“York Road, Lambeth,Nov. 30, 1844.Sir,In reply to your application, we beg to acquaint you that we are willing to undertake the ordinary works required in the finishings of the new Palace of Westminster. … The wainscot to be used in the joiner’s work is assumed to be from the best Crown Riga wainscot in the logs, and from pipe-staves of the best quality, in equal proportions, to beprepared for use by steaming, or otherwise.…Grissell & Peto.”Charles Barry, Esq.
“York Road, Lambeth,Nov. 30, 1844.
Sir,
In reply to your application, we beg to acquaint you that we are willing to undertake the ordinary works required in the finishings of the new Palace of Westminster. … The wainscot to be used in the joiner’s work is assumed to be from the best Crown Riga wainscot in the logs, and from pipe-staves of the best quality, in equal proportions, to beprepared for use by steaming, or otherwise.…
Grissell & Peto.”
Charles Barry, Esq.
Sir Charles Barry recommended this tender to the Treasury for acceptance; but we fancy that he was doubtful about the efficacy of steaming, as we think will appear from the following extract from an “Agreement between Sir Charles Barry and Messrs. Grissell and Peto, builders:
“First.That the wainscot is assumed to be from the log and pipe-staves in equal quantities; the prime cost of which, in inch boards,seasoned by steam, or other artificial means, so as to be fit for use, is calculated at 6½d.per foot superficial.
“Secondly.Thatif it should be found necessary to make use of thoroughly dry wainscot boardsfor the whole or any portion of the joiner’s work, seasoned by natural means (viz. exposure to the atmosphere), the prime cost of suchboards, with the addition of a profit of 7½ per cent., is to be allowed for them, over and above the price of 6½d.per foot superficial, the prime cost of wainscot boards provided for in the contract, as above stated.” (Italics are our own.)
Smoke drying in an open chamber, or the burning of furze, fern, shavings, or straw under the wood, is said to give it hardness and durability; and, by rendering it bitter, destroys and prevents worms. It also destroys the germ of any fungus which may have commenced. It is an old and well-founded observation that smoke drying contributes much to the hardness and durability of woods. Virgil appears to have been aware of its utility, when he wrote the passage which is thus translated by Dryden:
“Of beech, the plough-tail, and the bending yoke,Or softer linden, hardened in the smoke.”—Georgics, i., 225.
“Of beech, the plough-tail, and the bending yoke,Or softer linden, hardened in the smoke.”—Georgics, i., 225.
“Of beech, the plough-tail, and the bending yoke,Or softer linden, hardened in the smoke.”—Georgics, i., 225.
“Of beech, the plough-tail, and the bending yoke,
Or softer linden, hardened in the smoke.”—Georgics, i., 225.
Beckman, in his ‘History of Inventions,’ quotes a passage from Hesiod to the same effect; and adds, “as the houses of the ancients were so smoky, it may be easily comprehended how, by means of smoke, they could dry and harden pieces of timber.” In this manner were prepared the pieces of wood destined for ploughs, waggons, and the rudders of vessels:
“These long suspend, where smoke their strength explores,And seasons into use, and binds their pores.”—Virgil.
“These long suspend, where smoke their strength explores,And seasons into use, and binds their pores.”—Virgil.
“These long suspend, where smoke their strength explores,And seasons into use, and binds their pores.”—Virgil.
“These long suspend, where smoke their strength explores,
And seasons into use, and binds their pores.”—Virgil.
The late Brigadier-General Sir Samuel Bentham bestowed much time and attention in endeavouring to ascertain the quickest and best means of drying oak. Inhis letter to the Navy Board, 6th March, 1812, he says: “By exposing block shells to the smoke of burning wood, they become in the course of two or three days well seasoned in every respect, hard, bright coloured, and, as it were, polished. But it was found in a very short time that the acid with which the shells were thus impregnated very rapidly corroded the iron pins which passed through them.
“In Russia many small articles, such as parts of wheels, wheel carriages, and sledges, are prepared in this manner; so are wheels, at least in some parts of America; and sabots and other small articles in France.”
In speaking of artificial heat, he says, in the same letter:
“From all the opportunities I have had of examining the state of timber so prepared by artificial heat, the due seasoning without cracking has appeared to depend on the ventilation happening to beconstant, but veryslow, joined to such a due regulation of the heat as that theinteriorof the timber should dry, and keep pace in its contraction with the outer circles.”
Mr. T. W. Silloway, in ‘American Carpentry,’ remarks: “If timber be dried by heat, the outside will become hardened, and the pores closed, so that moisture, instead of passing out, will be retained within.”
Bowden remarks, “that the timbers of a small ship underwent the process of charring, either by suspending them over a fire of chips, or by burning the exterior with red-hot irons, so as to char the external surface. Air trunks were also formed between the timbers, for the purposeof evaporating moisture. The state of this vessel was examined five years after she was launched, and it appeared that, although the timbers had been very strongly charred, fungi had grown to a considerable extent on both sides abaft the fore channels, and that the plank near the magazine was completely decayed.”The power of vegetation broke through the incrusted barrier against external affection.
A method is in operation at Tourlaville, near Cherbourg, for which the inventor, M. Guibert, has taken out a patent, and it is said to give at once more expeditious and sure results than those obtained from the use of dry and hot air. It consists in filling the drying-stove with smoke, produced by the distillation of certain combustible matters, such as sawdust, waste tan, and smiths’ coals, &c. By means of a ventilator, ingeniously arranged, a rotatory movement round the logs laid to season is given to the smoke, so as to obtain an average uniform temperature in every part. By this plan, as the distillation of combustibles is always attended with a considerable discharge of steam, all cracks and splits are said to be prevented.
There is much force in Sir Samuel Bentham’s observations respecting the drying of timber by artificial heat: it is certainly not well to attempt to dry ittooquickly, for if it be subjected to great heat, a large portion of the carbon will pass off, and thereby weaken the timber. Timber too suddenly dried cracks badly, and is thus materially injured: planks of larch or beech are liable to warp and twist if their drying is hastened.
