DRY ROT,

A most destructive, and apparently infectious disease in timber, which, by decomposing the fibres, deprives it of all strength, and in no great length of time reduces it to a mass of dry dust; a circumstance from which it seems to have derived its name, which, perhaps, would better be expressed by that of sap rot.

Though this disease must from its nature have been co-existent with timber-trees, it would not seem to have excited much attention, and perhaps was not known, certainly not by its present name, beyond the middle of the last century; at some period, we rather think, of Sir John Pringle’s presidency of the Royal Society of London. But for a long time after this little notice appears to have been taken of it; its ravages being, in all probability, inconsiderable, in comparison with what they have been of late years. Even now, the disease is in fact chiefly confined to modern built houses and modern built ships, and more particularly to the ships of his majesty’s navy. The proximate cause of it has, therefore, rightly enough, as it would seem, been ascribed to the unseasonable state of [7:8:227]the timber, when placed in certain situations, and under particular circumstances. It could not fail, in the course of the late long protracted war, to become a matter of general observation, that a more rapid decay than usual had become almost universal throughout the fleet, and especially amongst the newest and most recently repaired ships. Many anxious inquiries were instituted, and experiments made, with the view of ascertaining the real cause of a decay, the further prevention of which was so highly important to the national welfare and security. The alarm was greatly increased when, in 1810, the Queen Charlotte, a first-rate ship of war, shortly afterwards launched at Deptford, was discovered, after a close examination, to have all her upper works infected with the dry rot ; or, in other words, the ends of most of the beams, carlings, and ledges, the joinings of the planks, &c. were observed to be covered with a mouldy, fibrous, and reticulated crust, and the parts of the timber so covered to be perfectly rotten. All the newspapers and journals of the day were filled with this alarming fact, and in consequence thereof a multitude of dry rot doctors proffered their assistance; one having a nostrum for eradicating the disease where it had made its appearance, and another for preventing its further approach. Some of these specifics were expensive and inconvenient, many of them impracticable of application, and most of them futile and objectionable in one way or another. These doctors, in fact, like the physicians for the human body when the seat of the disease is unknown, were labouring altogether in the dark, having no other guide to direct them than their own whims and fancies, each being ignorant of the effect of the respective experiments which they wished to try on this diseased machine.

Since the period in question a number of treatises have been written on the subject, for the prevention and cure of the dry rot in ships and houses; some wild and visionary enough, and others exhibiting the proofs of plain practical good sense, deduced from long observation, or the result of judicious experiment. Of the latter description may safely be mentioned A Treatise on the Dry Rot in Timber, written in 1815 by the late Mr Thomas Wade, who died previous to its publication, and whilst employed in making experiments in the dock-yards; and also another On the Prevention of Timber from Premature Decay, by Mr Chapman, 1817. A Treatise on the Dry Rot, by Mr Bowden of the Navy Office, is in many respects deserving of notice, in as far as the facts and his observations on the management of timber are carried; but he unluckily sets out with a fanciful theory, which, however, is not his own, concerning the generation of fungi, and their connection with the dry rot, to which, like most theorists, he endeavours to make all his facts subservient. In Mr M‘William’s Essay on the Origin and Operation of the Dry Rot, published in 1818, we find stuffed into a large quarto almost every theory and every fact gathered from preceding writers, from Aristotle down to Mr Ralph Dodd, civil engineer, who has also published his Practical Observations on the Dry Rot in Timber ; which work appears to be little more than an advertisement of A Dry Rot Preventive, a nostrum which, it would seem, is too valuable to be disclosed, without calling in the doctor that he may get his fee. We have also in print the opinions and the specifics of Mr Gregory, Mr Ogg, and many others of minor note, all of whom profess to explain the cause, to secure the prevention, and to effect the cure of the dry rot.

These authors are at variance amongst themselves, whether the common rot in timber, and the dry rot, be not one and the same disease. A little reflection, however, will, we conceive, lead us to consider them as essentially different, both in the symptoms, the progress, and the causes, though the effect of destroying the fibre of the wood is pretty nearly the same. If a post of wood, for instance, be driven into the ground, seasoned or unseasoned, it will speedily begin to decay just at the surface of the ground, or, as it were, between the earth and the air; if driven into the earth through water, as in a pond, the decay will commence at the surface of the water, or, as it is technically expressed, between wind and water, whilst all above water, and all that is constantly immerged in the water, as well as the part in the earth, will remain sound. Thus also a beam of wood let into a damp wall will begin to rot just where it enters the wall; so will wooden bannisters when they are let through the top and foot rails. In these and similar cases the rot* begins externally, and its progress is inwards, and is more or less accelerated by the alternate action of wind, heat, and moisture, being greatest when the alternatives of exposure to wet and drought are most frequent, and least when constantly immersed in water, or constantly preserved in a dry atmosphere. Such we conceive to be the usual process of the common rot in wood, and it is evidently occasioned by alternate exposure to the vicissitudes of the weather, to moisture and dryness, to heat and cold.

