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ent to melt it completely. When the fusion has continued the proper time, the furnace is allowed to cool a little. In this state the glass is exceedingly ductile, and will assume any shape, according to the fancy of the workman. The vessels thus formed must not be permitted to cool too quickly, hence they are put into a hot furnace, in order that the heat may pass off very gradually; this is called annealing.
Glass is often tinged of various colours, which is performed by mixing with it, while in fusion, some one of the metallic oxides. Thus blue glass is formed by the oxide of cobalt; green by the oxide of iron, or copper; violet by the oxide of manganese ; red by a mixture of the oxides of copper and iron; purple by the oxide of gold; white by the oxide of arsenic and zinc.; and yellow by the oxide ef silver, and by combustible bodies.
We shall give now a detail of the manual operations in the manufacture of glass.
Glass-blowing, the art of forming vessels of glass; the term, however, is exclusively applied to those vessels which are blown by the mouth. The operation is exceedingly simple; the workman has a tube of iron, the end of which he dips into a pot of melted glass, and thus gathers a small quantity of glass on the end of it; he then applies the other end of the tube to his mouth, and blows air through it; this air enters into the body of the fluid glass, and expands it out into a hollow globe, similar to the soap bladders blown from a tobacco pipe. Various methods are used to bring these hollow globes into forms of the different utensils in common domestic use, and several tools; the chief part of these are represented in PLATE-GL-Ass MAKING. The first and greatest of the glass-blowers' implements is the furnace ; it consists of two large domes set one over the other, the lower one stands over a long grating, (on a level with the ground) on which the fuel is placed ; beneath the grate is the ash pit, and a large arch, leading to it, conveys air to the furnace. In the sides of the lower dome, as many holes or mouths are made as there are workmen to make use of the furnace, and before each mouth a pot of melted glass is placed; the pots are very large, like crucibles, and will hold from three to four hundred weight of liquid glass; they are supported upon three small piers of brickwork, resting on the floor of the furnace. The form reverberates the flaine from the roof down upon the pots, and they are placed at some distance within the furnace, that the flame WOL. V.I.
may get between the wall and the poss. The upper dome is built upon the other, and its floor made flat by filling up round the roof of the lower dome with brickwork ; there is a small chimney opens from the top of the lower dome into the middle of the floor of the upper one, which conveys the smoke away from it, and a flue from the upper dome leads it completely from the furnace. The upper dome is used for annealing the glass, and is exactly similar to a large oven, it has three mouths, and in different parts a small flight of steps lead up to each. We now come to describe the smaller implements. Fig. 1 and 2, is a bench or stool with two arms a b at its ends, which are a little inclined to the horizon; the operator, when at work, sits upon the stool, and lays his blowing tube d across the arms, as shown in the figure. Fig. 3, are a pair of shears, or rather pliers, formed of one piece of steel; they have no sharp edges, and spring open when permitted; the workman has several of these of difierent sizes, which are hung upon hooks at e in the stool, fig. 4. Fig. 4, is a pair of compasses to measure the work, and ascertain when it is brought to the proper size; the workmen should have three or four of these. Fig. 5, a common pair of sheers, for cutting the soft glass. Fig. 6, a very coarse flat file. Fg. 7, is the blowing pipe; it is simply a wrought iron tube, about three feet long, at a it is covered with twine, to prevent it burning the workman’s hand. Fig. 8, a small iron rod, of which there should be several. Fig. 9, is a stool with a flat plate of cast iron laid upon it, and fis another flat plate upon the ground behind the stool. To explain the use of these tools, we shall describe the manner of forming a lamp or urn of glass, Fig. 10, with a wide mouth at top and a small neck g at bottom, through which the candle is inserted, and which is fitted into a brass cap to support the lamp by. The operation is conducted by three workmen. The first takes the blowing pipe 7, and after heating it to a red heat at the mouth of the furnace, dips it into the pot of melted glass...at the same time turning it round, that it may take up the glass, which has then much the consistence of turpentine : in the quantity of metal he is guided by experience, and must proportion it to the size of the vessel to be blown; he then brings it from the C
