VOIVRE, a town of France, in the dep. of the Vofges; 3 miles N. of St Diey.

VOJUSSA, a river of European Turkey, running into the Adriatic, 7 miles N. of Valona... VOKELMARK, a town of Auftria, in Carinthia, on the Drave; 26 miles SE. of Clagenfurt. Lon. 14. 56. E. Lat. 46. 45. N.

VOKSA, a river of Ruffia, in Viborgfkoe, which runs from lake Sama into lake Ladoga.

VOKSCHA, a river of Ruffia, which rifes in Uftiugfkoe, and joins the Mezen in Archangel, 16 miles N. of Olenskoi.

VOLÆ, an ancient city of the Equi. VOLANA, a town of the Samnites. VOLANDUM, an ancient town of Armenia. VOLANO, a town of Italy, in the dep. of the Lower Po, district and ci-devant duchy of Ferrara; 40 miles E. of Ferrara. Lon. 12. 36. E. Lat. 44. 52. N.

(1.) * VOLANT. adj. [volans, Lat. volant, Fr.] 1. Flying; paffing through the air. The valant or flying automata. Wilkins. 2. Nimble; active. -His volant touch. Milton.

Blind British bards, with volant touch. Philips. (2.) VOLANT, in heraldry, is when a bird, in a coat of arms, is drawn flying, or having its wings ípread out.

VOLAR, a town of Transylvania, 4 miles S. of Hunyad.

VOLATERRA, an ancient town of Etruria, famous for its bot baths. PERSIUS the fatirift was born in it. Strabo, 5.

(1.) * VOLATILE. adj. [volatilis, Lat.] 1. Fly. ing; paffing through the air.-The caterpillar waxeth volatile, Bacon.-There is no creature only volatile. Ray. 2. Volatile, Fr.] Having the power to pafs off by spontaneous evaporation, Volatile Hermes. Milton.-A volatile fufible falt. Nesuton. 3. Lively; fickle; changeable of mind; full of fpirit; airy.-A volatile temper, Watts.You are as giddy and as volatile as ever. Swift. ' (2.) VOLATILE. R. f. [volatile, Fr.] A winged animal. The air ferves for the flight of volatiles. Brown.

*

(3.) VOLATILE, in phyfics, is commonly used to denote a mixed body, whofe integrant parts are eafily diffipated by fire or heat; but it is more properly used for bodies whofe parts are easily feparated from each other, and dispersed in air.

(4) VOLATILE ALKALI, called in the new French nomenclature AMMONIA, one of the three alkaline falts. (See ALKALI.) It confifts, as M. Berthollet and feveral other chemists have proved, of 807 parts in 1000 of azot, and 193 of hydrogen. Several experiments, published by Dr Priestley, led the way to this analysis, though he himself did not fee their refult. It is chiefly procurable from animal substances by diftillation, during which procefs the azot and hydrogen necessary to its formation unite in proper proportions: it is not, how ever, procured pure by this process, being mixed with oil and water, and moftly faturated with carbonic acid. To feparate thefe fubftances, it is firft combined with an acid, the muriatic for inftance, and then difengaged from that combination by the addition of lime or pitch. In its greatest degree of purity it can only exift in a gaseous form, at leaft in the common temperature of the atmosphere.

It was at firft obtained chiefly from urine, and was therefore called fal urine; afterwards from horns, especially from thofe of the hert; hence its name, fal cornu cervi, “hart's horn." See CHEMISTRY, Index.

