CHAPTER VII.

ON THE PRESERVATION OF WOODEN BRIDGES, JETTIES, PILES, HARBOUR WORKS, ETC., FROM THE RAVAGES OF THE TEREDO NAVALIS AND OTHER SEA-WORMS.

“Perforated sore And drilled in holes, the solid oak is found By worms voracious, eaten through and through.”

SIR JOHN BARROW.

As the destruction of timber by fungi has been called the _vegetable_ rot, it may not be inappropriate to term the destruction of wood by various worms and insects, the _animal_ rot.

We have _four natural enemies_ to deal with: 1st, the _dry rot_, that attacks our houses, &c.; 2nd, the _worms_, or boring animals, which destroy our ships and harbours; 3rd, the _rust_, that eats our iron; and 4th, the _moisture and gases_, that destroy our stone.

There are three classes of destructive insects which prey upon timber trees, founded upon the manner in which they carry on their operations--viz. those which feed upon the leaves and tender shoots; those which feed upon the bark and the albumen; and those which feed upon the heart-wood.

It is to be observed that some of the insects which feed upon the heart of wood do not cease their ravages upon the removal of the tree; but that, on the contrary, the _Cossus syrex_, of our indigenous fauna, and the larvæ of the _Callidium bajutum_, which are often found in imported timber, continue to devour the wood long after it has been inserted in buildings. There seem to be very few means of defence against this class of destructive agents; and very few trustworthy indications of their existence, or of the extent of the ravages they have committed, are to be discovered externally; and it thus frequently happens that a sound, hearty-looking stick of timber may be so seriously bored by these insects as to be of comparatively little value for building purposes of any description. The soft and tender woods, and such as are of a saccharine nature in their juices, are the most liable to be assailed by worms; those which are bitter are generally, if not invariably, exempt; it is obvious, therefore, that those palatable juices, which are so conducive to their production and propagation, should be got rid of by thorough seasoning, and, if further precaution be necessary, that the infusion of some bitter decoction into the pores of the wood will be an effectual preventive; and for which those woods that are of a regular grain afford sufficient facilities. Ash, if felled when abounding in sap, is very subject to worms; beech, under similar circumstances, is also liable to their attacks; likewise alder and birch; in these woods water seasoning is sometimes found to be a good preventive; the sapwood of oak is also thus improved; the silver fir is subject to them; the sycamore is rather so; alder is said when dry to be very susceptible of engendering them; the cedar, walnut, plane, cypress, and mahogany are examples of woods which discourage their advances. It has been stated that Robert Stevenson (not the son of the “Father of Railways”), of Edinburgh, at Bell Rock Lighthouse (of which he was engineer), between 1814 and 1843, found that greenheart wood, beef wood, and bullet tree were not perforated by the _Teredo navalis_, and teak but slightly so. Later experiments show that the “jarrah” of the East, also, is not attacked. Lignum vitæ is said to be exempt. The cost of these woods prevents their general use.

In 1810, Stevenson first noticed the _teredo_ in piles, and specimens of the creatures in wood were sent to Dr. Leach, of the British Museum, in 1811, who examined them, and noticed their peculiarities. Stevenson, settled on Bell Rock during many years (like a new Robinson Crusoe), was enabled to watch the injuries done to the piles by the _teredo_. With piles which had been subjected to Kyan’s process before immersion, the wood was attacked at the end of the twenty-eighth month, and was entirely destroyed in the seventh month of the fifth year. With Payne’s, it lasted a year longer.

We can give the names of those who have given much time and attention to this subject. At the bottom of this page a list of works of reference[16] will be found useful. Messrs. Stevenson (engineer of Bell Rock Lighthouse), Harting (Member of the Academy of Sciences of the Pays-Bas), de Quatrafages, Deshayes, Caillaut, Hancock, Dagneau, de Gemini, Kater, Crepin (Engineer-in-Chief, of Belgium), and A. Forestier (Engineer-in-Chief of the Bridges, &c., of France).

The termite, or white ant, is the most destructive insect to timber on land, whilst the teredo reigns supreme of sea worms in the sea. The former we shall treat of in our next chapter, the latter we propose considering at some length in this.

The marine worm, of which there are accounts in all parts of the world, has been known, by its effects, for hundreds of years; indeed, Ovid spoke of it nineteen hundred years ago, and it is even mentioned by Homer. Fossil _terredines_ of great antiquity have been found near Southend; also pieces of petrified wood from the greensand, near Lyme and Sidmouth, bored by ancient species of _teredo_; also from Bath, and from Doulting, near Shepton Mallet, specimens of oolite, with petrified corallines in it, pierced by boring shells.

It is said that this worm is a native of India, and that it was introduced to Holland some 200 years ago, from whence it has spread through the ports of northern Europe.

The _Teredo navalis_[17] is very destructive to harbour works and piling. The Southampton water is particularly infested with it; in fact, the _teredo_ is found in every port to which coals are carried south of the Tees; in the Thames, as high up as Gravesend; and northward as far as Whitby. It is also found at Ryde, Brighton, and Dover. Traces of the ravages of the _Teredo navalis_, and of the _Limnoria terebrans_, have at various periods been found from the north of Scotland and Ireland, on almost every coast, to the Cape of Good Hope and Van Dieman’s Land, in the eastern hemisphere; and, in the western hemisphere, from the river St. Lawrence to Staten Island, near Terra del Fuego, almost in the Polar Sea; so that although this maritime scourge is rifest in warm climates, yet cold latitudes are not exempt from it.

At the Crystal Palace, Sydenham, may be seen the destructive _Teredo navalis_ in a bottle, and there may also be seen mahogany perforated by it, and fir piles from Lowestoft Harbour, which were rendered useless by the ravages of the worm and the _limnoria_ three years after they were driven, showing the necessity of defending timber intended for marine construction. A specimen of American oak from the dock gates of Lowestoft Harbour, which had been four years under water, and a part of a fir-pile from the dockyard creek at Sevastopol, also show the destructive powers of the _teredo_. At the South Kensington and British Museums, London, specimens of this worm may also be seen, as well as pieces of timber perforated by it.