furnace to the stool, fig. 9, and rolls the lump of glass upon it to bring it to a round form, a fter which he blows through the pipe, resting the glass upon the iron plate f behind the stool, as in the figure, and rolling it backwards and forwards. The blowing makes the glass hollow, and he has several methods of bringing it to a É. shape to be worked ; by simply lowing, it would assume a figure nearly globular; if he wants it any bigger, in the equatorial diameterg g, fig. 11, he lays the pipe on a hook driven in the side of the stool, and turns it round very quickly; the centrifugal force soon enlarges it in the equator. If, on the other hand, he wishes to lengthen its polar diameter, he holds the pipe perpendicular, the glass hanging downwards, its weight lengthening it, and to shorten the polar diameter, he holds the pipe upright, the glass at the top by blowing through the pipe the capacity is increased, and the thickness of the glass of the vessel diminished. We now suppose, that by a very dexterous application of the above methods the workman has brought it to the shape of fig. 11; he now carries it to the mouth of the furnace, and holds it in to get a fresh heat, (for by this time it is become too stiff to work easily) taking care to turn it round slowly, that it may not alter its figure. The vessel in this stage is delivered to the second, or principal workman, the other two being only assistants; he is seated upon the stool, figs. 1 and 2, and lays the blowing pipe, with the glass at its end, across its arm a b, and with his left hand rolls the pipe along the arms, turning the glass and pipe round at the same time; in his right hand he holds the pliers, fig. 3, whose blades are rubbed over with a small piece of bees’-wax, and as the glass turns round presses the blade of the shears against it, following it with the shears as it rolls, at the end or side, as occasion requires, until he has brought it to the proper size, which he determines by the compasses, fig. 4, though not materially altering its figure, the first workman kneeling on the ground and blowing with his mouth at the end of the pipe, which hangs over the arm b, when directed by his principal. The third workman now produces the small rod, fig. 8, which is dipped into the melting pot, to take up a small piece of metal to serve as cement; the end of this rod he applies to the centre of the glass, just opposite the blowing pipe, the principal workman directing it, by holding its end between his pliers, the rod by the small piece of glass on its end immediately sticks to the glass
vessel, and the third workman draws it away, both workmen turning their rods round, but in contrary directions; this operation forms a short tube on the end, as in fig 12. The principal workman then takes the short tube at i, between the blades of a pair of pliers, exactly like the others, but which are not covered with bees’-wax; the cold of these pliers instantly cracks the glass all round, and a very slight jerk struck upon the rod 8 breaks it off. A hole is now made in the end of the glass, which is enlarged by the pliers while the glass is turned, as in fig. 13, until the neck is brought to the proper size and length to fit the brass cap, as before described, and the inferior half of the lamp is brought to its shape and size in the same manner. In order to form the upper half, the third workman has in the meantime been preparing a round lump of glass K, fig. 14, on the end of one of the rods, fig. 8, this he applies hot to the end of the neck, it being guided by the principal workman, and it immediately holds tight, he then breaks of the other neck at 7, by the cold pliers, and thus separates it from the blowing pipe. The giass is now heated a third time, and brought from the furnace in the state, fig. 15, to the principal workman, who enlarges the small orifice at the end by turning it round, and holding the pliers against it, until he enlarges it, as in fig. 16, to the shape of fig. 10; it is now finished, and the third workman takes it to a stool strewed over with small coals, he rests the rod upon the edge of the stool, and with the file, fig. 6, files the joint at the bottom neck, which soon breaks off, and the lamp falls upon the coals, the distance being so very small, as to be in no danger of breaking; a boy now puts the end of a long stick into the open mouth of the glass, and thus carries it up the steps before described, places it in the annealing oven, where it remains some hours; when taken out it must be cooled gradually, and is fit for sale. In the history of glass, there is a fact deserving record; it is related by Pliny, that the discovery was owing to the following accident. Some merchants, with soda as part of their freight, had cast anchor at the mouth of the river Belus, in Phoenicia, and were dressing their dinner on the sand, making use of large lumps of the soda as supports for their kettles. The heat of the fire melted the soda, and the siliceous earth together ; the result was glass. The hint was not lost, and a manufacture in that trading country was
