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that no exterior application of any nature whatever, or modification of the surface merely, would give any efficacious guarantee of protection against the teredo. Even supposing that one or another of these means would prevent the young teredos from attaching themselves to the wood, yet the constant friction of the water or ice, or any accident, might break the surface of the wood sufficiently to give access to the teredo.

This seems a proper place to mention a practice in general use in Holland for warding off the teredo: this consists in covering wood with a coat-of-mail made of nails. This operation is very costly; for, to really protect wood in this way, it is important that the square heads of the nails join exactly; for insuring the best results, the armored piles are exposed in the open air for some time before being placed in the water, that rust, forming on the surface of the iron, may close up the interstices inevitably remaining between the heads of the nails. But this precaution is not infallible, as the commission examined piles more than once, in the course of its investigation, which had been several years in the water, and whose surface was entirely incrusted with rust more than a centimetre thick, but which were, nevertheless, eaten in the interior by the teredo.

Sluice-gates are frequently covered by sheets of iron, copper, or zinc. It is evident that, so long as such covering remains intact, there is no cause for anxiety on the score of the teredo. Unfortunately, experience has taught us that this protection is not permanent, but is rendered ineffectual by being broken by the force of the water or blocks of ice.

Nature affords sometimes, as we have seen above, a more efficacious protection in covering wood with barnacles or other shell-fish, with the condition that this covering be made before the young teredo attaches itself to the wood. Facts of this sort have led Lehmann to propose the planting on wood of the common mussel (Mytilus edulis).

IMPREGNATION OF WOOD WITH DIFFERENT SUBSTANCES. commission examined in this category the following methods:

- The

1. Sulphate of Copper.-The impregnation of the blocks with this salt was performed at the factory of MM. Van der Elst and Smit, at Amsterdam. Experience proved, even in the first summer (of 1859), that this preparation had absolutely no power against the teredo. Nevertheless, to make sure that the failure of this experiment was not due to insufficient preparation, the commission procured from the establishment of M. Boucherie, at Paris, two pieces of beech-wood covered with its bark, two pieces of beech without bark, and two pieces of pine, all prepared with sulphate of copper. These blocks, when exposed, did not resist the teredo any better than those prepared at Amsterdam. These trials completely confirmed the results obtained by the engineer Noyon ("On the Inefficacy of the Boucherie Process in Sea-Water," Annals of Bridges and Roads, April, 1859).

2. Sulphate of Protoxide of Iron (Green Vitriol).—The blocks were

impregnated with this salt at the establishment of MM. Van der Elst and Smit. The first summer proved that this method would not in the least prevent the wood from being destroyed by the teredo. And the same was true of the following method:

3. Acetate of Lead.-The blocks impregnated with this salt were prepared at the same establishment.

Surprise may be expressed that the commission did not try experiments with corrosive sublimate. It felt that it could dispense with them, as its inefficacy had already been sufficiently established by previous experiments on a large scale at the marine dock-yards at Rotterdam. Experiments with mercurial and arsenical salts were tried, in 1730 and later, but without satisfactory results.

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FIG. 15.-This cut was made from a piece of pine-slab, partially creosoted and exposed one season (1877) in the Gulf of Mexico. Only the dark-colored portion on the right side of the block was creosoted for this experiment. The rest of the block, untreated, was entirely riddled by the Teredo navalis, up to the edge of the creosoted portion, but that the destructive marine worm carefully avoided.

wood a silicate of lime. The pieces thus prepared were left in the open air during six months before being placed in the water, in order that the chemical combination might be as complete as possible. These pieces were exposed in the water at Nieuwe-Diep, in March, 1862, and

when withdrawn, in October of the same year, the preparation was found to be powerless as a protection against the teredo.

5. Oil of Paraffine. The firm of Haages & Co., at Amsterdam, delivered to the commission some pieces of oak and red fir injected with a substance produced by the dry distillation of peat, to which they gave the name of oil of paraffine. In the month of July, 1860, the commission placed at Stavoren and Nieuwe-Diep ten pieces thus prepared. They were examined in the course of the same year, after they had passed one summer in the water, and it was found that they had resisted the attacks of the teredo.

The commission conducted all its experiments thus: They placed in the water ten pieces of each variety of wood, treated according to the prescribed method, so that they could withdraw each year, during ten consecutive years, one of the pieces to be submitted to examination. In making the examination, they removed with an adze the outside of the wood to a depth of some millimetres, which was sufficient to show the galleries of the teredos, if there were any. The pieces found intact were replaced in the water, and the following year their condition was tested in the same way, by removing the shavings as before. By this plan the commission felt certain that, if the blocks were not injured by the teredo during several successive years, they did not owe that protection to a superficial covering, but that the wood itself resisted the destructive efforts of the teredo, and that there would be no reason for fearing that piles, prepared in a similar manner, would, at any time, lose their power of resistance, when injured on their surface by water or ice, or by slow dissolution of the active principle of the preservative substance.

When the pieces of wood treated with oil of paraffine were taken from the water in 1862, after a sojourn of more than two years, or rather during three summers, traces of the teredo were found in the pieces of oak, but not on those of red fir; but when examined in November, 1863, fully-developed teredos were found everywhere, in the fir as well as in the oak, in the pieces whose surfaces had been removed by the adze, but not more than in those which had not been submitted to any examination.

