« PreviousContinue »
find it difficult to equal with her needle and silk, the variety of colours and shades which he expresses by sparks of agate, ruby, amethyst, cornelian, jasper, lapislazuli, and other precious stones. The high-altar piece, together with the tables on each side, are entirely of this Florentine work.” The Fabrica Degli Uffici, erected at Florence by Cosmo I., was appropriated in part for the reception of various artists, who worked exclusively for the Grand Duke. “But among all the performances executed here,” says Keysler, “that styled Florentine work is the most elegant; sparks of precious stones, and particles of elegant marble, are so disposed as to represent the objects of nature in a very beautiful and surprising manner; but works of this kind require a rodigious time to complete them. A ower-piece lately finished, about a foot and a half in length, and half a foot in breadth, employed the artist above eighteen months; and a piece of embossed work, about the size of a common sheet of paper, representing the adoration of the Eastern magi, and a group of angels in the air, has already been forty years in hand, and under the direction of several masters. The late unhappy state of Italy, and the o of still further changes, has een so fatally destructive of the arts, that Florentine work will not soon be encouraged; and there is little doubt this laborious art will be almost lost. FLORIN is sometimes used for a coin, and sometimes for a money of account. See Coix. FLORY, FlowRy, or Fleuny, in heraldry, a cross that has the flowers at the end circumflex and turning down, differing from the potence, inasmuch as the latter stretches out more like that which is called patee. FLOTILLA, a name given to a number of ships which get before the rest in their return, and give information of the dearture and cargo of the flota and galeons. FLOUR, the meal of wheat-corn, finely ground and sifted. Flour, when carefully analyzed, is found to be composed, 1, of fecula, which is insoluble in cold water, but soluble in hot water; 2, of gluten; 3, of a saccharine matter, susceptible of the spirituous fermentation. FLOWER, in botany. By this term, former botanists, as Ray and Tournefort, &c. evidently meant the petals, or beautiful coloured leaves of the plant, which generally adhere to the seed-bud, or ru
diment of the fruit. Since the introduction of the sexual method, the petals have lost their importance, and are now only considered as a finer sort of cover, which is generally present, but not essentially necessary to the existence of a flower. A flower then, in modern botany, is as different in meaning from the same term in former writers, as from the vulgar acceptations of the word at this day. The petals, the calyx, nay, the threads or filaments of the stamina, may all be wanting, yet it is a flower still, provided the anthers, or male organ, and the stigma or summit of the style, the female organ, can be traced; and that either immediately in the neighbourhood of one another, as in most plants; on different parts of the same plant, as in the class Monoecia ; or on different plants raised from the same seed, as in the class Dioecia. In this manner is to be understood the general principle with which the sexual method sets out, that every vegetable is furnished with flower and fruit. The essence of the flower, therefore, consists in the anthers and stigma, which constitute a flower, whether the covers, that is, the calyx and petals, are present or not. Flow sh de luce. See Iais. Flowen de lis, or Flow ER de duce, in heraldry, a bearing representing the lily, called the queen of flowers, and the true hieroglyphic of royal majesty; but of late it is become more common, being borne in some coats one, in others three, in others five, and in some semée, or spread all over the escutcheon in great numbers. Flowkits, in chemistry, a term formerly applied to a variety of substances procured by sublimation, and were in the form of slightly cohering powder: hence, in all old books, we find mention made of the flowers of antimony, arsenic, zinc, and bismuth, which are the sublimed oxides of these metals, either pure, or combined with a small quantity of sulphur : we have also still in use, though not generally, the terms, flowers of sulphur, benzoin, &c. FLUATES, in chemistry, salts, of which the Fluoric Acid (which see) is the chief ingredient. Fluor spar, denominated fluate of lime, which is found in great plenty in many countries, and is very abundant in Derbyshire, where it obtains the name of Derbyshire spar, is the most important among the fluates. The chief properties of these salts are, 1. When sulphuric acid is poured upon them, they emit acrid vapours of fluoric acid, which corrode glass. 2. When heated, several of them phosphoresce. 3. They are not decomposed by heat, nor altered by combus