(5.) VOLATILE OILS, in chemistry. See CHEMISTRY, 1182-1198; alfo OIL, § 11. i. The ingenious Dr Thomson defcribes thefe oils as fol lows: (Syft. of Chem. vol. ii. p. 178, &c.) "Volatile oils, called alfo ESSENTIAL OILS, are diftinguished by the following properties. 1. Liquid; often almoft as liquid as water; fometimes vifcid. 2. Very combustible. 3. An acrid taste and a strong fragrant odour, 4. Boiling point not higher than 212. 5. Soluble in alcohol; and imperfectly in water. 6. Evaporate without leaving any stain on paper. By this laft teft it is easy to discover whether they have been adulterated with any of the fixed oils. Volatile oils are almost all obtained from vegetables, and they exist in every part of plants, but are never found in the fubftance of the cotyledons; whereas the fixed oils are almoft always contained in these bodies. When the volatile oils are contained in great abundance in plants, they ́ are fometimes obtained by fimple EXPRESSION. (See OIL, $ 11. ii.) This is the cafe with the oil of oranges, of lemons, and bergamotte. But in general they can only be obtained by DISTILLATION. Others are procured by the distillation of resinous bodies. The greater number of volatile oils are liquid, and fome are as tranfparent and colourless as water. This is the cafe with oil of turpentine. But for the most part they are coloured. Some of them are yellow, as the oil ef lavender; some brown, as the oil of rhodium; fome blue, as oil of chamomile; but the greater number are yellow or reddish-brown. Their odours are so various as to defy all defcription. Their tafte is always acrid, hot, and exceedingly unpleasant. The fpecific gravity of the volatile oils varies from o'8697 to 1'0439. Water diffolves a small portion of volatile oil, and acquires the odour and taste of the oil which it holds in folution. When heated, they evaporate very readily, and without alteration. They are much more combustible than fixed oils, owing to their greater volatility. They burn with a fine bright white flame, exhale a great deal of fmoke, depofit much foot, and confume a greater proportion of the oxygen of the atmosphere than fixed oils. The products of their combuftion are water and carbonic acid gas. From thefe facts it is concluded that they are composed of the fame ingredients as the fixed oils, but that they contain a greater proportion of hydrogen. When expofed to the action of cold, they congeal like the fixed oils; but the temperature necessary to produce the effect varies according to the oil. Some of them, as oil of anife and of fennel, become folid at the temperature of 50°; frozen oil of bergamot and of canella become liquid at 23°; oil of turpentine at 14°. Marqueron exposed feveral volatile oils to a cold of 17. They congealed, or rather cryftallized partially, and at the fame time emitted an elaftic fluid. Thefe crystals confifted partly of the oils themselves, partly of other fubftances. Some of them had the properties of BENZOIC ACID. Volatile oils, when expofed to the action of light in close vessels, and

excluded

excluded from common air, undergo very regular changes. Their colour becomes deeper, they acquire a great deal of confiftency, and their fpecific gravity is much increased. When expofed to the open air, their colour becomes gradually deeper, and they acquire confiftency, while they exhale at the fame time a very strong odour. The air around, as Dr Priestley firft afcertained, is deprived of its oxygen, a quantity of water is formed, and the oils at laft, for the most part, affume the form of refins. Volatile oils diffolve fulphur and phosphorus, and the folutions have nearly the fame properties as those made by fixed oils. They have no action on the metals, and feem scarcely capable of combining with the metallic oxides. They combine only imperfectly, and in small quantity, with alkalies and earths. The French chemifts give these combinations the name of SAVONULES. (See SAPONULE.) They absorb nitrous gas in great abundance, and with great facility, and feemingly decompofe it, acquiring a thick confiftence and a refinous appearance, as if they had abforbed oxygen. SULPHURIC ACID decompofes volatile oils; carbonated hydrogen gas is emitted, and charcoal is precipitated. NITROUS ACID inflames them, and converts them into water, carbonic acid, and charcoal. Oxy MURIATIC ACID converts them into fubftances analogous to refins. Volatile oils are applied to a great number of uses. Some are employed in medicine; fome, as oil of turpentine, are much used to diffolve refins, which are afterwards em ployed as VARNISHES; hot to add their ufe in painting and perfumery."

* VOLATILENESŚ. Į n. f. [volatilité, Fr. from * VOLATILITY. volatile.] 1. The quality of flying away by evaporation; not fixity. Upon the compound body, chiefly obferve the colour, fragility, or pliantnefs, the volatility or fixation, compared with fimple bodies. Bacon.-The volatility of metals. Bacon. The animal fpirits cannot have great subtilty and volatileness. Håle.— The volatility of mercury. Newton.-Oil, which, by reafon of its extreme volatility, exhales fpontaneously. Arbuthnot. 2. Mutability of mind; airinefs; livelinefs.

(1.) * VOLATILIZATION. n. f. [from volatiliae.] The act of making volatile.-Volatilization of the falt of tartar. Boyle.

(2.) VOLATILIZATION is alfo the art of rendering fixed bodies volatile, or of refolving them by fire into a fine fubtile vapour or fpirit, which eafily diffipates and flies away. All bodies, even the moft fixed, as gold, may be volatilized, either of themfelves, or with the admixture of fome volatile substance or spirit, by distillation or fublimation.

*To VOLATILIZE. v. a. volatilifer, French; from volatile.] To make volatile; to fubtilize to the highest degree.-Diffolving and volatilizing the oil. Newton-Spirituous liquors are far from attenuating, volatilizing, and rendering perspirable the animal fluids. Arbuthnot.

VOLCE, or VOLCA, an ancient people of Gaul, who dwelt between the Rhodanus and the Garonne.

VOLCANELLO, a volcanic island of the Me. Hiterranean, Between those of Lipari and Volcano.