The bottoms of ships, and timbers exposed to the action of the sea, are often destroyed by the _teredo_.

The gunboats constructed during the Crimean war suffered far more from dry rot and the _teredo_ than the shot and shell of the Russians. One cannot even guess at the mischief perpetrated every year all along our shores, in docks and harbours, by the boring animals that penetrate all woods not specially protected. We cannot count the number of the ships that have foundered at sea, owing to those few inches of timber, on which all depended, being pierced or destroyed by the worm or fungus.

In the short space of twelve years these destructive worms were known to make such havoc in the fir piles of a bridge at Teignmouth, that the whole bridge fell suddenly, and had to be totally reconstructed.

The wooden piers of Bridlington were nearly wholly destroyed by worms; and the pile fenders on the stone piers at Scarborough were generally cut through in a few years.

At Dunkirk, wooden jetties are so speedily eaten away that they require renewal every twelve or fifteen years. At Havre, a stockade was entirely destroyed in six months. At Lorient, wood only lasts about three years in the sea-water; and at Aix, the hull of a stranded vessel was found to have lost half its weight in six months, from the ravages of these animals.

The reason why Balaclava, in Russia, is not a place of considerable mercantile importance is owing in a great measure to the destructive ravages of the worms with which its waters are infested, and by which the hulls of ships remaining there for any length of time become perforated.

The piles of the jetties in Colombo Harbour, Ceylon, which are mostly of satin-wood, and about 14 inches in diameter, are so pierced by these worms in the course of twelve months as to require renewal.

The cofferdam at Sheerness was destroyed by the _teredo_. After a time, it was no uncommon occurrence to see several piles, apparently sound, floated away at each tide; indeed, they were so thoroughly perforated by the _teredo_ that in still weather, by putting the ear to the side of the pile, the worms could be heard at their boring labours.

The almost total destruction of the pier-head of the old Southend Pier in a few years, is another instance of the serious damages these worms cause. The old pier-head was erected in the year 1833, and in three years the majority of the wooden piles had been almost destroyed, and at the end of ten years, in addition to the piles being all eaten through by the worms, the whole structure had sunk 9 inches at the western end, so that in a short time it would have fallen. The materials with which the work was constructed were of good quality, the fir being Memel, and the oak of English growth; it was all perfectly sound in those places were the _teredo_ had not attacked it, and indeed portions of it were again used in the construction of the extension of the pier. The whole of the timber work was well coated with pitch and tar previously to being fixed, but notwithstanding these precautions, and an apparent determination to protect the pier-head by copper sheathing, brushing, cleaning, and constant watchfulness, the _teredo_ made its appearance, and committed such ravages that the entire destruction of the pier-head soon appeared inevitable. The _Teredo navalis_ first showed itself six months after the completion of the work, and was reported within twelve months to have seriously injured the piles above the copper, whilst at about low-water mark, of neap tides, nearly all the piles exhibited appearances of destruction, the _limnoria_, as well as the _teredo_, having seriously attacked them; and in less than four years from the completion of the pier-head, they had progressed in their work to such an extent that some of the piles were entirely eaten through, both above and below the copper sheathing; in consequence of this the stability of the structure was materially injured, and, on examination, it was discovered that the ground had been considerably washed away by the action of the sea, and that the piles below the copper were exposed to the action of the _teredo_.

The first appearances of the _Teredo navalis_ are somewhat singular, inasmuch as the wood which has been perforated by it presents to the casual observer no symptom of destruction on the surface, nor are the animals themselves visible, until the outer part of the wood has been broken away, when their shelly habitations come in sight, and show the perfect honeycomb they have formed; on a closer examination of the wood, however, a number of minute perforations are discovered on the surface, generally covered with a slimy matter; and on opening the wood at one of these, and tracing it, the tail of the animal is immediately found, and after various windings and turnings, the head is discovered, which, in some cases, is as much as 3 feet from the point of entrance; sometimes it will happen, especially if the wood has been much eaten, that their shelly tubes are partly visible on the surface, but this is rare; they enter at the surface, and bore in every direction, both with and against the grain of the wood, growing in size as they proceed.

The Rev. W. Wood writes, in 1863: “I have now before me a portion of the pier at Yarmouth, which is so honeycombed by this terrible creature that it can be crushed between the hands as if it were paper, and in many places the wood is not thicker than ordinary foolscap. This piece was broken off by a steamer which accidentally ran against it; and so completely is it tunnelled, that although it measures 7 inches in length and about 11 in circumference, its weight is under 4 ounces, a considerable portion of even that weight being due to the shelly tubes of the destroyers.”

The eggs of the _teredo_ affix themselves to the wood they are washed against, are then hatched, and the worm commences boring; each individual serves by itself for the propagation of the species; and they rarely injure each other’s habitations. Any timber, constantly under water, but not exposed to the action of the air at the fall of the tide, is extremely likely to be destroyed by them. They appear to enter the wood obliquely, to take the grain of the fibre, and more generally to bore with it downwards, where the perforations are left dry at low water.

It has been stated by some authorities that the _teredo_ is only a destructive creature, and seeks the wood as a shelter, from instinctive dread of some larger animals, but there is no doubt this insect feeds upon wood. Mr. John Paton, C.E. (to whom we are indebted for much information on these worms), in conjunction with Mr. Newport, the eminent physiologist and anatomist, on carefully dissecting this animal for the purpose of ascertaining its general character, and more particularly the nature of its food, found digested portions of wood in its body, so that there is no doubt that the _teredo_ does feed upon the particles of the wood, and to this its rapid and extraordinary growth must be mainly attributed.

