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ASBESTUS. AMIANTHUS. A mineral substance in which long capillary crystals are arranged in a fibrous mass. Several varieties of hornblende are of this kind, the most beautiful being the flax-like variety, called Amianthus, or mountain-flax. The term Asbestus signifies indestructible, while Amianthus means unstained, in allusion to the fact that this mineral is neither destroyed nor sullied by passing through fire. Veins of Asbestus occur in serpentine in Cornwall, and in micaceous slate at Glenelg in Inverness. In Upper Saxony, Silesia and Switzerland, Asbestus is found in veins of serpentine; in Bohemia, in metalliferous beds, accompanying magnetic iron-stone; in Dauphiny, in gneiss and mica slate.
The long and silky fibres of Amianthus have been woven into a fire-proof cloth, which in the mass is capable of resisting flame, though a single fibre would soon be reduced to a white enamel. The ancients were acquainted with the art of making this indestructible cloth, and used it to wrap the bodies of the illustrious dead on the funeral pile, that their ashes might not mix with the ashes of the wood. In the year 1702, an asbestus shrond, containing ashes and burnt bones, was discovered in the Vatican at Rorne. The scarcity and high price of this material caused its use to be confined to the richest families. It is said that Charlemagne had a tablecloth of amianthus, which he would sometimes throw into the fire, after dinner, to the great astonishment of Ins guests. Pliny says, that napkins made of this substance were better cleansed by throwing them into the fire than by washing. By the help of gloves made of asbestus, or amianthus, red-hot iron may be safely handled, or the hand may be placed in the midst of flames with impunity. Advantage has been taken of this circumstance, not only to perform various clever tricks, but for the more important purpose of saving human life. The art of making fire-proof cloth was revived by the Chevalier Aldini of Milan, and by him applied to protective uses. It was he who arranged and contrived the fire-proof dress, which enabled its wearer to walk amidst the flames unhurt. Clothing several firemen with these dresses, he caused them to go through various experiments to prove the efficacy of the apparatus, and to inspire them with confidence. They carried bars of red-hot iron, walked over iron-gratings through which the flame of fagots ascended, or plunged their heads into a fire of shavings, kept burning in a large raised chafing-dish. The firemen's dress, as invented by Aldini, consisted of cap, gloves, and stockings of asbestus cloth, while the body was covered with strong cloth steeped in a solution of alum. Outside this was a metallic dress of iron-wire gauze, with a casque or cap, and a mask for the face. The asbestus cap, likewise, covered the face down to the neck, having suitable perforations for the eyes, nose and mouth.
The art of weaving amianthine cloth was anciently accomplished by weaving fibres of flax with those of amianthus, and then passing the cloth through a
furnace, by which means the flax was destroyed, while the fire-proof material remained; but Aldini contrived to weave a much stronger cloth without the aid of any foreign substance. The fibres are prevented from breaking by the action of steam, the cloth is made loose in fabric, and the threads are about the fiftieth of an inch in diameter.
ASHLAR. A term applied by builders to the common or free-stones of various sizes as they come from the quarry. This term is also applied to the facing of thin squared stones on the brick and rubble walls of buildings. When the work is smoothed or rubbed so as to take out the marks of the tools by which the stones were cut, it is called plane ashlar; most of the public buildings of London, in which stone is used, are treated in this way. When the surface is wrought in a regular manner, like parallel flutes placed perpendicularly, it is called tooled ashlar, and is chiefly used in the basements of buildings, but when the surfaces of the stones are cut with a broad tool without much regularity, the work is said to be random tooled; when wrought with a narrow tool, it is said to be chiselled or boasted; if the tools be very narrow, the ashlar is said to be pointed; when the stones project from the joints, the ashlar is said to be rusticated; in this kind the faces may have either a smooth or a broken surface. According to Mr. Nicholson,1 neither pointed, chiselled, nor randomtooled ashlar are employed in good work; in some parts of the country herring-bone ashlar, and herringbone ramdom-tooled ashlar are used. The act of bedding the ashlar-facing in mortar, is called ashlaring.
ASHLARING, in carpentry, is the fixing of short upright quarterings between the rafters and the floor in garrets, in order to make more convenient rooms by cutting off the acute angles at the bottom. The triangular spaces on the sides are either left unoccupied or formed into cupboards or closets. Most of the garrets iu London are built in this way.
