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ssss1.See article “Trade Unionism,” in last chapter.

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The term “glass,” in a general sense, is applied to the hard, brittle, non-crystalline, transparent, opaque or translucent vitreous substance which results from fusing silica with active mineral solvents or fluxes, such as the alkalies, earthy bases, or metallic oxides. Silica exists in great abundance, in a free natural state, in the form of flints, quartz, and sand; and in the latter form it is now most generally used for glassmaking. When sand alkali and lead oxide are heated together to a high temperature, the sand is dissolved by the solvent action of the fused alkali and lead oxide until the whole becomes a molten mass of glass. The solvent action of the alkalies, soda potash or lead oxide, is very energetic whilst being heated, and the mass boils with evolution of gases until, at last, the solution, becoming complete, settles down to a clear quiescent molten liquid metal, which is quite soft and malleable, after the nature of treacle. In this condition it is ready for working. The time and temperature necessary for melting such mixtures vary according to the proportions and composition of the ingredients.