The _Teredo navalis_, or, as it is sometimes called, the Ship Worm, is one of the _Acephalous mollusca_, order Conchifera, and of the family of the _Pholadariæ_. It is of an elongated vermiform shape, the large anterior part of which constitutes the boring apparatus, and contains the organs of digestion, and the posterior, gradually diminishing in size, those of respiration. The body is covered with a transparent skin, through which the motion of the intestines and other remarkable peculiarities are plainly visible. The posterior or tail portion is armed at its extremity, with two shells, and has projecting from it a pair of tubular organs, through which the water enters, for the purpose of respiration; this portion is always in the direction of the surface, and apparently in immediate contact with the water, but does not bore. The anterior portion of the animal is that by which it penetrates the wood, being well armed for the purpose by having, on each side, a pair of strong valves, formed of two pieces, perfectly distinct from one another; the larger piece protects the sides and surface of the extremities, and has a shelly structure projecting from the interior, to which the muscles are attached; the smaller piece is more convex, and covers that part which should be regarded as the anterior surface of boring. This portion of the shell is deeply carniated, and seems to constitute the boring apparatus. The shells form an envelop around the external tegument of the animal, which even surrounds the foot, or part by which it adheres to the wood. The neck is provided with powerful muscles. The manner in which it appears to perforate the wood is by a rotary motion of the foot, carrying round the shells, and thus making those parts act as an auger, which is kept, or retained in connection with the wood, by the strong adherence of the foot. The particles of wood removed by this continued action of the foot, and the valves, are engorged by the animal, for between the junction of the two large shells there is a longitudinal fissure in the foot, which appears to be formed by a fold of this portion of the two sides, thus forming a canal to the oral orifice, and along which the particles of wood bored out, are conveyed to the mouth. The mouth, or entrance to the digestive organs, is of a funnel shape, and consists of a soft, or membraneous surface, capable of being enlarged, and leading into an œsophagus, which passes backwards towards the dorsal surface of the animal. At or near the termination of the œsophagus, there is a glandular organ, the use of which is possibly to secrete a fluid for assisting in the digestion of the wood, and not, as has been supposed, to act as a solvent; for if such were the case, it would most probably be situated at its commencement instead of at its termination. At a short distance behind this organ are two other large glandular bodies, the use of which may also be to secrete fluid for the purpose of digestion. The œsophagus terminates in a large dilatation, into which these organs pour their contents; at its posterior end the canal is dilated into a very large elongated sac, which extends backwards to about one-fourth of the length of the whole animal, and is filled with food, while from its anterior, or upper surface, it has an oval, muscular formation, from which the alimentary canal is continued forwards, and, after making a few turns, passes backwards, in an almost direct line, on the upper surface of the large sac, again passing backwards and forwards, until it finally arrives at its termination, which it passes round, and then proceeds, in a direct line, to the anal outlet. In the lower portion of the œsophagus, and also in the sac, distinct portions of woody fibre of an extremely minute character were found by the aid of the microscope of a power of three hundred, and this was the character of the whole of the contents of the alimentary canal.

The _teredo_ lines the passage in the wood with a hard shell; this shell is formed around, but does not adhere to the body; it is secreted by the external covering, which, in its first formation, is extremely fragile, but becomes hardened by contact with the water, and adheres to the wood, from which it may, however, be easily detached. The interior of this shell is not filled by the body of the _teredo_, but a large space around it is occupied with water, admitted through the small orifice in the surface of the wood through which the animal first entered; the water being drawn through the respiratory tubes, into the bronchial cavity of the body, is expired again through the same orifice, and this, in conjunction with the valve-like shells attached at this part, induces a current round the animal which removes the excreted fœtal matter. The shells are very smooth on the inner surface, but are somewhat rougher on the exterior; they are much harder and firmer in the cells of the older animals than in the young ones, and are composed of several annular parts, differing greatly in their length.

It is no less curious than wonderful to observe the mysterious instinct which apparently regulates the mechanical skill of the _teredo_, its own body supplying it with an implement of such admirable consistency and adaptation as to enable it to excavate a habitation for itself, so accurately formed that to a casual observer it would appear a mystery how so perfect a circle could be produced. It is only on examination that the raised and hollow parts of the wood become visible, and explain, in some degree, the auger-shaped contrivance that has been used for the purpose of perforating.

It has already been stated, that the wood is perforated by a rotary motion of the foot, the adhering part of which acts as a fulcrum, carrying round the shells, and thus giving immense power to the animal in its operations.

It is said that when Brunei was considering how to construct the Thames Tunnel, he was one day “passing through the dockyard (at Chatham, where he was employed by Government), when his attention was attracted to an old piece of ship-timber which had been perforated by that well-known destroyer of timber--the _Teredo navalis_. He examined the perforations, and subsequently the animal. He found it armed with a pair of strong shelly valves, which enveloped its anterior integuments; and that, with its foot as a fulcrum, a rotatory motion was given by powerful muscles to the valves, which, acting on the wood like an auger, penetrated gradually but surely; and that, as the particles were removed, they were passed through a longitudinal fissure in the foot, which formed a canal to the mouth, and so were engorged. To imitate the action of this animal became Brunei’s study. ‘From these ideas,’ said he, ‘by slow and certain methods; which, when compared with the progress of works of art, will be found to be much more expeditious in the end.’”[18]

Professor Owen suggests that the power of the _teredo_ to bore into wood depends on muscular friction, the muscular substance being perpetually renewed while the wood wastes away, of course, without renewal. Professor Forbes, Dr. Carpenter, and Dr. Lyon Playfair were appointed about twenty-five years ago by the British Association to examine into the natural history and habits of these boring animals, but they did not arrive at any definite conclusion as to whether the boring action of the _teredo_ was mechanical or chemical. Dr. Deshayes, on his return from Algiers, after making accurate drawings and careful investigations, came to the conclusion that the borings were effected by an acid secretion. Mr. Thomson, of Belfast, examined the operations of the _teredo_ on the pier at Port Patrick, and arrived at the same conclusion. The general opinion, however, is that the boring action is a mechanical one.

