Crown glass is the lest description of •indowl.dass. it is made without ally mixture of metallic oxide, anti is both specifically lighter, and much harder, than flint glass. Broad glass is an inferior kind of window-glass, made with a cheaper kind of alakli. Plate-glass is superior in quality and in appearance to all other glass. From the quantity of metal it contains. it must he almost. if not a'together. colourless— that sort which is tinged, being of an inferior quality. It is both blown and east. Plates which are blown are limited in dimensions, while those that are east are made of very great size, the limit caused by the expensiveness of the machinery required for the management of very large masses of the material. Plate-glass is necessarily costly, because of the numerous and laborious operations which it undergoes, and of the risks of fracture while subjected to them. in sashes it has a magnificence peculiar to itself; objects seen through it are not distorted ; and objects seen in it, have the same fur appearance. It is now made of very large dimensions.
Glass has also been introduced as a material for the manu facture of pipes. 1\1r. James llartley, of Bishopweartnouth
Glass Works, has, after extensive experiments, succeeded in establishing the practicability of making glass pipes, suitable for the conveyance of gas or water, and has, it is also said, proved that pipes, stronger than the ordinary metal ones, and much cheaper, may be made of glass.
A still more novel application of this material is noticed in The Builder, viz.. the importation from Antwerp of a small parcel of glass-tiles. These tiles are similar in form to the common clay-tile for roofing buildings, the advantage held out being their lightness, and being pervious to the rays of the sun. The latter quality is presumed to render them suitable for the roofs of green-houses, as they will not inter rupt the heat and light, whilst they are sufficiently strong to resist the effects of hail-storms, which will much reduce the cost of insurance on green-houses. They have the appear ance of the MI1111011 green glass, they vary in price from eleven to sixteen shillings per dozen, according to their thickness and weight. See STAINED GLASS.