; the consequence being, that the capillary tubes of the timber became filled with an insoluble substance. The process of creosoting timber, already referred to, was first patented by Mr. BETHELL, in the year 1848. One great advantage of creosoted timber is, that it perfectly resists the attacks of marine worms and insects, as well as the white ant of India, which is more than can be said for timber prepared with solutions of metallic salts. Even that prepared with corrosive sublimate (as in Ryan's patent) has no immunity in this respect, the albumen appearing to neutralize the poisonous property of the salt.

For ship-building purposes such chemically-prepared or “salted" timber is scarcely to be recommended, as it attracts much moisture and is very destructive to the metal fastenings. Empyreumatic oils and resinous solutions, although these certainly render the wood impervious to moisture, and preserve the iron or metal bolts from oxidation, are still very objectionable from the increased inflammability which they impart to the structure. The time necessarily required in preparing the wood with the preservative substance is also a great drawback to its employment in ship-building, where a delay of even two or three days, more especially in repairing, is often of serious consequence; and it should be remembered, the timber must be operated upon after it has been shaped converted.” Timber may be

very perfectly preserved from subsequent decay by long submergence in shallow salt-water, or, which is still better, in salt mud. When thus treated for a period of from ten to twenty years, the sap gets thoroughly washed out of the pores of the wood by the alternate absorption and expulsion of air or other gases caused by successive variations of temperature. It need scarcely be hinted, however, that such a mode of procedure, though sometimes

66

or

adopted in government dock-yards, would be ruinously expensive to the private ship-builder. Having pointed out the fatal objections generally attending the use of chemically-prepared timber for ships or houses, it remains to show what means can be employed (and that with tolerable certainty) for preserving the timber of these structures from premature decay. The means at our command for this purpose are summed up in the two words,“ seasoning" and " ventilation ;" namely, thorough seasoning or drying of the timber on shore, when this is practicable; but, by all means, good ventilation on board. If these well-known and universally approved principles were but carried out in an honest and commonsense fashion, we should hear but little of rotten gun-boats, or heavy repairs to frigates after a first commission. Though it is undoubtedly true that the closely packed timbers and double planking of a vessel of war present great obstacles to a thorough ventilation of the bottom, much may still be done by conducting currents of air down into the hold and between the timbers by means of wind-sails, or, if necessary, by fanners, worked either by steam or hand, and by so arranging the internal accommodation that there may be as little stagnation of air as possible. However well seasoned and dry the timber may be when the ship is launched, it will rapidly absorb moisture from the damp atmosphere of the hold, unless evaporation from its surface be kept up by a forced circulation of air.

It is certainly unbecoming the scientific character of the age that ships built hurriedly and cheaply, and of very inferior timber, by what are contemptuously called “slop” builders, are known to resist the ravages of dry-rot much better than the expensively and elaborately constructed ships of Her Majesty's dock-yards; nay, more, that these same "slopbuilt” ships, even when constructed entirely of green timber, (as they frequently are,) will last longer than a government ship built with the best seasoned oak.

The whole secret is, of course, the internal ventilation of the hold and frame of the ship. In a cheaply-built merchant-ship the timbers are spaced some distance apart, and the ceiling planks are not placed so close together as hermetically to seal the spaces between the timbers, the consequence being that good ventilation is maintained amongst the planks and timbers of the bottom and sides. Even when such a ship is built of green wood, the circulation of air is generally sufficient to season the timber in its place and prevent its decay, for the dry-rot fungus will not thrive in an atmosphere less moist and stagnant than that of an underground cellar. The shrinkage of green timber in such a case would also conduce to its preservation, by admitting the air between the ceiling planks.

These remarks are not intended to excuse the use of unseasoned timber in ship-building, a practice which should be resorted to only from dire necessity, but rather to show that if ships built of green timber can be preserved by what may be termed accidental ventilation, those built of seasoned timber should, á fortiori, be still more easily preserved by systematic ventilation. The action of heat in causing an upward current of air naturally suggests itself as a ready means of effecting this object on board ship. The dry-rot has been frequently arrested in a ship by thoroughly drying the timbers, holes having been previously cut in the ceiling planks to promote circulation. Yachts and other small vessels,

when not in use, may be preserved from dry-rot by hauling them out of the water in an exposed situation where the wind will get to them, keeping sky-lights and hatches open, and if a

a plank be removed from the bottom they are all the safer. Should they be entirely closed up, on the other hand, the dry-rot will flourish within like mushrooms in a hot-bed.