Although the _teredo_ appears to penetrate all kinds of timber, that which it seems to destroy with the greatest ease is fir, in which it works much more speedily and successfully than in any other, and perhaps grows to the greatest size. In a fir pile, taken from the old pier-head at Southend, a worm was found 2 feet long and ¾ inch in diameter, and indeed they have been heard of 3 feet in length and 1 inch in diameter. The soft, porous nature of the wood is no doubt the cause of their rapid growth, for in oak timber they do not progress so fast, or grow to so great a length, though in Sir Hans Sloane’s ‘History of Jamaica’ (1725) there are accounts of these animals destroying keels of ships made of oak, and even of cedar, although the latter is renowned, by its smell and resin, for resisting all kinds of worms.

There is another kind of worm which is very destructive to timber, which Smeaton observed in Bridlington piers. This is the TIMBER-BORING SHRIMP, or GRIBBLE, the _Limnoria terebrans_ (or _Limnoria perforata_, Leach), a mollusc of the family _Asselotes_, Leach. The _Limnoria terebrans_ is very abundant around the British shores. Its ravages were first particularly observed in the year 1810, by the late Sir. Robert Stevenson, engineer of the Bell Rock Lighthouse. While engaged in the erection of that structure he found the timber of the temporary erections to be soon destroyed by the attacks of the _limnoria_. So little was known of the _limnoria_ at the time that Dr. Leach, a well-known naturalist, who received some specimens from Mr. Stevenson, in 1811, declared it to be a new and highly interesting species. In 1834, the late Dr. John Coldstream wrote a very full and interesting description of the creature. The _limnoria_ resembles a woodlouse, and is so small as hardly to be perceptible in the timber it attacks, being almost of the same colour. Small as is this crustacean, hardly larger indeed than a grain of rice, it is a sad pest wherever submarine timber is employed, for it works with great energy, and its vast numbers quite compensate for the small size of each individual; for as many as twenty thousand will appear on the surface of a piece of a pile only 12 inches square. It proceeds in a very methodical manner, and makes its way obliquely inward, unless it happens to meet a knot, when it passes round the obstacle and resumes its former direction. The surface of the timber being first attacked, it proceeds progressively into the wood to the depth of about 1½ inch: the tunnels being cylindrical, perfectly smooth winding holes, about ⅟16th inch in diameter: it is necessary that the holes should be filled with salt water. The outward crust formed by these attacks then becomes macerated and rotten, and is gradually washed away by the beating of the sea. The _limnoria_ does not work by means of any tool or instrument like the _teredo_, but is supposed to possess some species of dissolvent liquor, furnished by the juices of the animal itself. Dr. Coldstream was of opinion that the animal effects its work by the use of its mandibles. From ligneous matter having been found in its viscera, some have concluded that it feeds on the wood, but since other molluscs of the same genus, _Pholas_, bore and destroy stonework, the perforation may serve only for the animal’s dwelling. The _limnoria_ seems to prefer tender woods but the hardest do not escape: teak and greenheart are about the only woods it does not attack. The rate at which the _limnoria_ bores into wood in pure salt water is said to be about one inch in a year; but instances have occurred in which the destruction has been much more rapid. At Lowestoft Harbour, square 14 inch piles were in three years eaten down to 4 inches square. At Greenock, a pile 12 inches square was eaten through in seven years. It is stated that a 3-inch oak plank, 12 feet long, would be entirely destroyed in about eight years. Joists of timber have been found at Southend Pier, 2 feet and 3 feet below high-water mark, where they had made rapid destruction. The _limnoria_ almost always works just under neap tides; it cannot live in fresh water, and whilst it is destroying the surface of a pile, the _teredo_ is attacking the interior: sometimes the former is found attacking the same timber as the Chelura. As with most of these creatures, the male _limnoria_ is smaller than the female, being about one-third her size. The female may be distinguished by the pouch in which the eggs and afterwards the young are carried. About six or seven young are generally found in the pouch.

The WOOD-BORING SHRIMP (_Chelura terebrans_) is a crustacean that nearly rivals the _teredo_ itself in its destructive powers. It makes burrows into the wood, wherein it can conceal itself, and at the same time feast upon the fragments, as is proved by the presence of woody dust within its interior. Its tunnels are made in an oblique direction, not very deeply sunk below the surface, so that after a while the action of the waves washes away the thin shell, and leaves a number of grooves on the surface. Below these, again, the creature bores a fresh set of tunnels, which in their turn are washed away, so that the timber is soon destroyed in successive grooved flakes.

According to Mr. Allman, its habits can be very easily watched, as if it is merely placed in a tumbler of sea water, together with a piece of wood, it will forthwith proceed to work, and gnaw its way into the wood. The apparatus with which it works this destruction is a kind of file or rasp, which reduces the wood into minute fragments. In this creature the jaw feet are furnished with imperfect claws, and the tenth segment from the head is curiously prolonged into a large and long spine. The great flattened appendages near the tail seem to be merely used for the purpose of cleaning its burrow of wood dust which is not required for food. The creature always swims on its back, and when commencing its work of destruction, clings to the wood with the legs that proceed from the thorax. The wood-boring shrimp is one of the jumpers, and, like the sand hopper, can leap to a considerable height when placed on dry land. It has been detected in timber taken from the sea at Trieste. It was first observed as an inhabitant of the British seas several years ago, by Mr. Robert Ball, of Dublin, and in January, 1847, it was described by Mr. Mullins, C.E., in a paper read before the Institution of Civil Engineers of Ireland, as being very injurious to the timber piles in Kingstown Harbour, near Dublin, and far more destructive than the _Limnoria terebrans_.