instantly established, and to this place it was for a long time confined. Glass was undoubtedly made in great perfection among the ancients. In their accounts, we read of drinking-glasses, glass prisms, and coloured glasses of various kinds. Glass was first used for windows in the 3d century of the Christian aera, but it did not come into common use till very long after this. Glass, painting on. See ENAMELLING. Glass, in sea affairs, the usual appellation for a telescope. A night-glass is a telescope made for viewing objects at night. Half-bour glass, called also the watch-glass, is used to measure the time which each watch has to stay upon deck. Half and quarter-minute glasses are used to ascertain the rate of the ship's velocity, measured by the log ; these glasses should be frequently compared with a good stop-watch, to determine exactly how many seconds they run. GLAUBER (John Rudolph,) an industrious chemist, was born in Germany. After passing a considerable time in travel, he settled at Ansterdam, about the middle of the seventeenth century. He wrote a number of works, mostly infected with the enigmatical jargon and unintelligible theory of the hermetic philosophy, yet containing some useful facts in true chemistry, and some processes of his own invention. His name is perpetuated in the purgative neutral salt called Glauber's, composed of the sulphuric acid and soda ; a valuable remedy, but, together with others of his invention, extolled by himself to an extravagant degree. He kept several of his medicines secret, and made advantage of them as nostrums. Of his works an abridged collection was made in German, which was translated into English in 1689; but they are now consigned to oblivion. Glauben’s salt. See Soda, Sulphate of It is found native; and, according to Bergman, it contains sulphuric acid, soda, and water, in the proportions of 27.15.58; that is, when saturated with water of crystallization. When efflorescent, the native Glauber's salt contains, beside pure sulphate of soda, some oxide of iron, and portions of muriate and carbonate of soda. It is found in old salt mines, on the borders of the salt lakes in different parts of the world, and on the surface of peat-mosses in France. It is also held in solution in the Natron lakes of Egypt, and the mineral springs of Carlsbad. Glauber's salt easily dissolves in water, and shoots into long and beautiful crys
tals, which contain a large quantity of water, in consequence of which they undergo the aqueous fusion, when exposed to heat. This salt, on account of its efficacy as a purgative, was formerly held in the highest esteem, and was de- . nominated sal mirabile Glauberi. It has been used in some countries as a substitute for soda, in the manufacture of white lass. GLAUCOPIS, or the wattle-bird, in natural history, a genus of birds of the order Picac. Generic character : bill incurvate and arched; lower mandible shorter than the upper, and carunculate beneath at the base ; nostrils depressed, half covered with a cartilaginous membrane; tongue cartilaginous, split, and ciliated at the end ; legs carinated at the back; feet formed for walking. The G. cinerea, or cinereous wattlebird, is about the size of a jay; it is found in every part of New Zealand: berries, and insects of, almost every kind, constitute its food ; it rarely perches on trees; but is often seen walking on the ground: its notes are said at different times to resemble whistlings and murmurings, and its flesh is good for the table. GLAUX, in botany, a genus of the Pentandria Monogynia class and order. Natural order of Calycanthema. Salicariae, Jussieu. Essential character: calyx one-leafed, bell-shaped : corolla none ; capsule one-celled, five-valved, five-seeded. There is only one species, viz. G. maritima, sea milk-wort, or black saltwort. It is common on the sea coast, and on salt marshes at a distance from the sea; it is a beautiful little plant, enlivening large tracts of the dreary situations where it is found ; the whole plant is succulent, and salt to the taste. It is also a native of the United States. GLAZING, in the arts, is the polishing or crusting over earthen ware. When earthen ware is properly baked, it is dipped into a composition called a glaze, made by mixing together in water, till it becomes as thick as cream, fifty-six parts of white lead, twelve of ground #. and three of ground flint glass. The ware, by being baked, acquires a strong property ofimbibing moisture, and in this state it is called biscuit; when dipped into the glaze, it attracts it into its pores,
