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When an ordinary timber tree is sawn across, it is seen to be made up series of more or less concentric rings——the annual rings, or rings of growthwhich surround a central small core, the pith, and the whole is enclosed by a more or less thick layer of bark. Through the mass of the wood passes a number of minute radial lines, the medullary rays, which begin at the outer surface of the wood and pass inward, some few reaching to the pith.
When the tree is living, the actual living growing part is confined to a thin layer—the cambium-lying between the wood on the inside and the bark on the outside, and forming both by the division of its cells. In this climate growth is at a standstill during the winter, but as soon as spring comes it recommences, the cambium cells divide up and become specialised, forming on the one side the wood and on the other the bark cells. At first, in spring, when the supply of nutriment is not very large, the cells are large and thin-walled, whilst, as the supply of nutriment becomes larger, the walls of the cells become thicker, and therefore the cavities smaller ; thus the outer portion of each annual ring is different in colour to the inner portion, and as the dark portion of one ring comes against the lighter portion of the next, the rings are clearly marked. In tropical countries, where growth keeps on all the year round, the distinction between the annual rings may be quite obliterated. The cells of the cambium become very much modified in form, the exact form varying with the nature of the wood, but the wood is always made up of elongated cells packed closely together, thus producing the fibre or grain of the wood, the fibres being more or less broken up by the cellular patches of the medullary rays, and through the mass running parallel with its fibres there may be ducts or passages, or long vessels.
Water in Wood. When the tree is living it always contains a very large quantity of water (50 to 70 per cent.), this being much greater in the younger parts of the plant than in the older, and greatest of all in the leaves. The amount of water varies with the season, and is always greatest when the growth is most active-in the summer. Even when there is most water present, however, the vessels are largely filled with air, so that the wood is lighter than water and will float, though the materials of which it is composed are actually heavier.
Felling Timber.— When wood is to be used for timber it should be felled in winter or early spring, when vitality is least active, as then the amount of water present is much less than at other seasons. The bark is then stripped off, and the wood is left exposed to the air, lifted off the ground and sheltered from the rain for months or years, till it becomes air-dried, and in this condition it may contain from 10 to 15 per cent. of water. The more perfectly the wood is dried, the more durable is it likely to be when used in structures.
Shrinkage of Wooll.- As the wood loses water it shrinks, and the shrinkage is greater in the case of the newer wood than the older, and as this new wood is outside, the contraction necessarily produces radial cracks. If planks be cut out of the wood before the shrinkage is complete, or if the wood be subsequently more thoroughly dried, they will warp, the warping always being determined by the greater contraction of the younger wood." Dry wood exposed to moist air will absorb moisture, and this causes an expansion exactly the reverse of the contraction produced on drying the absorption of water, and corresponding expansion being due to the presence of constituents in the cells, which absorb water and expand in so doing. The expansion may be so great that the cracks in a dried disc may completely close up.
Formation of Wood.-The cells in the living and growing cambium layer have thin walls of cellulose, and contain the nitrogenous matter known as protoplasm. As these cells become converted into woody tissue, the walls become very much thickened and changed in character. The protoplasm to a large extent disappears, and the cells and vessels contain various elaborated products, such as stareh, resins, gum, &c., the nature and quantity varying with the plant.
Cellulose.-The primary constituent of the cell wall in the young and growing plant is cellulose, a substance which is to be had in a nearly pure form in cotton and unsized paper. It has the formula (C. 1,605), and contains carbon 44:44 per cent., hydrogen 6:17 per cent., and oxygen 39-39 per cent. It is very inert to all ordinary decomposing agents, such as air and moisture, but is acted on by certain re-agents, yielding products which are of commercial importance.
When cellulose is treated with sulphuric acid it is converted into an amorphous mass known as amyloid. Advantage is taken of this reaction in the manufacture of parchment paper, which is paper which has been partially converted into amyloid by the action of sulphuric acid.
When cellulose is treated with a mixture of nitric and sulphuric acids it gives rise to nitro-substitution products, the most important of which C,, H, (NO,) ,0 020, is called pyroxyline or gun cotton, and is a powerful explosive
. Nitro-cellulose treated with camphor yields the substance celluloid, which is so largely used for the manufacture of small articles.
