hold to an equal amount of rubbing as they are moved nearer to the centre of the table or further from it. Sand is used to grind down the glass, and this is fed from a box above as required. The grinding by this process is found to be even and equal, and the machinery to work smoothly and steadily from the facility with which the plates accommodate themselves to the power applied. In other operations one plate has been ground upon the face of another, being turned over and ground on their opposite sides when the first are completed. After grinding they are smoothed with emery powder of finer and finer qualities, and are thus prepared for polishing. This is accomplished in the American machine by having the cast iron table covered with rings coated with felt, which are screwed to its surface. The polishing material applied to the felt is oxide of iron or rouge. Polishing sometimes brings out defects which were before concealed; the plates are consequently again assorted, and, if need be, reduced to smaller sizes. (For the methods of silvering them, see MIRROR.) Bending the large plates or the smaller sheets of glass for the purpose of fitting them for bow windows, &c., is an especial branch of the manufacture, more extensively practised at the works of Messrs. Cooper and Belcher at Newark, N. J., than elsewhere. A core of refractory material and suitable shape is introduced upon the floor of the furnace; and upon this is laid the sheet to be bent, which as it softens by gravity conforms itself to the shape of the bed upon which it is laid. -Of the various kinds of glass in common use, none require more care to insure the purity of the materials employed than the crystal or flint glass, of which are made many choice articles for domestic purposes, some of which are subjected to the processes of cutting or grinding and polishing. It possesses the properties of great transparency and high refractive power, which fit it for lenses for optical instruments. Flints calcined and ground were formerly used to furnish the silica, but pure sand is now generally used instead. Oxide of lead enters largely into its composition, and to this are due its brilliancy, density, and comparative softness. The oxide should be prepared especially for the purpose to insure its purity. Oxide of zinc has been found to produce similar effects. As the glass is essentially and peculiarly of metallic composition, it might better be distinguished by this name than by those now applied to it. In the melting it is found necessary to use pots closed at the top with the opening made in a short neck on one side; this is to protect the melted matter from the smoke, which would discolor it, but the economy of direct exposure to the flame is thus lost. The English pots hold each about 18 cwt. The fusion must be rapid and at intense heat, and this must be reduced as soon as the metal is thoroughly melted and refined by the escape of the bubbles of gas, or the product acts upon the alumina and iron of the pot, and is thus so contaminated as

to be worthless. The method of shaping the articles by blowing them in a mould is applied to many of the vessels made of flint glass; and that the polish may not be affected it is necessary to keep the moulds nearly at a red heat as they are used. This glass is also shaped by the American process of pressing the soft metal in a die of the required form, into which it is introduced. For large articles considerable pressure is applied. The die is kept at a heat approaching redness, and at each operation must be furnished at once with the exact quantity of melted glass necessary to fill it, a feat which requires skill and practice. The process called cutting glass is in reality grinding and afterward polishing it. It is easily effected upon the soft flint glass by applying the surfaces to be cut to the face of revolving disks of iron or copper fed with emery, or, for coarse grinding, with sand and water. Stones are also used instead of the metallic disks. The marks of the rough grinding are removed by a smooth grindstone, and the polishing is then completed by wooden disks, to which pumice or rotten stone, and finally the preparation of tin and lead called putty powder, are applied. The fine polishing of chandelier drops is effected by a lead wheel supplied with fine rotten stone and water. Glass globes and lamp shades acquire their interior ground surface by the wearing action of sand placed within them, the globes being themselves introduced into the interior of a drum which is caused to rotate rapidly. Letters and designs are engraved on glass by means of small disks of copper set in rapid revolution, and fed with fine emery mixed with oil (see GEM ENGRAVING); or they may be etched.-No glass is of such importance in the arts as that of which the lenses of optical instruments are made. Both flint and crown glass are applied to this use, each of which has its defects; the former, from the great difference in the densities of its ingredients, is with much difficulty obtained of homogeneous structure, an essential requisite in all glass used for optical purposes; and the latter is difficult to procure of uniform composition and texture, from the high temperature required for its fusion and the consequent tendency to devitrify in cooling; or if this is obviated by increased proportion of alkali in the composition, the excess of this causes attraction of moisture from the air and a damp surface to the lens. So difficult was it to obtain even a moderate quantity of homogeneous glass, that until the production of the lenses of Guinand, a Swiss clockmaker, in the early part of the present century, the size of the largest objectives was limited to about 3 inches. By methods of his own he made with his own hands the furnaces, crucibles, and mixtures he employed, and produced the glass, which he shaped and polished, giving without knowledge of mathematics the requisite proportion to the curves of its surface, and completed lenses of flint glass of great perfection of structure, 9 inches in diameter. The secret of his success in making the glass is believed to