In some of the large manufactories for cabinet work, the premises are heated by steam pipes, in which case they have a close stove in every workshop heated many degrees beyond the general temperature, for giving the final seasoning to the wood; for heating the cauls; and for warming the glue, which is then done by opening a small steam pipe into the outer vessel of the glue-pot. The arrangement is extremely clean, safe from fire, and the degree of heat is very much under control.
In some manufactories, the wood is placed for a few days before it is worked up in a drying-room heated by means of stoves, steam or hot water, to several degrees beyond the temperature to which the finished work is likely to be subjected. Such rooms are frequently made as air-tight as possible, which appears to be a mistake,[1]as the wood is then surrounded by a warm but stagnant atmosphere, which retains whatever moisture it may have evaporated from the wood.
Fire-stoves for drying the timber were placed in the magazine, bread-room, and other parts of the ‘Royal Charlotte’ ship; and the evil of this practice was soon shown, for the vessel became dry rotten intwelve months.[2]
Wood sometimes undergoes a baking process for veneering. Fourcroy has recommended baking timber in an oven, and he has asserted that it would render timber more durable; “but,” says Boyden, “it should be subjected to a very strong heat, lest in endeavouringto prevent vegetation, we should give it birth.” Captain Shaw[3]observes: “Any artificial heating which burns the air is most injurious to wood and all combustible materials, and renders them much more inflammable than they would be if only exposed to the temperature of the atmosphere.”
Scorching and charring are good for preventing and destroying infection in timber, but have to be done slowly, and only to timber that is already thoroughly seasoned; otherwise, by incrusting the surface, the evaporation of any internal moisture is intercepted, and decay in the heart soon ensues; if done hastily, cracks are also caused on the surface, and which, receiving from the wood a moisture for which there is not a sufficient means of evaporation, renders it soon liable to decay. Charring has little or no control over internal corruption, though it is a good preventive against external infection: it increases the durability of dry, but promotes the decay of wet timber. Farmers very often resort to this method for the preservation of their fence-posts; the charring should extend a little above their contact with the ground. Unless they discriminate between green and unseasoned timber, these operations will prove injurious instead of beneficial.
We have already quoted Sir Charles Barry in favour ofsteamingwood; we now intend giving the opinion of a former pupil of his with regard tocharringit. Mr. GeorgeVulliamy, architect to the Metropolitan Board of Works, in a specification for oak fencing which was fixed round the boundaries of Finsbury Park, London, in 1867, writes as follows:—“Dig out the ground for the upright standards where shall be directed, and fill in and ram round same with dry burnt earth, stones, and rubbish (the burnt clay will be provided); enclose the boundaries of Park, as shall be directed, withdry and well-seasonedheart of English oak,wroughtupright standards, 6 inches by 5 inches, and 8 feet 6 inches total length, with cut andsplayedtops, holes drilled for oak pins, and mortised for horizontal rails, as shown on detailed drawings; to stand 5 feet 3 inches out of ground, andthe ends in ground to be well charred before fixing.” (The italics are our own.)
Our ancestors used charcoal and charred wood, on account of their durability, for landmarks in the ground between estates. The incorruptibility of charcoal is well known. Amongst other advantages, rats will not touch it; neither will the white ants nor cockroaches, so common in the Indies, commit their depredations where charring has been employed.
The ‘Revue Horticole’ states that it has been proved by recent experiments, that the best mode of prolonging the duration of wood is to char it, and then paint it over with three or four coats of pitch. Many of the sleepers now laid down on the Belgian railways are charred, the engineers preferring this process to any other.
The superficial carbonization, or charring of wood, as a preservative means, has long been practised. The Venetians have used charring for timber for a long period,particularly for piles. In France, M. de Lapparent recently proposed to apply it to the timber used in the French Navy. Some experiments, which were undertaken with a view to determine its practicability, terminated satisfactorily; and the Minister of Marine ordered the process to be introduced into the Imperial dockyards.
M. de Lapparent makes use of a gas blowpipe, the flame from which is allowed to play upon every part of the piece of timber in succession. By this means the degree of torrefaction may be regulated at will. The method is applicable to woodwork of all kinds; and the charring, it is said, does not destroy the sharpness of any mouldings with which the wood may be ornamented.
In the ‘Journal des Savants,’ Feb. 15, 1666, appears the following: “The Portugals scorch their ships, insomuch that in the quick works there is a coaly crust of about an inch thick; but this is dangerous, it happening, not seldom, that the whole vessel is burnt.” It is no wonder that the Portuguese ships should frequently fire in the operation, as their plank was charred an inch deep. A mere charring, if done properly, after the timbers had been thoroughly seasoned by air, would have been sufficient.
Charring seasoned wood is known to be a most effectual mode of preservation against rot in timber: thus do piles, when charred, last for ages in water or moist soil. Charred wood has been dug up, which must have lain in the ground for 1500 years, and was then found perfectly sound. After the Temple of Diana, at Ephesus, was destroyed, it wasfound to have been built on charred piles; and at Herculaneum, after 2000 years, the charred wood was found to be whole and undiminished. But we find Sir Christopher Wren did not approve of charred piles, except in a soil where they would be constantly wet. So, in order to attain a firmer foundation for St. Paul’s Cathedral, he had the ground excavated to an immense depth before a stone of the building was laid.
From time immemorial it has been the practice, particularly in France, to burn the ends of the poles driven into the ground to preserve them from decay. According to the remark of the celebrated Carlomb, we should always take into serious consideration old and well-known customs; but in this instance it is easy to admit the preserving effect of carbonization. Mr. James Randall,[4]Architect, states that he “oxidated several pieces of wood with nitric acid, and with fire,” and these processes were attended with success. Nearly the last sentence in his work is, “oxidation onlycan be relied on, in all cases, as an effectual cure.”
In charring, the surface of the timber is subjected to a considerable heat, the primary effect of which is to exhaust the sap of the epidermis, and to dry up the fermenting principles. Here this is done by long exposure to the air; and, in the second place, below the outside layer completely carbonized, a scorched surface is found, that is to say, partly distilled and impregnated with the products of that distillation, which is creosoted; the antiseptic properties of which are well known.
