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which it has been preserved in a warm room, a slow and gradual, but partial annealing has taken place.
Prince Rupert's drops are so called from thenhaving been first brought to England by Prince Rupert, and exhibited before Charles I. in 1661. They are also called lacrym<e virtete or glass tears. When melted glass is allowed to drop into water it forms a globular portion at one extremity, and gradually tapers into a small tail at the other. (Fig. 48.) The greater number burst in the water, but those which remain entire exhibit all the properties of unannealed glass in a high degree. They will bear a smart stroke on the thick end without breaking, but if a small piece be snapped off from the tail, the whole will burst into powder with a smart F•)■1*crack. Under the exhausted receiver of an air-pump they appear to explode with more violence than in the air, and the powder is finer. If the Bologna phial or these drops be cautiously heated and slowly cooled, these peculiar properties are lost.
There are a few substances in nature which increase in bulk in passing from the fluid to the solid state; water and glass are examples. When glass is allowed to cool slowly, its particles arrange themselves in such a way as to form a fibrous texture, producing an elastic substance, and one susceptible of long continued vibrations; but when a quantity of melted glass is snddenly cooled, the surface first crystallizes and forms a solid shell or coating round the interior fluid parts, thereby preventing them from expanding as they become solid. This causes them to be compressed together with little mutual cohesion. Thus in the Prince Rupert's drops it is evident to the eye that the inner substance is cracked and divided into a multitnde of detached parts, held together by the smooth external coat. These internal particles tend to press outwards so as to occupy more space, but are prevented from doing so by this external coat. In consequence of this effort to expand, the greater number of glass drops burst in cooling; those which remain entire may have a thicker external coat than those which burst; they will bear a smart stroke upon them, because each drop on being struck vibrates as a whole, and does not transmit its vibrations from the exterior to the interior; but if the tail be broken off, a vibratory movement is communicated along the crystalline surface without reaching the internal parts; this allows them some expansion, and thus overcoming the cohesion of the thin outer shell, the glass is burst and dispersed in powder. In unannealed glass vessels, such as a drinking glass, the same thing occurs. If such a vessel be struck or thrown into vibration, the vibrations may continue for a considerable time before the internal parts overcome the resistance. If the vessel be thin, the regular crystallization of the surface may extend through the whole thickness, or the quantity of compressed matter in the middle may be 30 small as to be incapable of bursting the external crust. It often happens that a wine glass or other article of irregular
form breaks in cooling, simply from its unequal contraction at different parts.
Some writers regard the external crust as a hollow arch enclosing a quantity of loose materials, and the effect of scratehing this crust or breaking off a portion of it, to be the same as snddenly pulling out one of the voussoirs, whereby the whole system falls to pieces.
In the process of annealing, glass is kept during many hours in a state approaching the fluid; the heat increases the bulk of the outer or crystalline portions, and renders it so soft that the interior parts car. expand and crystallize regularly. Mr. Pellatt has shown experimentally that a re-arrangement of particles does occur in annealing. Two pieces of the same length of tube, each 40 inches long, were the subject of trial. One piece that was sent through the leer, contracted Tv of an inch more than the other which was cooled as in the open air. The Editor has also noticed that the fragments of a Bologna phial when put together do not fit, as the fragments of annealed glass do.
Lamp glasses, tubes for steam gages, and similar articles which are exposed to sndden transitions of heat and cold, may be more perfectly annealed than is done in the glass-house, by placing them in a vessel of cold water, and raising it slowly to the boiling temperature, and keeping the articles for some hours at that heat, and then allowing the whole to cool very slowly. Articles of flint-glass which have to be cut are, when found to be imperfectly annealed, subjected to this process, which is found preferable to passing them a second time through the leer. A lamp-glass is much less exposed to fracture after it has been once used, because the heat, if not too snddenly checked, completes the annealing.
The process of annealing is extensively employed for softening the malleable metals, which, under the action of the hammer or of the roller, have gradually increased in hardness and elasticity and in density from the close approximation of their particles. Steel often becomes remarkably hard and dense in the process of hammer hardening, or hardening without heat, which is frequently the only means of hardening some kinds of steel springs. In some descriptions of steel goods, which are formed by the hammer and then required to be filed into shape, as in scissors, or teeth to be cut as in files, the metal is softened by annealing. So also in the process of wire-drawing, the metal is greatly increased in hardness and elasticity, which if not removed from time to time by annealmg, would prevent the extension of the wire, and render it too brittle to be applied to any useful purpose. In rolling or flattening metals, the working and annealing are alternately repeated until the sheet reaches its limit of tenuity. The brazier who forms vessels of copper and brass solely by the hammer, can work on them only for a short time before they require annealing.
