Boron is a trivalent metalloid element found in nature only in combination, often in borates or silicates (such as in borax). Boron is used in metallurgy and nucleonics, being very important in nuclear reactors. It has the symbol B and is a dark brown or green amorphous powder, which stains the skin, has no taste or odour, and is only slightly soluble in water. It combines directly with oxygen, chlorine, nitrogen, etc. Boron has been obtained crystalline in an impure state, and is then nearly as hard as diamond, in the form of dust being used for polishing. Research Boron
Glass is an artificial hard, brittle, transparent or translucent, noncrystalline solid, consisting of metal silicates or similar compounds fused with an alkali. In its finest qualities glass is quite transparent, and is used for making windows, mirrors, bottles, composite armour plate for armoured fighting vehicles etc.
The ancient Egyptians carried the art of making glass to great perfection, and are known to have practised it as early as 2000 BC, if not earlier. The Assyrians, the Phoenicians, the Greeks and Etruscans were all acquainted with the manufacture. The Romans attained peculiar excellence in glass-making, and among them it was applied to a great variety of purposes. Among the most beautiful specimens of their art are the vases adorned with engraved figures in relief; they were sometimes transparent, sometimes of different colours on a dark ground, and very delicately executed. The Portland or Barberini vase is almost the only surviving specimen of this kind. The mode of preparing glass was known long before it was thought of making windows of it. The first mention of this mode of using glass is to be found in
Lactantius, in the 3rd century AD. St Jerome also speaks of glass being so used in 422 AD.
Benedict Biscop introduced glass windows into Britain in 674 AD. In church windows it was used from the 3rd century. The Venetians were long celebrated for their glass manufacture, which was established before 700 AD. Britain did not become distinguished for glass until about the commencement of the 16th century.
The excise laws relative to the glass manufacture were at one time complicated in the extreme, and tended to check improvements in glass-making. These laws were repealed in 1845 by Sir Robert Peel, as part of his free-trade policy, and beneficial effects were immediately apparent in the improved quality, cheapness, and greater variety of descriptions of glass produced. Traditionally, glass is largely made in France, Germany, Belgium, and the United States. For coloured glass Bohemia has long had a high reputation.
The first mention of the manufacture of glass in the United States is in Captain John Smith's 'History of Virginia', in which he speaks of a glass factory having been founded at Jamestown in 1615, and a second in 1622. The work was coarse, being chiefly confined to bottles. In 1754, a successful factory was established in Brooklyn by Bamper, a Dutchman. In 1779, factories were founded at Temple, New Hampshire, and in 1795 the industry was begun at Pittsburgh. By 1813 there were five glass factories at Pittsburgh. In 1840 there were eighty-one factories in the United States, by 1870, 201 factories flourished in different places and since then the industry rapidly increased.
Glass is formed by the fusion of siliceous matter, such as powdered flint or fine sand, together with some alkali, alkaline earth, salt, or metallic oxide. The nature of the glass will depend upon the quality and proportion of the ingredients of which it is formed; and thus an infinite variety of kinds of glass may be made, but in commerce five kinds are usually recognized:
1. Bottle or coarse green glass. 2. Broad, spread, or sheet window-glass. 3. Crown-glass, or the best window-glass. 4. Plate-glass, or glass of pure soda. 5. Flint-glass, or glass of lead.
Coloured glass may be mentioned as a sixth kind. The physical properties of glass are of the highest importance. Perhaps the chief of these is its transparency, and next to that its resistance to acids (except hydrofluoric acid). It preserves its transparency in a considerable heat, and its expansibility is less than that of any other known solid. Its great ductility, when heated, is also a remarkable property. It can, in this state, be drawn into all shapes, and even be spun into the finest threads. It is a bad conductor of heat, and is very brittle. It is usually cut by the diamond.
The works in which glass is made are called glass-houses. They were traditionally constructed of brick, and made of conical form. A large vault was made in the interior of the cone, extending from side to side, and of sufficient height to allow workmen to wheel in and out rubbish from beneath the furnace, which was placed over the vault, and separated from it by an iron grating. The materials used for the formation of the glass are sometimes calcined in a calcar or fritting furnace, and a chemical union between the ingredients commenced, forming a frit. But this process is not essential, and the materials, after being ground and thoroughly mixed up together, are usually placed at once in melting pots or crucibles made of Stourbridgefire-clay, or other similar material, the melting-pots being then placed in the melting furnace or oven. This is a kind of reverberatory furnace, traditionally circular in form, arched or domed above, and capable of keeping up an intense heat. The crucibles are placed in the furnace at equal distances from each other round the circumference, each pot being opposite to an opening in the wall of the furnace in order that the crucible may be charged or discharged by the workman from without. In the 19th century a furnace called a tankfurnace came into use which enabled melting pots to be dispensed with, as the material could be melted in and worked from the furnace directly.
