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tetrandra, heliocarpus, brionia zeylanica, aca- white; breast and belly reddish-grey. Four cia cornigera, bauhinia aculeata, prunus arme- other varieties from varieties of hues. Three niaca, amygdalus, morisona.
varieties inhabit the heaths of Europe, near the Glauds or glandules are usually found on banks of rivers ; two varieties are found on the the leaves, the petioles, the peduncles, or the coast of Coromandel. About nine inches long; sipules.
feeds on worms and aquatic insects; is very GLA’NDULE. s. (glandula, Lat.) A small restless and clamorous. gland serving to the secretion of humours 2. G. senegalensis. Senegal pratincole. Bill, (Ray).
legs, and whole body, brown. Inhabits near GLANDULOʻSITY.s. (from glandulous.) the Senegal; and also Siberia : nine and a half A collection of glands (Brown).
inches long. GLA’NDULOUS. a. (glundulosus, Latin.) 3. G. navia. Spotted pratincole. Brown Pertaining to the glands ; subsisting in the spotted with white; lower parts of the belly glands; having the nature of glands (Brown). and vent reddish-white, with black spots ; bill
GLANDULOUS LEAF, or GLANDULAR and legs black. Inhabits Germany: size of LEAF, in botany. A leat which has glands G. austriaca, either on the surface or on the serratures. GLA'REOUS. a. (glarieux, French, gla
GLANFORD BRIDGE. See BrugG. rcosus, Latin; from glaire.) Consisting of visGLANS PENIS, in anatomy. (Glans.) cous transparent matter, like the white of an The very
vascular body that forns the apes of egg: the penis. The posterior circle is termed the GLA'RING. a. Applied to any thing notocorona glandis. See CORPUS SPONGIOSUM rious; as, a glaring crime. URETHRE.
GLARUS, one of the thirteen cantons in GLANS UNCUENTARIA. See BEN NUX. Swisserland, bounded on the E. by the Gri
GLANVIL (Joseph), a learned and ingeni- sons; on the S. by the same, the canton of ous, but fancisul and credulous writer in the Uri, and that of Schweitz; and on the N. by 17th century, was born at Plymouth in 16:36, the river Linth. It is a mountainous country'; and bred at Osforil. He became a great ad- and their chief trade is in cattle, cheese, and mirer of Mr. Baxter, and a zealous person for a butter. The government is democratic: every commonwealth. After the restoration, he person of the age of sixteen has a vote in the published The Vanity of Dogmatizing; was Landsgemeind, or General Asseinbly, which chosen a fellow of the Royal Society; and, is held annually in an open plain. This assemtaking orders in 1662, was presented to the ri- Lly ratifies new laws, lays contributions, enters carage of Frome-Selwood in Somersetshire. into alliances, declares ivar, and makes peace.
This same year he published his Lux Orienta- The Lardamman is the chief of the republic, lis; in 1665 his Scepsis Scientifica ; and in the and is alternately chosen from among the proyear following, Some Philosophical Considera- testants and catholics; with this diference, iions touching the Being of Witches and Witch, that the former remains three years in office, erast, and other pieces on the same subject. the latter only two, Both secis live together In 1660 he published Plus Ultra ; or, The Pro- in the greatest harmony: in several parts, they rress and advancement of Knowledge since the successively perform divine service in the same Diys of Aristotle. He likewise published A church; and all the offices of siate are amiseasonable Recommendation and Defence of cably administered by both. The executive Reason ; and Philosophia Pia, or A Discourse power is in a council of regency, composed of of the religious Temper and Tendencies of the 48 protestants and 15 catholics; each sect has Experimental Philosophy. In 1678 he was its particular court of justice; and it is necesmade a prebendary of Worcester, and died in sary, in all lawsuits between persons of differ1680.
eni religions, that the person having the casting GLARE, in oryctology'. See ARENA, voice among the five or nine judges, who are
To GLARE. v. n. (glaeren, Dutch.) 1. To to determine the cause, should be of the same shine so as to dazzle the eyes (Fairfur). 2. To religion as the defendant. Glarus is surrounded Inok with fierce piercing eyes (Shakspeare). by the Alps except towards the north, where 3. To shine ostentatiously (leiton).
is the only entrance. The capital of this canTo GLARE. v. a. To shoot such splendour ton is of the same name, and is situated in lat. as the eyes cannot bear (Milton).