If the same post be well charred or covered over with a thick coating of paint, or varnish, or tar, no such effect will be produced externally, the coating being sufficient to protect it against the action of the weather; but if it should happen to be a green or unseasoned piece of wood so tarred or painted, in no great length of time the wood will be found to have begun to decay internally, whilst the outer surface appears uninjured, but at length it will also yield to the disease. If this piece of wood had been placed in a warm cellar or close room where there is little or no circulation of air, and more particularly if the room or cellar were damp, there would be perceived, in no great length of time, a fine mouldy coating spread over its surface, of a brownish yellow or dirty white; and shortly afterwards it would be found, on examination, to resemble in its form and structure some of the beautifully*ramified algae. or sea weeds; which in process of time would become more compact, the interstices being so completely filled up as to give to the whole mass the appearance and consistence of leather. “At first,” says one writer, “its appearance is that of fine fibres running on the surface in endless ramifications, resembling the nervous fibres of leaves; presently the interstices are filled up with a spongy or leather-like substance, assuming the character of that order of cryptogamous plants distinguished by the name of fungus?

By Mr Wade the general symptoms of dry rot are thus described: “The wood at first swells; after some time it changes its colour, then emits gases which have a mouldy or musty smell. In the more advanced stages of it the mass arises, and cracks in transverse directions. Lastly, it becomes pulverulent, and forms vegetable earth; and generally in some of these stages of decay the different species of fungus are found to vegetate on the mass.” ( Treatise on the Dry Rot in Timber. By Thomas Wade.)

These appearances do not invariably take place, the surface of the diseased timber sometimes remaining unchanged, while the process of rotting is going on within; they are, however, pretty constant. But however sound the surface may be, it will appear, on examining the piece of wood, placed in a situation similar to those above mentioned, that the whole of the interior fibres are decomposed, and become a mass of dust inclosed within a thin external shell. No charring of the surface, no paint, tar, or varnish, will prevent this process from taking place, [7:8:228]when the seeds of the dry rot exist, and are placed in a situation favourable for their growth, though they may prevent the external character of mouldiness from taking place on the surface.

The symptomatic difference, then, between the common rot and the dry rot may perhaps be thus defined. Common rot is a disease in timber, occasioned by the alternations of the weather acting on its surface, and destroying its fibres externally inwards. Dry rot is a disease in timber, occasioned by being shut up in warm, close, and moist situations, the effect of which is to destroy its fibres by a process acting internally outwards.

Without stopping to inquire in what manner, and by what agency, chemical or mechanical, or both, the common rot acts on the external fibres of the wood, the effect of alternate exposure to the weather is too well known to require any further proof as to its being the immediate cause. The immediate cause of the dry rot is equally obvious; but the predisposing state of the timber to contract the disease is not so clear a problem. Accordingly, theories without end have been hatched to explain the phenomenon. A writer in a public journal, who has slightly touched on the subject, thus explains it. “It is well known,” he observes, “that if a piece of green wood be laid across a fire, the air within, expanded by the heat, will drive out at each extremity a viscous fluid, possessing the property of disposing itself on the surface in reticulated filaments. The same appearance of nervous foliation is not uncommon in the intermediate spaces of the concentric layers of the alburnum of wood; and the core or heart of trees, and particularly of the pitch pine, after its passage in the heated hold of a ship, is often enveloped with a membranous corticle, like that which lies immediately beneath the bark. All these appearances are certain indications of the dry rot ; and they point out, with sufficient clearness, that the sap, or principle of vegetation, brought into activity, is the cause of the disease; the effect, though infinitely more rapid, is the same as that of the common rot. It is still a problem in what manner this sap circulates; but there is no doubt that the tubes and cells of the alburnum, or sapwood, are filled with it in the spring of the year, and that they are empty in the winter; that it is organized matter, developing itself by heat in all the various forms of new bark, leaves, and branches. The stem of a tree cut down will, on the return of summer, make an effort to push out leaves; a more feeble effort of this organized sap ends in the production of fungus only.” (Quarterly Review, No. 15.)

It is now, we apprehend, pretty well decided, that, like other vegetables, the fungi or mushroom tribe are propagated by seed so minute and numerous as to float about invisibly in the air, and to be carried into all manner of situations. The fine impalpable powder that issues from the common puff-ball, like a column of smoke, will give some idea of the almost inconceivable myriads of minute seeds which it incloses. Of these seeds, though myriads perish, yet others, by a concurrence of accidents, being thrown into proper situations favourable for their growth, reproduce the species. It cannot be supposed that the fibres found in the dung of animals, and particularly of the horse, known by the name of mushroom spawn, and from which our gardeners construct their mushroom beds, arc generated spontaneously in the belly of the animal, but that the seeds being devoured with his food, have found that degree of warmth, moisture, and soil, favourable to the development of the future plant; and this plant which the fibres exhibit, by care and cultivation increases and grows to the perfect state of all plants, and throws out above the surface the parts of fructification which we call the mushroom. If it 'be asked why the dung of a cow, which feeds on the same food with a horse, does not produce the spawn of mushrooms, the only answer to be given is, that it is not a proper nidus for the germination of the seed.