have consisted in keeping the mixture agitated by stirring when at its greatest liquidity, and then suffering it to cool and anneal in the pot. From the most perfect portions of the comparatively homogeneous mass thus obtained, the lenses were cut out by a process similar to that of sawing blocks of stone. By one of the sons of Guinand the secret was imparted to M. Bontemps; and in 1828 lenses were made in France of 12 to 14 inches diameter. In 1848 Bontemps removed to England, to join with the Messrs. Chance and co.; and the result of their operations has been the production of disks of flint glass 29 inches in diameter, weighing 2 cwt., and of crown glass 20 inches. These are of pure color, and of such homogeneous structure that the light is transmitted without polarization. Prof. Faraday, one of a committee appointed by the astronomical society of London to experiment upon the means of producing optical lenses, while Guinand's secret method of making these 6 inches in diameter was exciting the admiration of the scientific world, discovered the heavy glass called by his name, the composition of which has already been given, and which has proved of importance in investigations connected with the polarization of light; but its liability to change unfits it for general optical uses. Lenses both of flint and of crown glass are used in the object glass of achromatic telescopes, serving by their combination to counteract the unequal tendency of each to disperse the rays of light. The new optical glass of M. Maes of France has been found an excellent substitute for the crown glass lens; its basis is oxide of zinc, to which borax or boracic acid is added. The subject will be further treated in the article LENS.-The colored glasses are produced either upon the colorless composition called strass for imitations of precious stones (see GEMS, ARTIFICIAL), or by introducing the various oxides used for coloring into the materials of flint or other kinds of glass. Pigments are also applied to the surface of glass, and sometimes by their greater fusibility are burnt or melted in. Flint glass designed for vessels ornamented with colors may be employed of the composition already given as that of Mr. A. Pellatt, and to 6 cwt. of it the following ingredients are added for producing the respective colors: soft white enamel, 24 lbs. arsenic, 6 lbs. antimony; hard white enamel, 200 lbs. putty, prepared from tin and lead; blue transparent glass, 2 lbs. oxide of cobalt; azure blue, about 6 lbs. oxide of copper; ruby red, 4 oz. oxide of gold; amethyst or purple, 20 lbs. oxide of manganese; common orange, 12 lbs. iron ore and 4 lbs. manganese; emerald green, 12 lbs. copper scales and 12 lbs. iron ore; gold topaz color, 3 lbs. oxide of uranium. The colors produced by the metallic oxides are found to vary with the degree of heat employed. All the colors of the spectrum may be obtained with oxide of iron; and these various results do not seem to depend upon the different degrees of oxidation, but are thought to result from variations in mole