tibles. They combine with silica by means of heat. FLUENT, in fluxions, the flowing quantity, or that which is continually either increasing or decreasing, whether line, surface, solid, &c. See Fluxion. FLUID, in physiology, an appellation given to all bodies, whose particles easily yield to the least partial pressure or force impressed. All fluids, except those in the form of air or gas, are incompressible in any considerable degree. The Academy del Cimento, from the following experiment, supposed water to be totally incompressiA globe made of gold, which is less orous than any other metal, was completely filled with water, and then closed up; it was afterwards placed under a great compressive force, which pressed the fluid through the pores of the metal, and formed a dew all over its surface, before any indent could be made in the vessel. Now, as the surface of a sphere will contain a greater quantity than the same surface under any other form whatever, the academy supposed that the compressive power which was applied to the globe must either force the particles of the fluid into closer adhesion, or drive them through the sides of the vessel before any impression could be made on its surface; for although the latter effect took place, it furnishes no proof of the incompressibility of water, as the Florentines had no method of determining that the alteration of figure in their globe of gold occasioned such a diminution of its internal capacity, as was exactly equal to the quantity of water forced into its pores; but this experiment serves to shew the great minuteness of the particles of a fluid in penetrating the pores of gold, which is the densest of all metals. Mr. Canton brought the uestion of incompressibility to a more ecisive determination. He procured a glass tube, of about two feet long, with a ball at one end, of an inch and a quarter in diameter: having filled the ball and art of the tube with mercury, and brought it to the heat of 50° of Fahrenheit's thermometer, he marked the place where the mercury stood, and then raised the mercury by heat to the top of the tube, and there sealed the tube hermetrically; then, upon reducing the mercury to the same degree of heat as before, it stood in the tube # of an inch higher than the mark. The same experiment was repeated with water, exhausted of air, instead of mercury, and the water stood in the tube on
above the mark. Now, since the weight of the atmosphere on the outside of the ball, without any counterbalance from within, will compress the ball, and equally raise both the mercury and water; it appears that the water expands to of an inch more than the mercury, by removing the weight of the atmosphere. From this, and other experiments, he infers, that water is not only compressible, but elastic; and that it is more capable of compressibility in winter than in summer.
All fluids gravitate, or weigh, in proportion to their quantity of matter, not only in the open air, or in vacuo, but in their own elements. Although this law seems so consonant to reason, it has been supposed by ancient naturalists, who were ignorant of the equal and general pressure of all fluids, that the component parts, or the particles of the same element, did not gravitate or rest on each other; so that the weight of a vessel of water balanced in air would be entirely lost, when the fluid was weighed in its own element. The following experiment seems to leave this question perfectly decided : take a common bottle, corked close, with some shot in the inside to make it sink, and fasten it to the end of a scale beam; then immerse the bottle in water, and balance the weight in the opposite scale; afterwards open the neck of the bottle, and let it fill with water, which will cause it to sink; then weigh the bottle again. Now it will be found that the weight of the water which is contained in the bottle is equal to the difference of the weights in the scale, when it is balanced in air; which sufficiently shews that the weight of the water is the same in both situations. As the particles of fluids possess weight as a common property o bodies, it seems reasonable, that they should possess the consequent power of gravitation which belongs to bodies in general. Therefore, supposing that the particles which compose fluids be equal, their gravitation must likewise be equal; so that in the descent of fluids, when the particles are stopped and supported, the gravitation being equal, one particle will not have more propensity than another to change its situation, and after the impelling force has subsided, the particles will remain at absolute rest.
From the vity of fluids arises their pressure, which is always proportioned to the gravity. For if the particles of fluids have equal magnitude and weight, the gravity or pressure must be propor
tional to the depth, and equal in every horizontal line of fluid; consequently, the ressure on the bottom of vessels is equal in every part. The pressure of fluids upwards is equal to the pressure downwards, at any given depth. For, suppose a column of water to consist of any given number of particles acting upon each other in a perpendicular direction, the first particle acts upon the second with its own weight only; and, as the second is stationary, or fixed by the surroundin particle, according to the third law motion, that action and reaction are equal, it is evident that the action, or avity, in the first is repelled in an equal §. gree by the reaction of the second; and #. manner the second acts on the third, with its own gravity added to that of the first; but still the reaction increases in an equivalent degree, and so on throughout the whole depth of the fluid. The particles of a fluid, at the same depth, press each other equally in all directions. This appears to rise out of the very nature of fluids; for as the particles give way to every impressive force, if the pressure amongst themselves should be unequal, the fluid could never be at rest, which is contrary to experience; there. fore, we conclude that the particles press each other equally, which keeps them in their own places. This principle applies to the whole of a fluid as well as a part. For if four or five glass tubes, of different forms, be immersed in water, when the corks in the ends are taken out, the water will flow through the various windings of the different tubes, and rise in all of them to the same height as it stands in the straight tube: therefore the drops of fluids must be equally pressed in all directions during their ascent through the various angles of the tube, otherwise the fluid could not rise to the same height in them all. From the mutual pressure and equal action of the particles of fluids, the surface will be perfectly smooth and parallel to the horizon. If from any exterior cause the surface of water has some parts higher than the rest, these will sink down by the natural force of their own gravitation, and diffuse themselves into an even surface. See Hypnostatics. FLUIDs, motion of The motion of fluids, viz. their descent or rise below or above the common surface or level of the source or fountain, is caused either, 1. By the natural gravity or pressure of the fluid oft in the reservoir, or fountain;