The use of the annealingfurnace, is also essential in glass-making, the process of allowing the glass to cool there being called annealing. Unless this process be carefully managed, the articles formed in the glass-house can be of no use, from their liability to break by the slightest scratch or change of temperature.
Sheet glass is the commonest description of glass. It is composed of various ingredients in varying proportions, usually of sand, chalk, or limestone, sulphate of soda, and cullet or broken glass. A coarse variety of it may be made of a mixture of two parts by measure of soap-boilers' waste, one of soda-ash and one of cleaned sand. In France the materials employed are commonly: sand 100 parts, sulphate of soda 30, carbonate of lime 30, coke to aid in the reduction of the sulphate of soda 5, with some bioxide of manganese to correct the greenish tinge that glass with a soda base possesses. Traditionally when the materials were properly melted a quantity was taken out of the pot on the end of an iron tube about 5 feet long, and the workman by blowing into and swinging the tube while heating and reheating the glass, imparted a cylindrical shape to the newly-formed product. The rounded extremity of the cylinder (which was about 4 feet long or more) was softened in the furnace in order to enable the workman to blow a hole in it. This opening was made by heating the cylinder and then stopping up the tube with the thumb, when the expansion of the air caused the cylinder to burst open at the end. The other rounded end was detached after cooling by winding round its circumference a thread of red hot glass, which caused a clear fracture. The cylinder was then split open parallel to its axis by a diamond, and then conveyed to the flattening furnace where it was heated and opened out into a flat sheet of glass. It was afterwards placed in the annealingfurnace.
Crown glass is differently formed by different makers, but its composition is essentially the same as the best sheet glass. It used to be the only window-glass made in Britain, but its manufacture had been almost or altogether superseded by that of sheet glass by the start of the 20th century. The ingredients being melted and at the proper temperature, a quantity of the glass was withdrawn by the tube (to the amount, by successive addition, usually of 10 lbs in all). By various manipulations this from having the form of a hollow oblate spheroid was made to assume the form of a thin circular plate, with a thick part called the bull's eye in the centre, being the point at which an iron rod was attached to it for the purpose of causing it to revolve rapidly and spread out into a sheet before the furnace. The bull's eye used to be commonly seen in the windows of humble dwellings, the pieces of glass containing them being cheap.
Flint-glass or Crystal is one of the kinds largely made, being employed especially for table utensils, globes, ornaments, etc. Powdered flint was formerly employed in its manufacture, but fine white sand has been substituted. The other materials are red-lead or litharge, and pearl-ash (carbonate of potash). The following is said to be a good mixture : Fine white sand, 300 parts; red-lead or litharge, 200; refined pearl-ash, 86; nitre, 20; with a small quantity of arsenic and manganese. The furnace is kept at a very high temperature until the whole of the materials are fused. When the glass becomes translucent the temperature is diminished until it becomes a tenacious mass. Suppose a glass vessel is to be made, the iron tube is put into the crucible, and the required quantity of glass lifted out, which after certain adjustments is rolled into a cylindrical form on an iron table called the merver or marver. The workman
then blows the glass into the form of a hollow globe, and re-heats and blows until the globe becomes of the required thinness. An iron rod called the punty is now attached to the end of the glass furthest from the tube, and the tube detached. The workman now heats the glass on the punty, and sitting down upon a chair with smooth arms, he lays the punty upon them, and rolling it with his left hand he gives the glass a rotatory motion, while with an instrument in his right, somewhat like a pair of sugar-tongs, he enlarges or contracts the different parts of the vessel until it assumes the requisite shape. A pair of shear's is al.so made use of in certain cases. The article is then detached from the punty, and carried to the annealingfurnace. Many of the articles, after coming from the annealingfurnace, are sent to the cutter or grinder. The operation of grinding is performed by wheels of various diameter and of various edges, some of iron, others of stone, and some of wood. Rich and delicate designs may be cut upon the articles by means of small wheels of copper and steel upon which emery is kept constantly falling.
Ornamental figures may also be engraved, or rather etched, upon articles of glass by means of hydrofluoric acid, care being taken to place a coating of some substance over the parts not to be acted upon. Various ornamental forms are given to the surface of glass vessels by metallic moulds. The mould is usually of copper, with the figure cut on its inside, and opens with hinges to permit the glass to be taken out. The angles of moulded objects are always less sharp than those of cut-glass.