When Mr. Binmer was examined before the Commissionersof Woods, Forests, &c., in 1792, he stated “that all steamed plank should be afterwards dried andburntto extract the moisture.”
To a spontaneous carbonization must be attributed also the unchangeableness of that timber entirely black, which is met with everywhere in digging up the ground, where it has laid buried for ages. In the neighbourhood of St. Malo, France, these specimens are very common, and there most of the espaliers and vine props are made of wood, black as ebony, and famous for its durability. They have been cut from the trees of an old forest, submerged in the eighth century by an inroad of the sea, which formerly crossed a Roman road, leading from Brittany to Cotentin.
Not long after the beginning of the eighteenth century, the method of heating or charring timber, before it was worked up, and also that of stoving—that is, of heating in kilns with sand—were practised in the Royal dockyards. The ‘Royal William,’ one of the most remarkable instances of durability that the British Navy has supplied, was built either wholly or in part of timber that had been charred. It was launched in 1719; never repaired until 1757; and then, when surveyed afloat, in 1785, it appeared that the thick stuff and plank had beenburntinstead of beingkilned; and that the ends of the beams, the faying parts of the breast-hooks, crutches, resters, knees, &c., had been gouged in a manner then practised, which was calledsnail-creeping; by means of which the air was conveyed to the different parts of the ship.[5]
The reason this method has not been persevered in, but nearly abandoned, is owing to many causes: the difficulty and danger of the means adopted for charring, when either straw, fern, or shavings are made use of; the serious objection of burning the timber too deeply; or the encumbrance of the apparatus, and the length of time occupied, if sand-kilns sufficiently heated are used; and, finally, to indifference, or that system of routine, against which the wisest plans often contend in vain.
In house-building, the charring process should be applied to the beams and joists embedded in the walls, or surrounded with plaster; to the joists of stables, washhouses, &c., which, although exposed to the free air, are constantly surrounded by a warm and moist atmosphere, an active cause of fermentation; to the wainscotting of ground floors; to the flooring beneath parquet work; to the joints of tongues and rabbets; for carbonization by means of gas still leaves to the wood, for working purposes, all the sharpness of its edges. Charring is particularly useful in the junction of all broad surfaces, and more essentially in those which are cut either transverse or oblique to the grain of the wood, as the sap vessels are then exposed to the absorption of moisture. The butts of timbers are peculiarly liable to rot, because of affording a lodgment for moisture without a free passage for air. No seasoned timber should have its tubular parts exposed, nor should any timber have the saw marks upon it, because the torn filaments absorb and retain moisture. Allusion has already been made to the process adopted, near Cherbourg, for preventing the decay of timber by means of gas.
By carbonization, a practical and economical means is afforded to railway companies of preserving, almost for ever, the sleepers, and particularly oak, which cannot be impregnated easily by the injection of mineral salts. Let us suppose, for instance, that after, say ten or fifteen years, the sleepers on a line are taken up for the length of a mile, and replaced by new ones; the old, when rasped and burnt again, will serve for the replacing the following mile, and so on, one mile after the other. It might be equally serviceable to apply the same process to injected beech, for the reason that it is almost impossible to make the preserving liquid penetrate thoroughly the mass of the timber.
Mr. John Stephen Langton’s method of seasoning by extraction of the sap was patented in 1825, but is now almost wholly discontinued. It consists in letting the timber into vertical iron cylinders, standing in a cistern of water, closing the cylinders at top; and the water being heated, and steam used to produce a partial vacuum, the sap relieved from the atmospheric pressure oozes from the wood, and being converted into vapour, passes off through a pipe provided for the purpose. The time required is about ten weeks, and the cost is about ten shillings per load; but the sap is wholly extracted, and the timber is said to be fit and ready for any purpose; the diminution of weight is, with a little more shrinkage, similar to that in seasoning by the common natural process.[6]
Mr. Barlow’s patent provided for exhausting the air from one end of the log while one or more atmospheres press upon the other end. This artificial aerial circulation through the wood is prolonged at pleasure. However excellent in theory, this process is not practicable.
In October, 1844, M. Tissier proposed to place wood in a close vessel, and subject it to a current of hot dry air; and in 1847, Mr. Miller proposed to inject hot air through beams of wood to drive out the sap.
In 1851, M. Meyer d’Uslaw proposed to first dilate the pores of the wood with steam, and then place it in a hermetically closed chamber, and make a vacuum there.
The following system of preparing timber for the Navy was, not many years since, adopted in South Russia. A full account of the practice will be found in Oliphant’s ‘Russian Shores of the Black Sea,’ 1853. The only name we can give it is
A certain quantity of well-seasoned oak being required, Government issues tenders for the supply of the requisite amount. A number of contractors submit their tenders to a board appointed for the purpose of receiving them, who are regulated in the choice of a contractor not by the amount of his tender, but of his bribe. Thefortunateindividual selected immediately sub-contracts upon a somewhat similar principle. Arranging to be supplied with the timber for half the amount of his tender, the sub-contractor carries on the game, and perhaps the eighth link in this contracting chain is the man who, for anabsurdly low figure, undertakes to produce theseasonedwood.
His agents in the central provinces accordingly float a quantity of green pines and firs down the Dnieper and Bog to Nicholaeff, which are duly handed up to the head contractor, each man pocketing the difference between his contract and that of his neighbour. When the wood is produced before the board appointed to inspect it, another bribeseasonsit; and the Government, after paying the price of well-seasoned oak, is surprised that the 120-gun ship, which it has been built of it, is unfit for service in five years.
“Mark but my fall, and that that ruin’d me,Corruption.”—Shakspeare.
“Mark but my fall, and that that ruin’d me,Corruption.”—Shakspeare.
“Mark but my fall, and that that ruin’d me,Corruption.”—Shakspeare.
“Mark but my fall, and that that ruin’d me,
Corruption.”—Shakspeare.