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VOLCANIC, adj. Of or belonging to, or par taking of the nature of a volcano, or of the lava or other produce of one.

(1.)*VOLCANO...[Italian, from Vulcan.] A burning mountain.→Many volcanoes and fiery hills. Brown.-From the volcano grofs eruptions rike. Garth.-Furious eruptions of volcanoes. Bentley. Why want we then encomiums on the form, Or famine, or volcano ?

Young. (2.) VOLCANO, the largest of the LIPAL ISLANDS, in the Mediterranean; fo named from its chief mountain, which is a volcano, and has been ascertained to have been burning fince the time of the Roman republic; being taken notice of by Pliny, Eufebius, and other ancient authors. Fazzell, a Sicilian author, gives a particular defcription of it. It lies S. of the ifle of LIPARI from which it is feparated by a channel 11⁄2 miles broad. It is 12 miles in circumference.

(3.) VOLCANO, another volcanic island, in the S. Pacific Ocean, 24 miles from Egmont. Los. 16. 4. E. Lat. 16. 17. S...

(4.) VOLCANO is a name given to burning mountains, or to vents for fubterraneous fires. The number of volcanoes with which we are at prefent acquainted is very confiderable, not much lefs than 1oo. In Europe there are Ætna, Vefuvius, Hecla, Stromboli, Volcano; in Afia, one in Mount Taurus,' three in Kamtfchatka, five in Japan, two in the Philippines, and a great number more scattered through the islands in the South Sea; in Africa, one in Fez, one in the inland of Bourbon, one in Fuego, one of the Cape Verd inlands; and in America, feveral in the Andes, Morne Garou in St Vincent, and two discovered by Captain Cook on the W. coast of N. America. There are others, but these are best known. It is remarkable, that all the volcanoes with which we are acquainted, four or five perhaps excepted, are fituated at a small distance from the fea. Moft of them have been burning from time immemorial; fome few, however, have burst out in our time. Volcanoes all occupy the tops of mountains; we find none of them in plains: fome of them indeed, which are fituated in the ocean, do not rife much above the furface; but even thefe volcanoes feem to be the apices of mountains, the greater part of which are covered by the fea. The fubftances ejected by volcanoes are fixed and inflammable air, water, afhes, pumice-itonés, stones that have undergone no fufion, and lava. The phenomena which take place during the eruptions of volcanoes have been so fully defcribed under the articles ÆTNA,ÉTNA, HECLA, ICELAND, and VESUVIUS, that any repetition here would be improper. Al that remains, therefore, is to mention the opinions of philofophers concerning the caufes of volcanoes; for the real caufe, we are afraid, after all that has been done, remains ftill unknown. The most elaborate theory that has yet appeared is that of M. Houel.

(5.) VOLCANOES, THEORIES OF. According to him, water is neceffary for the formation of vol canoes. All volcanoes are near the sea; they are even extinguished when the sea retires from them; for we can ftill perceive the craters of volcanoes in feveral lofty inland mountains, which difcover what they have been formerly. He supposes that

a long

a long feries of ages was neceflary for the formation of a volcano, and that they were all formed under the furface of the fea. The firft explofion which laid open the foundations of the deep, a would poffibly be preceded by an earthquake. The waters would be parted by a vaft globe of burning air, which would iffue forth with a tremendous noife, opening at the fame time a large and wide vent for the immenfe flame that was to follow; and which, as it iffued from the bottom fo of the fea, would be spread over its furface by the firft gufts of wind which followed. A fire which was to burn through thousands of years, could not be faint or feeble when it was firft lighted up. Its firft eruptions therefore have undoubtedly been very violent, and the ejected matter very copious. For a long feries of ages it would continue to difcharge torrents of lava from the bosom of its naective earth, and its first crater would be compofed of the fragments of the fame earth. Thus, according to our author, the foundations of the burning mountain would be laid in the bottom of the sea; and even then it would have an hollow cup or crater on the top fimilar to that which is to be found on all volcanoes at prefent. But the queftion now very naturally occurs, by what means was the internal fire preserved from extinction by the waters of the ocean, which muft thus have been incumbent upon it? To this he replies that "The fire, having difpofed the fubftances in fufion to make an eruption, next laid open the earth, and emitted as much matter as it could difcharge, with force fufficient to overcome the refiftance of the column of water which would oppofe its afcent; but as the strength of the fire Ndiminished, the matter discharged was no longer expelled beyond the mouth; but, by accumulating there, foon closed up the orifice. Thus only fmall orifices would be left, fufficient for giving vent to the vapours of the volcano, and from which only fmall bubbles of air could afcend to the furface of the water, until new circumftances, fuch as originally gave occafion to the eruption of the volcano, again took place in the bowels of the earth, and produced new eruptions either through the fame or other mouths. The appear. ance of the fea over the new formed volcano, in its state of tranquillity, would then be fimilar to what it is betwixt the islands of Bafilizzo and Pariaria. Columns of air-bubbles are there afcending at the depth of more than so feet, and burft on their arriving at the furface. This air would continue to difengage itself with little disturbance as long as it iffued forth only in finall quantity, until, at the very inftant of explofion, when prodigious quantities, generated in the burning focus, would make their way all at once; and the fame phenomena which originally took place would again make their appearance." A volca no, while under water, cannot act precifely as it does in the open air. Its eruptions, though equally ftrong, cannot extend to fo great a diftance. The lava accumulates in greater quantity Found the crater; the fands, afhes, and pozzola. no are not carried away by the winds, but are depofited around its edges, and prevent the marine fubftances which are driven that way by the waters from entering. Thus they agglomerate with VOL. XXIII.