We have already referred to the _lesson_ the celebrated engineer, Brunel, received from observing the _teredo_; and we can state that architects have also received _lessons_ from nature. Sir Christopher Wren constructed his spire of St. Bride’s Church, London, after observing the construction of the delicate shell, called _Turretella_, which has a central column, or newel, round which the spiral turns. Brunelleschi designed the dome of Sta. Maria, at Florence, after studying the bones of birds and the human form; and Michael Angelo followed Brunelleschi in constructing the dome of St. Peter’s, Rome.[19]

The LEPISMA is also a destructive little animal, which begins to prey on wood in the East Indies, as soon as it is immersed in sea water. The unprotected bottom of a boat has been known to be eaten through by it in three or four weeks.

These worms, it must be remembered, do not live except where they have the action of the water almost every tide, nor do they live in the parts covered with sand. The wooden piles of embankments and sea locks suffer very much from their depredations, and in the sea dykes of Holland they cause very expensive annual repairs.

The Dutch used to coat their piles with a mixture of pitch and tar, and then strew small pieces of cockle and other shells, beaten almost to powder, and mixed with sea sand, which incrusted and armed the piles against the attacks of the _teredo_. We believe it was a frequent practice in London, about half a century ago, to place small shells in the wooden pugging between the floor joists to deaden sound.

Having described the chief peculiarities of these worms, shown their mode of working, and the extent to which their destructive powers may be carried, it will now be necessary to consider the various schemes which have been proposed and tried to prevent their desolating ravages. These may be divided into _three_ classes, viz. the natural, chemical, and mechanical.

1st. By using woods which are able to resist the attacks of sea worms.

2nd. By subjecting piles to a chemical process.

3rd. By adopting a mechanical process.

First. We have not any English woods which resist their attacks. Elm (used for piles in England) or beech (used for piles, if entirely under water, in France) cannot withstand the _teredo_; while oak cannot battle successfully against wood-beetles in carvings. It is therefore necessary to inquire whether foreign woods are any better.[20] Unfortunately the great expense of importing them into England prevents their use for piles.

Nearly all our foreign woods used for engineering and building purposes come from the Baltic or Canada: they are fir and pine. Memel timber from the Baltic is comparatively useless unless thoroughly creosoted; and Canadian timber is not so good as the Baltic wood. At Liverpool and some of the western ports of England Canadian timber is preferred to Baltic, although we believe the reason to be that they cannot get the latter, except in small quantities at a time.

The following is a list of timber woods which, according to good authorities, resist for a long period of time the attacks of sea worms. It should be borne in mind, however, that the timber should be cut, during the proper season, from a large and full-grown tree; and, to prevent splitting, it should be kept from the direct action of the sun when first cut; it should have all the bark and sapwood removed, and allowed to dry a certain time before being used.

WOODS WHICH RESIST SEA WORMS.

_Australia, Western._--Jarrah, beef-wood, tuart.

_Bahama._--Stopper-wood.

_Brazil._--Sicupira, greenheart.

_British Guiana._--Cabacalli, greenheart, kakarilly, silverballi (yellow).

_Ceylon._--Halmalille, palmyra, theet-kha, neem.

_Demerara._--Bullet, greenheart (purple heart-wood), sabicu.

_India._--Malabar teak, sissoo, morung sál, dabu, than-kya, ilupé, anan, angeli, may-tobek. (Teak resists the _teredo_, but is not proof against barnacles.)

_Jamaica._--Greenheart.

_North America._--Locust.

_Sierra Leone._--African oak, or tortosa.

_South America._--Santa Maria wood.

_Philippine Islands._--Malacintud, barnabá, palma-brava.

_Tasmania._--Blue gum.

_West Indies._--Lignum vitæ.

Second. The chemical, viz. Kyan’s process of corrosive sublimate; Payne’s process of sulphate of iron and muriate of lime; pitching and tarring; Burnett’s process of chloride of zinc; and arsenic, or other mercurial preparations, have all failed, with the exception of Bethell’s process of oil of tar. The failure must proceed from one of two causes; either that the sea-water decomposes the poisonous ingredients contained in the wood, or that these poisonous compounds have no injurious effect on the worms; it appears, however, that both these causes have been in operation, principally the latter.

Without a series of the most minute experiments, it is impossible to form any general notion of the action of sea-water on timber. Common salt, chlorides of calcium and magnesium, sulphate of soda, iodides and bromides of the same metals, are known to exist in sea-water, and in great abundance in the torrid zone. What effect these different ingredients may have upon saturated timber it is difficult to say, but it is extremely probable that they do have an effect.

With regard to the different poisonous compounds having no injurious effect on the worms, it should be remembered that all cold-blooded animals are much more tenacious of life than those of a higher temperament, and in descending the scale of animal creation, the tenacity of life increases, and this principle is more developed. A frog, which though cold-blooded, is an animal of a much higher order than the _teredo_, will not only live in hydrogen gas, but also in a strong solution of hydrocyanic acid, while at the same time a single drop placed on the nose of a rat, or in the eye of a rabbit, would produce instant death. A somewhat similar occurrence is noticed in the ‘British and Foreign Medical Review,’ for July, 1841, showing the slow effects of prussic acid on the common snake and turtle.

It may therefore be inferred, that as it requires a large quantity of the most virulently poisoned matter to destroy animals of a much higher order than the _teredo_, it would take a still greater quantity to affect those animals as they exist in their own element.

The preserving property of soluble salts, such as corrosive sublimate, sulphate of copper, &c., was considered to be founded upon their power of coagulating the albumen, and the sap of wood, thereby rendering that sap less liable to decay; but that very quality of combining with the albumen, destroyed the activity of the poison of the salts. A given quantity of corrosive sublimate of mercury, which if administered to a dog would kill it, would, when mixed with the white of an egg, become coagulated, and if swallowed in that state would be perfectly harmless; so a piece of wood, saturated by those salts, could be eaten by a worm without injury.