46. 56 N, Lon. 9. 1 E. GLARE. s. (froin the verb.) 1. Overpower- GLASGOW, a city of Scotland, in the ing lustre; splendour, such as dazzles the eyes county of Lanerk, situated on the banks of the (Pope). 2. A fierce piercing look (Milton). Clyde, which, by an act of parliament, and at
GLAREOLA. Pratincole. In zoology, a a considerable expence, has been within these genus of the class aves, order grallæ. Bill last thirty years made navigable for vessels strong, stout, straight, hooked at the tip; nos. drawing seven feet six inches of water. It was trils at the base of the bill linear, oblique; formerly the sce of a bishop, said to have been gape of the mouth Jarge ; feet four-toed; toes founded in the sixth century, and erected into Jong, slender, connected at the base by a mein- at archbishopric in the 15th. The cathedral branie; tail forbed, consisting of twelve feathers. escaped the ill-directed zeal of the reformers, Three species, as follow :
and still remains at least a venerable monu1. G. austriaca. Austrian pralincole. Above ment of Gotlıic architecture, preserved by the grey,brown; col'ar black ; chin and thrca care of the inhabitants. In the year 1972,
Glasgow was erected into a royal borough. In them by their great Hermes. Aristophanes, the year 1611, the city received a charter from Aristotle, Alexander, Aphrodiseus, Lucretius, and James VI., and, in 1636, another from king St. John the divine, put it out of all doubt that Charles I., with considerable power and privi- glass was used in their days. Pliny relates, that it leges, which charters were confirmed by acts of was first discovered accidentally in Syria, at the parliament in 1661 and 1690. The principal mouth of the river Belus, by certain merchants drivtrade of Glasgow formerly was the curing and continue there, and dress their victuals by makexporting of salmon and herrings, the principal ing a fire on the ground, where there was great market for which was France, from whence plenty of the berb kali; that plant, burning to they imported wines, brandy, and salt. On ashes, its salts mixed and incorporated withi the the union with England, in the year 1707, the sand, or stones fit for vitrification, and thus promerchants of Glasgow first eniered into the duced glass ; and that, this accident being known, American trade. And, in the year 1775, they the people of Sidon in that neighbourhood imported upwards of 57,000 hogsheads of to- essayed the work, and brought glass into use bacco, 5000 of sugar, upwards of 110 puncheons since which time the art has been continually imof rum, and 500 bags of cotton. Since the proving. Be this as it may, however, the first decline of the American trade, the merchants glass-houses mentioned in history were erected in Hare found out new channels, and the trade is the city of Tyre, and here was the only staple of still increasing. Varieties of manufactures are lay on the shore for about half a mile round the
the manufacture for many ages. The sand which earried on at Glasgow, the principal of which mouth of the river Belus was peculiarly adapted seem to be in the article of cotton, pottery, to the making of glass, as being neat and glittercoarse earıben ware, hats, stockings, gloves, ing; and the wide range of the Tyrian commerce ropes, cordage, glass, and several others. The gave an ample vent for the productions of the furnumber of inhabited houses in Glasgow is up- nace. waris of 12,000, and 86,380 inhabitanis. Mr. Nixon, in his observations on a plate of Glasgow was originally one parish, but pow, glass found at Herculaneum, which was destroyed for be benefit of the poor and ease of mi- A.D. 80, on which occasion Pliny lost his life. nisters, divided into eight, with as many offers several probable conjectures as to the uses churches, besides three chapels of ease. to which such plates might be applied. Such Glasgow contains several hospitals and charita- plates, he supposes, might serve for specula, or ble foundations, and a public ir firmary. The looking-glasses; for Pliny, in speaking of Sidon. vniuersity of Glasgow was founded in the year reflection of images from these ancient specula
adds, siquidem etiam specula excogitaverat: the 1 +5+, under the directiou of a chancellor, rec- being effected by besmearing them bebied, or tor, dean, principal, and fourteen professors. tinging them through with some dark colour. Distance 45 miles from Edinburgh. Lat. 55. Another use in which they might be employed W.13 42 X. Lon. 4. 2 W.
