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sam of capaiva, are employed in proper proportions. For the solution of these bodies the strongest alcohol ought to be used, which may very properly indeed be distilled over alkali, but must not have stood upon alkali. The utmost simplicity in composition, with respect to the num ber of the ingredients in a formula, is the result of the greatest skill in the art; hence it is no wonder, that the greatest part of the formulas and recipes that we meet with are composed without any principle at all.

In conformity to these rules, a fine colourless varnish may be obtained, by dissolving eight ounces of gum sandarach and two ounces of Venice turpentine in thirty-two ounces of alcohol by a gentle heat. Five ounces of shell-lac and one of turpentine, dissolved in thirty-two ounces of alcohol by a very gentle heat, give a harder varnish, but of a reddish cast. To these the solution of copal is undoubtedly preferable in many respects. This is effected by triturating an ounce of powder of gum copal, which has been well dried by a gentle heat, with a drachm of camphor, and, while these are mixing together, adding by degrees four ounces of the strongest alcohol, without any digestion.

Between this and the gold varnish there is only this difference, that some substances that communicate a yellow tinge are to be added to the latter. The most ancient description of two sorts of it, one of which was prepared with oil, and the other with alcohol, is to be found in "Alexius Pedemontanus Dei Secreti," Lucca, of which the first edition was published in the year 1557. But it is better prepared, and more durable, when made after the following prescription: Take two ounces of shell-lac, of arnatto and turmeric of each one ounce, and thirty grains of fine dragon's blood, and make an extract with twenty ounces of alcohol in a gentle heat.

Oil varnishes are commonly mixed immediately with the colours, but lac or lacquer varnishes are laid on by themselves upon a burnished coloured ground: when they are intended to be laid upon naked wood, a ground should be first given them of strong size, either alone or with some earthy colour, mixed up with it by levigation. The gold lacquer is simply rubbed over brass, tin, or silver, to give them a gold colour.

Pere d'Incarville has informed us, that the tree which affords the varnish of China is called tsi-chou by the Chinese. This

tree is propagated by off-sets. When the cultivator is desirous of planting it, he takes a branch, which he wraps up in a mass of earth, my means of flax. Care is taken to moisten this earth; the branch pushes out roots, and is then pruned and transplanted. This tree grows to the size of a man's leg.

The varnish is drawn in spring. If it be a cultivated tree, it affords three gatherings. It is extracted by incisions made in the spring: and when the varnish, which is received in shells, does not flow, several hog's bristles, moistened with water or saliva, are introduced into the wound, and cause it to run. When the tree is exhausted, the upper part of it is wrapped in straw, which is set on fire, and causes the varnish to precipitate to the bottom of the tree, where it flows out of perforations made for that purpose.

Those who collect the varnish set out before day-break, and place their shells beneath the apertures. The shells are not left longer than three hours in their place, because the heat of the sun would evaporate the varnish.

The varnish emits a smell, which the workmen are very careful to avoid respiring. It produces an effect which they call the bud of the varnish.

When the varnish issues from the tree it resembles pitch. By exposure to the air, it gradually becomes coloured, and is, at last, of a beautiful black.

The juice which flows from incisions made in the trunk and branches of the rhus toxicodendron possesses the same properties. It is a white milky fluid, which becomes black and thick by the contact of the air.

To make the varnish bright, it is evaporated by the sun: and a body is given to it with hog's gall and sulphate of iron.

The Chinese use the oil of tea, which they render drier by boiling it with orpiment, realgar, and arsenic.

To varnish any substance, consists in applying upon its surface, a covering of such a nature, as shall defend it from the influence of the air, and give it a shining appearance.

A coat of varnish ought, therefore, to possess the following properties: 1. It must exclude the action of the air; because wood and metals are varnished, to defend them from decay and rust. 2. It must resist water; for otherwise the effect of the varnish could not be permanent. 3. It ought not to alter such co

lours as are intended to be preserved by this means.