In the same manner may the perfect plant be produced from the seed, carried up into the longitudinal tubes of a growing tree, by the rising of the sap; though it would seem that the process of vegetation in the parasite thus lodged will not commence so long as the vital principle of the sap in the tree remains in activity. Indeed it is pretty evident, from numerous observations, that the process of fermentation is necessary to the growth of all fungi; and this may explain why in the diseased and decayed parts of a tree only are fungi found to grow whilst it is in a living state.

The sap, therefore, may be the cause of the dry rot, in as far as it is favourable to the growth of fungi, as it would seem to be when in a state of fermentation, though it never can by any process be convertible into this order of cryptogamous plants. But the appearance of fungi, though a frequent, is by no means a constant symptom of dry rot; and, therefore, Mr Bowden’s definition of dry rot, with his whole doctrine, must fall to the ground. “The nature oĩ. dry rot is a vegetable substance, ’ ' and this substance, he tells us, is fungus. Though not very happily expressed, his meaning is intelligible enough from what follows. “This secretion of nature (the juice of a tree) which was destined to appear in the form of leaves, branches, &c. being diverted from its original intention, assumes a new form from its own native energies. Vegetation commences in the various tubes of the wood, under the form of those fine fibrous shoots which have been already described (as mushroom spawn). It continues to increase in every direction, until, by an extraordinary manifestation, it happily averts the otherwise unforeseen but certain destruction of the vessel. It may confidently be asserted, therefore, that this is the primary, chief, and predisposing cause of dry rot ; and this opinion may be further confirmed by an inquiry into the nature of the juices and fungi, and the manner in which the timber is affected.” (A Treatise on Dry Rot, by A. Bowden.)

Mr Bowden having totally mistaken the nature of fungus, by adopting the erroneous principle of the writer in the Quarterly Review, labours hard to prove, and with considerable ingenuity, “that dry rot is caused by a vegetative substance, and that it is one of the species of fungi;" and this doctrine he illustrates in the case of spent bark from the tan-pits, of which he says, “when taken out and exposed to the heat of summer, the juices appear desirous of obeying the laws of nature ; and being no longer capable of adding to the bulk of a tree, is satisfied with wearing the humble garb of a mushroom nay, so enamoured is he with the similarity of oak bark, and fungus, and tannin, that “an examination of the fungous coat taken from the end of a timber, would afford a strong presumption, from its exact resemblance to leather, that it owes its existence to no other cause than that which communicates such peculiar qualities.” Into such absurdities will crude theories sometimes drive their authors.

Mr Wade has sounder notions on the nature of fungi; he knew they possessed the principle of reproduction, and that their seeds, under favourable circumstances, will vegetate; that the proper nidus for the reception of certain species of fungus appears to be wood in a state of progressive decomposition, or the remains of wood entirely decomposed; that, however, the effect produced by these plants and decaying timber is reciprocal, the latter furnishing food for the former, while the decomposition of the wood is accelerated by the growth of the fungus, the gaseous and soluble products being taken up by the [7:8:229]plants, as quickly as these principles are disengaged. The whole tribe of parasitic fungi may, in fact, be considered as the wolves and tigers of the vegetable world, destroying ultimately every plant they fix upon, and most rapidly where the principle of vegetation has ceased to act, and the putrefactive fermentation of the juices has in consequence commenced.

The real efficient cause then of the dry rot, is that of the juices of the timber being brought into a state of putrefaction, occasioned generally by exposure to a moderate degree of heat and moisture in a stagnant atmosphere. “To favour this process,” says Mr Wade, “as much as possible, the air and water should not be renewed, as they undergo a decomposition, which takes place very slowly.” From the structure of timber being composed longitudinally of an assemblage of pipes or tubes, it is only necessary that one end of a log of wood should be placed in a damp or wet situation, to occasion the moisture to be conveyed to the opposite end by capillary attraction; and hence arises the infectious nature of the disease, which will always spread wherever the moisture finds its way; and even where there is no moisture, it will be created by the filaments of the fungi working their way through the tubes of the dry wood, and carrying it with them. Hence, also, the rapid decay in ships of war, from the great internal heat occasioned by the number of men, the moisture, and the close air. Hence, also, in houses, the dry rot always first appears in the lower apartments, where the floors, partitions, skirting-boards, &c. are supplied with moisture from the wet walls on the ground. In the London houses there is generally a room on the basement story, called the housekeeper’s room, which is boarded, and carefully covered over with an oiled floor-cloth. In such a room the dry rot is sure to make its appearance. The wood absorbs the aqueous vapour which the oil-cloth will not allow to escape; and being assisted by the heat of the air in such apartments, the decay goes on most rapidly; and, as Mr Wade observes, “if the seed of fungus be present, the plant is developed in all the superfluity of vigour exhibited in a hothouse, where the same means are resorted to, namely, an atmosphere scientifically and artificially heated, and highly charged with aqueous vapour.” Timber may, in fact, have the seeds of dry rot within it, and yet by proper treatment be kept sound for a great length of time. Thus ships laden with particular cargoes afford remarkable instances of the effects of such cargoes on their duration. The warm moisture created by a cargo of hemp is communicated to the timber, and promotes a rapid putrefaction. Mr Chapman says, that the ship Brothers, built at Whitby, of green timber, proceeded to Petersburg for a cargo of hemp. The next year it was found on examination that her timbers were rotten, and all the planking, excepting a thin external skin. A lading of cotton is always injurious to the ship, and even teak is affected by a cargo of pepper. The timber which is brought from America in the heated hold of a ship, is invariably covered over, on being landed, with a complete coating of fungus. It was the too general use of this timber in his majesty’s ships that at one time increased the disease to such an alarming degree. Those ships, on the contrary, which are employed constantly in the coal and lime trade, are very durable, and have been known to last for a century. These effects are obviously to be ascribed to the exclusion of air in the one case from, and the free admission of it in the other to, the interior surface of the ship, assisted, in the latter instance, by the absorption of moisture, by the coals and lime, from the timbers and planking.