and the ware becomes presently dry; it
is then exposed a second time to the fire, by which means the glaze it has imbibed is melted, and a thin, glassy coat is formed upon the surface. The colour is more or less
yellow, according as a greater or less proroportion of lead has been used. The ead promotes also the vitrification ; the flint serves to give a consistency to the lead during the time of its vitrification, and to prevent its becoming too fluid, and running down the sides of the ware, and thereby leaving them unglazed. This kind of glazing by lead is liable to be attacked by acids, and of acting in some degree as a poison; a substitute has therefore been recommended, which conconsists of equal parts of white glass and soda finely pulverized, and exposed to a strong heat till quite dry, and with this the vessels are varnished or glazed. See PoTTERY. GLEANING, in law. It hath been said, that, by the common law and custom of England, the poor are allowed to enter and glean upon another's ground, after the harvest, without being guilty of trespass; and that this humane provision seems borrowed from the Mosaical law; but it is now positively settled, by a solemn judgment of the court of Common Pleas, that a right to glean in the harvest field cannot be claimed as a general right by every person at common law; nor as a custom by the poor of a parish, legally settled. GLEBE, or Glebe-land, is a portion of land, meadow, or pasture, belonging to, or parcel of, the parsonage or vicarage, over and above the tythes. Glebe lands, in the hands of the parson, shall not pay tithes to the vicar; nor, being in the hands of the vicar, shall they pay tithes to the parson. By statute 28 Hen, VIII. c. 11, every successor, on a month's warning after induction, shall have the mansion-house, and the glebe belonging thereto, not sown at the time of the predecessor's death. He that is instituted may enter into the glebe-land before induction, and has right to have it against any strangers. GLECHOMA, in botany, English ground-ivy, a genus of the Didynamia Gymnospermia class and order. Natural order of Verticillatae. Labiata, Jussieu. Essential character: calyx five-cleft; each pair of anthers converging in form of a cross. There is but one species, viz. G. hederacea, ground-ivy. GLEDITSIA, in botany, a genus of the Polygamia Dioecia class and order. Natural order of Lomentaceae. Leguminosae, Jussieu. Essential character : hermaphrodite ; calyx four-cleft; corolla fourpetal led; stamens six ; pistil one, le
gume. There is only one species, with several varieties. GLEE, in music, a vocal composition in three or more parts, generally consisting of more than one movement, the subject of which may be either gay, tender, or grave; bacchanalian, amatory, or pathetic. GLEET, in medicine, the flux of a thin, limpid humour from the urethra. GLINUS, in botany, a genus of the Dodecandria Pentagynia class and order. Natural order of Coryophyllei. Ficoideae, Jussieu. Essential character: calyx five-leaved; corolla none; nectaries cloven bristles; capsule five-cornered, fivecelled, five-valved, containing numerous seeds. There are three species. GLOBBA, in botany, a genus of the Diandria Monogynia, class and order. Natural order of Scitamineae. Cannae, Jussieu. Essential character: calyx superior, trifid; corolla equal, trifid; capsule three-celled ; seeds very many. There are four species. GLOBE, a round or spherical body, more usually called a sphere, bounded by one uniform convex surface, every point of which is equally distant from a point within, called its centre. Euclid defines the globe or sphere, to be a solid figure described by the revolution of a semi-circle about its diameter, which remains unmoved. Also, its axis is the fixed line or diameter about which the semi-circle revolves; and its centre is the same with that of the revolving semi-circle, a diameter of it being any right line that passes through the centre, and terminated both ways by the superficies of the sphere. Euclid, at the end of the twelfth book, shews that spheres are to one another in the triplicate ratio of their diameters, that is, their solidities are to one another as the cubes of their diameters. And Archimedes determines the real magnitudes and measures of the surfaces and solidities of spheres and their segments, in his treatise “De Sphaera et Cylindro.” viz. 1. That the superficies of any globe is equal to four times a great circle of it. 2. That any sphere is equal to two-thirds of its circumscribing cylinder, or of the cylinder of the same diameter and altitude. 