for adorning the walls of their apartments, by Glasgow (Port), a town in Renfrewshire, way of wainscot, to which Pliny is supposed to on the S. side of the Clyde, erected in 1710, to refer by his vitreæ cameræ, lib. xxxvi. cap. 25. § serve as the seaport of the city of Glasgow, 64. Mr. Nixon farther conjectures, that these from which it is distant about 21 miles. g'ass plates might be used for windows, as well as
GLASS, vitrum, a transparent, solid, brit- the jainina of lapis specularis and phengites, tle, facti. ious body, produced by a mixture of which were improvements in luxury mentioned by earthy or metallic, with saline substances fused Seneca, and introduced in his time, Ep. xc. Howe together by the action of fire.
ever, there is no positive authority relating to the The word is formed of the Latin glastum, a plant using of glass-windows earlier than the close of called, by the Greeks, isatis; by the Pomans, tie the third century : Manifestius est (says Lactantrum; by the ancient Britons, guadum; by the tius), mentem esse, quæ per oculos ea quæ sunt English, wcad. We find frequent mention of this opposita, transpiciat, quasi per fenestras lucente plant in ancient writers, particularly Cæsar, Vi- vitro aut speculari lapide obductas. truvius, Pliny, &c. who relate, that the ancient
The first time we hear of glass made among the Britons painted or dyed their bodies with glastum, Romans was in the reign of Tiberius, when Pling guarium, vitrum, &c. i. e. with the blue colour relates that an artist bad his bouse demolished for procured from this plant. And hence the facti- making glass malleable, or rather flexible; though tious matter, we are speaking of, came to be call. Petronius Arbiter and some others assure us, that ed glass, as having always somewhat of this the emperor ordered the artist to be beheaded for bluishn'ss in it.
his invention. At what time the art of glass-making was first It appears, however, that before the conquest of invented is altogether uncertain. Some imazine it Britain by the Romans, glass-houses had been to have been invented before the food: but of erected in this island, as well as in Gaul, Spain, this we have no direct proof, though there is no and Italy. Hence in many parts of the country improbability in the supposition; for we know, are to be found annulets of glass, having a narrow that it is almost impossible to excite a very vio: perforation and thick rin, deneminatıd by the rebent fire, such as is necessary in metallurgic ope- maining Britons gleineu naigreedh, or glass adrations, without vitrifying part of the bricks orders, and which were probably in former times stones wherewith the furnace is built. This, in- used as annulets by the druils. It can scarcely deed, might furnish the first hints of glass-mak. be questioned that the Britons were sufficiently ing; though it is also very probable, that such well versed in the manufacture of gass, to form imperfect vitrifications would be observed a long out of it many more useful instruments than the time before people thought of making any use of glass bals. History indeed assures us, that they m.
did manufacture a considerable quantity of glass The Egyptians boast, that this art was taught vessels. These, like their annuels, were most probably green, bine, yellow, or black, and many but even surpassed, the Venetians; and we are of them curiously streaked with other colours. now no longer supplied from abroad. The process in the inanufacture would be nearly The French made a considerable improvement the same with that of the Gauls and Spaniards. in the art of glass, by the invention of a method The sand of their shores, being reduced to a suf- of casting very large plates, till then unknown, Scient degree of fineness by art, was mixed with and scarce practised yet by any but themselves three-fourths of its weight of their nitre (much the and the English. That court applied itself with a saire with our kelp), and both were melted toge- laudable industry to cultivate and improve the ther. The pietal was then poured into other ves glass manufacture. A company of glass-unen was sels, where it was left to harden into a mass, and established by letters patent; and it was provided afterwards replaced in the furnace, where it be- by an arret, not only that the working in glass came transparent in the boiling, and was after should not derogate any thing from nobility, but wards figured by blowing or modelling in the even that none but nobles should be allowed to lathe into such ressels as they wanted.