ι If we are arrived at the right conclusion as to the cause of dry rot in timber, we can be at no loss with regard to the mode of treatment for the prevention of the disease. The experiments for this purpose have been very numerous, but may be classed under three general heads; desiccation or seasoning; immersion in earth, sand, or water; and impregnation with some foreign matter, which will resist putrefaction.

The most simple and common mode of preventing the decomposition of vegetable matter, is by depriving it of moisture. Various schemes have been put in practice for drying the juices in large logs of timber. Time alone will do it when the wood is placed in favourable situations, that is to say, in a dry atmosphere, and constantly exposed to a free circulation of air; but time will also produce the rot in timber when piled up in stacks in the open air, imbibing moisture from the earth, and exposed to the vicissitudes of the seasons, and the alternatives of weather; scorched at one time by the heat of the sun, at another drenched with rain, and rent and split in every possible way by the freezing of the water which has insinuated itself into the pores and crevices of the wood. It was formerly, and, indeed, till very lately, the practice to let ships of war remain on the stocks in frame for two, three, or four years, to season, as it was called; but there never was so mistaken a notion. “When a ship,” says Mr Wade, “is built, exposed to the weather, the lower part forms a grand reservoir for all the rain that falls; and as the timbers in that part are placed as close together as possible, the wet escapes very slowly. Those timbers are always soaked with moisture, and, to some distance from the keel, exhibit a green appearance; their green matter, when viewed through a microscope, is found to be a beautiful and completely formed moss, which vegetates at the expense of the timber. If to season timber be only to dry it, the sooner it is dried the better; and when completely dry, it cannot too soon be employed in ship-building, when it should be kept dry. It cannot answer any end to have seven years wear out of a ship on the stocks.” At length our ship-wrights are convinced of this truth, and every ship of war now building in the dock-yards has excellent roofs placed over them, with the sides open to admit a free current of air, but to exclude all moisture, as well as the rays of the sun (See Dock-Yards) ; a practice which we have tardily adopted from the Swedes and the Venetians. A new system seems also to have been adopted on the piling the timber stacks. Instead of their being placed on old, useless, and often rotten logs of timber resting on the ground, they are now insulated from the earth on stone or iron pillars; and in place of their surfaces coming in contact with each other, pieces of wood are placed between them so as to admit of a circulation of air. Nothing further appears to be wanting but to protect the tops and the ends of the stocks or piles from the effects of the weather.

Of the various modes of artificial and rapid desiccation, that of charring is perhaps the best; but it is liable to two objections, the first is, that if the surface be completely charred, it diminishes very much the strength of the timber; and, secondly, it the more readily attracts moisture. The juices of timber may be drawn off or hardened by kiln-drying; but this also disturbs the arrangement of the fibres, and deprives the wood of a great part of its strength.

The experiments made by Mr Lukin for the rapid seasoning of green oak timber, promised at one time much success, but ended in disappointment. He conceived, that if the acid and the watery particles were driven out of a piece of oak timber by some process which should prevent the surface from splitting, the fibres would be brought closer into contact, and whilst the log lost in weight it would gain in strength. With this view he [7:8:230]buried a piece of wood in pulverized charcoal in a heated oven. The log wore a promising appearance; the surface was close and compact; it had lost in its weight and dimensions; but when divided with the saw, the fibres were discovered to have started from each other, exhibiting a piece of fine net-work, resembling the inner bark of a tree.

His next contrivance was to supply the place of the fluids driven out by heat, with some other substance of an oily or resinous nature, which, while it destroyed the principle of vegetation, should preserve the timber in a compact state. For this purpose he erected a large kiln in Woolwich dock-yard, capable of containing from two to three hundred loads of timber. At each end, on the outside, was a retort in which the saw-dust of the pitch-pine was submitted to distillation. From the heads of these retorts were iron pipes, perforated with holes like a cylinder, continued along the upper part of the kiln the whole length in the inside. By this arrangement it was expected, that while the heat of the kiln drove off the aqueous matter of the timber, the product of the saw-dust, which resembled weak oil, or rather spirit of turpentine, would drop through the holes in the tubes upon the logs, and supply its place. But before the process of transfusion was judged to be complete, an explosion took place, which proved fatal to six of the workmen, and wounded fourteen, two of whom shortly afterwards died. The explosion was like the shock of an earthquake; it demolished the wall of the dock-yard, part of which was thrown to the distance of 250 feet; an iron door, weighing 280 pounds, was driven to the distance of 230 feet, and other parts of the building were borne in the air upwards of 300 feet. The experiment was not repeated.