ASPHALTUM or native bitumen, pit coal, lignite or brown coal, petroleum or rock oil, naphtha and a few other substances, are now regarded as products of the decomposition of organic, and especially vegetable matter, beneath the surface of the earth, in situations where water is present but atmospheric air is almost entirely exclnded. Being deposited at the bottom of seas, lakes or rivers, and subsequently covered up by accumulations of clay and sand, the organic substances undergo a kind of fermentation, by which the above-named bodies are slowly produced. [See Coal.]—The true bitumens, of which there are a large number, seem to have been produced from coal of lignite by the action of subterranean heat. [bitcmen.] Asphaltum is also called mineral pitch, Jew's pilch, compact bitumen and maltha. It is found in considerable quantities on the shores of the Dead Sea, or Lacus Asphaltites, where it is called by the Arabs Hajar Mousa or Moses' stone. There is a thick bed of asphaltum at Arlona in Albania. It also occurs at Coxitambo near Cuenca in South America. It
(1) "Architectural Dictionary," by Peter Nicholson, Architect. London, lain.
abounds also in the West India islands of Barbadoes and Trinidad. In the latter island it forms a lake or rat her plain, known by the name of the Tar Lake, called by the French Le Brai, from its resemblance to and answering the purpose of ship piteh. It lies in the leeward side of the island, on a point of land which extends into the sea about two miles. This cape or headland is about 50 feet above the level of the sea. From the sea it appears a mass of black vitrified rocks, but on closer examination is found to consist of bituminous scoriae, vitrified sand, and earth cemented together. In some parts, beds of cinders only are found. In approaching it there is a strong sulphurous smell, which is prevalent in many parts of the ground 8 or 10 miles from it. The bituminous plain is separated from the sea by a margin of wood that surrounds it. From its colour and even surface, it appears like a lake of water, and in hot and dry weather, its surface to the depth of an inch is liquid, and so cohesive that no one can walk upon it. It is circular in form and about 3 miles in circumference. On first approaching it, it has the appearance of a plane as smooth as glass, but a nearer inspection shows it to be broken up by numerous cracks and fissures, resembling the markings on the back of a turtle, which being sometimes filled with water, make the whole surface appear level. The bitumen resembles pit coal in consistence and appearance, only its colour is rather more grey. It breaks into small fragments of a cellular appearance, and glossy, with a number of minute shming particles interspersed through its substance; it is very friable, and when liquid is of a jet black colour. Some parts of the surface are covered with a thin brittle scoria a little elevated. Mr. Anderson, who describes this lake,1 could form no idea as to its depth, for in no part could he find a substratum of any other substance, and although the smell of sulphur was strong, no appearance of that substance was to be detected. The general odour, however, was that of piteh. No impression could be made on the surface without an axe; at the depth of a foot it was a little softer, with an oily appearance, in small cells. A small portion held in a flame hisses and cracks like nitre, emitting minute sparks with a vivid flame. A piece put into the fire boils up a long time without sutTering much diminution; a thin scoria then forms over the surface, under which the rest remains liquid. The absorption of heat by the black mass of the lake is so great, that the rain-water is evaporated from it very quickly. The bitumen is much used for ships' bottoms, and is said to kill the Borer or Teredo, which is so destructive to ships in that part of the world.
In many parts of the woods this substance is found in a liquid state: it smells stronger of tar than when indurated, and adheres strongly to anything that it touches. This liquid substance is petroleum or naphtha, holding asphaltum in solution. It is found in various parts of Europe, but most abundantly in the Birman Empire. "The town of Rainanghong
(I) " Philosophical Transactions of the Royal Society," Vol. 1XXIX.
is the centre of a small district, in which there are some hundred petroleum wells in full activity. The district in which they are situated consists of a sandy loam, resting upon alternate strata of sandstone and indurated clay: under these is a layer of pale blue argillaceous schistus, impregnated with petroleum of considerable thickness, and resting upon coal. The petroleum flows into the well when it is sunk a few feet into the schistus, and when it begins to fail, the well is deepened. It is remarkable that no water ever penetrates into these wells. The annual quantity of petroleum produced by the district, exceeds 400,000 hhds. The uses of petroleum where it abounds are very important: it serves the lower classes instead of oil for lamps, and when mixed with earth or ashes it answers the purpose of fuel. A composition of petroleum and resin is an excellent material for covering wood-work, and paying the bottoms of ships and boats, as it protects the timber from the attacks of insects and worms. When rectificd by distillation it affords naphtha.'