work in it. It is not probable that the arrival of the Romans An extensive manufactory of this elegant and would improve the glass manufacture among the valuable branch of commerce was first established Britons. The taste of the Romans at that time in Lancashire, about the year 1773, through the was just the reverse of that of the inhabitants of spirited exertions of a very respectable body of this island. The former preferred silver and gold proprietors, who were incorporated by an act of to glass for the composition of their drinking-ves- parliament. From those various difficulties con. sels. They made, indeed, great improvements in stantly attendant upon new undertakings, when their own at Rome, during the government of they have to contend with powerful foreign estaNero. The vessels then formed of this metal rio blishments, it has not, however, been conducted valled the bowls of porcelain in their dearness, with any great degree of success. aud equalled the cups of erystal in their transpa- The properties of glass are very remarkable, rency. But these were by far too costly for com- some of which follow, non use; and therefore, in all probability, were 1. It is one of the most elastic bodies in nature. never attempted in Britain. The glass common. If the force with which glass balls strike each ly made use of by the Romans was of a qua- other be reckoned 16, that wherewith they recede Hity greatly inferior; and, froin the fragments by virtue of their elasticity will be nearly 15. which have been discovered at the stations or 2. When glass is suddenly cooled, it becomes towns of either, appear to have consisted of a exceedingly brittle; and this brittleness is somethick, sometimes white, but mostly blue green, times attended with very surprising phænomena. metal.
Hollow bells made of annealed glass, with a small According to the venerable Bede, artificers skilled hole in them, will fly to pieces by the heat of the in making glass for windows were brought over hand only, if the hole by which the internal and into England in the year 674 by abbot Benedict, external air communicate be stopped with a finger. who were employed in glazing the church and Lately, however, some vessels made of such anmonastery of Weremouth. According to others, nealed glass have been discovered, wbich have they were first brought over by Wilfrid, bishop of the remarkable property of resisting very hard Worcester, about the same time. Till this time strokes given froin without, though they shiver to the art of making such glass was unknown in Brie pieces by the shocks received from the fall of very tain; though glass windows did not begin to be light and minute bodies dropped into their cavities. common before the year 1180: till this period These glasses may be made of any sbape; a!! they were very scarce in private houses, and con- that need be observed in making them is, that sidered as a kind of luxury, and as marks of great their bottom be thicker than their sides. The magnificence. Italy had them first, next France, thicker the bottom is, the easier do the glasses from whence they came into England.
break. One whose bottom is three fingers breadth Venice for many years excelled all Europe in in thickness flies with as much ease at least as the the fineness of its glasses; and in the thirteenth thinnest glass. Some of these vessels have been century the Venetians were the only people that tried with strokes of a mallet sufficient to drive a had the secret of making crystal looking-glasses. nail into wood tolerably hard, and have held good The great glass-works were at Muran, or Murano, without breaking. They have also resisted the a viliage near the city, which furnished all Europe shock of several heavy bodies let fall into their cawith the finest and largest glasses.