It is necessary, therefore, that a varnish should be easily extended or spread over the surface, without leaving pores or cavities, that it should not crack nor scale; and that it should resist water. Now resins are the only bodies that possess these properties.

Resins, consequently, must be used as the bases of varnish. The question which of course presents itself must be, then, how to dispose them for this use; and for this purpose they must be dissolved, as minutely divided as possible, and combined in such a manner, that the imperfections of those which might be disposed to scale may be corrected by others.

Resins may be dissolved by three agents: 1. By fixed oil. 2. By volatile oil. 3. By alcohol. And accordingly we have three kinds of varnish: the fat or oily varnish, essential varnish, and spirit varnish.

Before a resin is dissolved in a fixed oil, it is necessary to render the oil drying. For this purpose the oil is boiled with metallic oxides, in which operation the mucilage of the oil combines with the metal, while the oil itself unites with the oxygen of the oxide. To accelerate the drying of this varnish, it is necessary to add oil of turpentine.

The essential varnishes consist of a solution of resin in oil of turpentine. The varnish being applied, the essential oil flies off, and leaves the resin. This is used only for paintings.

When resins are dissolved in alcohol, the varnish dries very speedily, and is subject to crack; but this fault is corrected by adding a small quantity of turpentine to the mixture, which renders it brighter, and less brittle when dry.

The coloured resins, or gums, such as gamboge, dragon's blood, &c. are used to colour varnishes.

To give lustre to the varnish after it is laid on, it is rubbed with pounded pumice. stone and water: which being dried with a cloth, the work is afterward rubbed with an oiled rag and tripoli. The surface is, last of all, cleaned with soft linen cloths, cleared of all greasiness with powder of starch, and rubbed bright with the palm of the hand.

VARNISH also signifies a sort of shining coat, wherewith potter's ware, delftware, china-ware, &c. are covered, which gives them a smoothness and lustre. Melted lead is generally used for the

first, and smalt for the second. See ENAMELLING.

VARNISH, among medalists, signifies the colours antique medals have acquired in the earth. The beauty which nature alone is able to give to medals, and art has never yet attained to counterfeit, enhances the value of them; that is, the colour which certain soils in which they have a long time lain tinges the metals withal; some of which are blue; others with an inimitable vermilion colour; others with a certain shining polished brown, vastly finer than Brazil figures.

VARRONIA, in botany, so named from Marcus Terentius Varro, a genus of the Pentandria Monogynia class and order Natural order of Asperifolia. Borraginex, Jussieu. Essential character: corolla five-cleft; drupe with a four-celled nut. The are nine species.

VAS, a vessel either for mechanical, chemical, culinary, or any other uses. In anatomy, all the parts which convey a fluid are called vessels, as the veins, arteries and lymphatics.

VASA concordia, among hydraulic au thors, are two vessels, so constructed as that one of them, though full of wine, will not run a drop, unless the other, being full of water, do run also.

VASE, a term frequently used for ancient vessels dug from under ground, or otherwise found, and preserved in the cabinets of the curious. In architecture, the appellation vase is also given to those ornaments placed on corniches, sochles, or pedestals, representing the vessels of the ancients, particularly those used in sacrifice; as incense pots, flower-pots, &c. They serve to crown or finish façades or frontispieces; and hence called acroteria. The term vase, however, is more particularly used in architecture to signify the body of the Corinthian and Composite capital; otherwise called the tambour or drum, and sometimes the campana or bell.

VATERIA, in botany, so named from Abraham Vater, professor of medicine and botany, at Witteberg, a genus of the Polyandria Monogynia class and order. Natural order of Guttiferæ, Jussieu, sential character: calyx five-cleft; corolla five petalled; capsule three-valved, one-celled, three-seeded. There is only one species, viz. V. indica.

Es

VATICA, in botany, a genus of the Dodecandria Monogynia class and order. Natural order of Guttiferæ, Jussieu. Essential character: calyx five-cleft; petals five; anthers fifteen, sessile, four-celled.