The bad effects of applying artificial heat to the seasoning of green timber were strongly exemplified by a practice introduced very generally into our ships of war which had exhibited indications of the dry rot, particularly in the Queen Charlotte. Enormous fires were made in stoves placed in various parts of the ship, and the heat led in tubes to the cavities between the timbers, &c. The consequence of which was, as might be expected, an increase of the mischief they were intended to prevent. Every part of the ship was converted into a hot-house, and every part where the seeds of fungi had been deposited began to throw out a luxuriant crop of mushrooms; and where these did not appear, the juices of the wood were thrown into a state of fermentation, and, in the course of a twelvemonth, a great part of her upperworks became a mass of rottenness. After staving the powder magazines of some of the ships, there appeared under their floors, which are contiguous to much moisture, numbers of large excrescences of a leathery consistence, of the size and shape of a quart glass-decanter; and in all such parts where two surfaces of the wood were imperfectly brought into contact, were whole masses of fungi.

Another mode, of very ancient standing, was practised for getting rid of the juices of timber. This was supposed to be effected by felling the tree in the winter season, when the sap had descended and the vessels were empty. But by this practice the bark of the oak, so valuable in the process of tanning, was lost, as it will strip only from the wood in the spring of the year, when the sap is said to be rising. The supposed superior quality of the wood when winter-felled, and the general practice of felling oak timber at that season, may be inferred from a statute of James I. by which it is enacted, that no person or persons shall fell, or cause to be felled, any oaken trees meet to be barked, when bark is worth 2s. a cart-load (timber for the needful building and reparation of houses, ships, or mills, only excepted), but between the first day of April and last day of June, not even for the king’s use, out of barking time, except for building or repairing his majesty’s houses or ships.

The old Sovereign of the Seas is the standing example generally quoted to prove the beneficial effects of winter-felled timber. We are informed by one writer that, when taken in pieces, after forty-seven years’ service, the old timber was still so hard that it was no easy matter to drive a nail into it, and all future writers have taken it for granted that this was owing to its being winter-felled. Mr Pett, however, who built her, takes no notice of any such circumstance. He merely says he was commanded by the king, on the 14th May 1635, to hasten into the north to procure the frame-timbers, plank, and trenails, for the great new ship at Woolwich. But he left his son behind to ship the moulds, provisions, and workmen, in a hired ship, to transport them to Newcastle; that the frame, as it was got ready, was sent in colliers from Newcastle and Sunderland; and that, on the 21st December, in the same year, the keel was laid in the dock; and in less than two years after this she was launched. Now, as it was the middle of May before Mr Pett received his majesty’s commands to procure timber for this ship, and as she was on the stocks the same year, it is not very probable that the timber procured and sent in colliers from Newcastle to Woolwich was felled in the winter; much less could it have been “stripped of its bark in the spring, and felled the second succeeding autumn,” as Mr Wade has it.

Neither is there the least proof of the old Royal William, recently broken up, when a century old, being built of winter-felled timber. The fact is, that she was rebuilt half a dozen times, and the only old and original timber remaining in her was in the lowest part of her hull, always immersed in the salt water externally, and washed with the bilge-water internally; and the wood from this part of her, when broken up, was perfectly sound, but quite black, having the appearance of being charred.

As far as experiments have been made, there is no reason to conclude that timber felled in the winter is at all more durable than that which is felled at the usual time. In the year 1793, the Hawke sloop of war was ordered to be built, one side being of timber that had been barked in the spring and felled in the winter, and the other side with timber felled at the usual time. In 1803 she was reported to be in so bad a state of rottenness, that she was ordered to be taken in pieces, when no difference whatever could be discovered in the state of the timbers of the two sides. It is said, however, in Derrak’s Memoirs of the Navy, “that the timber had been stripped in the spring of 1787, and not felled until the autumn 1790,” and this is given as an explanation of the failure. Why the barking in the spring should add to the durability of timber, is not easily conceived, if the object be to fell the timber when all the sap-vessels are empty, as, if the sap descends at all, which is doubtful, it might be expected to descend more freely when the bark is on than off the tree. The experiments which, we understand, are now making by the commissioners of his majesty’s woods and forests, will, it is to be hoped, throw more light on a subject so vitally important to the British navy. In France, so long ago as 1669, a royal ordonnance limited the felling of timber from the 1st October to the 15th April; and the conservators of the forests directed that the trees should be felled when the “wind was at north,” and “in the wane of the moon ;” and we find an instruction of Bonaparte, that “as ships built of timber felled at the moment of vegetation must be liable to rapid decay, and require immediate repairs, from the effect of the fermentation of the sap in those pieces which had not been felled at the proper season ;” the agents of the forests should abridge the time for felling naval timber, which should take place “in [7:8:231]the decrease of the moon, from the 1st November to the 15th March.”