A few words can only be given to a most important matter, viz., thesecond seasoning, which many woods require. If floor-boards are only laid down at first on the joists of a building, and at the expiration of one year wedged tight and nailed down, those unsightly openings caused by shrinkage, which form a harbour for dirt and vermin, will be avoided, as the wood will have had an opportunity of shrinking. Doors, sashes, architraves in long lengths, will also be better if made up some time before they are required for use. Many Indian woods require a second seasoning—kara mardá, for instance, a favourite wood with Indian railway engineers. Even sál and teak are not exempt. Teak shrinks sideways least of all woods. In the ‘Tortoise,’ store ship, when fifty years old, no openings were found to exist between the boards; yet Colonel Lloyd says he found the teak timbers used byhim in constructing a large room in the Mauritius to have shrunk ¾ of an inch in 38 feet. Thus a space of ⅜ of an inch must have been left at each end of the beam, where moisture could lodge and fungi exist, obtaining their nourishment from the wood. If unseasoned teak is used for ships, dry rot will in time find a place. It may be said that teak is a very hard wood, and very durable; yet “the mills of the gods,” says an ancient philosopher, “grind slow, very slow, but they grind to powder;”and so do the fungi mills.
Long years of practical experience has shown that timber, however prone to dry or wet rot, may be preserved from both by the use of certain metallic solutions, or other suitable protective matters.
All the various processes may be said somewhat to reduce the transverse strength of the timber when dry, and the metallic salts are affected at the iron bolts or fastenings. The natural juices of some woods do this; and bolts which have united beams of elm and pitch pine will often corrode entirely away at the junction.
The processes adopted for resisting the chemical changes in the tissues of the wood are all founded on the principle that it is essential to inject some material which shall at once precipitate the coaguable portion of the albumen retained in the tissues of the wood in a permanent insoluble form, so that it will not hereafter be susceptible of putrefactive decomposition. For this purpose, many substances, many solutions, have been employed with variable success, but materials have been sometimes introduced for this purpose which produced an effect just the opposite to what was anticipated.
Experience has shown that timber is permeable, at least by aqueous solutions, only so long as the sap channels are free from incrustation.
Such in general is the case with beech, elm, poplar, and hornbeam, the capillary tubes of which are always open, or, at least, close very slowly. At the same time it may be said that there must remain ever in these species some parts impervious to injection, whilst it is almost impossible but that a certain portion of the fibres will be more or less incrusted. The sap woods, on the other hand, of every species appear quite pervious.
Very little is known of any preservative process adopted in ancient times. Pliny observes that the ancients used garlic boiled in vinegar with considerable success, especially with reference to preserving timber from worms: he also states that the oil of cedar will protect any timber anointed with it from worm and rottenness. Oil of cedar was used by the ancient Egyptians for preserving their mummies. Tar and linseed oil were also recommended by him. The image of the goddess Diana, at Ephesus, was saturated with olive and cedar oils; also the image of Jupiter, at Rome; and the statues of Minerva and Bacchus were impregnated with oil of spikenard.
The idea of preserving wood by the action of oil is therefore by no means new; but it is somewhat curious that the earliest modern processes should also be by means of oil. Theoils most properto be used arelinseed,rapeseed, or almost any of the vegetable fixed oils. Oak wood, rendered entirely free from moisture, and then immersed in linseed oil, is said to be thus prevented from splitting: the time of immersion depending on the size, &c. Palm oil is preferable to whale oil, because impregnation with the latter, although in many instances eligible, causeswood to become brittle. It is, however, probable that whale oil, when combined with other substances, such as litharge, coal pitch, or charcoal, may lose much of that effect. As cocoa-nut oil, which is, under low temperature, like the oil expressed from the nuts of the palm tree, is known to be highly preservative of timber and metallic fastenings, we may expect the same result from the latter, and thereby avoid that extreme dryness and brittleness of the timber which Mr. Strange complained of in the Venetian ships that had been seasoned for many years in frame under cover. Cocoa-nut oil beat up with shell lime orchunam, so as to become putty, and afterwards diluted with more oil, is used at Bombay and elsewhere as a preservative coat or varnish to plank. It cannot become a varnish without the addition of some essential oil; and the oil of mustard is used; which, of course, will produce the desired effect. In the first volume of the Abbé Raynal, on the European settlements in the East and West Indies, he mentions that an oil was exported from Pegu for the preservation of ships; but as he does not say what oil, no conclusion can be drawn further than as to the probability of its being one of those already noticed.
Experience has proved that evenanimal oilsare so far injurious to timber as torender it brittle, whilst they preserve it from rottenness; and that, on the other hand, a mineral salt more or less combined with fatty substances does not produce that effect. The staves of whale-oil casks become quite brittle, whilst those of beef, pork, and tallow barrels remain tough and sound. Shipsconstantlyin the Greenland trade have their timbers and plankspreserved so far as they have become impregnated with whale oil.
Experiments with fish oil prove that of itself, unless exposed to sun and air, it may be injurious; that it loosens the cohesion of timber; but thatanimal fat, combinedwith saline matter,is preservative.
Fish oil used alone is ineligible, because capable of running into the putrefactive process, unless as a thin outside varnish. In hard, sound timber, it will hardly enter at all; and if poured into bore-holes in the heads of timbers, it will insinuate itself into the smallest rents or cracks, and waste through them. Used alone, or with any admixture, it is absorbed and dried quickly on wood in a decomposing state or commencing to be dry rotten. Used with litharge, it dries after some days; but with lamp-black it has scarcely so much tendency to dry as when used alone. Paint of fish oil and charcoal dries very quickly where there is absorption, and the charcoal extends its oxidating or drying effect to the fish oil in its vicinity.
We give the following to prove what we have written, and also to serve as an example for those who wish to try experiments:—
EXPERIMENTS ON FISH OIL.June 9.—Upon a piece of old oak scantling, with its alburnam on one side in a state of decay, fish oil was poured several times, viz. on this day, on June 25, and July 3, which it rapidly absorbed in the decayed part.July 26.—It was payed (or mopped) with fish oil and charcoal powder, and the following day it was put under an inverted cask.October 1.—The end of this piece was covered with a greenish mould.This proves that fish oil must be injurious, except where exposed to sun and air to dry it.