Asphaltum varies considerably in purity, according to the quantity of different earthy substances mingled with it. When nearly pure its colour is almost black or dark brown, and it does not soil the fingers. When rubbed, it gives off a pitehy odour. Its specific gravity varies with its purity, from about 1 to 1.10. It is insoluble in water; but aleohol takes from it about 5 per cent. of a yellow resin, and ether dissolves it to the extent of about 70 per cent. Asphaltum is very inflammable: it burns with a red smoky flame, and consists principally of a substance which M. Boussingault names asphallene, composed of C20 H16 03.
A few years ago, as M. Dumas remarks, asphaltum produced an industrial fever, unparalleled in the annals of the useful arts. Its valuable properties were strongly exaggerated, and it was applied to uses for which it was evidently unfitted. Repeated failures led to a reaction, and asphaltum soon fell into a neglect as unmerited as the previous high degree of favour with which it was regarded.
During this period of excitement, several companies were formed in England, for the purpose of making asphaltum roads and pavements, for paving terraces, railway platforms, kitehens and stables, for roofing, and for protecting buildings from damp. In 1837, Mr. Claridge obtained a patent for the peculiar application to these purposes of the asphaltum from Scyssel on the Rhone, in the department de l'Ain, and also published a pamphlet entitled "Instructions for the use of the Sevsscl Asphaltic Mastic," from which the following particulars are derived.
The principal ingredient in this mastic is a dark brown bituminous limestone, found near the Jura Mountains. The stone is reduced to powder and mixed with a portion of mineral tar when intended to be applied as a cement, as in covering roofs, lining tanks, &c.; but when intended to be used for flooring and for pavements, sea grit is used in addition. The
(2) Cox: "Asiatic Researches.'
Aikin: "Dictionary of Che
put into the caldron, and when this is melted, 56ibs. of the mastic are added, the whole being stirred repeatedly with a curved loop of iron attached to a handle, Kg. 72, so as to detach any portions of the mastic from the sides and bottom of the vessel and prevent burning. AVhen the contents arc properly melted, the caldron is covered up for a quarter of an hour, after which another 56 lbs. of mastic arc stirred in. The caldron is again covered for a short time, and additional quantities of tar and mastic are added in the proportion of llb. of the former to lewt. of the latter, until the caldron is full. When the whole is completely melted and fit for use, jets of light smoke will proceed from the mixture, and the mastic will drop freely from the stirrer. The only kind of tar to be used in this mixture, is that with which the limestone is impregnated. If the mastic is required to be very stiff, as for paving kitehen floors, a smaller proportion of tar is to be used. In such cases, also, a larger proportion of grit is mixed with the mastic, and when it is desired to convert fine asphalte into coarse, 30lbs. of fine clean grit are to he added to 112lbs. of mastic, with **. ». from llb. to 2£lbs. of tar. When the melting is complete, the mastic is conveyed quickly to the spot where it is intended to be used, either in iron ladles or heated iron buckets. The caldron ought to be as close to the work as
c, Fig. 73, formed by mixing 7 parts clear river sand or gravel, and 1 part fresh grey-stone lime in powder. The quantity of water should be only just sufficient to moisten the mass, which must he immediately levelled and rammed solid. The hollows must then be filled up with a finer concrete, B, and the whole be allowed to dry before laymg the asphaltum. Unless this precaution be attended to, the heat will convert the moisture of the concrete into vapour, and fill the asphaltum with air holes. This may to a great extent be prevented by sifting fine cinder dust over the concrete, and in rainy weather if the work cannot be protected by a tarpaulin, sheets of tarred brown paper may be spread over the concrete and the asphaltum be poured over these. The thickness of the layer of asphaltum, A, is regulated by slips of wood, arranged so as to divide the pavement into compartments not exceeding 30 inches wide, when only one workmen or spreader is employed, but double that size when two spreaders are engaged. The work is levelled -by a curved wooden spatula assisted by a floating rule or long straight ruler, stretching across the layer of asphaltum, over which it is moyed backwards and forwards, the wooden gauges supporting its ends. If the surface is intended to be smooth, a mixture of equal parts of silver-sand and slate dust, or of 2 parts silver-sand to 1 of dead plaster of Paris or powdered chalk, is sifted over the asphalte before it is perfectly set, and rubbed in with a flat heavy tool of wood. If the pavement is required to be rough, clean sharp grit is sifted thinly over it and beaten into the mastic with a heavy wooden block. When one portion of the pavement is complete, it is desirable to proceed to lay the next but one, leaving the intermediate space to be filled in afterwards when the first layer is quite cold and firm, so as to prevent its being injured. In laying these pavements the parts most exposed to wear are somewhat increased in thickness. In laying them upon suspension bridges or other flexible surfaces, the concrete is spread on a planked flooring, the joints of which are covered with battens nailed at one edge
only to allow the necessary play: a sheet of thin canvass is then spread evenly over the concrete and secured with nails, and upon this the mastic is spread. By mixing differently coloured sands with the mastie, and disposing it in patterns, imitations of mosaic work may he formed.