A French naturalist, M. de Quatrefages,[21] in 1848, suggested that a weak solution of mercury (corrosive sublimate) thrown into the water will destroy the milt of the _teredo_, and consequently prevent fecundation of the eggs, thus exhausting the molluscs in the bud. He proposed that ships should be cleared of this terrible pest by being taken into a closed dock, into which a few handfuls of corrosive sublimate should be thrown and well mixed with the water. He considered that about 1 lb. of sublimate would be sufficient for 20,000 cubic metres (metre = 39·37 English inches) of water; but on account of the cost it would be advisable to use salts of lead or copper. This proposition of de Quatrefages reminds us of Chapman’s suggestion, in 1812, to get rid of dry rot in ships, viz. by sweeping out the hold, laying from two to four tons of copperas in her bottom, and as much fresh water let in upon it as would make a saturated solution to soak into the wood.

M. de Quatrefages placed the four salts he used in his experiments in the following order, according to merit: 1st, corrosive sublimate; 2nd, acetate of lead; 3rd, sulphate of copper; and 4th, nitrate of copper.

In America, white oxide of zinc is used as a marine paint for ships and piles. In the United States Navy Yard at Gosport it is spoken well of, and very frequently employed. It is said to be much superior to white-lead, red-lead, verdigris, or coal-tar, and that timber covered with two coats of white zinc is neither attacked by the worm, nor do barnacles attach to it when immersed in salt water.

We can only find one instance of timber impregnated with water-glass having been tested against this subtle foe. Water-glass is certainly worth a further trial.

The instance we refer to occurred about forty years ago. In 1832, Dr. Lewis Feuchtwanger, of New York, was permitted by the Ordnance Department, under the direction of Commodore Perry, to perform experiments with water-glass on piles in the Brooklyn Navy Yard, and in various docks. The piles in the docks were destroyed by the _teredo_ so fast that they _had to be replaced every three years_. The experiments proved highly satisfactory: the piles which had been so treated lasting many years, without any indication of being attacked by sea-worms.

The reader is referred to some works on water-glass mentioned below,[22] which are worthy of attentive perusal.

Third. The mechanical processes. They are few in number, and rather expensive.

At Saint Sebastian, in Spain, the piles of the wooden bridge standing in the sea have been guarded against the attacks of sea-worms in the following manner: Each pile is surrounded by a wooden box, and the space between filled up with cement. After six years it was proved that the piles were in a perfect condition, whilst the outer boxes were completely riddled by the worms. A similar method to this was adopted, some years since, to many of the piles in the Herne Bay Pier, which were affected by sea-worms. Several attempts had been made to protect the timber, by saturating it under various processes, with, however, only doubtful success. At last, a wooden casing was formed round each pile, leaving a space of about an inch all round, which was rammed full of lime or cement concrete. That process appeared to be perfectly successful, as the pier-master, who first adopted the method, stated that some of the piles had been so treated for three or four years, and although the worms had commenced their ravages, they appeared to have been checked, and not to have been able to exist when so enclosed.

In 1835, Brunel suggested an easy way of defending piles, which was to give them in the first instance a coat of tar; then powder them with brick-dust, which would render the wood sufficiently hard to receive a coat or two of cement. This is similar to the Dutch method.

Some foreigners use sheet lead nailed on to piles, and wrapped close round with well-tarred rope.

Copper sheathing has often been used for the protection of piling in piers and harbours. The destruction of copper by the action of sea-water is a matter which has long occupied the attention of scientific men, and it appears to be well ascertained that the decay does not result from the bad quality of the copper, for, according to Mr. Wilkinson, no difference could be discovered between the composition of copper that had endured well, and that which had been rapidly destroyed. Copper sheathing was used at Southend, but without success, for although nearly all the piles were covered with it for about 9 feet or 10 feet, the _limnoria_ not only penetrated between the copper and the timber, but the copper had decayed to such an extent as in some cases to be no thicker than the thinnest paper; it was soft, and peeled off the wood very easily, and in two or three years would probably have been entirely destroyed.

Covering the surface of the timber with broad-headed scupper nails, arranged in regular rows with their heads at no great distance from each other, is a method which has been satisfactorily employed in various parts of the world, in Swedish and Danish vessels, even up to the present time, and, indeed, it was also practised by the Romans. The scupper-nailed piles at Southend, after twelve years’ exposure to the sea, were perfectly sound, and although the nails were not driven close together in the first instance, yet the corrosive action was so great as to form a solid impenetrable metallic substance, upon which the worms refused to settle. Scupper nails have been proved at Yarmouth, as well as at other places, to have protected timber for forty years, but the process is expensive, as it costs one shilling per square foot. They should be about half an inch square at the head.

Captain Sir Samuel Brown, R.N., states that from numerous experiments and observations, he is satisfied that at present there is really no specific remedy against the attacks of sea-worms upon timber, except iron nails. He proposes to encase the piles with broad-headed iron nails resembling scupper nails, but considerably larger, and he says that in the course of a few months corrosion takes place, and spreads into the interstices. The rust hardens upon the pile, and becomes a solid mass which the worm will not touch. Experiments tried at the Trinity Pier, Newhaven, and Brighton Pier, have established the effectiveness of his method.

At the Cape of Good Hope, and many other places, wood piles are cased in iron, and occasionally iron piles are used instead of wood, at great cost. Further experience is desirable as to the durability of cast iron[23] in salt water, especially as to its peculiar property of conversion, after a few years’ immersion in the sea, into a carburet of iron, closely resembling plumbago, so that it may be easily cut with a knife. This, of course, diminishes its powers of resistance acting upon the framing it is intended to strengthen. In the course of the construction of the Britannia Bridge, about one hundred thin plates were delivered, which were not used on account of some error in their dimensions. They were left on the platform alongside the straits, exposed to the wash and spray of the sea; and after about two years were literally so completely decomposed as to be swept away with a broom into the water, not a particle of iron remaining.