There is but one species, viz. V. chinensis, a very rare plant, and as yet scarcely

known.

each other in all directions, and is succulent and tender.

The cortical layers, which constitute VATICAN, a magnificent palace of the the interior part of the bark, are composPope, in Rome, which is said to consisted of thin membranes, and increase in

of several thousand rooms; but the parts of it most admired are, the grand staircase, the Pope's apartment, and especially the library, which is one of the richest in the world, both in printed books and manuscripts.

VAULT, in architecture, an arched roof, so contrived that the stones which form it sustain each other. Vaults are, on many occasions, to be preferred to soffits, or flat ceilings, as they give a greater height and elevation, and are besides more firm and durable.

VECTOR, or Radius Vector, in astronomy, is a line supposed to be drawn from any planet moving round a centre, or the focus of an ellipse, to that centre, or focus. It is so called, because it is that line by which the planet seems to be carried round its centre; and with which it describes areas proportional to the times. VEER, a sea term, variously used. Thus veering out a rope, denotes the letting it go by hand, or letting it run out of itself. It is not for letting out any running rope except the sheet.

VEGETABLE. See BOTANY, PLANT, &c. A vegetable is composed of a root, stem, leaves, flowers, fruits, and seeds; and when all these different parts are fully developed, the vegetable is said to be perfect. When any are deficient, or at least less obvious, the vegetable is said to be imperfect. The root is that part of the plant which is concealed in the earth, and which serves to convey nourishment to the whole plant. The stem, which commences at the termination of the root, supports all the other parts of the plant. When the stem is large and solid, as in trees, it is denominated the trunk, which is divided into the wood and the bark.

The bark constitutes the outermost part

of the tree, and covers the whole of the plant from the extremity of the roots to the termination of the branches. The bark is composed of three parts, namely, the epidermis, the parenchyma, and cortical layers. The epidermis, which is a thin transparent membrane, forming the external covering of the bark, is composed of fibres crossing each other. When the epidermis is removed, it is reproduced.

The parenchyma, which is immediately below the epidermis, is of a darkgreen colour, composed of fibres crossing VOL. XII.

number with the age of the plant. The. wood immediately under the bark is composed of concentric layers, which increase with the age of the plant, and may be separated into thinner layers, which are The composed of longitudinal fibres. wood next the bark, which is softer and whiter, is called the alburnum. The inharder, and is denominated the perfect terior part of the trunk is browner and

wood.

In the middle of the stem is the pith, which is a soft, spongy substance, composed of cells. In old wood this part entirely disappears, and its place is occupied by the perfect wood.

The leaves are composed of fibres arranged in the form of net-work, which proceed from the stem and foot-stalk, by which they are attached to the branches. These fibres form two layers in each leaf, which are destined to perform different functions. The leaves are covered with the epidermis, which is common to the whole of the plant. Each surface of a leaf has a great number of pores and glands, which absorb or emit elastic fluids.

Flowers are composed of different parts. The calyx or cup is formed by the extension of the epidermis; the corolla is a continuation of the bark, and the stamina and pistilla, the internal parts of fructification, are composed of the woody fibres and pith of the plant. Fruits are usually composed of a pulpy parenchymatous substance, containing a great number of vesicles, and traversed by numerous vessels. Seeds are constituted of the same utricular texture, in the vesicles of which is deposited a pulverulent or mucous sub. stance. These cells have a communication with the plants by means of vessels, and by these is conveyed the necessary nourishment during germination.