In the application of asphaltum with a view to exclude damp, as in the floors of cellars and basements, a brick invert laid in asphaltc as a cement should be used, as at D, Fig. 74. Asphalted bricks and tiles for such purposes are prepared by heating them, and placing them in rows upon a flat surface between gauges rising to a sufficient height to allow a layer of the mastic a quarter of an inch thick to be spread over them: before the mastic is quite set, the bricks are separated from each other by passing a knife between them. In Fig. 74, the arrangement is shown for excluding water from a cellar, A is a
section of the wall, B the watermark on the outside, c an asphalted brick lining, D a similar lining for the invert, E and G a bed of concrete, and p the asphaltc floor of the cellar. In some cases, alternate layers of concrete and asphaltc may be adopted instead of a brick invert. Directions are also given in the pamphlet for making skirtings of asphaltum, for lining cisterns, and for covering roofs, &c., but enough has been stated to show the general method of applying this material. The thickness of asphaltum used for pavements, varies from half an inch to an inch and a quarter, the former being sufficient for common floors and court-yards, and the latter for carriage pavements. A thickness of from half an inch to five-eighths is sufficient for roofs and the coverings of arehes for preventing the passage of water, and for the lining of tanks and ponds; and about a quarter of an inch is sufficient for the ground line of brickwork to prevent damp from rising.
An asphaltum surface admits of easy repair. By placing some hot mast ic upon the place requiring it, the part may be cut away without injuring the adjacent work. The mastic thus removed may be
remelted, and the edges of the old work bemg cut square, the hot material will readily adhere to them if free from dust and moisture.
ASSAYING is a branch of chemical analysis, the object of which is, to determine the quantity of gold or silver in any mixture with the baser metals. It thus differs from chemical analysis, which takes account of all the ingredients of the body under examination. As gold and silver have for many ages afforded the most obvious standard of value in civilized countries, and considering what vast quantities of coin, plate, trinkets, and plate ornaments are being constantly produced, it was of great importance to persons who deid in such articles, to be able to decide quickly, and with certainty, on the exact portion of alloy which each piece might contain, and its exact weight to the minutest subdivision of weights. At an early period, in this country the trade of the goldsmith not only comprised as now the dealers in or makers of gold and silver articles, but also that trade which has, since the separation of the two ancient branches, received the name of Bankers. No tax was then, as now, levied on manufactured plate, but all articles made of gold and silver were to be of the same degree of purity as the coin of the realm. "Whatever was manufactured in London or in some of the larger places, was ordered to be assayed and stamped by the warders of the craft in such town; but whatever was made in places 'where no touch was ordained,' was to be stamped by the maker, and if found beneath the proper standard, it was confiscated to the crown.1 In this state of affairs, any article of plate would be of the same value, in equal weights, as gold or silver in ingots; and hence, as occasion might require, the vessels being worth no more than their weight, would be on every pressing emergency readily converted into coin. The workmanship of plate would in that age cost but little, as luxury had not reached the point in that kind of art, which it soon afterwards attained in the hands of Benvenuto Cellini at Florence, and of his successors in the other parts of Europe. The taste displayed in the forms and decorations of gold and silver utensils was very coarse, both in France and in England. Voltaire, in his General History, says, that the work of the goldsmiths in Paris was so bad that the King, (Louis XII.) in 1501, forbade the manufacture, so that the French had their plate from Italy. There seems good reason to believe, that the English of that period did not excel the French artisans in the fabrication of gold and silver articles. We may thus account for what we find often stated in the reeords of that age, that the religious houses, the nobility, and rich individuals, gave up to the monareh, on pressing emergencies, their plate for the public service. Such a surrender in the present day, when a heavy tax and the workmanship of artists make plate of silver of more than double its value in weight, would be deemed a most oppressive requisition, whereas at the period referred to, the difference between making
(1) Bills of Parliament, 2d Henry VII. cap. 12 and 13
payments in coined money or in manufactured gold and silver, would amount but to a trifle."'