We have already stated that the chemical processes have failed with the exception of Bethell’s process of oil of tar, generally known as the creosoting process. This method, _when properly carried out_, thoroughly protects wood from the ravages of the _teredo_ and other marine worms. The breakwaters and piers at Leith, Holyhead, Portland, Lowestoft, Great Grimsby, Plymouth, Wisbeach, Southampton, &c., have been built with creosoted timber, and in no case have the _Teredo navalis_, _Limnoria terebrans_, or any other marine worms or insects been found to attack these works, as certified to by the engineers in whose charge the several works are placed. In the cases of Lowestoft and Southampton we are enabled to give the detailed reports.

A most searching examination, lasting many days, was made in 1849, upon every pile in Lowestoft Harbour, by direction of Mr. Bidder; and the report of Mr. Makinson, the Superintendent of Lowestoft Harbour Works, contains the subjoined statement:

“The following is the result, after a close and minute investigation of all the piles in the North and South Piers.

“_North Pier._--The whole of the creosoted piles in the North Pier, both seaward and inside the harbour, nine hundred in number, are sound, and quite free from _teredo_ and _limnoria_.

“_South Pier._--The whole of the creosoted piles in the South Pier, both seaward and inside the harbour, seven hundred in number, are sound, and quite free from _teredo_ and _limnoria_.

“There is no instance whatever of an uncreosoted pile being sound. They are all attacked, both by the _limnoria_ and the _teredo_, to a very great extent, and the piles in some instances are eaten through. All the creosoted piles are quite sound, being neither touched by the _teredo_ or the _limnoria_, though covered with vegetation, which generally attracts the _teredo_.”

There was only one instance of a piece of creosoted wood, in Lowestoft Harbour, being touched by a worm, and that was occasioned by the workmen having cut away a great part of one of the cross heads, leaving exposed the interior or heart of the wood, to which the creosote had not penetrated. At this spot a worm entered, and bored to the right, where it found creosote; on turning back and boring to the left, but finding creosote all around, its progress was stopped, and it then appeared to have left the piece of wood altogether.

In 1849, Mr. Doswell, who had the conduct of experiments on different descriptions of wood at Southampton, where the river was so full of the worm that piles of 14 inches square had been eaten down to 4 inches in four years, reported as follows: “From my examination, last spring tides, of the specimen blocks attached, on the 22nd February, 1848, to some worm-eaten piles of the Royal Pier, I am enabled to report that Bethell’s creosoted timbers all continue to be unaffected by the worms; that the pieces saturated with Payne’s solution continue to lose in substance by their ravages; and that the unprepared timbers diminish very fast, except the American elm, which stands as well (or nearly so) as that prepared by ‘Payne’s solution.’”

The following are the detailed particulars:

BETHELL’S CREOSOTED BLOCKS, PLACED FEBRUARY 22, 1848.

Memel, at low water of spring tides } Unaffected by worms. Red pine, at low water of neap tides } Yellow fir, at high water of neap tides A few barnacles.

PAYNIZED BLOCKS, PLACED APRIL 6, 1848.

Red pine, at low water of spring tides Worm-eaten. American elm, at low water of neap tides } A few barnacles. Fir, at high water of neap tides }

UNPREPARED BLOCKS, PLACED APRIL 6, 1848.

Memel, at low water of spring tides Much worm-eaten. American elm, at low water of neap tides A few barnacles. Fir, at high water of neap tides Much worm-eaten.

On 1st January, 1852, Mr. Doswell ascertained that, notwithstanding the number of _teredines_ and _limnoria_ to be found in the Southampton Waters, none of the creosoted blocks had been attacked by them.

According to M. Forestier, similar results have been obtained at Brighton, Sunderland, and Teignmouth.

Allusion has already been made to Mr. Pritchard, of Shoreham, with reference to preserving timber. On July 26, 1842, he presented a report to the Treasurer of the Brighton Suspension Chain Pier Company, upon the preservation of timber from the action of sea-worms. We give a portion of it, as follows:

“Stockholm tar has been used, and proved to be of little service; this tar is objectionable owing to its high price, and also from its being manufactured from vegetable substances. All tars containing vegetable productions must be detrimental to the preservation of timber, especially when used in, and exposed to, salt water. This tar does not penetrate into the wood, and in a very few months the salt acid of the sea will eat it all away.

“Common gas or coal tar has been used to a great extent, and its effects are apparent to all. It does a very great deal of harm, forms a hard or brittle crust or coat on the wood, and completely excludes the damp and unnatural heat from the possibility of escape, owing to its containing ammonia, which burns the timber, and in a few years it turns brown and crumbles into dust. Indeed, timber prepared with this tar will be completely destroyed on this coast and pier by the ravages of the _Teredo navalis_, and the _Limnoria terebrans_, in five or six years.

“Also Kyan’s patent, or the bi-chloride of mercury, has been used, but has proved equally useless. The sleepers Kyanized five years ago, and in use at the West India Dock warehouses, have been discovered to decay rapidly, and the wooden tanks at the Anti-Dry-Rot Company’s principal yard are destroyed.

“I would recommend you for the future to use ‘oil of tar and pyrolignite of iron’ (Bethell’s patent). This process will, without a doubt, succeed. I have proved in hydraulic works on this coast that it will fully prevent the decay in timber piles, destroy sea-worms, and supersede the necessity of coating the piles with iron nails. In Shoreham Harbour, for instance, there is a piece of red pine accidentally infused with pyrolignite of iron, which after being in use twelve years is perfectly sound. There is another waleing piece, the very heart of English oak, Kyanized, and in use only four years, which is like a honeycomb or network, completely eaten away by the _teredo_ and other sea-worms. I have fully proved the efficiency of this method at different harbours and docks. Sixteen years ago I had timber prepared with it, and in use on the shores of the Dee, and it is at the present moment perfectly sound. The pyrolignite of iron must be used of very pure quality; the timber must be dry; afterwards the oil of tar must be applied, and not on any account must it contain a particle of ammonia. The immense destruction on the coast of timber by the sea-worms, and the important fact that at the Chain Pier there are not twenty of the original piles remaining at the present time, is of itself sufficient to awaken anxiety.”