Articles of iron and steel are sometimes annealed by piling them in an open fire, and raising them slowly to a red heat: they are then left to cool gradually. This method is injurious on account of a scale of oxide which forms on the surface, thereby depriving the steel of a portion of its carbon, which confers the property of imparting a keen edge, so essential to cutting mstruments. Articles of iron and steel ought to be annealed in close vessels, or in a trough or recess made of fire brick, and covered up with ashes or clean sand; or if a small vessel be employed, the cover may be of the same material as the vessel. The oven or trough is heated by the flame of a furnace passing under and round it until the whole is at a red heat. It is then allowed to cool without letting in the air. Goods thus treated become softer than by the common method, and the surfaces have a metallic whiteness imparted by the carbonaceous matter of the ashes. Annealed goods lose their brittle character so that they can be bent without breaking. The fracture before being annealed is smooth and short; after that process it is rough, and exhibits bright parts of a crystalline appearance. Copper and brass suffer less from being annealed in an open fire than iron and steel: but a close vessel is necessary in order to preserve their metallic lustre. Very small brass wire is sometimes annealed by holding it in the flame of burning hay and straw.
Soft metals, such as tin, lead, and zinc, after being hardened by hammering may be softened by the action of boiling water. Most of the hard metallic alloys when made red hot, suffer no great change whether they be snddenly quenched in water or not. Pure hammered iron after annealing becomes equally soft whether it be cooled snddenly or slowly; but some inferior kinds of iron become hard by immersion in water. Steel receives by sndden cooling that extreme degree of hardness, combined with tenacity, which adapts it beyond every other material for cutting tools, especially as it admits of being regularly graduated from extreme hardness to the softest state when subsequently heated or tempered. The following are a few examples of the method of treating steel, so as to produce extreme hardness, and ending with the reverse condition. A thin heated blade worked between a cold hammer and anvil, or other good conductors of heat, becomes perfectly hard. A thicker piece of steel cooled by exposure to the air on the anvil becomes rather hard, but not too hard to be filed. When it is placed on cold cinders, or other bad conductor of heat, it becomes softer; but it becomes softer still when placed in hot cinders, or within the fire, and allowed to cool, by gradual extinction. When the steel is encased in close vessels with charcoal powder, and raised to a red heat, and allowed to cool in the furnace, it assumes its softest state; uuless, indeed, it be made to undergo partial decomposition by enclosing it in a close vessel with iron turnings or filings, or with the scale from the smith's anvil, or with lime or other matters which attract carbon from its surface; this reduces it to the state of pure soft iron. Some descriptions of cast-iron may be made as hard as the hardest steel, forming what are called chilled iron castings. The reverse process is annealing with partial decomposition; this forms what is called
malleable iron castings, and the process is so successful that cast-iron nails may be clenched. The purest iron, and most varieties of cast-iron may be superficially converted into steel by a process called Case-hardening. For further particulars on this interesting subject we must refer to Hardening And Tempering.
The change which is produced by annealing is not well understood. Most of the malleable metals assume two distinct forms; one crystalline, which is the result of slow cooling, and the other fibrous, which is brought about by hammering or rolling. If hammered or rolled beyond a certain point, the metals become so hard that they cannot be bent without breaking. If annealed beyond a certain point the metals become crystalline. Thus, zinc may be drawn into a very flexible and tenacious wire, but if kept in boiling water too long it resumes its original brittleness, and displays a crystalline appearance when broken. The particles of the metal change their arrangement without altering the external form, and this change may be brought about in various ways; thus, brass wire loses its tenacity by exposure to the fumes of an acid, and even by air acting on its surface in a damp atmosphere. Henee it is necessary to preserve wire, such as is used in the manufacture of pins, in a dry air or under the surface of water.
ARNOTTO. Annotta, a red colouring matter obtained from a plant (Bixa orellana), Fig. 49,
common in the West Indies, where it is extensively cultivated on the banks of rivers, sometimes giving its name to the district, as Annotta Bay, on the northern coast of Jamaica. The arnotto plant is a small tree with deep-green, shining leaves, and clusters of purplish flowers. These arc succeeded by bristly heart-shaped capsules, or seed-pods, containing numerous seeds covered with a soft, sticky rind of a bright red colour. It is a thick extract of this rind made into cakes and balls, which forms the arnotto of commerce. The cakes are usually of two or three pounds weight each, and arc packed in casks with large flag leaves, hcnce the term flag arnolto. A superior kind, called roll arnolto, is a harder and more concentrated extract, of which but little is imported. The colour obtained from fresh pods of the plant is much superior to that of either of these preparations, leading to the conclusion that the method of preparing them, which is by a high degree of heat and fermentation, is injurious to the colour. cover, which is luted on, and a lute is also applied to the j unction with the lower vessels. Heat from wood fuel is then applied, and after some hours firing the stony portion of the ore is left in the top crucibles, while the bottom ones contain the sulphuret which is known in commeree as crude antimony. In some works a small cireular furnace is used for heating the crucibles which contain the ore, and the recipients being placed on the outside, the fused sulphuret flows into them by a channel which connects the two together. By this means the furnace can be worked constantly, whereas by the former method the cooling of both crucibles occasions a waste of fuel. The arrangement will be understood from Kg. 51.