Although the assay of the precious metals is very simple in principle, great skill is required in assaying. A skilful assayer is able from the sample of a few grains to determine the standard of very large masses of the most valuable metals. The principle of assaying is as follows:—when gold, silver, and platinum are exposed to the air, either in the solid state or in a state of fusion, they do not oxidize like the other metals, but retain their metallic lustre, on which account they obtained their name of perfect or noble metals. Hence, when a noble metal is alloyed with an inferior metal, if the alloy be melted in contact with the air, the latter will gradually become oxidized, and the scales of oxide rising to the surface can be removed from time to time, until the whole of the baser metal is separated. AVhen the baser metal does not oxidize very readily, as is the case with copper, this separation becomes more difficult, and even impossible by heat alone if the proportion of copper be small; but by adding to the mixture a portion of some metal which oxidizes very readily, such as lead or bismuth, the more refractory metal oxidizes with greater ease, and thus the noble metal is left pure. On this account, litharge or oxide of lead was termed by the old chemists the bath of the noble metals, scouring or cleansing them, as it were, from their alloys of base metal, and leaving them bright and pure. In the re fining of gold and silver, tins process is often conducted on a large scale; but in assaying, where small samples only are operated on, the process of cupellation is adopted.
! earthen vessel /, called a muffle, of an oven form, vaulted at top with a level floor at bottom; it rests upon a plate which is covered with loam nearly an inch thick: it is open at one end and closed everywhere else except a few narrow slits through the top and sides. It is shown separately in Fig. 76, with the mvffle plate Fig. 77, of the same size as the bottom of the muffle; the open end comes in contact with a door at the side of the furnace, and is generallyluted thereto, so as to separate it entirely from the burning fuel. The body of the muffle is surrounded with coals, and before cupellation, is gradually heated to a glowing redness. Its use is to protect the small crucibles or cupels, ranged on its floor, from any impurities from the fuel, and at the same time to afford the melted metal a free access of heated air to promote the oxidation. The cupels, shown in section within the muffle, Fig. 75, arc cubical or circular in form, with a shallow depression at the top to contain the metal, and small in proportion to the size of the muffle, so that a number of them may be at work at the same time. They are made of such substances as are not acted on by the fused oxides, and their texture is sufficiently loose to allow these oxides to penetrate them readily, and yet admit of being handled. Many substances fulfil these conditions, but the ash of burnt bone is generally used. The ash is powdered and sifted, and then repeatedly washed with water, to remove all saline and soluble matters: when dried, it consists of phosphate of lime with alittle carbonate. This substance made into a paste with water or beer, is pressed into a mould to the proper shape: it is then taken out and dried at a gentle heat, and is lastly ignited to expel all moisture.
Before the cupels are put into the muffle, a little powdered chalk or sand is sprinkled on the floor of the muffle, to prevent the adhesion of the cupels by the litharge soaking through them. As the cupels cannot absorb more than their own weight of litharge, the quantity of tine metal to be assayed should not require more lead than the weight of the cupel.
For the assay of silver a clean piece of the metal is taken, not more than 36 grains, and less if the alloy appear to be considerable. It is flattened and weighed in a very sensible balance. It is then wrapped up in the requisite quantity of pure lead rolled out into a sheet; or the silver and the lead are folded together in a piece of paper. The muffle and the cupel being at a full red heat, the silver and the lead are put into the cupel with a pair of pincers, when they immediately melt. Aikin gives a beautifu. and accurate description of the phenomena:—" The melted metal begins to send off dense fumes, and a minute stream of red fused matter is seen perpetually flowing from the top of the globule down its sides to