or, 2. By the pressure or weight of the air on #. surface of the fluid in the reservoir, when it is at the same time either taken off or diminished on some part in aqueducts or pipes of conduit. 3. By the spring or elastic power of compressed or condensed air, as in the common water engine. 4. By the force of pistons, as in all kinds of forcing pumps, &c. 5. By the power of attraction, as in the case of tides, &c. FLUIDITY. The state of bodies when their parts are very readily moveable in all directions with respect to each other. Many useful and curious properties arise out of this modification of matter, which form the basis of the mechanical science called hydrostatics, and are of considerable importance in chemistry. But the attention of the chemist is chiefly directed to the state of fluidity, as it may affect the component parts of bodies. A solid body may be converted into a fluid by heat. The less the temperature at which this is effected, the more fusible the body is said to be. All fluids, not excepting the fixed metals, appear, from various facts, to be disposed to assume the elastic form, and this the more readily the higher the temperature. When a fluid is heated to such a degree as that its elasticity is equal to the pressure of the air, its interior parts arise up with ebullition. The capacity of a dense fluid for caloric is greater than that of the same body when solid, but less than when in the elastic state. If this were not the case, the assumption of the fluid and elastic state would be scarcely at all progressive, but effected in most cases instantly as to sense. See CALonic. The state of dense fluidity appears to be more favourable to chemical combination than either the solid or elastic state. In the solid state, the cohesive attraction prevents the parts from obey. ing their chemical tendencies; and in the elastic state, the repulsion between the parts has, in a great measure, the same effects. Hence it has been considered, though too hastily, as a chemical axiom, that corpora non agunt nisi fuida. FLUOR spar, the native fluate of lime. See the next article. FLUORIC acid, in chemistry, is obtained from fluor spar, or, as it is technically called, fluate of lime. It has not yet been decomposed, unless it be among the grand discoveries of Mr. Davy, not yet announced to the world. We have attended the lectures of this professor, and think, in one of them, he said he had decomposed the fluoric acid : for want, however, of any written document on the subject, we must content ourselves with a summary account of the properties of this acid, which were investigated with accuracy and precision by Scheele and Priestley. The spar was not distinguished from others of a similar appearance till about the year 1768, when Margraff attempted to decompose it by means of the sulphuric acid. He found that it consisted of a white sublimate, and a peculiar acid; the sublimate proved afterwards to be lime, and the acid being denominated fluoric acid, it is now called the fluate of lime. Margraff found, to his astonishment, that the glass retort in which the experiment had been made was corroded, and even pierced with holes. Fluoric acid may be obtained by putting a quantity of the spar in powder into a retort, pouring over it an equal quantity of sulphuric acid, and then applying a gentle heat. A gas ensues, which may be received in the usual manner, in jars, standing over mercury. This gas is the fluoric acid, which may be obtained dissolved in water, by luting to the retort a receiver containing that fluid. The distillation is to be conducted with a very moderate heat, to allow the gas to condense, and to prevent the fluor itself from subliming. Soon after the discovery of this acid, it was doubted whether it possessed those properties that rendered it different from all other acids. Scheele, however, who had already investigated the subject, instituted another set of experiments, which completely established the fact. The properties of this acid are, that, as a gas, it is invisible, and elastic like air: but it will not maintain combustion, nor can animals breathe it without death. In smell it is pungent, something similar to muriatic acid. It is heavier than common air, and corrodes the skin. When water is admitted in contact with this É. it absorbs it rapidly; and if the gas e obtained by means of glass vessels, it deposits at the same time a quantity of silica. Water absorbs a large portion of this gas, and in that state it is usually called fluoric acid by chemists. It is then heavier than water, has an acid taste, reddens vegetable blues, and has the property of not congealing till cooled down to 23°. The pure acid may be obtained again from the compound by