Arnotto dissolves entirely in water or milk, and is much used in colouring cheese and butter in England and Holland, the colouring matter being diffused in the milk previous to the manufacture. The Spaniards employ this substance in colouring and flavouring their chocolate and soups, esteeming it wholesome and stomachic. Dyers obtain from it the reddish colour called aurora. The liquid sold under the name of Nankin dye is a solution of arnotto in potassa, and pure water. A solution is also made in aleohol, and used in varnishing and lacquering. The Indians paint their persons with a mixture of arnotto, gum, and lemon-juice, as a preservative against the attacks of insects. Arnotto also has a fabulous reputation of being an antidote to the poison of the cassava root, which has fatal properties when raw, although, when cooked, it is a wholesome food. The consumption of arnotto in Great Britain has greatly increased of late years. In 1820, it amounted to but little more than 50,000lbs.: three or four times that quantity is now imported. The botanical position of the arnotto plant, is in a small group of tropical plants, called bixads, now inclnded by Lindley in the natural order Flacourtiaceve.
ANTHRACITE, [See Coal.]
ANTIMONY is a metal discovered by Basil Valentine, a monk of Erfurth, and an alehemist of the fifteenth century. It is related that having thrown some of it to the hogs it purged them violently, after which they became fat; and thinking that his brother monks might derive benefit from a similar dose, he administered it; but the effects were fatal, for the monks died; hence the medicine was called anti-moine or anti-monk. The ancients appear to have been acquainted with some of the compounds of this metal,' which Pliny names stibium, a word still used to express the metal, or in chemical symbols Sb. Its equivalent is 129.
Metallic antimony has a distinct platy, crystalline structure, and by particular management may be obtained in crystals which are rhombohedral; this metal has a bluish white colour, and a strong lustre; it is very brittle, and can be easily reduced to powder. Its specific gravity is 6.8. It melts at a temperature just short of redness, and boils and passes off in vapour at a white heat. It has a peculiar taste and smell, especially in the state of vapour. Antimony is not oxidized by the air at common temperatures; but when strongly heated it burns with a white flame, producing an oxide which often forms beautiful
(1) The sulphuret was used by the ladies of Rome as a cosmetic for painting the eyebrows and the edges of the eyelids. The smoke-black of a kind of resin, or oY the shells of almonds, is now used for the purpose by females in the East.
crystals. If a globule of antimony melted at tho blow-pipe be thrown upon a sheet of paper or a board, it sparkles and bursts into a number of small spheroids, which remain hot for a considerable time, and move about the paper leaving traces of oxide behind them. There are three compounds of antimony and oxygen, viz., the oxide, antimonious, and antimonic acids. These acids combine with bases forming salts, which are distinguished as antimonites and antimoniates.
Antimony is dissolved by hot hydrochloric acid with evolution of hydrogen, and the production of a chloride formerly called butter of antimony, a substance sometimes used with sulphate of copper for bronzing gun-barrels, the iron decomposing the chloride, and depositing a thin film of antimony on its surface. Nitric acid oxidizes antimony into antimonic acid. Sulphuric acid has scarcely any action on it.
Antimony is found in many parts of Europe, but the mines of this metal are not numerous; it occurs native in Sweden, in France, and in the Hartz; but its principal ore is the sulphuret, which occurs massive and crystalhzed. There are several varieties, of which the most common is the radiated. This is of a grey colour, brittle, and frequently crystallized in four and six-sided prisms. The sulphuret is associated with quartz, sulphate of baryta, and carbonate of lime, from which it is separated by fusion; a method of purification analogous to the mechanical preparation of other ores, but on account of the great fusibility of the sulphuret of antimony this separation is accomplished by means of heat. For this purpose the ore is placed in large crucibles, C C, (Fig. 50,) perforated with a number of small holes in
In the department of La Vendde, in France, this method is improved by heating the ore on the concave sole of a reverberatory furnace. This sole is formed of clay and chareoal, and communicates with a recipient outside by means of a channel, the upper extremity of which is stopped with ashes during the melting. The charge consists of 7 or 8 cwt. of the ore, and each tapping yields about 4 cwt. of crude antimony, which is about 50 per cent: in other places the yield is not more than from 30 to 40 per cent. Wood is the fuel employed.