Treated with an ammoniacal solution of copper oxide the cellulose is dissolved, and is reprecipitated from the solution on addition of acid. When such a solution is evaporated it leaves a gummy mixture of copper, oxide, and cellulose. Willesden water-proof paper is prepared by passing paper through the ammoniacal solution and then drying it. The amorphous layer of copper, oxide, and cellulose left on the surface is perfectly water-proof.
Composition of Wood.- As the growing cells become differentiated into the wood cells, and the walls become thickened, the cellulose undergoes very great changes. On the outer side of the cambium layer various complex adipocelluloses are formed, and on the inner side various ligno-celluloses. Ordinary woody tissue is largely made up of ligno-cellulose--a mixture of cellulose and lignine. Lignine has the composition C, H,. 020, and contains, therefore, 55-5 per cent. of carbon, and it is comparatively richer in hydrogen than cellulose. In addition, the cells contain, intermixed with the cellulose and lignine, small quantities of complex bodies containing nitrogen. The cells themselves may contain starch and other materials stored up by the plant for its future use, and the vessels may contain resins and other complex bodies.
Wood, therefore, cannot be regarded as being a definite substance, but rather as being a mixture of substances, some of which are much less stable, and are more readily attacked by organisms and inorganic re-agents than others.
The average composition of dry wood is about–Carbon, 50 per cent.; hydrogen, 6 per cent.; oxygen, 41 per cent.; nitrogen, 1 per cent. ; and ash (mineral matter), 2 per cent. ; but all the constituents vary somewhat according to the nature, age, &c., of the wood.
Seasoning of Timber. - Wood, as has been mentioned above. is always seasoned before use. The object of the seasoning is to get rid of as much water as possible, and thus to reduce the weight and to dry up the more easily decomposable matters in the sap. Air seasoning is generally used. The wood is then stacked so as to be protected from sun and rain, and so as to be freely exposed to the air on all sides-a free circulation of air being one of the chief essentials of good seasoning. Air seasoning may occupy from two to four years. In water seasoning the wood is kept under water for some time. In hot-air seasoning the wood is exposed to air artificially warmed to a temperature of from 100 degrees Fahr. to 250 degrees Fahr. Various other methods of seasoning are used occasionally.
Varieties of Wood.-Many woods are used for constructive purposes, and they vary very much in character and properties. Some are used on account of their strength, others on account of their colour or the grain which they show on the cut surface, and others for other characteristics.
The only classification of woods that need be mentioned here is their division into soft and hard. The soft woods are chiefly derived from the coniferous trees, and contain various resins, though the birch, which yields a soft wood, is not a conifer. All the other timber trees yield hard woods. The hard woods are usually more durable than the soft woods.
Durability of Wood.- Wood, under suitable corditions, is very durable, but under others it decays rapidly. The constituents of wood are so inert that the decay is never brought about by tho action of chemical forces alone, but always requires the aid of the lower forms of life; the conditions, therefore, which favour the decay of wood are always those which favour the growth and development of the organisms which produce it.
Dry Rot.— The best-known disease of wood is that known as dry rot. The wood becomes darker in colour, decreases in weight, acquires a musty smell, and
may become so soft that it can be cut with a knife, “almost like cheese" if it be wet, but, if dry, crumbling under very slight pressure to a brown powder, and thus the wood becomes weak and thoroughly rotten. Dry rot is produced by the growth of a fungus (Merulius lacrymans), which lives on the wood and ultimately destroys it. The spores of the fungus germinate on damp timber; their germinal tilaments pass into the wood, pierce through the cell walls and among the cells, so as to draw nutriment from the nitrogenous matter, lignine, and other materials present on which they can live, and thus, as it uses up part of the material, it disintegrates and breaks up the remainder.