EXPERIMENTS ON FISH OIL.
June 9.—Upon a piece of old oak scantling, with its alburnam on one side in a state of decay, fish oil was poured several times, viz. on this day, on June 25, and July 3, which it rapidly absorbed in the decayed part.
July 26.—It was payed (or mopped) with fish oil and charcoal powder, and the following day it was put under an inverted cask.
October 1.—The end of this piece was covered with a greenish mould.This proves that fish oil must be injurious, except where exposed to sun and air to dry it.
A compound of fixed oils and charcoal is liable to inflame, but as a thin covering or pigment it may not be so.
Thepetroleumoil-wells, near Prome, in Burmah, have been in use from time immemorial. Wood, both for ship-building and house-building, is invariably saturated or coated with the product of those wells; and it is stated that the result isentire immunity from decayand the ravages of the white ant. At Marseilles, and some other ports in the Mediterranean, it used to be the practice to run the petroleum, which is obtained near the banks of the Rhone, into the vacancies between the timbers of the vessels, to give them durability. It was sometimes, for the conjoint purpose of giving stability and duration to vessels, mixed with coarse sand or other extraneous matters, and run in whilst hot between the ceiling and bottom plank, where it filled up the vacancies between the timbers in the round of their bottoms, excepting where necessary to be prevented. The great objection to the use of petroleum is its inflammability.Creosote, its great rival for wood preserving, is also inflammable, and not so agreeable in colour; but it isconsiderably cheaper, which is an important matter.
As we are now about to enter upon the subject of patent processes, &c., it appears desirable to lay down certain principles at the commencement, in order to assist the reader as much as possible.
Almost every chemical principle or compound of any plausibility has been suggested in the course of the last hundred and fifty years; but the multiplicity and contradictionof opinions form nearly an inextricable labyrinth. To commence.
1st. It seems obvious thatthe sooner the sap is wholly removed from the wood the better,provided the woody fibre solidifies without injury.
2nd. Thatthe wood should be impregnated with any strongly antiseptic and non-deliquescent matter,which must necessarily be in solution when it enters the wood. No deliquescent remedy is eligible, because moisture is injurious to metallic fastenings.
3rd.The wood should be first dried, and its pores then closed with any substance impervious to air and moisture, and at the same time highly repellant to putrescency.The most essential requisites in a preservative of timber being a disposition todryness, and a tendency to resistcombustionas far as consistently obtainable.
4th.Any process to be successful ought not to be tedious, very difficult, or too expensive.These are important elements in the success of any patent.
Very little is known of any preservative process previous to the year 1717, when directions were given by the Navy authorities toboiltreenails, and dry them before they were used. But whether the custom had prevailed before this time, or whether their strength and durability were increased by it, there are no means of ascertaining. It does not appear that any substance was put into the water to decompose the juices; but as they are soluble in warm water, perhaps the power of vegetation might have been destroyed without it.
In 1737 Mr. Emerson patented a process of saturatingtimber withboiled oil, mixed with poisonous substances; but his process was very little used. This, we believe, was thefirstpatent on wood preserving.
About 1740, Mr. Reid proposed to arrest decay by means of a certainvegetable acid(probably pyroligneous acid). The method of using it was by simple immersion.
In 1756, Dr. Hales recommended that the planks at the water-line of ships should be soaked inlinseed oil, to prevent the injury to which wood is subject when alternately exposed to wet and dry; and indeed, many ships were built in which a hollow place was cut in one end of each beam or sternpost, which might constantly be kept filled withtrain oil. Amongst other ships so constructed, the ‘Fame,’ 74, may be mentioned. When, after some years, this ship was repaired, it was found that as far as the oil had penetrated, namely, from 12 to 18 inches from the end, the wood was quite sound, whilst the other parts were more or less decayed. The Americans used to hollow out the tops of their masts in the form of cups or basins; bore holes from the end a considerable way down the masts; pour oil into these; cover them over with lead; and leave the oil to find its way down the capillary vessels to the interior of the timber.[7]
In 1769, Mr. Jackson, a London chemist, with a view to the prevention of decay, obtained permission to prepare some timber to be used in the national yards, by immersing it in a solution ofsalt water,lime,muriate of soda,potash,salts, &c., the result of which dose was, that several frigates in the Navy subjected to the process were renderedmore perishable than if they had been constructed of unprepared timber. The solution was filtered into the wood partly by means of holes made in it. Chapman proposed a similar method of preserving the frames of ships, viz. by boring holes in the timbers, and pumping asolution of copperasin water into them. He believed every part of the vessel would thus be impregnated.
Mr. Jackson also prepared the frame of the ship ‘Intrepid’ with another solution. The ship lasted many years. Bowden thought it was asolution of glue. Chapman suggestedslaked lime, thinned with a weaksolution of gluefor mopping the timbers of a ship.
Shortly after Mr. Jackson’s process was started, Mr. Lewis attempted to accomplish the preservation of timber by placing it surrounded by pounded lime, in spaces below the “surface of the earth.” The use of lime has also been advocated by Mr. Knowles, Secretary of the Committee of Surveyors of the Navy, who has written an able work on the ‘Means to be taken to Preserve the British Navy from Dry Rot’ (1821).
Between 1768 and 1773 a practice prevailed of saturating ships with common salt; but this was found to cause a rapid corrosion of the iron fastenings, and to fill the vessels between decks with a constant damp vapour. In ‘Nicholson’s Journal,’ No. 30, there is an article signedNauticuson this subject. Vessel owners had long ago observed that those ships which have early sailed with cargoes of salt are not attacked by dry rot. Indeed, several instances are attested of vessels whose interiors were lined with fungi having all traces of the plant destroyed by accidental orintentional sinking in the sea. Acting on such hints, a trader of Boston, U. S., salted his ships with 500 bushels of the chloride, disposed as an interior lining, adding 100 bushels at the end of two years. Such an addition of dead weight is sufficient objection to a procedure which has other great disadvantages. Salt should never be applied as an antidote against the dry rot, on account of its natural powers of attracting moisture from the atmosphere, which would render apartments almost uninhabitable, from their continual dampness. Those who have lived for any length of time in a house at the sea-side, the mortar of which has been partly composed of sea sand, will have observed the moist state of the paper, plastering, &c., in wet weather. Bricks made with sea sand are objectionable.
