Common glass is made from three substances with which you are all more or less familiar; namely, sand, sodium carbonate (washing soda), and lime.

If sand and soda or potash are mixed and heated to a high temperature, they melt together and produce a glass which dissolves in water. This is known as "water glass" and it is used in many ways: to preserve eggs, to cement fire bricks, to make fireproof cement, and so on. If, however, lime is added and the mixture is heated to a high temperature, a glass is produced which is not soluble in water. This is the glass you know.

The three most common kinds of glass are: Venetian glass, made from sand, soda, and lime; Bohemian glass, from sand, potash, and lime; and crystal or flint glass, from sand, potash, and lead oxide.

Water runs up tube

Second Step In Making Window Panes

Fig. 22. Ironing the cylinders flame