The conditions which favour the development of the fungus are of two kinds -those of the wood itself, and those of the surroundings. The less perfectly the wood has been dried, the more readily will the fungus be able to find nutriment. Moisture is essential to the development of these forms of life, and unless this be present the “rot” cannot set in. "Dry timber kept dry is proof against dry rot” (Marshall Ward's “ Timber and Some of its Diseases,” page 191). One of the prolific causes of dry rot is the use of wood not sufficiently seasoned. Professor Ward says, “ It is clearly an act worthy of a madman to use fresh, 'green' timber for building purposes; but it seems certain that much improperly dried and by no means - seasoned' timber is employed in some modern houses. Such wood is peculiarily exposed to the attacks of any spores or mycelium that may be near.”
As to the surroundings, dampness is one of the most important favourable conditions; and if the wood itself be not damp, it may be in contact with damp masonry or other things, and may be surrounded by a damp, stagnant atmosphere. These, with darkness and moderate warmth, are just the conditions under which the fungus can grow and flourish.
Obviously, therefore, if dry rot is to be prevented, not only must the timber be put in dry, but it must be kept dry, and the space around it must be kept thoroughly ventilated.
It must be remembered that the disease is always propagated by the spores or mycelium of the fungus. As these spores are extremely small, not more than foon of an inch in diameter, and are very light, they will be easily carried about, and one piece of timber may infect many others. Dry rot, as far as it is known, only attacks wood in buildings, &c., and is unknown in the forest. There are, however, many other fungi which produce similar results. fine forest, it is frequently found that the stumps of the trees which have been cut down, whilst little changed in appearance, have become so rotten that they can easily be broken up, and often they fall in a powder under pressure. This change is due to the action of various fungi, the function of which in nature is, no doubt, to break up and destroy useless wood.
Wet Rot.-Growing trees are as subject to decay as cut timber, the heart wood being usually attacked, the tree being often left hollow. This is likewise usually, if not always, due to the action of a fungus, which, living on the nutritive portions of the wood, breaks up and destroys the remainder.
Other Cases of Decay – Wood decays more or less rapidly in almost all positions, the decay being always the result of the growth of the fungi, or other low forms of life, at the expense of the wood, since the constituents of the wood are so inert that-apart from the action of living organisms – there would be little tendency to decay.
Preservation of Timber.---Obviously, if the decay of timber is produced by the action of living organisms, the decay can be prevented by destroying the organisms, or making the conditions such that they cannot thrive.
If the wood is perfectly dry, painting the surface, or covering it with a later of some impervious material, may preserve the timber ; but if it be at all daip, then such a coating will do more harm than good, for it will prevent the
escape of moisture, even if the surface be exposed to the air. It very often happens therefore, that a carefully painted piece of timber will be destroyed, except for a thin external shell.
The fungus is killed by creosote, mercuric-chloride, copper sulphate, and many other mineral poisons; but the mere application of these to the surface of the wood is of little avail, as decay may still go on in the interior. Similarly, charring is only a very partial protection; the layer of charred wood gives sonie protection, and in charring the wood below will be more or less thoroughly dried, but moisture will soon be absorbed again, and then decay may set in.
The only satisfactory method of preventing the ' rot is to thoroughly saturate the timber with the antiseptic solution—that is, the air in the cells and vessels must be completely, or at any rate to a large extent, displaced by the antiseptic solution, so that the material on which the fungus has to feed is effectively poisoned.
In Bethell's process, which is perhaps the most generally used, the wood is dried, placed in an iron cylinder, and creosote is pumped in at a temperature of about 120 degrees Fahr., and at a pressure of about 170 lb.
per square inch. Very frequently the vessel is first exhausted of air, so as to facilitate the escape of the air from the wood. Soft wood may absorb about 10 lb. of creosote per cubic foot, whilst hard wood, such as oak, will take very much less. Creosoting seems to be the most efficacious method of preserving timber.
Kyan's process (Kyanising) consists in saturating the wood with a solution of mercuric-chloride (corrosive sublimate); in Boucherie's process, copper sulphate is used; and in Burnett's, zinc chloride.
Attacks of Animals.—Under some conditions, wood is liable to be attacked by animals of various kinds, boring animals occurring both in earth and in water. For wood which has to be buried in earth, charring seems to be a fairly good protection, and creosoting also answers very well.-Practical Engineer.