As fluoric acid produces an insoluble compound with lime, it may be employed to detect the presence of that earth when held in solution. Two or three drops only of the acid will cause a milky cloud or precipitate to or. if any lime is present. Fluoric acid has been applied to engraving or etching on glass, and was used, according to Beckman, nearly a century and a half o for that purpose, by an artist at Nuremberg, who obtained it from digesting fluor spar in nitric acid. Since, however, the discoveries of Scheele and Priestley,it has been more generally used, and the art is performed by covering the glass with wax, and then that part where the figures are to appear is laid hare, and the whole is exposed for some time to the hot vapour of fluoric acid. This simple rocess is employed with great advantage in writing labels on glass vessels, and in graduating thermometers, &c. See Thomson's Chemistry. FLUSTRA, in natural history, hornwrack, a genus of worms, of the order Zoophyta. Animal a polype, proceeding from porous cells; stem fixed, foliaceous, membranaceous, consisting of numerous rows of cells united together, and woven like a mat. About eighteen species have been described. FLUTE, an instrument of music, the simplest of all those of the wind kind. It is played on by blowing it with the mouth, and the tones or notes are changed by stopping and opening the holes disposed for that purpose along its side. The ancient fistulae, or flutes, were made of reeds, afterwards of wood, and last of metal; but how they were blown, whether as our flutes, or as hautboys, does not appear. FLUTE, German, is an instrument entirely different from the common flute. It is not, like that, put into the mouth to be played, but the end is stopt with a tampion or plug; and the lower lip is applied to a hole about two inches and a half, or three inches, distant from the end. The instrument is usually about a foot and a half long; rather bigger at the upper end than the lower; and perforated with holes, besides that for the mouth, the lowest of which is stopped and opened by the little finger's pressing on a brass, or sometimes a silver key, like those in hautboys, bassoons, &c. Its sound is exceedingly sweet and agreeable ; and serves as a treble in a concert. FLUX, a general term made use of to denote any substance or mixture added to assist the fusion of minerals. In the large way, limestone or fluor spar are used as fluxes; but in small assays, the method of the great operations is not always followed, though it would be very frequently of advantage to do so. The fluxes made use of in assays, or philosophical experiments, consist usually of alkalies, which render the earthy mixtures fusible, by converting them into glass; or else glass itself into powder. Alkaline fluxes are either the crude flux, the white flux, or the black flux. Crude flux is a mixture of nitre and tartar, which is put into the crucible with the mineral intended to be fused. The detonation of the nitre with the inflammable matter of the tartar is of service in some operations; though generally it is attend. ed with inconvenience, on account of the swelling of the materials, which may throw them out of the vessel, if proper care be not taken either to throw in only a little of the mixture at a time, or to provide a large vessel. White flux is formed by projecting equal parts of a mixture of nitre and tar. tar, by moderate portions at a time, into an ignited crucible. In the detonation which ensues, the nitric acid is decom
posed, and flies off with the tartarous acid, and the remainder consists of the potash in a state of considerable purity. This has been called fixed nitre. Black flux differs from the preceding, in the proportion of its ingredients. In this the weight of the tartar is double that of the nitre ; on which account the combustion is incomplete, and a considerable portion of the tartarous acid is decomposed by the mere heat, and leaves a quantity of coal behind, on which the black colour depends. It is used where metallic ores are intended to be reduced, and ef. fects this purpose by combining with the oxygen of the oxide. There is danger of loss in the treatment of sulphurous ores with alkaline fluxes; for, though much or the greater part of the sulphur may be dissipated by roasting, yet that which remains will form a sulphuret with the alkali, which is a very powerful solvent of metallic bodies. The advantage of M. Morveau's reducing flux seems to depend on its containing no uncombined alkali. . It is made of eight [. of pulverized glass, one of calcined orax, and half a part of powder of char. coal. Care must be taken to use a glass which contains no lead. The white glasses contain in o: large proportion, and the green bottle glasses are not perhaps entirely free from it. Flux, in medicine, an extraordinary issue, or evacuation of some humours of the body. See Medicine. FLUXION, in mathematics, denotes the velocity by which the fluents or flowing quantities increase or decrease; and may be considered as positive or negative, according as it relates to an increment or decrement. The doctrine of fluxions, first invented by sir Isaac Newton, is of great use in the investigation of curves, and in the discovery of the quadratures of curvilinear spaces, and their ratifications. In this method, magnitudes are conceived to be generated by motion, and the velocity of the generating motion is the fluxion of the magnitude. Thus, the velocity of the point that describes a line is its ão. and measures its increase or decrease. When the motion of this point is uniform, its fluxion or velocity is constant, and may be measured by the space described in a given time; but when the motion varies, the fluxion of velocity at any given point is measured by the space that would be described in a given time, if the motion was to be continued uniformly from that term.