Plants contain different orders of vessels, which are distinguished from each other by their course, situation, and uses. Lymphatic vessels serve for the circulation of the sap. They are chiefly situated in the woody part of the plant. The peculiar vessels which generally contain thick or coloured fluids are placed immediately under the bark; they are smaller in number than the sap vessels, and have thin interstices filled up with utriculi or cells with which they form a communi

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cation. Some of these proper vessels are situated between the epidermis and the bark, which are readily detected in the spring. Some are situated in the interior part of the bark, forming oval rings, and filled with the peculiar juices of the plant Another set of proper vessels is placed in the alburnum, near the centre of the stock or trunk, and sometimes in the perfect wood. The utriculi or cells constitute another set of vessels, which seem to resemble a flexible tube, slightly interrupted with ligatures at nearly equal distances, but still preserving a free communication through its whole length. They vary in form, colour, and magnitude, in different vegetables, and exist in the roots, the bark, leaves and flowers. The trachea, or spiral vessels, which are readily detected in succulent plants, appear in the form of fine threads, and may be drawn out to a considerable length without breaking These vessels are very numerous in all plants, especially under the bark where they form a kind of ring, and are disposed in distinct bundles, in trees, shrubs, and stalks of herbaceous plants.

VEGETABLE acids, in chemistry. The acids which exist in many vegetables are at once recognised by their taste. These acids were formerly denominated essential salts of vegetables, and it was supposed that all essential salts were the sanie, and were composed of tartar, or vinegar. But Scheele's discovery of the citric, malic, and gallic acids, which, possessing distinct properties from those of tartaric and acetic acids, proved the contrary. Some vegetables contain only one acid, as oranges, and lemons, which contain citric acid only. In other vegetables two acids are found, as in gooseberries and currants, the malic and citric acids; and sometimes three, as the tartaric, citric,' and malic acids, which exist together in the pulp of the tamarind. As the acids which exist in vegetables have been already described, under their respective heads, it is now only necessary to enumerate the vegetable acids, specifying at the same time some of the plants from which they are obtained.

Acetic acid has been discovered in the sap of some trees, and in the acid juice of cicer arietinum. Oxalic acid exists in combination with potash, in the leaves of the oxalis acetosella, or wood-sorrel. In other species belonging to the same genus, and in some species of rumex, it is in the state of acidulous oxalate of potash. Oxalate of lime has been found in the

root of rhubarb. Citric acid is found in the juice of oranges and lemons, in the berries of two species of vaccinium, &c. Malic acid exists, unmixed with other acids, in the apple, the barberry, plum, sloe, elder, &c. In the gooseberry, in the cherry, strawberry, currants, and some other fruits, malic and citric acids are found nearly in equal proportions. Malic acid has been found mixed with tartaric acid in the agave Americana, and in the pulp of tamarinds, along with citric acid. Vauquelin found it combined with lime, forming a malate of lime, in the sempervivum tectorum,or house-leek. Gallic acid is found in a great number of plants, and in them it exists chiefly in the bark. Benzoic acid is found in benzoin, balsam of Tolu and Peru, liquid styrax, cinnamon and vanilla. Fourcroy and Vauquelin suspect that it exists in the anthoxanthum odoratum, or sweet-scented grass, which communicates the aromatic flavour to hay. Prussic acid has been found in the leaves of the lauro-cerasus and peach, in bitter almonds, in the kernels of apricots; and it is supposed that it exists also in the kernels of peaches, of plums, and cherries. It is obtained from the kernels of apricots, by distilling water off them with a moderate heat; and if lime be added to the concentrated infusion of bitter almonds, a prussiate of lime is formed. Phosphoric acid has been found in different parts of plants; but it is generally combined with lime, forming a phosphate of lime.

VEIN, in anatomy, a vessel which carries the blood from the several parts of the body to the heart. The veins are composed principally of a membranaceous, a vasculous and a musculous tunic; but these are vastly thinner than in the arteries. See ARTERY.

VELESIA, in botany, so named from Christoval Velesius, examiner, first physician, and demonstrator of botany, in the College of Apothecaries at Madrid, a genus of the Pentandria Digynia class and order. Natural order of Caryophyllei. Caryophylleæ, Jussieu. Essential character; calyx filiform, five-toothed; corolla five-petalled, small; capsule one-celled; seeds numerous, and a single row. There is but one species, viz. V. rigida, a native of the South of Europe.