6. Oil of Creosote. This is, as is very well known, a product of the dry distillation of coal-tar, separated by distillation from the more volatile parts, which serve for the preparation of benzole and naphtha, the residuum being pitch. Experiments had already been tried abroad, as well as in Holland, with this substance, and from the beginning of their experiments the commission paid especial attention to this very important method of preparation.

Wood of various kinds, prepared with creosote-oil at the works of the Society for the Preparation and Preservation of Wood, at Amsterdam, was placed in the sea in the month of May, 1859, at Flessingue, Harlingen, and Stavoren. In the month of September following, at

Flessingue, the pieces of oak, pine, and red fir, were found intact, while those unprepared were perforated. In the month of October, of the same year, the pieces of creosoted pine and fir at Harlingen showed a perfect state of preservation. At Harlingen the treated and untreated pieces were fastened together; the teredo penetrated the latter, but had not touched the creosoted wood. The same was true of the creosoted wood exposed at Stavoren, when visited in 1859.

At Nieuwendam, in March, 1859, three pieces each of oak, pine, and red fir, all creosoted at Amsterdam, were exposed in the sea. They were examined in September of the same year. They had been fastened together by cross-pieces of unprepared wood: it was found that the teredo had penetrated, at the juncture of these cross-pieces, even into the creosoted wood, and that sometimes he stopped immediately beneath the surface, at others he penetrated to a depth of several millimetres; in the oak, he worked his way into the interior through those parts of the surface which were not in contact with the unprepared wood.

Experiments with creosote-oil were recommenced in July, 1860, with ten pieces each of oak and red fir, following the plan indicated in paragraph 5; the localities chosen were Nieuwe-Diep and Stavoren; in the latter place the pieces which remained intact the previous year were again placed in the water after their surface had been removed by the adze. Still later, in August, 1861, a further trial was made at these same places with pieces of pine, beech, and poplar, sent to the commission by Mr. Boulton, and prepared at his works in London.

All these pieces were examined toward autumn in 1862, 1863, and 1864; while the unprepared pieces, placed near the others as counterproofs, were found each year filled with teredos, one could not discover any traces of the teredo in the creosoted pieces except in the oak creosoted at Amsterdam; in cutting these, it was found that the creosote had penetrated them very imperfectly.

A third examination, in 1864, showed that all the pieces prepared by Mr. Boulton, and which had been exposed in the sea since August, 1861, were entirely intact; the most careful examination could not show the slightest trace of the worm, even in the pieces withdrawn from the water in 1862 and 1863, and each time scraped to a depth of several millimetres and again placed in the water. They resisted the attacks of the teredo perfectly.

An equally favorable and decisive result was obtained from the pieces of fir creosoted at Amsterdam. Notwithstanding they had been exposed in the sea since July, 1860, during five consecutive summers, nothing could be discovered which resembled the galleries of the teredo: one of the pieces, at a point where the color of the wood indicated an insufficient penetration of the creosote-oil, showed a very slight worm-eaten appearance; but the absence of the calcareous deposit, and

the whole character of the opening, indicated clearly that it should be attributed to some other animal than a teredo.

As to the unprepared pieces, there only remained small ends, which reached above the water. All the rest was converted into a spongy mass, which broke at the slightest effort.

The experiment with the creosoted oak was less satisfactory. In all the pieces were found, here and there, galleries of the teredo, but always in small numbers; in sawing the wood, it was found that the injuries were invariably in those parts where the color showed that the oil had not been able to penetrate. Although, as far as is known, no effort has been made elsewhere to preserve oak from the teredo, the commission places great value upon experiments with this wood. In fact, for many marine works, oak cannot be replaced by any soft wood which absorbs creosote-oil easily. Hence, the commission has had creosoted at Amsterdam, by a newly-perfected process, some pieces of oak, which were exposed in 1864 at Nieuwe-Diep; these will not be examined until tested during three summers.'

Petroleum has also been recommended to the commission, but it was not deemed worth while to experiment with it, especially on account of its high price; even although petroleum should prove to be as efficacious as creosote-oil for protecting wood against the teredo, its price would prevent its use for that purpose.

EXPERIMENTS WITH EXOTIC WOODS, OTHER THAN ORDINARY WOODS OF CONSTRUCTION.-The commission has not been able to make many experiments in this direction. It acquired a certainty that the greenhart of Surinam, the bulletrie, the American oaks, and wood as hard as mamberklak, are not spared by the teredo. The commission received a large piece of the wood of guaiacum, which had been five or six years in the water at Curaçoa, and was found to be entirely eaten by the teredo-an evident proof that even the hardest woods are not safe from the attacks of that mollusk.

The commission has received, it is true, many communications relative to different kinds of woods known to be poisonous to fish, but it has not had an opportunity to experiment with them. We await some light on this point, from researches which the Government has ordered to be made at our possessions in both the East and West Indies.

CONCLUSIONS.-By way of recapitulation, the results of the experiments, tried by the commission during six consecutive years, were as follows:

1. The different coatings applied to the surface of wood, with the design of covering it with an envelope on which the young teredo cannot attach itself, offer only an insufficient protection; these coverings are likely to be injured either by mechanical means, such as the action of the water, or by being dissolved by the water. Just so soon as

1 American oaks of coarse, open fibre are easily impregnated.—TRANSLATOR.

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