The facts are so numerous and so strong in favour of the durability of timber when steeped in water or buried in earth or sand, that no doubt whatever can be entertained of the efficacy of such a practice. At Brest all the timber used in ship-building is deposited in the narrow creek of the harbour which runs through the middle of the dock-yard, and it is said that the Brest built ships never had the dry rot. The same practice prevailed at Cadiz and Carthagena. Indeed there is reason to think that steeping in fresh water is a preventive of dry rot, probably by dissolving the juices of the timber. It was an ancient practice, and we believe is still followed in some parts of England, to place the timber intended for thrashing-floors in the midst of a stream of water, to harden it; and all the oak plants intended for the wainscotting of the old mansions were previously steeped in running water.

“I know it,” says Mr Chapman, “to be the opinion of some well-informed men, whose sentiments are highly deserving of notice, that the sap of trees does not descend, but, like the arterial blood, is prevented by valves from returning; as a proof of which, it is asserted, that freshcut timber, if laid in a running stream, with the but-end towards the current, will have the water percolating through it, and carrying off the mucilaginous matter, but not otherwise.” “There can be no doubt,” he adds, “that the effect will be produced sooner in this direction than the other, and it should therefore be attended to.” The reason is obvious; the extractive matter, which is the chief, though not the only, cause of putrefaction, is dissolved and driven off. The usual mode of preserving timber for masts, is to keep it immersed in water in what are called mast-locks. The mast of the Kangaroo sloop of war was dug out of the mud at the bottom of the mast-pond, at Deptford dock-yard, where it had been fifty years, and was one of the most serviceable masts in the navy. Burying timber in sand is a usual process for preserving it in warm climates. Yet, with all these facts and long experience, it was but the other day that the steeping of timber in salt water was practised in the king’s dock-yards, and this originated in an accident. The Resistance frigate went down in Malta harbour. But as she had been reported in such a state of dry rot, or rather the surface of her timbers so covered with fungus, as to render it expedient to send her home, she was suffered to continue under water for many months. On her arrival in England it was observed that all appearance of fungus had vanished, and she remains a sound ship to this day. Yet even this fact does not seem to have attracted much attention. But when the dock-yard was removed from the northern to the southern side of Milford-haven, a few loads of timber that was covered with fungus were suffered to remain in the water for several months; and it was observed that, after being taken out and stacked in the new yard, the timber did not exhibit those appearances of dry rot which the same timber did most abundantly which had not been immersed in the salt water. This fact being reported to the navy board, it was proposed to sink one of two sister ships, the Mersey and the Eden, both alike infected with the dry rot, in Plymouth Sound. The Eden was the ship selected for this purpose. She remained under water for about eighteen months, and, on being raised, every trace of fungus had totally disappeared, whilst the Mersey was almost wholly covered with it. After remaining a year at home perfectly sound, she was sent out to the East Indies, where she now is.

It is said, and there seems to be no reason for doubting the fact, that the planks of ships near the bows, which are obliged to be boiled in water or steam in order to bend them, are never infected with the dry rot: if the water in which they are boiled be strongly impregnated with salt, the effects w ould probably be more durable and decisive.

In a lecture read by Mr Ogg, a salt refiner, to the Plymouth Institution, on the prevention and cure of dry rot in ships of war, common salt is strongly recommended, for its cheapness, its wholesomeness, and its easy application; but he proposes a saturated solution of salt, in which he would steep not only single logs or planks, but the whole frame of a ship, or even the ship itself, “Let every ship in the navy,” says the salt refiner, “be immersed a sufficient time in this fluid, and let every new ship be prepared in the same way, and dry rot would be heard of no more. But how is this to be accomplished? I answer, provide a dock or docks sufficiently capacious to receive five, ten, or twenty ships, and the work is done.” As common sea-water will answer the purpose equally well, the apparatus of extensive docks and water saturated with salt are wholly unnecessary. But Mr Ogg, like Mr Bowden, appears to mistake the real cause of dry rot. “I affirm,” says he, “that dry rot is occasioned by the vegetative principle; brine will destroy this principle; then sink the ship in brine.” The experiments in the case of the Resistance and the Eden show that brine is not necessary.

The Dutch having observed that their busses, in which the herrings were caught and stowed away in pickle, lasted longer than any other craft, adopted the practice of filling up the vacancies between the timbers and planks of ships with salt, and of boring holes in the large timbers and cramming them full of salt. The Americans also found, that the ships employed in carrying out salt for their fisheries and domestic purposes were the most durable; and both they and the Dutch are glad to get a cargo of salt into a new ship, as the surest means of preserving her. The carpenter of the Franklin, an American seventy-four gun ship, when at Spithead, told some of her visitors, that at the junction of the beams, and at the but-ends of the timbers, pieces were cut, and the hollow part filled with salt, and covered over with felt, for the purpose of preserving those parts where two surfaces are imperfectly brought together, from the dry rot, where it is always most prevalent.