When sulphuret of antimony is roasted in contact with the air, oxide of antimony is formed, which unites with that portion of the sulphuret which has not been decomposed. In this way several oxysulphurets are formed, which melt, and yield in cooling some brown vitreous substances, which are known in commeree as glass of antimony, licer of antimony, or crocus. Glass of antimony consists of 8 parts of oxide and 1 of sulphuret. It is transparent, and of a reddish yellow colour. Crocus contains 8 parts of oxide and 2 of sulphuret; it is opaque, and of a yellow-red colour. Liver of antimony is opaque, and of a deep brown colour; it consists of about 4 parts sulphuret and 8 parts oxide.
The reduction of the crude antimony to the metallic state is attended with some difficulty, for antimony is a metal sufficiently volatile to occasion great loss, but not volatile enough to pass over by distillation. The first process in the reduction is to roast the crude antimony at a very moderate heat, whereby, in 100 parts, 86 parts ought to be converted into protoxide, and the sulphur disengaged, to be converted into sulphurous acid; but in practice not more than about 60 or 65 parts of the protoxide are obtained. These 65 parts are next mixed with 8 or 10 parts of chareoal-powder, sprinkled with a strong solution of carbonate of soda. The mixture is placed in crucibles, and kept at a good red heat until the fusion is complete. By this process regulus of antimony is pro
duced, while the scoriae consist of a double sulphuret of antimony and sodinm. The object of the carbonate of soda is to reduce a portion of the sulphuret of antimony by forming sulphuret of sodinm, which combines with the remainder of the sulphuret of antimony in such a way as to cause it to collect in the scoriae.
From the crucibles the metal is run into hot and greased moulds; but it is not as yet sufficiently pure to assume the crystalline form so much prized in commeree. It is remelted, with a portion of the scoriae obtained in previous reductions, together with a certain proportion of the roasted mineral. The result of this second process is the production of an increased quantity of scoriae and the purification of the metal.
Of the 65 parts of roasted sulphuret 45 parts of regulus are obtained in the first fusion, and this quantity is reduced to about 42 in the second; or, in other words, 100 parts of sulphuret of antimony, which ought to produce 73 of regulus, actually produce only 40 or 44. A portion is lost by volatilization, and another portion remains in the scoriae. The scoriae is known in commeree as crocus or kcrmes, and is used in veterinary medicine. It consists of sulphuret of antimony and alkaline sulphuret.
As iron combines readily with antimony, the sulphuret is sometimes reduced by heating it in contact with iron filings: as the iron tends to unite with the antimony, when in excess, an atom and a half of iron is employed to each atom of sulphuret of antimony, or 45 parts iron filings to 100 parts sulphuret of antimony.
M. Dumas states that many manufacturers keep their processes secret, which sufficiently accounts for the defective state of this branch of metallurgy; for, had they been tnrown open to scientific chemists, they would have been investigated and improvea.
In some smelting-houses there is a loss of regulus amounting to 33 per cent., and a much larger expenditure of fuel than is necessary. The secret consists in giving to the surface of the ingots a beautiful stellated appearance, which the alehemists formerly regarded as a mysterious guide to the secrets of transmutation, and which is now valued in commeree as an indication of superior purity in the metal. But it is well known that when pure antimony is cooled very slowly, in a still place, the crystallization is always very beautiful; and these conditions suffice to account for an appearance the importance of which is exaggerated by the manufacturer.
Antimony combines with the other metals, and renders them brittle; and, as this effect was especially remarked in the case of gold, the alehemists distinguished it by the title of regulus, or the little king, from its power of ruling over the noble metal, and destroying its malleability. The chief alloys of antimony are type-metal, consisting of 4 lead and 1 of antimony; stereotype-metal, 6 lead and 1 antimony; music-plates, consisting of lead, tin, and antimony; Britannia-metal, consisting of 100 parts tin, 8 antiniony, 2 bismuth, and 2 copper. Petcter is sometimes formed of 12 parts tin and 1 part antimony. Antimony is also used in medicine, its two most important compounds being antimonial powder and tartar-emetic: the former, also called James's powder, is said to consist of 43 parts phosphate of lime and 57 oxide of antimony; the latter is a tartrate of potassa and antimony. Antimony is also used in the preparation of some enamels and other vitreous articles.