Salt waterseasoning has already been referred to in the last chapter, but as it is so closely connected with salt seasoning, the further and final consideration of salt water seasoning may be fitly dealt with here. Salt water will not extract the juices from the timber like fresh water. It is only by destroying the vegetation that salt water can be advantageous, but it would require a very long time to impregnate large timber to the heart so as to destroy vegetation. It is well known that wood is softened, and in time decomposed, by extreme moisture. Fifty years since, the master builder at Cronstadt complained that the oak from Casan, which was frequently wet from different causes in its passage of three years to Cronstadt, was so water-soaked as never to dry; and also from the information of Mr. Strange, it appears “that the practice at Venice of the fresh-cut timber being thrown into salt water, prevents its everbecoming dry in the ships, and that the salt water rusted and corroded the iron bolts.” In fine, vessels built with salt water seasoned wood are perfect hygrometers, being as sensible to the changes of the moisture of the atmosphere as lumps of rock salt, or the plaster of inside walls where sea sand has been used.
In Ceylon, the timber of the female palm tree is much harder and blacker than that of the male, inasmuch as it brings nearly triple its price. The natives are so well aware of the difference that they resort to the devise of immersing the male tree insalt waterto deepen its colour, as well as add to its weight.
Vessels impregnated withbay salt, or the large grained salt of Leamington or of Liverpool (pure muriate of soda), will possess decided advantages; as also will vessels that have been laden withsaltpetre, if it has been dispersed amongst their timbers.
Ships (the timbers of which had been previously immersed in salt water) have been broken up after a few years’ service, and the floor timbers taken out quite sound: but when exposed to the sun and rain in the summer months, their albumen has been in a decomposed or friable state.
By the answers to queries given to Mr. Strange, the British Minister at Venice, in or about 1792, it appears that several of the Venetian ships of war had then lain under sheds for fifty-nine years; some in bare frames, and others planked and caulked: that these ships show no outward marks of decay; but their timbers have shrunk much, andbecome brittle; that some of the most intelligentship builders were of opinion that great prejudice had arisen from the prevalent custom of throwing the timber fresh cut into salt water, and letting it lie there until wanted; that afterwards it dried, and withered on the outside, under the sheds, while the inside, being soaked with salt water, rotted before it became dry; and this was one reason, amongst others, why Venetian ships, though built of good timber, lasted so short a time; for the salt moisture not only rots the inside of the beams and timbers, but of course rusts and corrodes the iron bolts.
Salt water,sea-sand, andsea-weedare now used for seasoning “jarrah” wood in Western Australia. This wood is considered a first-class wood for ship-building, but it is somewhat slow to season, and if exposed before being seasoned it is apt to “fly” and cast. The method adopted is as follows: The logs are thrown into the sea, and left there for a few weeks; they are then drawn up through the sand, and after being covered with sea-weed a few inches deep, are left to lie on the beach, care being taken to prevent the sun getting at their ends. The logs are then left for many months to season. When taken up they are cut into boards 7 inches wide, and stacked, so as to admit of a free circulation of air round them, for five or six months before using them. Sea-weed or sea-ware, cast upon the shores, contains a small quantity of carbonate of soda, and a large proportion of nitrogenous and saline matters, with earthy salts, in a readily decomposable state. They also contain much soluble mucilage. The practice of seasoning timber by heating it in asand bathwas formerly adopted by the Dutch, and by the Russians in building boats.Mr. Thomas Nichols (in a letter to Lord Chatham, when First Lord of the Admiralty) states “that the same end, viz. preservation of timber from decay, might probably be acquired by burying the timber in sand, which acts as an artificial sap,” in the same manner as mentioned in Townsend’s ‘Travels through Spain,’ to be used with the masts of ships of war at Cadiz.
Peat mosshas been recommended (because the sulphates of iron, soda, and magnesia are found in it), but it failed when tried.
With reference to Mr. Lewis’s proposal to preserve wood by means of lime, it must be remembered thatquicklime, with damp, has been found to accelerate putrefaction, in consequence of its extracting carbon; but when dry, and in such large quantities as to absorb all moisture from the wood,the wood is preserved,and the sap hardened. Vesselslongin the lime trade have afforded proof of this fact; and we have also examples in plastering-laths, which are generally found sound and good in places where they have been dry. Whitewash orlimewaterhas been strongly recommended for use between the decks of ships, as being unfavourable to vegetation: it should be renewed at intervals of time, according to circumstances. It has been applied with good effect to the joists and sleepers of kitchen floors; but to be effectual it should be occasionally renewed. Effete, or re-carbonated lime, is injurious to timber, like other absorbent earths; so also are calcareous incrustations formed by the solution of lime in water, as appears from Von Buch’s ‘Travels in Norway,’ in which he says, “that in the fishing country (near Lofodden,beyond the Arctic circle) the calcareous incrustations brought by water, filtering through a bed of shells, soon cause the vessels and wood to be covered with and destroyed by green fungi.” The ends of joists of timber inserted in walls are frequently found rotten; and where not so, it may probably be owing to the mortar having been made with hot lime, and used immediately, or to the absence of moisture. It does not appear practicable to use limewater to any extent for preserving timber, because water holds in solution only about ⅟500th part of lime, which quantity would be too inconsiderable; it, however, renders timber more durable, but at the same time very hard and difficult to be worked (p. 73).
Vessels constantly in thecoaltrade have generally required little repair, and have lasted until in the common course of things they were lost by shipwreck. This must be owing to the martial pyrites which abound in all coals; and also from the sulphuric acid arising from the quantity of coal dust which finds its way through the seams of the ceiling, and adheres to the timber and planks.