With regard to the opinion of foreigners on the subject of creosoting, we cannot do better than quote the report of the commission or committee (instituted in 1859) of the Royal Academy of Sciences, Holland, upon the means of preserving wood from the _teredo_, published at Haarlem in 1866. It is as follows:

“To conclude, it results from experiments which the committee has directed during six consecutive years, that--

“1st. Coatings of any sort whatever applied to the surface of the timber in order to cover it with an envelop upon which the young _teredo_ will not fasten offer a very insufficient protection; such an envelop soon becomes damaged, either by mechanical action, such as the friction of water or ice, or by the dissolving action of water; and as soon as any point upon the surface of the wood is uncovered, however small it be, the _teredoes_ of microscopic size penetrate into the interior of the wood.

“Covering wood with plates of copper, or zinc, or flatheaded nails are expensive processes, and only defend the wood as long as they present a perfect and unbroken surface.

“2nd. Impregnation with soluble metallic salts generally considered poisonous to animals does not preserve the wood from the invasions of the _teredo_; the failure of these salts is partly attributable to their being soaked out of the wood by the dissolving action of the sea-water, partly also to the fact that some of these salts do not appear to be poisonous to the _teredo_.

“3rd. Although we cannot venture to say that there may not be found in the colonies a wood that may resist the _teredo_, yet we may affirm that hardness of any timber is not an obstacle to the perforations of this mollusc. This has been proved by the ravages it has made on the Gaïac and Mamberklak woods.

“4th. The only means which can be confidently regarded as a preservative against the ravages of the _teredo_ is the creosote oil; nevertheless, in the employment of this agent great care should be taken regarding the quality of the oil, the degree of penetration, and the quality of the wood treated.”

These results of the experiments of the committee are confirmed by the experience of a large number of engineers of ponts et chaussées (bridges and causeways) in Holland, England, France, and Belgium. For example, very lately a Belgian engineer, M. Crepin, expressed himself as follows in his Report, dated 5th February, 1864, upon experiments made at Ostend:

“The experiment now appears to us decisive, and we think we may conclude that fir timber well prepared with creosote oil of good quality is proof against the _teredo_, and certain to last for a long time. Everything depends, therefore, upon a good preparation with good creosote oil, and on the use of wood capable of injection. It appears that resinous wood is easiest to impregnate, and that white fir should be rejected.”

M. Forestier, the able French engineer at Napoléon-Vendée sums up as follows the results of the experiments undertaken by him in the port of Sables-d’Olonne, viz.:

“These results fully confirm those obtained at Ostend, and it appears to us difficult not to admit that the experiments of Ostend and Sables d’Olonne are decisive, and prove in an incontestable manner that the _teredo_ cannot attack wood properly creosoted.”

It thus appears that there are three preservative methods, which, according to experience, will save timber piles from the ravages of the worms, viz.: 1st. By using woods able to resist unaided their attacks. 2nd. The mechanical method, which is, by covering the piles with scupper nails, &c. This process is, however, very expensive, especially as the four sides of the pile must be covered; and, moreover, it affords no protection to the timber from internal rot or decay. 3rd. The chemical, or “creosoting” method. This process is cheaper than the last; it preserves the wood from decay, and no worms will touch it.

When unprepared piles are placed in the sea, there is every probability, sooner or later, of their being attacked by the _teredo_. This animal, however, is not left in peaceable enjoyment of the dwelling which it has constructed, and the food which it loves, but is liable to be attacked by an enemy, an _annelide_, to which the late M. de Haan has given the name of _Lycoris fucata_. This animal is to be found wherever the _teredo_ exists, indeed its eggs and larva are to be met with in the midst of those of the mollusc. M. Kater has remarked that the adult _lycoris_ dwelling in the mud which it enters during winter, and into which the piles are driven, climbs up the pile to the hole formed by the _teredo_, where, in some manner, it sucks or eats its victim; then having enlarged the entrance to the hole, it enters and rests in the place of the _teredo_. After a time it goes back to the entrance, and commences to seek for fresh prey.

The _lycoris_ is narrow and not very long, provided laterally with a great many little feet terminating in points and covered with hair, and having in front a pair of hard superior jaws, pointed horns, and the inferior jaws bent round in the form of hooks. Behind the head are four pairs of tubuliform gills. It is with these arms that this little animal pursues and devours the _teredo_.

One day M. Kater was fortunately able to observe the operations of the _lycoris_, One of these animals coming out of a hole in the wood which he inhabited, seized upon a _teredo_, which M. Kater had previously deposited at the bottom of the vessel containing the wood. He saw the _annelide_ seize the _teredo_, hurry away with it to the hole which he occupied, and so completely devour it that he finally left only the two valves of the shell. Our illustrations of the _teredo_ and _lycoris_ are derived from the works of Mr. Paton and M. Forestier; and our own sketches.

If the _lycoris_ would only destroy the _teredo_, when the mollusc was in its infancy, what an invaluable little annelide it would be!

It appears to us a great pity that the woods we have named, or some of them, are not brought over to England in large quantities for harbour works. In Ceylon and India, the trees are felled by Indian wood-cutters at little cost; they are then dragged to the river banks by elephants or buffaloes, to be floated down the rivers to the different ports, so that labour is cheap. The question then remains, how to get the woods to England? When the ‘Great Eastern ship has finished carrying cables, perhaps its owners will not object to send the ship on a few voyages with heavy cargoes to India, Demerara, &c., bringing home “teredo-proof woods,” _at moderate charges for freight_?

Finally, to place the subject in a practical form, we think the Institute of Civil Engineers, of London, would be heartily thanked by the engineering world if they would appoint a committee to inquire into the damages done to works by sea-worms; why they are found in some parts of a roadstead or harbour, and not in others; to consider the different remedies which have been proposed, their cost, and method of application; what course should be adopted to prevent sea-water injuriously affecting iron piles; and lastly, to publish a detailed account of their experiments and recommendations.