Sap-wood should always be removed from the timbers and planks of a ship, as, from its spongy texture and imperfect development, it is more liable to dry-rot than the heart-wood (besides being much weaker ;) and when the dry-rot has once commenced, either in a ship or a house, it is rapidly propagated by contagion. The process of seasoning timber quickly by a current of heated air will be found amply detailed in the article Ship-Building.

Timber is bought and sold by solid measure, according to the number of cubic feet in the tree or log. The measurement of timber is therefore the operation by which these cubic contents are determined ; that is, multiplying together the three dimensions, the mean length, the breadth and the depth of each log. If the log should vary much in size in different parts, then the length, breadth and depth of each of these parts must be multiplied together, and the contents of the log will be the sum of the products. When the log tapers, a mean breadth or depth is taken; the object in every case being, to attain the most correct approximation to the contents of the log. In measuring rough logs it is, however, usual to gird the log at the measuring place with a string, and then, folding the string into four equal parts, to assume this fourth part of the girth to be one side of the square area at the measuring place; which area, when multiplied by the length, will give the solid contents of the log: The arithmetical operation, simple as it is, is universally superseded by the more simple and far more correct plan of referring to published tables of contents, calculated for every foot in length of a log, and every quarter of an inch in the side of the

square. Those most generally used for this purpose are in HOPPERS’ Practical Mea

In measuring standing timber the length is taken as high as the tree will measure 24 inches in circumference, less than which measurement is not considered as timber. At half this height the measurement for the mean girth of the timber in the stem of the tree is taken; one-fourth of this girth is assumed to be the side of the equivalent square area. The buyer has in general the option of choosing any spot between the buttend and the half-height of the stem as the girding-place. All branches, as far as they measure 24 inches in girth, are measured in with the tree as timber. An allowance, which varies according to circumstances, is generally deducted for the bark. In oak it is from about one-tenth to one-twelfth of the circumference at the girding place; in other sorts of timber it is less. In all, however, this allowance depends much upon special agreement.

It is usual to speak of timber by the load, which means 50 cubic feet of squared timber, or 40 cubic feet of rough timber. A load of plank is dependent upon its thickness. Thus, it will require 200 square feet of three-inch plank to make the load of 50 cubic feet; therefore, the load of plank is the number of square feet of its respective thickness which is necessary to make the load of 50 cubic feet. Deals are measured according to their thickness and lengths, by the hundred, reckoning 120 to the hundred.

surer.

PRINCIPAL PLANTS AND THEIR USES.

EAGLEWOOD-BARWOOD-BRAZILETTO-W00D-CASSIA-Gum COPAL-ACACIA.

We are indebted for the following summary to the monthly Chemist and Druggist, London, 1861.-Eds. M. M.

ALOEXYLUM.—One of the two sorts of Calambac, Eaglewood or Lign Aloes, a fragrant substance, more grateful to Oriental nations than any other perfume, is the produce of the species Agallochum. LOUREIRO states that it consists of a concretion of the oily particles into a resin in the centre of the trunk, being brought on by some disease of which the tree ultimately dies. It is said to be stimulant, corroborant, cephalic and cardiac, and its scent is stated to be employed against vertigo and paralysis.

BAPHIA.—The dyewood, known under the name of Camwood or Barwood, is the produce of the species Nitida. It is stated to be employed, in conjunction with sulphate of iron, in the production of the dark red color of the English Bandana handkerchiefs.

Bauhinia.—Fibers which are employed for the purpose of making ropes are obtained from the species Parviflora, Racemosa and Vahlii. A brownish-colored gum is said to be produced by the species Emarginata and Retusa. The buds and dried flowers of the species Tomentosa are said to be employed by the Indian practitioners in dysenteric affections. An astringent bark`is yielded by the species Variegata, which is used in medicine, and also for dyeing and tanning leather. Various other species are reported to be employed in Brazil for their mucilaginous properties.