Great Britain receives the larger portion of its supply of antimony from Singapore, which receives it from Borneo. It is imported in the shape of ore, and commonly as ballast.
ANVIL. An instrument on which malleable metals are placed during the process of hammering. Anvils are sometimes made of cast-iron, but when required to be very hard or bright they are made of wrought iron and faced with steel. In such case the core or body is prepared at the forge, by welding together a number of rude blocks of iron. When the core is rudely shaped, three square holes are made ia it, one in the bottom and one at each side, for the purpose of receiving a bar of iron connected with a crane near the forge, by which the anvil is held in the fire, and turned about while being forged. The common smith's anvil consists of seven pieces:— 1, the core, or body; 2, 3, 4, 5, the four corners for enlarging the base; 6, the projecting end, containing a square hole for the reception of a set or chisel in cutting pieces of iron; and 7, the beak, or conical end, which is used for turning pieces of iron into a cireular form, for welding hoops, &c. All these pieces are separately welded to the core. When the anvil is of large size two hearths are used, in one of which the core is raised to the welding heat and in the other the piece. They are then taken out and welded together by rapid hammering until they cohere. The whole is then heated again, and hammered until the proper shape is obtained.
The best anvils are faced with steel. This steel facing is shaped, heated, and laid on the anvil at a welding heat, the facing, however, being less heated than the anvil, and hammered rapidly until it is closely united: the whole is then finished by repeated heatings and hammerings. The anvil is next hardened by raising it, but especially the face, to a full red heat, and quenching it in a large quantity of cold water. It is of importance to cool it rapidly, and for this purpose a stream of water is to be preferred. In this process the steel facing will sometimes crack, unless it is thin. Should the hardening be successful, the facing is ground until it is perfectly even, and the edges are made sharp or round as required. When the anvil is to be used for planishing metals, it is polished with emery and crocus.
The smith's anvil is generally placed on a loose wooden block, such as the root end of an oak tree. Anvils used for cutting and for files are inserted into large blocks of stone. The more firmly the anvil is connected with the earth, the more effective is the blow of the hammer.
Locksmiths use a smaller kind of anvil called the stake, which is moveable, and is usually placed on the work-bench. It is used for setting small cold work straight, or for cutting or punching on with the cold chisel, or cold punch.
AQUA FORTIS. A common term, first applied by the alehemists to dilute Nitric Acid, on account of its strong corrosive action on many animal vegetable, and mineral substances.
AQUA REGIA. A term applied by the alehemists to a mixture of nitric and hydrochloric acids: it has the property of dissolving gold, which neither of the acids possesses separately. Two parts of hydrochloric and one of nitric acid are most effective. A partial decomposition of both acids takes place, and water, chlorine, and nitrous acid are the result. When a metal is placed in aqua regia it absorbs the chlorine, and is dissolved. This acid is the common solvent of gold and platinum.
AQUEDUCT, a conduit or channel for the conveyance of water, from the genitive case of aqua, water, and ductus, a conduit; hence the old method of spelling this word, Aquceduct, is more correct than the present. According to this derivation, any pipe or channel for the conveyance of water is an aqueduct; but the term is usually limited to those structures of masonry which are elevated above ground for the purpose of conveying a stream of water in a regular but slightly descending current across valleys and over plains.
An abundant supply of pure and wholesome water is essential to the health and prosperity of every town and city, and accordingly we find that in all ages and countries special provisions have been made to secure so desirable an object. The ruins of the aqueducts constructed in Palestine in the reign of Solomon still remain, and travellers describe the Pools of Solomon in connexion with a scheme for supplying Jerusalem with water. In the ruined cities of Central America, which still excite the astonishment of the traveller, the remains of aqueducts are also found; but of all the ancient aqueducts those of the Romans are most caleulated to excite admiration, constructed as they were to pour into the city whole rivers of water for the use of the public baths, fish ponds, artificial lakes, gardens, villas, and private houses within and around the city. Some of these aqueducts extended thirty, forty, and even sixty miles from the city, in one continuous covered channel of stone, which was carried by means of areades over the widest and deepest valleys, and by tunnels for miles through mountains and the solid rock. It is indeed a matter of painful regret that with our vastly increased engineering skill and improved means, the metropolis of a powerful nation like Great Britain should continue to languish and to suffer disease and misery, for want of an abundant supply of pure water.
Our knowledge of the aqueducts of ancient Rome is derived as well from repeated surveys of the stupendous ruins which still exist, as from a special treatise on the subject by Frontinus, who was