чере

thefe bodies, and thus a pyramidal mount is form ed of all the materials together. In this manner Mr Houel fuppofes that the mountain was gradually raised out of the fea by the accumulation of lava, &c. at every eruption, and that the cavern of the volcano was gradually enlarged, being driven down into the bottom of the cavern by the continued action of the ftones which the volcano is conftantly throwing up; that it was there fufed, and at laft thrown out at the top of the mountain to accumulate on its fides. Mr Houel's opinion about the volcanic fire we shall give in his own words. "We cannot form any idea of fire fubfifting alone, without any pabulum, and unconnected with any other principle. We never behold it but in conjunction with fome other body, which nourishes and is confumed by it. The matter in fufion, which iffues from the focus, is but the incombustible part of that which nourishes the fire, and into the bofom of which that active principle penetrates in search of pabulum. But as the fire acts only in proportion to the facility with which it can diffolve and evaporate, I am of opinion, that it is only the bottom of the volcano on which it acts; and that its action extends no farther than to keep thefe fubftances which it has melted in a conftant ftate of ebullition. That fufible matter being discharged from the mouth of the volcano, and hardening as it is gradually cooled by the ac tion of the air, produces that fpecies of ftones which are diftinguished by the name of lavas. This lava, even when in the focus, and in a state of fluidity, muft alfo poffefs a certain degree of folidity, on account of the gravity and denfity of its particles. It therefore opposes the fire with a degree of refiftance which irritates it, and requires, to put it into a ftate of ebullition, a power proportioned to the bulk of the mafs. That quantity of matter, when diffolved by the action of the fire, muft conftantly refemble any other thick fubftance in a state of ebullition. Small explofions are produced in various parts over the furface of every fuch fubftance, while in a state of ebullition; and, by the bursting of thefe bubbles, a great number of fmall particles are fcattered around. This is the very procefs carried on in the focus of a volcano, though on a scale immensely more large; and the vast explosions there produced expel every body which lies in their way with the utmost violence; nor is there any piece of laya which falls down from the upper part of the arch of weight sufficient to refift this violent centrifugal force. No estimate can be made of the power of these explosions, but by obferving the obstacles they overcome, and what enormous bodies are raifed up and thrown to an immense height and distance. Such vaft pieces of lava are to be feen on the top of Vefuvius and Lipari, that the projectile force by which they have been thrown out appears altogether incredible. No perfon can harbour the leaft fufpicion of their having been laid there by any human power; and the appearance of them demonftrates that they have been ejected from the bottom of the volcano, not in a ftate of fufion, but coherent and folid. A piece of lava lies on the top of tna of more than a cubic fathom in bulk, and whofe weight therefore cannot be less than 16 tons. What an ama