Green or bottle-glass is formed of the coarsest materials, such as coarse sea or river sand, lime, and clay, and the most inferior alkalies, as soap-boilers' waste, and the slag of iron ore. A cheap mixture for this kind of glass may be made of common sand and lime, with a little clay and sea salt. The manipulations of the traditional glass-blower in fashioning bottle-glass into various forms were in general the same as those performed by the flint-glass blower. Wine and beer bottles, which are required to be all of a certain capacity, are blown in moulds, so that their containing portion may be as nearly as possible of the requisite size. When the articles are made they are carried to the annealingfurnace. Green bottle-glass is preferable to all other kinds for vessels required to contain corrosive substances; it is less fusible than flint glass, and
thus is better calculated for many chemical purposes.
Plate-glass is a fine and thick glass cast in sheets. One maker's ingredients are as follows: white sand, 300 lbs; soda, 200; lime, 30; oxide of manganese, 2; oxide of cobalt, 3 ounces; and fragments of glass (cullet) equal to the weight of sand. After being melted in large crucibles, and the liquid glass having been thoroughly skimmed, it is transferred by a copper ladle to smaller pots (cuvettes). When the glass in the smaller crucible is ready for casting it is poured upon an iron casting-table, and a large metal cylinder moved along spreads the glass into a broad uniformsheet. The subsequent stages of the process are concerned with the discovery of flaws, the squaring of the edges, the grinding of the surfaces plane, the grinding of the sides, and the polishing. Before grinding and polishing the glass is what is called common 'rough plate,' and in this state it is much used for roofing, cellar-lighting, etc, being non-transparent. 'Rolled plate,' which is cast on a table that imparts a surface of grooves, flutings, lines, etc, is extensively used for the same purposes.
There are several other kinds of glass that may be noticed. Pressed glass is flint-glass formed into articles by pressing into moulds of iron or bronze, a fine surface being afterwards attained by heating so that a thin film on the surface melts.
Slag glass is glass from the slag of blast-furnaces mixed with other ingredients; it is largely used for bottles.
Optical glass is made of special varieties of flint and crown glass.
Strass, which was used for imitating gems, was a very dense flint-glass, colours being imparted by metallic oxides.
Spun glass is glass in the form of very fine threads, in which state it may be woven into textile fabrics of great beauty.
Toughened or hardened glass, having certain properties owing to its being heated to the melting point and plunged into an oleaginous mixture, was invented prior to the start of the 20th century, but was not developed into a working product until the mid-20th century, and is now very commonly used for windows.
Coloured glass is of two kinds - entirely coloured, the colouring matter being melted along with the other ingredients; or partially coloured, a quantity of white glass being gathered from one pot, and dipped into the other containing the coloured glass, by which the whole receives a skin of coloured glass. The colouring matters are chiefly the metallic oxides. A beautiful yellow colour is imparted by silver in union with alumina (powdered clay and chloride of silver being used), also by uranium and by glass of antimony; red colours by oxide of iron, copper, and gold; green by protoxide of iron, oxide of copper, oxide of chromium, &c.; blue by cobalt; orange by peroxide of iron with chloride of silver. ohemia is particularly famous for its manufactures of articles in coloured glass. Research Glass
Hydrofluoric acid, fluohydric acid or hydrogen flouride is a strong acid obtained by the action of concentrated sulphuric acid on fluorspar in a leaden vessel, which, though monobasic, forms double salts of the alkali metals by union of a molecule of salt and of acid. Hydrofluoric acid is a solvent of silica and silicates. Hydrofluoric acid is obtained in aqueous solution by heating calciumfluoride with concentrated sulphuric acid and condensing the gas given off in water.
The anhydrousacid is a colourless liquid, with a boiling-point just above the ordinary temperature. It is usually used in aqueous solution, and is kept in caoutchouc bottles. It blisters the skin and is used for etchingglass. When the vapour is used the etching is transparent, but with the solution it is dull. The glass to be etched is coated with a thin layer of wax, and the design traced with a fine pointed instrument, and after etching the wax is dissolved away and the design becomes visible. Hydrofluoric acid is also used to decompose and dissolve silicates in mineral analysis. Research Hydrofluoric Acid
Slag is the chemical compound resulting during the smelting of metallic ores. It results because of the action of the flux on impurities in the ore. Slag generally consists of silicates, formed by the combination of silica with alumina, lime, magnesia, oxides of iron or other metals. By the formation of slag, the impurities in the ore are removed, and if the metallic contents of the slag are of no value the slag is regarded as smelters' refuse. Some slags, however, consisting mainly of metallic oxides produced during the refining processes, are resmelted and such slags are termed cinder or scoria. As slag has to be separated from the valuable metallic material, its fluidity, at the smelting temperature, is an important factor, and some substances such as an oxide of zinc are apt to make slags pasty.