(Charring posts set in the ground is a very poor protection against the attacks of white ants, especially when unsapped posts are used. The charred portion cracks, and thus gives clear access to the untouched timber beneath the burnt portion.—Ed. Q.A.J.]
HOW TO MAKE A SAFETY LIGHT. Take a clear glass bottle, such as a small vial, and put a small piece of phosphorus about the size of a pea into it, and see that the cork is sound and a good fit. Then get a little of the clearest olive oil, such as that sold for table use, heat it to boiling point, and then pour it on top of the phosphorus. Fill the bottle about one-third full, and then cork tightly.
When requiring a light, remove the cork to allow air to enter, and then cork up again, and the whole of the empty space in the bottle will now become luminous, giving sufficient light to read the time by a watch, or for other purposes when a night light is required.
As the light becomes dim it is only necessary to withdraw the cork again to allow a fresh supply of air to enter.
A bottle used like this will continue to give light for some months; but it should be kept warm during the winter for should the oil become solid through the cold the vial will have to be held in the hand for some time to warm it sufficiently to act.
WARTS THERE are many so-called remedies for warts on animals which are more or less non-effective. The latest we have heard of appears to have proved successful in the case of dogs. A gentleman in England had a beagle puppy whose mouth, tongue, lips, and face were covered with white warts closely packed together. Several so-called remedies were tried without result, and the dog clied, choked. A year or two after he had a cob with warts over the shoulder, neck, and face, when, either in print or from hearsay, he learned that warm bullock's blood would remove them. This was tried, on the principle that if it did no good it could do no harm ; result, after two or three dressings the warts disappeared, and did not come any more. Another case.
Five years ago he had six greyhound saplings, whose mouths, tongue, and lips, outside and in, were covered with warts. It was two days after discovery before he was able to get to the butcher when killing. By this time a fine crop of warts had developed. The method was this : As soon as the bullock was knocked down and stuck, the dogs' heads were dipped in a bowl of the live blood, and all the parts affected were well rubbed with it while warm (after it begins to clot or solidify it is no use). The day after the first dressing the warts turned brown. Two days after they were dressed again. The following day they (the warts) began to get soft, and looked rotten, many of them falling out on being handled. After two days, dressed again, when they all disappeared, leaving small marks such as smallpos leaves. After a time nothing could be detected at all.
He gives this as his experience. At all events, it is harmless and painless, and the price of a pint or two to the butcher is not costly.
This remedy might be tried in the case of fowls. Warts chickens may, however, be absolutely cured by dipping the fowls' heads in urine. After a few applications of this remedy the warts disappear. We cured nine valuable cochin chickens in this inamner, whose heads were a mass of warts.
A NEW TEXTILE PLANT.
APOCYNUN VENETUN. A NEW textile plant is being experimented with in Russia (says United States Consul Atwell, of Roubaix). This is the Apocynum renetum, a bush about 6 feet high, yielding a silken fibre. It grows in Europe, Siberia, Asia Minor, North of India, Manchuria, and Japan, and it has long been used by the Tureomans in the manufacture of cords and woven goods. It has never been cultivated, and grows best inland under water for part of the year. The fibre has great strength, and its cultivation would require no care. In 1895 the Russian Government began to use it for bank-note paper, and the results were so excellent that the plant has since been cultivated at Poltava.
HOW LONG PLANTS WILL LIVE. Annuals.--Some plants grow up, flourish, produce seeds, and die in one year; they are called annuals. These are again divided into the hardy—such as the rocket larkspur, candytuft, nemophila ; the half-hardy, which need protection and artificial heat in their early stages, such as the China aster, phlox drummondi, marigold; and the tender annuals which should be cultivated in a greenhouse. Biennials are plants which flower and bear fruit only in their second
year, and then die. They do not flower in their first year. The foxglove is a biennial, so also is the wallfower, stock, carrots, turnips, parsnips, &c. Biennials may become annuals if sown early and forced to develop their flowers, while, if seeding be prevented, some may last longer than two years.
Perennials.—Plants which continue for several years, and which exhibit a great variation of longevity.