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SUPPLEMENT TO THE CATALOGUE OF WOODS.

115

MEMOIR ON THE PRESERVATION OF WOODS-continued.

these, when of a neutral kind, as the chloride of soda, often equalled in bulk that of the wood itself, without causing any addition to its weight; the acid and alkaline fluids were less abundantly absorbed, apparently from contracting the vessels by their astringent action. It is stated that the pyrolignite of iron effected the preservation of the substance when equal to less than a fiftieth of the weight of the green wood. These points are all separately treated in the original paper.

2. The hardness of the wood was considered by various workmen to be more than doubled by the action of the pyrolignite.

3. The flexibility, (due to a certain presence of moisture,) was increased in a remarkable manner by the chloride of lime and other deliquescent salts, the degree of elasticity depending upon their greater or less concentration. As a cheap substitute for the above, the stagnant water of salt marshes was adopted, with a fifth of the pyrolignite, for the greater certainty of preservation. Pieces of prepared deal, 3 millimètres thick and 60 centimètres long, were capable of being twisted and bent in all directions, as into screws, also into three circular coils; the wood immediately regained its figure when released; this condition lasted eighteen months, that is, until the time his paper was read.

4. The warping and splitting, principally due to the continual effect of the atmosphere in abstracting and restoring the moisture, was stayed by impregnating the wood with a weak infusion of the chloride, so as always to retain it to a certain degree moist; one-fifth of pyrolignite was also added in this case. The seasoning of the wood was also considered to be expedited by the process, and which was not found to interfere with the ordinary use of oil-paint, &c. Large boards of the prepared wood, some of which were painted on one or both sides, and similar boards of unprepared wood, were compared ; at the end of twelve months, the former were perfect as to form, the latter were warped and twisted as usual.

5. The inflammability and combustibility of the woods were also prevented by the earthy chlorides, which fuse on their surfaces by the application of heat, and render them difficult of ignition. Two similar cabins were built of prepared and of ordinary wood respectively, and similar fires were lighted in each; the latter was entirely burned, the other was barely blackened.

6. In respect to colours infused by the aspiratory process, the vegetable colours were found to answer less perfectly than the mineral, and the latter succeeded best when the colour was introduced at two processes, so that the chemical change, (that of ordinary dyeing,) occurred in the pores of the wood itself. Odorous matters, required to be infused in weak alcoholic solutions, or essential oils, they were considered to be equally durable with those supplied by the hand of nature; and resins similarly introduced were found to increase amazingly the inflammability of the woods, and to render them impervious to water.

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SUPPLEMENT TO THE CATALOGUE OF WOODS.

MEMOIR ON THE PRESERVATION OF WOODS-continued.

In a word, the method promises the means of working almost any desired change in the constitution and properties of woods, when the fluids are presented to them before the vitality of the tree has ceased. It is true we have as yet only two years' trial of these experiments, but they have been scientifically deduced, and their inventor is still engaged in prosecuting them. It is to be hoped, and also expected, that these interesting and flattering promises of success will be realized, and even extended, when tried by that most severe of all tests, time *.

* Since I collected the above particulars from the number for June, 1840, of Les Annales de Chimie et de Physique, pp. 113 to 157, I have been favoured by J. E. Puddock, Esq, with a printed copy of the English translation of the original paper, preceded by the report of Messrs. De Mirbel, Arago, Poncelet, Audouin, Gambey, Boussingault, and Dumas, on the part of l'Académie des Sciences, confirming the value of the invention. In France, Dr. Boucherie has relinquished his brevet, and thrown the process open to the public in consideration of a national reward; and immense preparations are being there made, by the Minister of Marine, for the employment of the preservative process for the French navy, &c. In England Dr. Boucherie and Company have obtained two patents, and Mr. Puddock, their agent, has specimens of pine, plane-tree, &c., variously prepared and coloured, with the pyrolignite of iron, the prussiate of iron, the prussiate of copper, and various other metallic salts, &c.

CHAPTER VII.

MATERIALS FROM THE ANIMAL KINGDOM*.

SECT. I.-PORCELANOUS AND NACREOUS SHELLS, BONES, &c. THE hard solid substances derived from the Animal Kingdom, are parts of the external or internal skeletons, as shells and bones; or of the instruments of sustenance and defence, as horns, hoofs, nails, claws, teeth, &c.: these, together with the various coverings of animals, whether hair, feathers, scales, &c. are alike composed of animal and earthy matters, almost exclusively albumen, gelatine, and lime, combined in various proportions, and with a structure more or less interspersed with animal fibre. Many of these are either formed by the deposition of successive annual layers, or they are altogether yearly renewed.

A brief consideration of the chemical difference between their component parts, and of their respective proportions, in such as are used in the arts, will show the reasons for their various characters, and different treatment with tools.