VELLA, in botany, a genus of the Tetradynamia Siliculosa class and order Natural order of Siliquosæ or Cruciformes. Cruciferæ, Jussieu. Essential character: silicle with a partition twice as large as the valves, ovate on the outside. There

are two species, viz. V. annua, annual vella, or cress rocket; and V. pseudo cytisus, shrubby vella.

VELOCITY, swiftness, or that affection of motion, whereby a moving body is disposed to run over a certain space in a certain time.

In the doctrine of fluxions it is usual to consider the velocity with which magnitudes flow, or are generated. Thus, the velocity with which a line flows is the same as that of the point, which is supposed to describe or generate the line. The velocity with which a surface flows is the same as the velocity of a given right line, that, by moving parallel to itself, is supposed to generate a rectangle, always equal to the surface. The velocity with which a solid flows may be measured by the velocity of a given plane surface, that by moving parallel to itself, is supposed to generate an erect prism, or cylinder, always equal to the solid. The velocity with which an angle flows is measured by the velocity of a point, supposed to describe the arc of a given circle, which subtends the angle and measures it. All these velocities are measured at any term of the time of the motion, by the spaces which would be described in a given time by these points, lines, or surfaces, with their motions continued uniformly from that term. The velocity with which a quantity flows, at any term of the time while it is supposed to be generated, is called its fluxion. See FLUXIONS.

VELOCITY of bodies moving in curves. According to Galileo's system of the fall of heavy bodies, which is now universally admitted among philosophers, the velocities of a body falling vertically are, at each moment of its fall, as the square roots of the heights from whence it has fallen; reckoning from the beginning of the descent. And hence he inferred, that if a body descend along an inclined plane, the velocities it has, at the different times, will be in the same ratio: for since its velocity is all owing to its fall, and it only falls as much as there is perpendicular height in the inclined plane, the velocity should be still measured by that height, the same as if the fall were vertical. The same principle led him also to conclude, that if a body fall through several contiguous inclined planes, making any angles with each other, much like a stick when broken, the velocity would still be regulated after the same manner, by the vertical heights of the different planes taken together, considering the last velocity as the same that the body would acquire by

a fall through the same perpendicular height.

This conclusion continued to be acquiesced in till the year 1672, when it was demonstrated to be false, by James Gregory, who shows what the real velocity is, which a body acquires by descending down two contiguous inclined planes, forming an obtuse angle, and that it is different from the velocity which a body acquires by descending perpendicularly through the same height; also that the velocity in quitting the first plane is to that with which it enters the second, and in this latter direction, as radius to the cosine of the angle of inclination between the two planes.

This conclusion, however, it is observed, does not apply to the motions of descent down any curve lines, because the contiguous parts of curve lines do not form any angle between them, and consequently no part of the velocity is lost by passing from one part of the curve to the other; and hence he infers, that the velocities acquired in descending down a continued curve line are the same as by falling perpendicularly through the same height. This principle is then applied, by the author, to the motion of pendulums and projectiles.

Varignon too, in the year 1693, followed in the same track, showing, that the velocity lost in passing from one right lined direction to another, becomes indefinitely small in the course of a curve line and that therefore the doctrine of Galileo holds good for the descent of bodies down a curve line, viz. that the velocity acquired at any point of the curve is equal to that which would be acquired by a fall through the same perpendicular al

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VELVET, a rich kind of stuff, all silk, covered on the outside with a close, short, fine, soft shag, the other side being a very strong close tissue. The nap, or shag, called also the velveting, of this stuff is formed of a part of the threads of the warp, which the workmen puts on a long narrow-channelled ruler or needle, which he afterwards cuts by drawing a sharp steel tool along the channel of the needle to the ends of the warp.

VENEERING, or VANEERING, a kind of inlaying, whereby several thin slices or leaves of fine woods, of different kinds, are applied and fastened on a ground of some common wood. There are two kinds of inlaying; the one which is the most common and more ordinary, goes no further than the making of compartments of

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