[An abstract of a Lecture on —ldquo; Glass,—rdquo; deli vered before the Mechanics' Institute, at Cin-cinnafe, Ohio, by Prof-iChas. W. Wright] “Who, when he saw the first sand or ashes by a casual intenseness of heat, melted into a metalline form, rugged with excrescences, and clouded with impurities, would have imagiued that, in this shapeless lump, lay concealed so many conveniences of life as would, in time,: constitute a great part of the happiness of the world ? Yet, by some such fortuitous liqui-laction was mankind taught to procure a body at once in a high degree solid and transparent, which might admit the light of the sun, and exclude the violence of the wind ; which might extend the sight of the philosopher to new ranges of existence, and .jharm him at one time with the unbounded extent of mate rial creation, and at another with the endless subordination of animal life ; and what is yet of more importance, might supply the decays of nature, and succor old age with subsidiary sight. Thus was the first artificer in glass employed, though without his knowledge or expectation. He was facilitating and pro longing the enjoyment of light, enlarging the avenues of science, and conferring the high est and most lasting pleasures; he was ena bling the student to contemplate nature, and the beauty to behold herself.” Of the origin of the discovery of the art of manufacturing glass, we know positively no thing. Pliny mentions the art of glass-ma king as carried on in Sid on and Alexandria. The story ot its having been discovered by the accidental fusion of sand and soda in an ordinary fire, is without any foundation in truth, for the heat ot a common fire is insuf ficient to cause these substances to combine and form glass. In England the first establishment for the manufacture of glass was erected in the year 1557 ; and yet, notwithstanding glass-making, .has been carried on for such a if!eat length of time, we are mainly indebted to Berzelius, who died but a few years since, for our know ledge of the chemistry of this most interesting subject. Glass is a salt, and is generally composed of silicic acid or sand, combined with soda or potassa, and various other bases. When soda is used a more brilliant lustre is obtained, but it is apt, when used in excess, to communicate a greenish tint to glass. When potassa is used, a perfectly colorless glass is formed, but which is not so brilliant as when soda is the base em-ployed. The silicates of soda and potassa never show any disposition to assume the crystalline form, but remain amorphous and transparent. Lime is sometimes added to the materials for ma king glass, and increases its brilliancy and hardness. Oxyde of lead is occasionally used and has the effect of rendering the glass soft, fusible, very brilliant, and perfectly transpa rent. Common window glass is composed of the silicates of soda and lime. It is of a greenish color and not very fusible. When long ex posed to the atmosphere the soda is partially dissolved out by the moisture! and its trans parency impaired. In the vicinity of stables and other places where ammonia is evolved by the putrefaction of organic matter, the si lica of the glass is affected, and its transpa rency diminished. Bohemian glass, crown glass, and plate-glass used for covering pictures, and for mir rors are composed of silicates of potassa and lime. This is the kind of glass used for stain ing and other ornamental work. This glass is affected in the same manner by atmosphe ric and other agents, as common window-glass. Strass, crystal, and flint-glass are composed of the silicates of potassa and lead. Glass of this composition is very fusible, perfectly transparent, and possesses great refractive power for light. Jewellers use this kind of glass in the imitations of the precious stones. This variety of glass is blackened when long exposed to an atmosphere containing sulphu retted hydrogen gas, from conversion of the lead into the sulphide of that metal. Bottle-glass, besides containing the silicate of soda or potassa, is also composed of the si licates of oxyde of iron, magnesia, and alu mina. It is used in the construction of car boys, wine-bottles, and all low-priced articles of glass- ware. Silicic acid, when combined with soda or potassa, or both, forms a glass that is soluble in water, and which has been used to render cloth and wood incombustible, by applying it as a varnish. It is the lime or oxyde ot lead that renders glass comparatively insoluble in water. Glass is colored or stained with various me tallic oxydes. Thus a blue color is communi cated to glass by the addition of the oxyde of cobalt. The coloring power of cobalt ex ceeds that of any other substance. The oxydes of iron, copper, and gold, produce the various shades of red that are seen in ornamental glass ware. The oxydes of antimony and uranium are employed to give a yellow tint, and a green is produced by the oxyde of chromium. Glass beads are made by cutting rings irom small glass tubes, and destroying the sharp edges by heating them in charcoal dust till they become perfectly smooth by fusion.
This article was originally published with the title "Lectures on Chemistry.—No. 6"