CESALPINEA.—Braziletto-wood, which yields fine red and orange colors, is said to be the produce of the species Braziliensis. Brazilwood, employed for dyeing red, rose-color and yellow, is stated to be yielded by the species Crista. Nicaragua, Lima or Peachwood, employed for dyeing red or peach-color, is produced by the species Echinata. The exact species yielding these three dyewoods cannot, however, be said to have been yet determined with certainty. The wood of the species Echinata is stated to possess tonic properties. The legumes of the species Coriaria,“the Libidibi, or Divi-divi pods," furnish us with one of the most astringent substances known; they are extensively employed for tanning purposes. The roots of the species Moringa and Nuga are said to be diuretic. An oil is stated to be obtained from the species Oleosperma. The legumes of the species Papai, termed Pi-pi, are employed for similar purposes to those of the species Coriaria, but are very inferior to them. The Bukkum, Bookum or Sappan-wood of India, used for dyeing red, is the produce of the species Sappan. The root known as Sappan-root, or yellow-wood, is employed for dyeing yellow.

Cassia.—The seeds of the species Absus are very bitter, and somewhat aromatic and mucilaginous. They are employed in Egypt as a remedy for ophthalmia, under the title of Chichon, or Cismatan. The bark of the species Auriculata is stated by Roxburgh to be employed in medi

cine, and for the purposes of tanning and dyeing leather ; the flowers are said to be used for dyeing yellow. The pulp of the fruit of the species Fistula (Cathartocarpus Fistula) possesses purgative properties, and is officinal in our pharmacopæia. That of the species Braziliana, which is probably only a variety of the above, has a larger, longer and rougher fruit. It is employed in veterinary medicine, under the title of Horse Cassia, and possesses similar properties. The several kinds of Senna met with in commerce consist of the leaflets of various species, but the exact species yielding some of them cannot at present be said to have been accurately determined. The species Officinalis var. Lanceolata, and the species Obovata, are generally considered to be the source of the Alexandrian Senna. The common East Indian, Mecca or Bombay Senna is considered by Royle to be the produce of the species Officinalis var. Acutifolia. PEREIRA attributes it to the species Elongata of LEMAIRE, while Forskal states it to be from the species Lanceolata of Forskal and LINDLEY. Tinnevelly Senna is said to be furnished by the species Officinalis var. Elongata. (C. Lanceolata of Royle.) These are the three kinds which are officinal in our pharmacopeias, and are generally employed in this country. Alexandrian Senna is frequently adulterated with the leaves of Solenostemma (Cynanchum) Argel. Nat. Ord. Asclepiadaceæ. The Asclepias, or Milkweed order, Tephrosia Apollinea. Nat. Ord. Leguminosæ, &c. These sophistications may at once be detected by the leaflets being equal-sided at their base, whereas the Sennas are all unequal. Tripoli Senna is stated to be the produce of the species Ethiopica, American of the species Marilandica, and Aleppo of Obovata.

CERATONIA.—The fruit of the species Siliqua, known as Carob, Locust, Algaroba Bean, St. John's Bread, possesses a sweet, nutritious pulp, supposed by some to have been the food of St. John in the wilderness. It is said to be used in the south of Spain as a food for horses, and is now imported into this country as a food for cattle. Singers are said to chew it for the purpose of improving their voice. The seeds are stated to have been the original carat weights of the jewellers.

CODARIUM.—The fruit of the two species Acutifolium and Obtusifolium, known as Brown and Velvet Tamarinds in Sierra Leone, have an agreeable pulp, which is eaten.

COPAIFERA.-Several species of this genus, if not all, furnish the oleoresin known as Balsam of Copaiba, the quality of which, probably, varies with the species. Among the principal species are probably Coriacea, Langsdorfii, Multijuga, Officinalis, &c. The species Bracteata and Pubiflora furnish the Purple-heart or Purple-wood of Guiana, which is largely employed for mortar beds and the manufacture of musket ramrods.

DIALIUM.—The species Indicum yields a fruit having a delicate, agreeable pulp, less acid than that of the Tamarind. It is termed the Tamarind Plum.

Eperua.—The species Falcata is the Wallaba tree of Guiana, which, according to Sir R. SCHOMBURGHK, yields a very durable wood, of a deep red color, frequently variegated with whitish streaks. The bark is bitter, and is stated to be used by the Arawaak Indians as an emetic.

GLEDITSCHIA.—The species Triacantha yields a fruit similar to that of the Ceratonia Siliqua. In North America it is termed the Honey Locust.

GUILANDINA.-The species Bonduc, or Nicker tree, yields a bitter tonic

« EdellinenJatka »