cular arrangement, induced perhaps by the action of light. Some of the methods of coloring the surface of glass are too ingenious and curious not to be noticed. The quantity of coloring matter required is often exceedingly small, and may advantageously be incorporated merely with the outer portion of the glass. This is effected in the blowing by dipping the lump of clear glass, when shaped upon the marver, into the pot of melted colored glass, and then blowing it to the shape required, and flashing out if desired to convert it into panes. The color may be afterward reduced in intensity by grinding, and colorless facets be produced by cutting through the outer portion to the clear glass beneath. "Casing" is a somewhat similar process. The article of flint glass when partially blown is inserted into a thin shell of colored glass, prepared at the same time for its reception, and the blowing is continued till the inner one fills the shell, with which it is afterward well incorporated by softening in the furnace and further blowing. Several partial casings of different colors may be thus applied. Painting is the external application of colors mixed with a flux of much easier fusion than the glass, and with some vehicle, as boiled oil or spirits of turpentine. The mixture is laid on with a brush as in ordinary painting, or by blocks as in printing cloths; and the glass being then exposed to heat, the flux melts and sinks into the body. None of the clear bright colors are perceived until the work is completed, and the artist consequently labors under great disadvantage in applying the materials that are to produce them. He is guided either by lines drawn on the back side, which show through, or by a cartoon or drawing on paper placed there. The flux, if the coloring oxides are such as not to be affected by oxides of lead and bismuth, is composed of 100 parts of pulverized quartz, 125 of oxide of lead, and 50 of oxide of bismuth; or, if otherwise, with the same quantity of quartz are mixed 75 parts of glass of borax, 123 of saltpetre, and 123 of pure carbonate of lime. In the early use of glass for windows, especially those of churches, brilliant colors were highly esteemed, and great success was attained in the methods of coloring. The art fell into disuse, and the processes were lost, though the receipts for them were still to be found in the ancient treatises. This was particularly the case with the bright red color, which was imparted by the ancients with the protoxide of copper. In later times it was found impracticable to succeed with this on account of the tendency of the copper to pass to a peroxide and produce a green tinge; of late the practice is again introduced with success by the Tyne company in England, at Choisy in France, and other places. The discovery of the preparation of gold and tin, called purple of Cassius, also afforded another means of producing a brilliant red, as noticed in GEMS, ARTIFICIAL. Notwithstanding the introduction of processes not formerly known, and a more

exact understanding of the effects of the various oxides, which probably cause the art to be now better understood than ever before, the colors are considered less brilliant than those of ancient times. From this description it appears that what is called glass painting, which is more properly a process of staining, differs from all other styles of the pictorial art, except the painting of porcelain. The colors are different, being wholly of mineral composition, and are not merely laid on the outside, but are fixed by being fused into the material, undergoing in the operation chemical changes that develop the brilliancy and transparency of which the compounds are susceptible. Thus the colors are removed from the influence of external causes of change, and are permanently retained upon the most fragile of materials. Soon after the introduction of glass into windows its appropriateness as a medium when colored for ornamentation of churches and other public edifices was perceived, and its first use for this purpose is believed to have been at the time when the ancient basilicas were converted into Christian temples, which, it is said, were adorned with stained glass. The magnificent churches erected on the continent of Europe in the 9th century were also generally thus ornamented. The glass was in small pieces brilliantly colored throughout, and set in leaden lines which were the outlines of the designs. Pictorial illustrations are not known to have been introduced before the 11th century. At that period there was a glass pic ture in a church window of the monastery of Dijon, which represented the mystery of the holy eucharist. In the year 949 mention was made, according to Mrs. Merrifield, of "a portrait of King Constantine (VII.) admirably executed on stained glass." In the ancient glass pictures the figures were formed of pieces of stained glass, and the shadows were laid on with dark colors and fixed in the fire. Intense colors were exclusively employed, the ruby and blue always predominant. The ground was mosaic in circles, squares, and lozenges, of massive forms, and filled with foliated ornaments in the Roman style. Over this were medallions representing historical and biographical subjects from the lives of the saints. When figures came to be introduced they were generally grotesque and distorted; but the costumes were remarkably correct. The designs always harmonized with the style of architecture, stately and magnificent in the Norman structures, and light and elegant in those of the early English models in the 13th century. In these the brilliant positive colors were made more subsidiary, appearing in borders, geometric bands, and central points, while the ground was of a neutral gray, produced by lines crossing each other at right angles. The designs were also more correctly drawn, and shaded with greater delicacy. For the violet tint always before used for the faces of the figures was substituted a gray or brown upon colorless glass. The pieces of glass were of larger size, and a single figure often was made to occupy a