Albumen, the principal ingredient of these animal substances, * The author begs to premise, that having but little personal experience in the subject-matters of this present chapter, he has not hesitated to draw largely from the Manuel du Tourneur, and also from two valuable papers "On Horn and Tortoiseshell," and "On Bone, and its uses in the Arts," by Arthur Aikin, Esq., read before the Society of Arts in 1832, 1838 and 1839, and published in their Transactions, Vol. LII., Part 2, pp. 334—379; in which, in addition to the information on the points here to be discussed, are contained many interesting particulars on the physiology, and on the historical and present uses of these substances: an article on Tortoiseshell, in Gill's Technological Repository, 1827, Vol. I., p. 332, (derived from the Franklin Journal and l'Encyclopédie Méthodique,) has likewise been consulted: the several extracts will be respectively noticed.

The author has been further enabled by the kindness of various practical friends, to advance other examples and particulars, and to procure specimens of several of the materials in their different stages of manufacture. In accordance with the prescribed plan of the work, he has dwelt more at length on those parts which the amateur may practise with comparatively few apparatus.

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and which exists in the purest form in the white of eggs, is hardened by a degree of heat less than the boiling temperature of water, and is insoluble in the same. Gelatine, of which jelly and glue are different examples, is softened by heat, and rendered fluid by the addition of water; both are easily cut and scraped, in all their various stages from soft to hard, and during this change they contract very materially, but without entirely losing their elasticity.

The earthy matters of the animal solids, principally the phosphate and carbonate of lime, are widely different from the foregoing, and also from the substances of the woods, metals, &c. They are inelastic, and often crystalline, and therefore incapable of being cut into shreds or shavings; as when they are divided they become smaller fragments or particles, which are always angular: they are comparatively uninfluenced by water or small changes of temperature, and are incapable of contraction.

When the earthy and crystalline structures prevail, the animal substances are harsh, incapable of absorbing moisture, or of alteration of size or form; when the animal and fibrous characters prevail, they are easily cut, and they absorb moisture, soften, and swell*.

In some of the shells, the quantity of animal matter is so small, and the lime is in so hard and compact a form, that they are very brittle, partially translucent, generally they have smooth surfaces, and are incapable of being cut with a knife or tools; such shells are called porcelanous, from their resemblance to porcelain; they include most of the univalve shells, such as the whelks, limpets, and cowries. Most of these can only be worked upon after the manner of the lapidary, with emery and other gritty matters harder than themselves, by which means they are

* The numbers attached to the following substances show, in a rough manner, the rate per cent. of animal matters respectively contained; the remainder, principally carbonate and phosphate of lime, being neglected.

Enamel of teeth, the hardest of the class, contains from 2 to 3 per cent. of animal matter, (Berzelius). Porcelanous shells are nearly similar. Nacreous shells, 24 per cent. (Hatchett). Ivory, 24 per cent. (Ure,) 25 per cent. (Merat Guillot.) Bone, 33 per cent. (Berzelius). Horn, is coagulated albumen and lime, with per cent. of phosphate of lime, (Ure). Tortoiseshell is nearly the same as horn. The horn of the buck and hart are intermediate between bone and ordinary horn (Ure).

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cut and polished, as will be explained in speaking of that art; by analysis they are considered closely to agree with the enamel of the teeth.

The nacreous shells, (thus named from nacre, the French for mother-of-pearl,) are most commonly known in the shells of the pearl-bearing oyster of the Indian Seas, (Ostræa margaritifera,) but they include the generality of the bivalve shells, as the various oysters, muscles, &c.; within they are smooth and iridescent, without they have a rough coat or epidermis.

These kinds contain a larger proportion of animal matter, which is considered to be arranged in alternate layers with the carbonate of lime; and as these shells also are impenetrable to water, they neither shrink nor swell. The pearl shells are less frangible and hard than the porcelanous shells, and they admit of being sawn, scraped, and filed, with ordinary tools; but they are harsh, scratchy, and disagreeable under the operation.

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The beautiful iridescent appearance of the pearl shells is attributed to their laminated structure, which disposes their surfaces in minute furrows, that decompose and reflect the light; and owing to this lamellar structure, they also admit of being split into leaves, for the handles of knives, counters, the purposes of inlaying, &c. but they are very apt to follow, and even to exceed the curvature of the surface, and therefore splitting is not much resorted to, but the different parts of the shell are selected to suit the several purposes as nearly as possible; and the excess of thickness is removed upon the grindstone in preference to risking the loss of both parts in the attempt to split them. The usual course in preparing the rough pearl shell for the arts, is to cut out the square and angular pieces with the ordinary brass-back saw, and the circular pieces, such as those for buttons, &c., with the annular or crown saw, fixed upon a lathe mandrel. The sides of the pieces are then ground flat upon a wet grindstone, the edge of which is turned with several grooves, as the ridges are considered to cut more quickly than the entire surface, from becoming less clogged with the particles ground off. The pieces are finished upon the flat side of the stone, and are then ready for inlaying, engraving, polishing, &c. according to the purposes for which they are intended. Cylindrical pieces are cut out of the thick part of the shell, near the joint or

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