There are, however, very serious objections to the immersion of ships in a strong solution of salt, and the practice of inserting salt in the vacant space between the timbers, which may not, perhaps, apply with equal force to their immersion in sea-water. It is observed by a writer in the Quarterly Review for October 1814, that “the attraction for moisture which salts and acids possess, would keep the whole interior of the ship dripping wet; which would not only destroy the ship with the wet rot, but the ship’s company also, whose health, experience has proved, is best preserved by keeping the ship as dry as possible; and thus the remedy would be worse than the disease.” These bad effects have unquestionably been experienced, the muriate of magnesia, which exists in sea-water, being one of the most deliquescent salts; but whether the abstraction of moisture from the atmosphere be of long duration, is a fact which remains to be proved. In corroboration of the injurious effects above described, Mr Strange, in his Evidences, observes, “that the practice at Venice of the fresh cut timber being thrown into salt water prevents its ever becoming dry in the ships, and that the salt water rusted and corroded the iron bolts.” Mr Chapman also observes that “the Florida, a twenty gun ship, taken from the Americans, and subsequently commissioned in the British service, had been salt-seasoned; and the result was, that in damp weather every thing became[7:8:232] moist, the iron work was rusted, and the health of the crew was impaired; in fine,” he adds, “vessels so circumstanced are perfect hygrometers; being as sensible to changes of the moisture in the atmosphere as lumps of rock salt, or slips of fuci, or the plaster of inside walls where sea-sand has been used.”

Mr Chapman, however, is of opinion, that vessels impregnated with bay-salt, or the large grained salt of Limington or of Liverpool (being pure muriate of soda, without admixture with the bitter deliquescent salts), will possess decided advantages, as would also vessels laden with saltpetre, if it has been dispersed among their timbers; and Mr Ogg sees no difficulty in refining salts so as to deprive it of its deliquescent quality. But if a very weak solution of salt, or even fresh water, shall be found to answer the purpose, the objection against immersing timber in sea-water seems to be got rid of. That it will immediately destroy all vegetable life in the delicate fibres of the fungus, and also prevent its future growth, is quite clear; and if it shall be found to prevent also the putrefactive process, it may be considered as the most advisable way to prepare timber for all purposes of house carpentry and ship-building.

A great variety of substances besides common salt, indeed almost any salt or acid, will destroy and prevent the growth of fungus. Sir Humphry Davy recommends a weak solution of the corrosive sublimate as the most efficient. A solution of sulphate of iron or copperas is much used in Sweden for hardening and preserving wood for wheel-carriages, &c. It is first boiled in this solution for three or four hours, and then kept in a warm place to dry, by which process it is said to become so hard and compact that moisture cannot penetrate it. “The wooden vessels,” says Mr Chapman, “in which the sulpho-ferruginous solution is finally placed for the copperas to crystallize, become exceedingly hard, and not subject to decay." A solution of alum has been recommended; but Mr Chapman seems to think that its earthy basis would become a nidus of putrefaction. The wood, however, which is used about alum works, becomes hard and durable, and resists fire in an extraordinary manner. All timber, in fact, when completely saturated with saline matter, is more or less indestructible, and absolutely incombustible. A solution of arsenic has not been found to prevent the dry rot. With regard to the impregnation of oils there are various opinions, some thinking them beneficial and others injurious to the durability of timber. It is known, however, that ships in the Greenland trade have their timbers and planks preserved as high up as they are impregnated with whale oil from the blubber; and Mr Chapman says, that one of the masters of a Greenland ship having payed her upperworks with twelve or more successive coats with whale oil in hot weather, they became covered with a thin varnish, much harder and more compact than if filled with successive coats of turpentine. Resinous substances, however, are probably better than oil.

After a variety of experiments and sensible observations, Mr Chapman sums up the three great operations by which timber may be brought to resist the tendency to dry rot.

1. To deprive the timber of its mucilage, which is very liable to fermentation.

2. To impregnate timber with any strongly antiseptic and non-deliquescent matter.

3. To dry timber progressively by the sun and wind, or by the latter alone; and then to close its pores completely with any substance impervious to air and moisture, and at the same time highly repellant to putrescency.

Mr Wade recommends the impregnation of timber with sulphates of copper, zinc, or iron, rejecting deliquescent salts, as they corrode metals, and would destroy the bolts and metal fastenings of a ship. He observes, that timber impregnated with saline matter is no longer capable of fermentation, and that, of course, the gases necessary for the nutriment of fungi are not evolved. Selenite is recommended as being insoluble, or nearly so, and not liable to any alteration in the ordinary temperature of the atmosphere; but all salts, he observes, composed of barytes, should be rejected, because, though they are plentiful, cheap, and have some qualities eminently fitting them to be employed for this purpose, yet they are, without any exception, very poisonous.

From all experiments that have been made, it appears that the most effectual method of preventing the dry rot, and of giving durability to timber, is that of depriving the sap of its mucilage, more especially in the alburnum, where it most abounds; for though seasoning in the dry way will coagulate and harden the extractive matter of timber, yet when exposed to heat, moisture, and a stagnant air, the process of putrefaction will commence, and all the symptoms of dry rot will speedily make their appearance. It will be preferable, therefore, that such timber as is likely to be exposed to the vicissitudes of weather, should be seasoned by immersion or impregnation, rather than by the dry way.