vities, from the height of two or three feet; as The glass manufacture was ñrst beguin in Eng- musket-balls, pieces of iron or other metal, psland in 1557: the finer sort was made in the rites, jasper, wood, bone, &c. But this is not sure place called Crotched Friars, in London; the tine prising, as other glasses of the same shape and ilint glass, litile inferior to that of Venice, was first size will do the same: but the wonder is, that tak. made in the Savoy-house, in the Strand, London, ing a shiver of flint of the size of a small pea, an! This manuiacture appears to have been much im- letting it fall into the glass only from the height of prored in 1635, when it was carried on with sea- three inches, in about two seconds the glass flis, coal or pit-coal instead of wood, and a monopoly and sometimes at the very moment of the shock; was granted to sir Robert Mansell, who was allo- nay, a bit of flint no larger than a grain dropped ed to import the fine Venetian milit glasses for into several glasses successively, though it did not drinking, the art of making which was not brought immediately break them, yet when set by, they to perfection before the reign of William III. But all flew in less than three quarters of an hour. the first glars plates, for looking-glasses and coach. Some other bodies produce this effect as well as windows, were made in 1675, at Lambeth, by the fiint; as sapphire, diamond, porcelain, hard-tem. encouragement of the duke of Buckinghain; who pered steel; also marbles such as boys play with, in 1670 introduced the manufacture of fine glass and likewise pearls. These experiments were into England, by means of Venetian artists, with made before the Royal Society, and succeeded amazing success. So that within a century past, equally when the glasses were held in the hand, the French and English have not only conje up to, when they were rested on a pillow, pat in water,
or filled with trater. It is also remarkable, that their axis, and also a progressive motion towards the glasses broke upon having their bottoms slight- the fire, even when their supports are declining Iy rubbed with the finger, though some of them from the fire, so that the tubes will move a little did not fly till half an hour after the rubbing. If way up hill towards the fire. When the tubes are the glasses are every where extremely thin, they do placed in a nearly upright posture, leaning to the not break in these circumstances.
right hand, the motion will be from east to west; Some have pretended to account for these phæ- but if they lean to the left hand, their motion wil nomena, by saying, that the bodies dropped into be from west to east; and the nearer they are the vessels cause a concussion which is stronger placed to the perfectly upright posture, the lesa tban the cohesive force of the glass, and conse- will the motion be either way. If the tube is quently that a rupture must ensue. But why placed horizontally on a glass plane, the frag, does not a ball of iron, gold, silver, or copper, ment, for instance, of coach window-glass, instead which are perhaps a thousand times heavier than of moving towards the fire, it will more from it, Aint, produce the same effect? It is because they and about its axis in a contrary direction to what are not elastic. But surely iron is more elastic it had done before; nay, it will recede from the. than the end of one's finger. Mr. Euler has en- fire, and more a little up hill when the plane in deavoured to account for these appearances from clines towards the fire. These experiments are his principles of percussion. He thinks that this recorded in the Philosophical Transactions. They experiment entirely overthrows the opinion of succeeded best with tubes about 20 or 22 inches those who measure the force of percussion by the long, which had in each end a pretty strong pin vis viva, or absolute apparent strength of the fixed in cork for an axis. stroke. According to his principles, the great The reason given for these phænomena is the hardness and angular figure of the flint, which swelling of the tubes towards the fire by the heat, makes the space of contact with the glass ex- which is known to expand all bodies. For, say tremely small, ought to cause an impression on the adopters of this hypothesis, granting the exist. the glass vastly reater than lead, or any other ence of such a swelling, gravity must pull the tube metal; and this may account for the fint's break- down when supported near its extremities; and a ing the vessel, though the bullet, even falling from fresh part being exposed to the fire, it must also a considerable height, does no damage. Hollow swell out and fall down, and so on. But, without cups made of green bottle-glass, some of them going farther in the explanation of this hypothree inchies thick at the bottom, were instantly ihesis, it may be here remarked, that the fundabroken by a shiver of fint, weighing about two mental principle on which it proceeds is false : for grains, though they had resisted the shock of a though fire indeed makes bodies expand, it does musket-ball from the height of three feet. not increase them in weight; and therefore the