whole window, standing beneath an elaborate blue or red canopy. In the background among the architectural fragmentary designs still appeared the old Roman foliated ornaments, but intermixed with original studies from nature, a style of the art which was afterward carried to great perfection. Not only leaves, plants, and trees, but even landscapes and buildings in perspective, appeared in the latter half of the 15th century; the smaller objects being introduced among the elaborate geometrical figures, which were arranged somewhat like frames around the principal figures. The Scripture pieces were often explained by legends painted upon the phylacteries, and in the background were represented rich blue or red hangings of damask. Among the glass pictures of the 16th century are found the finest specimens of the art. The most eminent painters practised it, as Albert Dürer, Claude, Palissy, and others, and their works are still admired in the churches of that period, as the Cologne cathedral, York minster, and many others. But in the next century the art had entirely declined, and has since found few votaries, for the reason, as Labarte suggests in his "Illustrated Handbook," that its intention was perverted in the transformation of an art of purely monumental decoration into an art of expression. For this oil painting possessed greater resources, and glass painting necessarily fell into neglect. In some modern attempts it is remarked that the primary object of the glass in transmitting light appears to be overlooked and sacrificed in the opaque shadows introduced. In 1830 a gorgeous glass picture representing the tourney between Henry VIII. and Francis I., at Ardres, June 25, 1520, was exhibited in Oxford street, London. It was a window 18 feet by 24, consisting of 350 pieces of glass, fitted into metal astragals, which were so concealed in the shadows that the whole appeared as one sheet of glass. It contained more than 100 life-size figures, 40 of which were portraits, among which were the two queens, Anne Boleyn, and Cardinal Wolsey. The picture was unfortunately destroyed by fire on the night of June 31, 1832.-ENAMELLED GLASS. Two varieties of enamelled glass, one known as "etched enamelled glass with clear ornaments," and the other as "flocked enamelled glass," are now largely made in Newark, N. J., in the works of Messrs. Cooper and Belcher of New York, the only manufacturers in the United States of the articles in large sheets, and the contractors for the enamelled glass for the New York crystal palace, for which 60,000 feet was furnished. The increasing demand for these beautiful varieties has recently led them to more than double the capacity of their works. The vitreous enamel which gives the opacity to this kind of glass was first devised by John Davenport of Burslem, England, who patented the process in July, 1804. From that time till 1837 the ornamental etching was effected by a tedious and expensive method by hand. William Cooper, then of Edinburgh, now the

Mr.

senior partner of the above named firm, in that year secured a patent for a new method of cutting ornamental devices by machinery, &c., on which is based the system now in use. The enamel substance is ground to an impalpable powder, and laid with a brush in a pasty state upon the glass. After the paste is dried, the ornament is etched out by machinery or by hand, and the glass is then softened in the intense heat of the reverberatory furnace till the enamel is vitrified and incorporated with it. From this it is removed to the annealing kiln, the capacity of which is 2,000 or 3,000 superficial feet of large sheets, which is the usual amount of a week's work. The flocked variety of enamelled glass is prepared by the same method as that of the clear etched glass just described, except that a fine, smooth, opaque surface, like satin, much softer and smoother than that of ground glass, is previously given to the whole surface before the enamel is applied. This variety has in great part supplanted the other, and is justly much admired for the softness of the light diffused through it, and for the delicacy and beauty of the elaborate and artistic designs with which it is ornamented. Sheets of it are prepared up to 60 inches in length.Etching is also applied to the ornamenting of glass, a process which is effected by the property of hydrofluoric acid to eat into the material, as described in the article FLUORINE. The glass is first covered over with a varnish that resists the action of the acid, and when this coating is dry, the lines to be etched are marked through it by means of a point. The acid is then poured on, and is allowed to remain till it has produced the desired effect. The difficulties and danger attending the use of the acid restrict this process to the ornamenting of large polished plates, and to the labelling in indelible letters the bottles of chemists and apothecaries.-GLASS, SOLUBLE, also known by the name of soluble silica, is a preparation of silica and caustic potash, either in equal parts, or in the form of a double silicate of potash and soda, which is soluble in boiling water. Attention was first directed to it by the chemist Von Fuchs as a suitable composition for rendering combustible bodies fire proof; and in 1824 portions of the new theatre in Munich were coated with it. He also employed the composition in the style of fresco painting called stereochromy, as a means of fixing the colors permanently (see FRESCO PAINTING); and it was used not only upon plastered walls, but with perfect success by Echter directly upon the sandstone of the Strasbourg minster. Von Fuchs proposed to render wood fire-proof, and even linen also, by means of it; to protect surfaces from the action of the weather; to prepare with it artificial stone; and to use it as a cement for glass and porcelain. But it appears to have been most successfully applied by Prof. Kuhlmann at Lille, who, as described by Liebig, manufactures it in enormous quantities to prevent the decay of walls and edifices, even when built of