In this disease, as in those incident to animal life, prevention is much easier than cure. In fact, there is no other cure for the part affected than excision, and the sooner it is done the better, as the disease spreads most rapidly when fungi are propagated, throwing their minute fibres into the tubes of the contiguous sound wood, and producing that moisture which is a condition absolutely necessary to the putrefactive process. If, however, the fibre of the wood is still sound, and the roots of the fungi extend not beyond the alburnum near to the surface, immersion in sea water, as in cases of the Resistance and the Eden, or impregnation with some of the solutions above mentioned, may stop the progress of the disease; but the only safe cure, we apprehend, is that of cutting out the infected part. The sinking of the Royal George at her moorings has not been the means of preserving her timbers. On being visited in the diving-bell, her oaken sides were broken down into a confused mass of timber and black mud; having, no doubt, been too far gone in decay when the fatal accident happened; but her fir deck appeared as sound as the day when she sunk.

It is a great mistake to suppose that the ancients were unacquainted with the dry rot, or premature decay of timber. Pliny has a number of valuable observations on the preservation of timber, and on its decay occasioned by the juices; and, among other things, recommends that a tree should be cut to the heart all round, in order to let the juices escape, and that it should not be felled until the whole had run out. He knew that the sappy part of oak was more subject to rot, and advised that it should be cut away in squaring. He knew, too, that resinous and oleaginous matter in wood preserved it; observing, that the more odoriferous a piece of timber is, the more durable. He knew that much depended on the close texture of timber, and that box, ebony, cypress, and cedar, might almost be considered as indestructible. We also know that cedar, teak, and mahogany, are very durable woods.

The felling of timber while young and full of vigour, making usc of the sap-wood or alburnum, and applying it to ships and buildings in an unseasoned state, have no doubt contributed to make the disease of dry rot infinitely more common and extensive than it was in former times, when our ships were “hearts of oak,” and when in our large mansions the wind was suffered to blow freely through them, and a current of air to circulate through the wide space left between the pannelled wainscot and the wall.
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In those old mansions which yet remain, and in the ancient cathedrals and churches, we find nothing like the dry-rot, though perhaps perforated sore

And drill’d in holes, the solid oak is found

By worms voracious eaten through and through.

Numerous examples of the extraordinary duration of timber may be produced, both from complete desiccation and exposure to the air, and from the complete exclusion of air and immersion in earth or water. Without adducing the surturbrandt of Iceland, covered with several strata of solid rock, or the logs of wood dug out of peat-moss, the antiquity of which is mere conjecture, we may instance the mummy cases of Egypt as being in all probability the most ancient timber in existence that has been worked by the hand of man. When Belzoni entered the splendid tomb of the kings of Thebes, in which was the transparent sarcophagus of gypsum, he found two human figures larger than life sculptured in wood, in as good preservation as if it had been worked in his own time; but the sockets of the eye, which had been copper, were entirely wasted away. We are told by Pliny, that the image of Diana at Ephesus, supposed to be of ebony, remained entire and unchanged, though the temple itself was ruined and rebuilt seven times. He adds that, in his own time, the image of Jupiter in the capitol, made of cypress wood, was still fresh and beautiful, though set up in the year after the foundation of Rome 551, nearly three hundred years before. He further says that there was a temple of Apollo at Utica, the timbers of which, being of Numidian cedar, are said to have stood 1188 years. The roof of Westminster Hall, which is constructed of chestnut, has stood for more than three hundred years, and is probably better now than when newly erected. Similar instances of the long duration of timber have occurred in situations where the atmospheric air has been excluded. In the Leverian Museum was a post said to be dug out of Fleet Ditch, charred at the lower end, having the name of Julius Caesar cut into it. The foundation on which the stone piers of London Bridge are laid consist of huge piles of timber driven close to one another, on the top of which is a floor of planks ten inches thick, strongly bolted together; on these the stone piers rest, at above nine feet above the bed of the river, and, at low water, may be seen or felt at a very few inches below the surface. These piles have been driven upwards of six hundred years, and, from the solidity of the superincumbent weight, it maybe concluded that they are perfectly sound. In the old city wall of London, timber is frequently dug out as sound and perfect as when first deposited there. As the last instance of the extraordinary preservation of timber, we may mention, that, in digging away the foundation of the Old Savoy Palace, which was built about six hundred and fifty years ago, the whole of the piles, consisting of oak, elm, beech, and chestnut, were found in a state of perfect soundness, without the least appearance of rottenness in any part of them, and the plank which covered the pile-heads was equally sound. Some of the beech, however, after being ' exposed a few weeks to the air, but under cover, had a coating of fungus spread over the surface; which affords a striking proof of the immense length of time that the seeds of this parasite will remain dormant, without parting with the principle of vegetable life, which is called into activity from the moment that they are deposited in a situation favourable to their growth. In this instance we have only to suppose that the indurated juices of the wood became dissolved by its exposure to the moist atmosphere, and the phenomenon of fungous vegetation is capable of receiving a satisfactory explanation. (μ.)