Slags vary in chemical composition, but those which crystallise are regarded as definite chemical compounds. The colour of slags affords n indication of the composition, for example green denotes the presence of iron and copper oxide produces a red slag. Slags are used for various purposes, as ballast for railways, macadamising roads, making into bricks and others. Some slags may be burnt with lime, thus making an efficient hydraulic cement, and slag from the basic Bessemer process forms a fertiliser containing phosphorus. Research Slag
The amphiboles are a large group of minerals, the silicates of many different bases, the commonest being alumina, iron oxide, lime, magnesia and the alkalis. They are constituents of many crystalline igneous rocks and of metamorphic schists. In many of their properties they closely resemble the pyroxenes. They occur generally in black or dark green crystals, usually long, narrow and blade-like, and owing to their perfect cleavages their surfaces are smooth and bright. The commoner varieties are hornblende, actinolite and tremolite. Research Amphibole
Brucite, named after Named after Dr. Archibald Bruce of New York, is a mineral decomposition product of magnesiumsilicates, especially serpentine. It has the formulae Mg(OH)2 and a relative hardness of 3. It is found in Texas, where it is white with a grey, green or blue tinge and is used in sugar-refining, in medicine as an antacid and laxative and as a source of magnesium. Brucite has an incredibly high melting-point making it useful for lining kilns and furnaces. Research Brucite
Clay is the name of various earths, which consist of hydrated silicate of aluminium, with small proportions of the silicates of iron, calcium, magnesium, potassium, and sodium. All the varieties are characterized by being firmly coherent, weighty, compact, and hard when dry, but plastic when moist and comprising very fine-grained materials (less than 0.004 mm in diameter), smooth to touch, not readily diffusible in water, but when mixed not readily subsiding in it. Their tenacity and ductility when moist and their hardness when dry has made them from the earliest times the materials of bricks, tiles, pottery, etc.
Of the chief varieties porcelain-clay, kaolin, or china-clay, a white clay with occasional gray and yellow tones, is the purest. Potter's-clay and pipe-clay, which are similar but less pure, are generally of a yellowish or grayish colour, from the presence of iron. Fire-clay is a very refractory variety, always found lying immediately below the coal; it is used for making fire-bricks, crucibles, etc. Loam is the same substance mixed with sand, oxide of iron, and various other foreign ingredients. The boles, which are of a red or yellow colour from the presence of oxide of iron, are distinguished by their conchoidal fracture. The ochres are similar to the boles, containing only more oxide of iron. Other varieties are f'uller's-earth, Tripoli, and boulder-clay, the last a hard clay of a dark-brown colour, with rounded masses of rock of all sizes embedded in it, the result of glacial action.
The distinctive property of clays as ingredients of the soil is their power of absorbing ammonia and other gases and vapours generated on fertile and manured lands; indeed no soil will long remain fertile unless it has a fair proportion of clay in its composition. The best wheats both in Britain and the European continent are grown on calcareous clays. Research Clay
Feldspar or felspar is a name given to a group of minerals, closely related in crystalline form, and all silicates of alumina with either potash, soda, lime, or, in one case, baryta. They occur in crystals and crystalline masses, vitreous in lustre, and breaking rather easily in two directions at right angles to each other, or nearly so. The colours are usually white or nearly white, flesh- red, bluish, or greenish. The group includes the monoclinic (orthoclastic) species orthoclase or common potash feldspar, and the rare hyalophane or baryta feldspar; also the triclinic species (called in general plagioclase) microcline, like orthoclase a potash feldspar; anorthite or lime feldspar; albite or soda feldspar; also intermediate between the last two species, labradorite, andesine, oligoclase, containing both lime and soda in varying amounts. The feldspars are essential constituents of nearly all crystalline rocks, as granite, gneiss, mica, slate, most kinds of basalt and trachyte, etc. The decomposition of feldspar has yielded a large part of
the clay of the soil, also the mineral kaolin, an essential material in the making of fine pottery. Common feldspar is itself largely used for the same purpose. Research Feldspar
Gyrolite is a white or colourless, glassy-looking secondary mineral. A silicate of calcium, gyrolite is formed through the alteration of pre-existent calciumsilicates and is found mainly in crevices of basalt or as white spherules on a basalt groundmass, rarely larger than 5 cm in diameter. Gyrolite was first discovered in 1851 and was confirmed as a distinct mineral in 1855. Gyrolite aggregates are often accompanied by apophyllite, quartz and zeolites such as analcime. Research Gyrolite
Kaolinite is a hydrous silicate of aluminium with the formulae Al2Si2O5(OH)4 and a relative hardness of 3. It has a crumbly habit and forms the basis of most clay. Kaolinite is derived from the decomposition of feldspars, particularly aluminiumsilicates and is one of the most important of the natural industrial substances, used for bricks, ceramics, and many other applications. Research Kaolinite
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Boron