very inferior stone, and for the use of print works and tapestry factories in fixing colors upon cotton and paper. In England also its preparation was early undertaken by Mr. F. Ransome of Ipswich, where many tons of the material are produced every week at the works of the "Patent Silicious Stone Company." Its preparation as a protective coating or as a cement depends on the principle, that when a caustic alkali in combination with silica becomes carbonated by exposure to the atmosphere, the silica is deposited in the pores of the material to which it is applied, and adheres closely to it; or if the stone be calcareous, as marble for instance, a chemical union takes place between the lime and liberated silicic acid. Mr. Ransome, finding this preparation imperfect from the liability of the silica to be washed away by the rains before it could set, applied a second solution consisting of chloride of calcium, which has the effect of causing a silicate of lime of great tenacity and indestructible by atmospheric influences to be immediately produced. His process is as follows: The walls being cleaned, a solution of silicate of soda or potash (the specific gravity of which may be varied to suit the nature of the stone) is applied with a brush; and when dry, the coating is in like manner brushed over with the chlo ride of calcium solution. The lime immediately combines with the silica, filling the pores of the stone, while the soluble salt of chlorine and soda which is also produced is removed at once by an excess of water. The union of the silica with the stone is found to be as perfect as that of the original particles of the stone itself. The soluble silica is prepared by dissolving carbonate of soda or potash in water, and then rendering the alkali caustic by the use of quicklime. The lime being removed, quartz crushed to powder is dissolved in the liquid in an iron boiler with the aid of steam pressure.

GLASS PAPER, a preparation similar to that of emery paper, made by dusting pulverized glass obtained from the fragments of broken wine bottles upon paper, which is brushed over with thin glue. The glass is first assorted by sifting into lots of different fineness. Instead of paper, thin cotton cloth is sometimes used.

GLASS SNAKE, a North American reptile, improperly called a snake, of the genus ophisaurus (Daudin), belonging to the order saurophidia of Gray, and to the chalcidian or cyclosaurian family of saurians of Duméril and Bibron. The head is lizard-like, sub-oval, with rounded snout, covered above with numerous polygonal plates, large anteriorly, the frontal the largest; the tongue arrow-shaped, triangularly grooved in front, free in its anterior extremity, on which the papillæ are granular; the nostrils are near the snout, lateral, opening upward; the eyes are small, protected by 2 movable unequal lids; there are several rows of short conical teeth, about 36 in number, on the roof of the mouth, chiefly on the pterygoid bones; the intermaxillary teeth are conical, the

