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

Water runs up tube

Second Step In Making Window Panes

Second Step In Making Window Panes

Ironing the cylinders flame

Fig. 22. Ironing the cylinders flame