3. That the curve surface of the segment of a globe, is equal to the circle whose radius is the line drawn from the vertex of the segment to the circumference of the base. 4. That the content of a solid sector of the globe is equal to a cone whose altitude is the radius of the globe, and its base equal to the curve superfices or the base of the sector, with many other properties. And from hence are easily deduced these practical rules for the surfaces and solidities of globes and their segments; viz. 1. “For the Surface of a globe,” multiply the square of the diameter by 3.1416; or o the diameter by the circumference. 2: “For the Solidity of a Globe,” multiply the cube of the diameter by .5236 (viz. onesixth of 3.1416); or multiply the surface by one-sixth of the diameter. , 3. “For the surface of a Segment,” multiply the diameter of the globe by the altitude of the segment, .# the product again by 3.1416. 4. “For the Solidity of a Segment,” multiply the square of the diameter of the globe by the difference between three times that diameter and twice the altitude of the segment, and the product again by .5236, or one-sixth of 3.1416. Hence, if d denote the diameter of the globe, c the circumference, a the altitude of any segment, and p = 3.1416; then
The surface. The solidity. In the globe pd-cd} pd In the segment pad 3 pd: x 34–2a See MENsun Ation.
GLOBE, in practical mathematics, an artificial spherical body, on the convex surface of which are represented the countries, seas, &c. of our earth; or the face of the heavens, the circles of the sphere, &c. That with the parts of the earth delineated upon its surface is called the terrestrial globe; and that with the constellations, &c. the celestial globe. These globes are placed in frames, with other appurtenances. Their principal use, besides serving as maps to distinguish the outward parts of the earth, and the situation of the fixed stars, is, to illustrate and explain the phenomena arising from the diurnal motion of the earth.
The globes commonly used are composed of plaister and paper in the following manner: A wooden axis is provided, somewhat less than the intended diameter of the globe, and into the extremes two iron wires are driven for poles: this axis is to be the beam or basis of the whole structure. On the axis are applied two spherical, or rather hemispherical caps, formed on a kind of wooden mould
or block. These caps consist of pasteboard or paper, laid one lay after another on the mould, to the thickness of a crownpiece; after which, having stood to dry and embody, making an incision along the middle, the two caps thus parted are slipo off the mould. They remain now to e applied on the poles of the axis, as before they were on those of the mould; and to fix them in their new place, the two edges are sowed together with packthread, &c. The rudiments of the globe thus laid, they proceed to strengthen and make it smooth and regular. In order to this, the two poles are hasped in a metalline semi-circle of the size intended, and a kind of plaster made of whiting, water, and glue, heated, melted, and incorporated together, is daubed all over the paer surface. In proportion as the plaster is applied, the ball is turned round in the semi-circle, the edge of which pares off whatever is superfluous, and beyond the due dimension, leaving the rest adhering in places that are short of it. After such application of plaster, the ball stands to dry; which done, it is put again in the semi-circle, and fresh matter applied: thus they continue alternately to apply the composition, and dry it, till the ball every where accurately touches the semicircle; in which state it is perfectly smooth, regular, and complete. The ball thus finished, it remains to paste the map or description on it. In order to this, the map is projected in several gores or gussets, all which join accurately on the spherical surface, and cover the whole ball. To direct the application of these gores, lines are drawn by a semi-circle on the surface of the ball, iii. it into a number of equal parts, corresponding to those of the gores, and subdividing those again answerably to the lines and divisions of the gores. The papers thus pasted on, there remains nothing but to colour and illuminate the globe, and to varnish it, the better to resist dust, moisture, &c. The globe itself thus finished, they hang it in a brass-meridian, with an hour-circle and a quadrant of altitude, and thus fit it inte a wooden horizon. There are ten principal circles represented upon globes, viz. six greater and four lesser ones. The greater circles are the horizon, meridian, and equinoctial, as it is called on the celestial, and equator on the terrestrial globe, the ecliptic drawn along the middle of the zodiac, and the two colures.