That Mr. Euler's theory cannot be conclusive sides of the tube, though one of them is expanded any more than the other, mast appear evident from by the fire, must still remain in equilibrio; and a very slight consicieration. It is not by angue hence we must conclude, that the cause of these lar bodies alone that the glasses are broken. The phænomena remain yet to be discovered. marbles with which children play are round, and 4. Glass is less dilatable by heat than metalline yet they have the same effect with the angular substances, and solid glass sticks are less dilatable fint. Besides, if it was the mere force of percus- than tubes. This was first discovered by Col. sion which broke the glasses, undoubtedly the Roy (see Phil. Trans. vol. Ixvii. p. 663), in makfracture would always take place at the very in ing experiments in order to reduce barometers ta stant of the stroke; but we have seen, that this a greater degree of exactness than hath hitherto did not happen sometimes till a very considerable been found practicable; and since his experi. space of time had elapsed. It is evident, there- ments were made, one of the tubes 13 inches fore, that this effect is occasioned by the putting long, being compared with a solid glass rod of the in motion some subtile fluid with which the sub- same length, the fornier was found by a pyromestance of the glass is filled, and that the motions ter to expand four times as much as the other, in of this fluid, when once excited in a particular a heat approaching to that of boiling oil. On ac. part of the glass, soon propagate themselves count of the general quality which glass has of through the whole or greatest part of it, by which expanding less than metal, M. de Lue recommeans the cohesive power becomes at last too mends it to be used in pendulums: and be says it weak to resist them. There can be little doubt has also this good quality, that its expansions are that the Aaid just now mentioned is that of always equable and proportioned to the degrees plectricity. It is known to exist in glass in of heat; a quality which is not to be found in ang very great quantity; and it also is koown to he other substance yet known. capable of breaking glasses, eren when annealed 5. Glass appears to be more fit for the conwith the greatest care, if put into too violent a densation of vapours than metallic substances. motion. Probably the couling of glass hastily An open glass filled with water, in the sun mer may make it more electric than is consistent with time, will gather drops of water on the ontsisie, its cohesive power, so that it is broken by the just as far as the water in the inside reaches; and least increase of motion in the electric fuid by a person's breath blown on it manifestly moistens friction or oth-rwise. This is evidently the case it. Glass also becomes moist with dew, when me, when it is broken by rubbing with the finger; but tais do pot. why it should also break by the mere contact of 6. A drinking-glass partly filled with water, and Bint and the other bodies above mentioned, has rubbed on the brim with a wet linger, yields milpot yet been satisfactorily accounted for.
sical notes, higher or lower as the glass is inore or Amost remarkable phænomenori also is produc. less full, and will make the liquor frisk and leap ed in glass tabes placed in certain circumstances. about. See ARMONICA. When these are laid before a fire in an horizontal 7. Glass is possessed of extraordinary electrical position, having their extremities properly sup- virtues. See ELECTRICITY, passim. portcd, tbey acquire a rotatory motion sound GLASS (blanufacture of). Glass is made from hand, flints, spar, or some other silicious matters. furnace; as do all others where much of the arsen White sand is the substance in the most repute at nic is employed. present, as it requires no preparation for coarse “ For looking-glass plates, washed white sand goods; and for the finest wasbing in fair water is 60lbs., purified pearl-ashes 25lbs., pitre 15lbs., and sufficient: whereas flints require a tedious process seven pounds of borax. If properly managed, this of calcination, and after that to be pulverized. glass will be colourless. But if it should be tinged Many other substances may be used for experi- by accident, à trifling quantity of arsenic, and an anent; though sand only is employed in the ma- equal quantity of magnesia, will correct it; az nufactory.
ounce of each may be tried first, and the quantiIt is also necessary that the silicious matter ly increased if necessary. should be fused in contact with something called “ The ingredients for the best crown-glass must a flux. The substances proper for this purpose be prepared in the same manner as for lookingare lead, borax, arsenic, nitre, or any alkaline glasses, and inixed in the following proportions: matter. The lead is used in the state of red lead, 60lbs. of white sand, 30lbs. of pearl ashes, and and the alkalies are soda, pearl ashes, sea salt, 151bs. of nitre, borax a pound, and half a pound and wood ashes. When red lead is used alone, it of arsenic. gives the glass a yellow cast, and requires the ad. “Tbe composition for common green window dition of nitre to correct it. Arsenic, in the same glass is 120lbs. of white sand, 30lbs. of unpurified manner, if used in excess, is apt to render the pearl ashes, wood ashes well burnt and sifted, 60lbs. glass milky. For a perfectly transparent glass, common salt 20lbs., and five pounds of arsenic. the pearl ashes are found much superior to lead; “ Common green bottle-glass is made from perhaps better than any other flux, except it be 200lbs. of wuodashes, and 100lbs. of sand; or borax, which is too expensive to be used, except 170lbs. of ashes, 100lbs. of sand, and 50lbs. of the for experiments, or for the best looking-glasses. lava of an iron-furnace: these materials must be