maxillary simple and nearly cylindrical, about 40 in all above and 36 below; the external ear is a small oval opening just behind the angle of the mouth. There is no distinct neck; the body is elongated and snake-like, covered with small, smooth, slightly imbricated scales, disposed in circles around the body, about 120 in number; there is no vestige of anterior or posterior limbs externally, and only their rudiments internally; there is a deep groove separating the sides of the body from the abdomen, most visible during respiration, and which doubtless affords the free movement of the ends of the ribs necessary for progression. The tail forms at least of the total length, round, and tapering gradually to the tip, covered with about 140 rings of scales. Though the shape of this reptile is snake-like, the movable lids, external auditory openings, less movable vertebræ, less extensile tongue, rudimentary sternum, and above all the consolidation of the bones of the skull and jaws, sufficiently show its saurian affinities. The length varies from 2 to 3 feet. The head above is mottled with black and green, with a yellowish tinge on the jaws; the body and tail above are marked with longitudinal and transverse lines of black, green, and yellow, each scale marked with these 3 colors; the under surface is yellowish, brightest on the abdomen; some slight varieties of color are described. It is found on the Atlantic coast from southern Virginia to Florida, and as far west as the Mississippi, Missouri, and Ohio rivers; it has been seen west of the Alleghanies as far north as Michigan. From the smallness of its gape it cannot destroy and swallow large prey, like the serpents; it cannot climb nor swim, but passes its life on the surface of dry places or in natural cavities in the ground, living principally on mollusks, insects, annelids, and other small animals, and perhaps also partly on vegetable food like the sweet potato. It can move with considerable speed, and is taken uninjured with difficulty on account of the ease with which the joints of the tail are separated; the name of glass snake was given on account of this extreme fragility. The breaking of the tail into small pieces in this and in some scincoid reptiles seems to be the result of a reflex action in the spinal cord, as an irritation of this nervous centre will cause a separation even after the tail is divided from the body. Dr. Burnett ("Proceedings of the Boston Society of Natural History," vol. iv. p. 223) ascertained that the caudal muscles in this reptile do not pass from one vertebra to another, but that a portion are inserted into the skin, while others terminate midway between one vertebra and the next, dovetailed as it were between the fibres sent from that vertebra, and attached to them only by the myolemma; so that there is no rupture of muscular fibres, but only a separation of one layer of muscles from the adjoining one, when the tail of the animal is broken; the detached portion is said to be reproduced in a year. The glass snake in its anatomical

peculiarities of structure resembles the chalcidian amphisbæna and the scincoid blindworm (anguis fragilis), which see.

GLASSBRENNER, ADOLF, a Berlin humorist, born March 27, 1810. His principal work, Berlin wie es ist und trinkt, was published from 1832 to 1850. A new edition of his Verbotene Lieder appeared in Berlin in 1851, and of his Neuer Reineke Fuchs in 1854. His racy delineations of life, some of which have appeared under his nom de plume of Brennglas, have become very popular, especially in Berlin. Banished from that city in 1850 on account of his sympathies with the democratic party, he has since chiefly resided in Hamburg.

GLASSITES, a religious sect in Scotland, whose founder was John Glass (1695–1773), a minister of the Scottish established church, who was deposed in 1728 for avowing opinions adverse to all legal establishments of religion. Robert Sandeman advocated the same opinions about the middle of the century, from whom the sect is sometimes called Sandemanians. They hold peculiar views of justifying faith and ecclesiastical polity, maintaining a spiritual union of their members which is not represented by any visible church. They observe also certain practices which they suppose to have been prevalent among the early Christians, as love feasts, washing of each other's feet, plurality of elders, and mutual exhortations. In 1851 there were 12 Glassite congregations, with accommodations for about 2,000 persons.

GLASTONBURY, a market town and parish of Somerset, England, 25 m. S. W. from Bath; pop. in 1851, 3,125. The town occupies an eminence nearly surrounded by marshy flats, and derives its interest and importance almost wholly from its ruins, prominent among which are those of a famous Benedictine abbey, founded, it is said, by St. Augustin in 605, rebuilt in great splendor about a century later, and enriched by the liberality of successive princes until the time of Ethelred I. It suffered from the Danes, and before the conquest, when the Normans robbed it of both wealth and influence, had gained considerable importance and celebrity. Its half ruined walls were rebuilt by Stephen and Henry II., and its abbot was honored with a mitre and a seat among the barons in parliament. At one time it was annexed to the see of Wells, the incumbent of which was called bishop of Glastonbury. On the suppression of monasteries by Henry VIII. it enjoyed a revenue of £3,508 138. 44d. In 1539 Richard Whiting, the last abbot, for refusing to surrender the abbey to the king, was hanged in his robes on Torhill with two of his monks. The abbey ruins, consisting of portions of the church, the chapel of St. Joseph of Arimathea, and a building called the abbot's kitchen, are comprised in a quadrangle of 60 acres, which was once encompassed by a high wall. utation for sanctity clung to Glastonbury long after the reformation, and as late as 1751 we hear of 10,000 invalids flocking hither in a sin

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