In 1779, M. Pallas, in Russia, proposed to steep wood insulphate of iron(green vitriol) until it had penetrated deeply,andthen inlimeto precipitate the vitriol. Neumann, in his first volume of ‘Chemistry,’ on the article green vitriol, says, “That in the Swedish transactions this salt is recommended for preserving wood, particularly the wheels of carriages, from decay.
“When all the pieces are fit for being joined together, they are directed to be boiled in a solution of vitriol for three or four hours, and then kept for some days in awarm place to dry. It is said that the wood by this preparation becomes so hard and compact that moisture cannot penetrate it, and that iron nails are not so apt to be destroyed in this vitriolated wood as might be expected,but last as long as the wood itself.”
In 1780 the marcasite termed by the minersmundic, found in great abundance in the tin mines in Devonshire and Cornwall, was employed, in a state of fusion, to eradicate present and to prevent the future growth of dry rot; but whether its efficacy was proved by time is not known. A garden walk where there are some pieces of mundic never has any weeds growing; the rain that falls becomes impregnated with its qualities, and in flowing through the walk prevents vegetation.
In 1796 Hales proposed tocreosotethe treenails of ships: this was forty-two years previous to Bethell’s patent for creosoting wood.
About the year 1800, the Society of Arts’ building in the Adelphi, London, being attacked by dry rot, Dr. Higgins examined the timbers, caused some to be removed and replaced by new, and the remainder to be scraped and washed with a solution ofcaustic ammonia, so as by burning the surface of the wood to prevent the growth of fungi.
At the commencement of the present century, a member of the Royal Academy of Stockholm called attention to the use ofalumfor preserving wood from fire. He says, in the Memoirs of that Academy, “Having been within these few years to visit the alum mines of Loswers, in the province of Calmar, I took notice of some attempts made to burn the old staves of tubs and pails that hadbeen used for the alum works. For this purpose they were thrown into the furnace, but those pieces of wood which had beenpenetratedby the alum did not burn, though they remained for a long time in the fire, where they only became red; however, at last they were consumed by the intenseness of the heat, but they yielded no flame.” He concludes, from this experiment, that wood or timber for the purpose of building may be secured against the action of fire by letting it remain for some time in water wherein vitriol, alum, or any other salt has been dissolved which contains no inflammable parts.
In Sir John Pringle’s Tables of the antiseptic powers of different substances, he statesalumto be thirty times stronger than sea-salt; and by the experiments of the author of the ‘Essai pour servir à l’Histoire de la Putréfaction,’ metallic salts are much more antiseptic than those with earthy bases.
In 1815 it occurred to Mr. Wade that it would be a good practice to fill the pores of timber withalumine, or selenite; but two years after, Chapman observed, “Impregnation of ships’ timbers with asolution of alumoccurred to me about twenty years since, because on immersion in sea-water the alumine would be deposited in the pores of the timber; but I was soon informed of its worse than inutility, by learning that theexperiment had been tried, and, in place of preserving, hadcaused the wood to rot speedily. Impregnation withselenitehas been tried in elm water-pipes. On precipitation from its solvent it partially filled the pores, and hardened the wood, butoccasioned speedy rottenness.” If, by using asolution of alumto render wood uninflammable, we at the same time cause it torot speedily, it becomes a questionwhether the remedy is not worse than the disease. Captain E. M. Shaw, of the London Fire Brigade, in his work, ‘Fire Surveys’ (1872), recommendsalum and water. Probably he only thought of fire, and not of rotting the wood. The alum question does not appear to be yet satisfactorily settled.
While upon the subject of uninflammable wood, we may state that in 1848, upon Putney Heath (near London), by the roadside, stood an obelisk, to record the success of a discovery made in the last century of the means of building a house which no ordinary application of ignited combustibles could be made to consume: the obelisk was erected in 1786. The inventor was Mr. David Hartley, to whom the House of Commons voted 2500l., to defray the expenses of the experimental building, which stood about one hundred yards from the obelisk. The building was three stories high, and two rooms on a floor. In 1774, King George the Third and Queen Charlotte took their breakfast in one of the rooms, while in the apartment beneath fires were lighted on the floor, and various inflammable materials were ignited to attest that the rooms above were fire-proof. Hartley’s secret lay in the floors being double, and there being interposed between the two boards sheets of laminated iron and copper, not thicker than stout paper, which rendered the floor air-tight and thereby intercepted the ascent of the heated air; so that, although the inferior boards were actually charred, the metal prevented the combustion taking place in the upper flooring. Six experiments were made by Mr. Hartley inthis house in 1776, but we cannot ascertain any particulars about them, or any advantages which accrued to the public from the invention, although the Court of Common Council awarded him the freedom of the City of London for his successful experiments.
In 1805 Mr. Maconochie proposed to saturate with resinous and oily matters inferior woods, and thus render them more lasting. This proposal was practically carried out in 1811 by Mr. Lukin, who constructed a peculiar stove for the purpose of thus impregnating wood under the influence of an increased temperature. The scheme, however, had but very partial success, for either the heat was too low and the wood was not thoroughly aired and seasoned, or it was too high and the wood was more or less scorched and burnt. Mr. Lukin buried wood inpulverized charcoalin a heated oven, but the fibres were afterwards discovered to have started from each other. He next erected a large kiln in Woolwich dockyard, capable of containing 250 loads of timber, but an explosion took place on the first trial, before the process was complete, 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 dockyard, part of which was thrown to the distance of 250 feet; an iron door weighing 280 lb. 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.
Mr. Lukin was not so fortunate in 1811 as in 1808, for in the latter year he received a considerable reward fromthe Government for what was considered a successful principle of ventilating hospital ships.
In 1815 Mr. Wade recommended the impregnation of timber with resinous or oleaginous matter (preferring linseed oil to whale oil) or withcommon resindissolved in a lixivium ofcaustic alkali, and that the timber should afterwards be plunged into water acidulated with any cheap acid, or with alum in solution. He considered that timber impregnated with oil would not be disagreeable to rats, worms, cockroaches, &c., and that the contrary was the case with resin. He also recommended the impregnation of timber with sulphate ofcopper, zinc, or iron, rejecting deliquescent salts, as they corrode metals.