B

zing

zing force then muft it have required, not only to raife this enormous mafs from the volcanic focus, but to make it defcribe a parabola of about a league in diameter after it had come out of the crater! When we confider how much the volcanic focus is funk below the base of the mountain, that the mountain itself is 10,000 feet high, and that confequently there must have been a power fufficient to raife fuch a mafs 12,000 feet perpendicular, the boldeft in agination must be loft in amazement. This may ferve to give us fome idea of the nature of that power which operates in the foci of volcanoes; a power which is unknown and inconceivable, and may jufily be reckoned among the mysteries of nature.' "The pabulum by which the internal life is fupported, Mr Houel thinks to be fubftances contained in the mountain itfelf, together with bitumen, fulphur, and other inflammable materials which may from time to time flow into the focus of the volcano in a melted state through fubterraneous ducts, and the explosions he afcribes to water making its way in the fame manner. The water is converted into ftem, which fills the cavern and pushes the melted lava out at the crater; this opinion is corroborated by the copious fmoke which always precedes an eruption. But, combined with the water, there is always a quantity of other fubftances, whofe effects precede, accompany, or follow the eruptions, and produce all the various phenomena which they difplay. The eruption of water from Etna in the year 1775 proceeded undoubtedly from this caufe. The fea, or some of the refervoirs in Etna or the adjacent mountains, by fome means difcharged a vast quantity of water into the focus of the volcano. That water was inftantly refolved into vapour, which prefently filled the whole cavern, and iffued from the mouth of the crater. As foon as it made its way into the open atmosphere, it was condensed again into water, which streamed down the fides of the mountain in a dreadful and deftructive torrent. Thus we have given a view of Mr Houel's theory, according to which volcanoes originally began at the bottom of the fea; and not only the mountain, but all the adjoining country, was formed by. fucceffive eruptions. It is rather a theory of mountains raised by fubterraneous heat than of volcanoes, and does not attempt to explain the origin of the fire, which is the principal difficulty; neither does his theory account for the immenfe height to which matters are fometimes thrown during eruptions. This indeed it is impoffible to account for, without fuppofing that the refiftance of the air is diminished. The exceffive oppofition of the atmosphere to bodies moving with very great degrees of velocity has been taken notice of under the article PROJECTILES. If it has fo much effect then upon folid and round globes of iron, what ought it to be on irregular maffes of rock, or streams of liquid lava? Nevertheless, in the great eruption of Vefuvius in 1779, Sir William Hamilton informs us, that a vaft ftream of lava was projected to the height of at leaft 10,000 feet above the top of the mountain. Had the air relifted this liquid matter as it does a cannon-all, it must have been dafhed in pieces almoft as foon as it iffued from the crater. Either

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the extreme heat of the lava, therefore, or fome other caufe, muft have contributed very much to diminish, or rather, in a manner to annihilate the refiftance of the atmosphere at that time. As for the lighter materials, though they may be suppo fed to be carried to a vaft diftance by the wind, after being projected to a great height in the air, it is inconceivable how their motion was not fud. denly stopped, and they scattered all around the top of the volcano by the violence of the blaft. Subftances of this kind, when quietly carried up with smoke, will indeed fly to a great diftance; for we are affured, that the ashes of the great fire at London in 1666 were carried by the wind to the diftance of 16 miles. It is therefore the lefs incredible, that thofe of the great eruption of Vefuvius in 1779 fhould be carried to the diftance of 100 miles, as we are informed was the cafe. To account for the volcanic fire, Dr Woodward and others have had recourfe to the hypothefis of a central fire, to which the volcanoes are only fo many chimneys or fpiracles. Dr Hutton, in his theory of the earth, adopts the fame opinion; but as it did not immediately concern the subject of which he treated, he evades any question concerning its origin, by declaring himself fatisfied of its exiftence without any inquiry into its ori gin. Others, as Dr Lifter, have had recourse to the well known experiment of the fermentation of fulphur and iron, which will take fire when mixed in confiderable quantity, and moistened with water. Pyrites, therefore, which are a natural mixture of these two fubftances, it is fuppofed, may naturally give rife to volcanoes. Inftances are indeed adduced, which undeniably prove that thefe fubftances will spontaneously take fire when thrown together in large heaps. Beds of pyrites, therefore, taking fire in the earth by means of a fermentation occafioned by water, are now generally fuppofed to be the cause of volcanoes; and the obfervation, that volcanoes are generally near the fea, is thought to confirm this hypothefis. When the matter is properly confidered, however, it must be evident, that neither of these hypothefes can answer the purpose. The central fire of Dr Woodward and others is à caufe too magnificent even for volcanoes. If any fuch fire is fuppofed, we muft imagine a burning globe in the centre of the earth, whofe heat is fufficient to vitrify the moft folid and refractory terrestrial substances. But of what dimenfions are we to suppose this globe? Is it one, two, three, four, or more thoufands of miles in diameter ?-Very large indeed it muft be; for we could fcarce suppose that ftones could be projected even from the depth of 500 miles into the air. But even this fuppofition is inadmiffible for as the fire of volcanoes is at times exceedingly augmented from fome cause or other, were this caufe general, as it must be in cafe of a burning central globe, the whole num ber of volcanoes exifting on earth would be in a ftate of eruption at once. Befides, if we were to fuppofe a burning globe of 7000 miles in diameter to fuffer the leaft dilatation throughout its vaft bulk, which must be the undoubted confequence of an augmentation of heat from any unknown cause, all the volcanoes in the world would not be fufficient to give vent to it, though they should spout

forth