The materials for making glass must first be well mixed.” reduced to powder, which is done in mortars or The inaterials employed in the manufactory of by horse-mijls. After sitting ont the coarse parts, glass are by chemists reduced to three classes, the proper proportions of silex and Aux are mixed namely, alkalies, earths, and metallic oxides. together and put into the calcining furnace, where The fixed alkalies may be employed indifferthey are kept in a moderate heat for five or six ently; but soda is preferred in this country. The hours, being frequently stirred about during the sola of commerce is usually mixed with common process. When taken out the matter is called salt, and combined with carbonic acid. It is frit. Frit is easily converted into glass by only proper to purify it from both of these foreign pounding it, and vitrifying it in the melting pots bodies before using it. This, however, is seldom of this glass furnace: but in making fine glass it done. will sometimes require a small addition of flux to The carths are silica, lime, and sometimes a the frit to correct any fault. For, as the Aux is little alumina. Silica constitutes the basis of the most expensive article, the manufacturer will glass. It is employed in the state of fine sind or xather put too little at first than otherwise, as he flints; and sometimes, for inaking very fine glass, 420 remedy tiis defect in the melting pot. Tlie rock crystal is employed. When sand is user, it beat in the furnace must be kept up until the glass ought it possible to be perfectly white; for when it js brought to a state of perfect fusion; and during is coloured with metallic oxides, the transparency this process any scuin which arises must be re- of the glass is injured. Such saud can only be 211oved by ladles. When the glass is perfectly employed for very coarse glasses. It is necessamelted, the glass-blowers commence their opera- ry to free the sand from all the loose earthy par. tions.
ticles with which it may be mixed, which is done The following compositions of the ingredients by washing it well with water. for glass are extracted from the Handmaid to the Lime renders glass less brittle, and enables it to Arts :
withstand better the action of the atmosphere. “ For the best fint-glass, 120lbs. of white sand, It ought in no case to exceed the twentieth part 50lbs. of red lead, 40lbs. of the best pearl-ashes, of the silica employed, otberwise it corrodes the 20lbs. of nitre, and five ounces of magnesia; if a glass pots. This indeed may be prevented by pound or two of arsenie be added, the composition throwing a little clay into the melted glass; but in will fuse much quicker, and with a lower tempe. that case a green glass only is obtained. rature.
The metallic oxyds employed are the red oxyd “ For a cheaper fint-glass, 120lbs. white sand, of load or litharge, and the white oxyd of arsenic. 35lbs. of pearl-ashes, 40lbs. red lcas), 13lbs. of nitre, The red oxyd of lead, when added in sufficient six pounds of arsenic, and four ounces of magne- quavtity, enters into fusion with silica, and forms sia.
a glass without the addition of any other ingre" This requires a long heating to make clear dient. Five parts of minium and two of silica form glass; and the heat should be brought on gradual- a glass of an orange-colour and full of striæ. Its ly, or the arsenic is in danger of subliming before specific gravity is five. The red oxyd of lead the fusion commences. A still cheaper composi- renders glass less brittle and more fusible; but, rion is made by omitting the arsenic in the fore- when added beyond a certain proportion, it injures going, and substituting common sea salt.
transparency and the whiteness of glass. “ For the best German crystal glass, 120lbs. of The white oxyd of arsenic answers the same calcined Aints or white sand, the best pearl-ashes purposes with that of lead; but on account of its 70lbs., saltpetre 10lbs., arsenic lialf a pound, and poisonous qualities it is seldom used. It is custofive ounces of magnesia. Or, a cheaper compo- mary to add a little nitre to the white orpil of arsition for the same purpose is, 1201bs. of sand or senic, to prevent the heat from reviving it, and fints, 461bs. of pearl-ashes, seven pounds of nitre, rendering it volatile. When added beyond a cersix pounds of arsenic, and tive ounces of magne- tain proportion, it renders glass opaque and milky sia. This will require a lows continuanre in the like the dial-plate of a watch. When any com.