In 1815 Mr. Ambrose Boydon, of the Navy Office, strongly recommended that the timber, planks, and treenails of ships should be first boiled inlimewaterto correct the acid, and that they afterwards should be boiled in athin solution of glue, by which means the pores of the wood would be filled with a hard substance insoluble by water, which would not only give the timbers durability, by preventing vegetation, but increase their strength. Glue, he thought, might be used without limewater, or glue and limewater mixed together.
In 1817 Mr. William Chapman published the result of various experiments he had made on wood withlime,soap, andalkalineandmineral salts. He recommended a solution of a pound ofsulphate of copperor blue vitriol (at that time 7d.per pound) dissolved in four ale gallons of rain water, and mopped on hot over all the infected parts, or thrown over them in a plentiful libation. He also recommendedone ounce ofcorrosive sublimate(then 6s.per pound) to a gallon of rainwater applied in the same manner to the infected parts. For weather-boarded buildings he considered one or more coats of thincoal tar, combined with a small portion ofpalm oil, for the purpose of preventing their tendency to rend, to be a good preservative.
Messrs. Wade, Boydon, and Chapman published works on dry rot about this time.
In 1822 Mr. Oxford took out a patent for an improved method of preventing “decay of timber,” &c. The process proposed was as follows: “The essentialoil of tarwas first extracted by distillation, and at the same time saturated withchlorine gas. Proportions ofoxide of lead,carbonate of lime, andcarbon of purified coal tarwell ground, were mixed with the oil, and the composition was then applied in thick coatings to the substances intended to be preserved.”
On 31st March, 1832, Mr. Kyan patented his process ofcorrosive sublimate(solution of thebi-chloride of mercury) for preventing dry rot; which process consisted as follows: A solution of the corrosive sublimate is first made, and the timber is placed in the tank. The wood is held down in such a way, that when immersed on the fluid being pumped in, it cannot rise, but is kept under the surface, there being beams to retain it in its place. There it is left for a week, after which the liquor is pumped off, and the wood is removed. This being done, the timber is dried, and said to be prepared. Sir Robert Smirke was one of the first to use timber prepared by Kyan, in some buildings in the Temple,London; and he made some experiments on timber which had undergone Kyan’s process. He says, “I took a certain number of pieces of wood cut from the same log of yellow pine, from poplar, and from the common Scotch fir; these pieces I placed first in a cesspool, into which the waters of the common sewers discharged themselves; they remained there six months; they were then removed from thence, and placed in a hotbed of compost under a garden-frame; they remained there a second six months; they were afterwards put into a flower border, placed half out of the ground, and I gave my gardener directions to water them whenever he watered the flowers; they remained there a similar period of six months. I put them afterwards into a cellar where there was some dampness, and the air completely excluded; they remained there a fourth period of six months, and were afterwards put into a very wet cellar. Those pieces of wood which underwent Kyan’s process are in the same state as when I first had them, and all the others to which the process had not been applied are more or less rotten, and the poplar is wholly destroyed.
“I applied Kyan’s process to yellow Canadian pine about three years ago, and exposed that wood to the severest tests I could apply, and it remains uninjured, when any other timber (oak or Baltic wood) would certainly have decayed if exposed to the same trial, and not prepared in that manner.
“As another example of the effect of the process, I may mention that about two years ago, in a basement story of some chambers in the Temple, London, the woodflooring and the wood lining of the walls were entirely decayed from the dampness of the ground and walls, and to repair it under such circumstances was useless. As I found it extremely difficult to prevent the dampness, I recommended lining the walls and the floor with this prepared wood, which was done; and about six weeks ago I took down part of it to examine whether any of the wood was injured, but it was found in as good a state as when first put up. I did not find the nails more liable to rust.’
“I have used Kyan’s process in a very considerable quantity of paling nearly three years ago; that paling is now in quite as good a state as it was, though it is partly in the ground. It is yellow pine. Some that I put up the year before, without using Kyan’s process (yellow pine), not fixed in the ground, but close upon it, is decayed.”
This evidence, by such an experienced architect as the late Sir Robert Smirke was, is certainly of great value in favour of Kyan’s process.
The recorded evidence upon the efficiency of this mode of treating timber for its preservation is somewhat contradictory. On the Great Western Railway 40,000 loads were prepared, at an expenditure of 1¾ lb. of sublimate to each load, the timber, 7 inch, being immersed for a period of eight days, and the uniformity of the strength of the solution being constantly maintained by pumping. Some samples of this timber, after six years’ use as sleepers on the railway, were found “as sound as on the day on which they were first put down.” This timber was prepared by simple immersion only, without exhaustionor pressure. Some of the sleepers on the London and Birmingham Railway, on the other hand, which had been Kyanized three years only, were found absolutely rotten, and Kyan’s process was there consequently abandoned.
This process is said to cost an additional expense to the owner of from fifteen to twenty shillings per load of timber. Mr. Kyan at first used 1 lb. of the salt in 4 gallons of water, but it was found that the wood absorbed 4 or 5 lb. of this 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.
Simple immersion being found imperfect as a means of injecting the sublimate, attempts were afterwards made to improve the efficiency of the solution byforcingit into the wood. Closed tanks were substituted for the open ones, and forcing pumps, &c., were added to the apparatus. The pressure applied equalled 100 lb. on the square inch. With this arrangement a solution was made use of having 1 lb. of the sublimate to 2 gallons of water; and it was found that three-fourths of this quantity sufficed for preparing one load of timber. The timber was afterwards tested, and it was ascertained that the solution had penetrated to the heart of the logs. Mr. Thompson, the Secretary to Kyan’s Company, stated, in March, 1842, that experience had proved “that the strength of the mixture should not be less than 1 lb. of sublimate to 15 gallons of water; and he had never found any well-authenticated instance of timber decaying when it had been properly prepared at that strength.” As muchas 1 in 9 was not unfrequently used. Kyan’s process is now but very rarely used; Messrs. Bethell, of King William Street, London, adopt it when requested by their customers. We have given the statements which have been made for and against this patent, but after a lapse of forty years it is difficult to reconcile conflicting statements.