Brian Nason, age 9, of Fredericton, N. B., for his question:

What is glass made of?

Once in a great while, Mother Nature mixes up a batch of glass. She uses silica, the common mineral from which most sand is made and she heats it up in the furnace of a seething volcano. The rocky silica melts into molten lava and, when it cools, becomes obsidian. Masses of this glassy black rock are found where volcanos once raged in Yellowstone Park.

It would cost far too much to heat a furnace as hot as a volcano. The cost of the fuel would make glass too expensive for everyday use. But we know how to make sandy silica melt with less heat. The trick was discovered long, long ago when a group of sailors spent the night on a sandy beach. They made a fire of driftwood and in the morning they found lumps of clear glass among the ,ashes .

Those sailors were not chemists and they did not know what happened, but we do know. The sand was made from the mineral silica. The driftwood ashes contained potash which is a strong soda or alkali. When silica is heated together with strong soda, it melts at a far lower temperature. It becomes a tacky fluid and when it cools it is glass.

This simple soda and silica glass, however, is very fragile. It melts in water, which is why we call it water glass. But when one more ingredient is added to the recipe, the finished glass is hard and firm. This third ingredient is lime. We enjoy many different kinds of glass and each one calls for a slightly different recipe, Traces of lead, magnesium, zinc, aluminum and other substances add spec;al qualities to the glass. Tints may be added with traces of copper, iron or even gold. But the basic ingredients of any glass‑making recipe are always silica, alkali and lime.

Sand provides the mineral silica, but it must be the right kind of sand. It must be fairly coarse end fairly pure. For examples if it contains a trace of iron, the finished glass will be green and no good for window panes.

Potash or sodium carbonate may be added to provide the alkali or strong soda for the recipe. Limestone i s usually added to provide the necessary lime. These three ingredients are cheap and plentiful. A load of old broken glass is added to the brew and the furnace heated to about 3,000 degrees Fahrenheit. This is very hot, but not nearly as hot as a volcano. The heat causes the ingredients to melt together and become a clear, tacky fluid.

While it is still hot or warm, the glass can be made into any shape we want. It may be rolled or pressed, molded or blown. Plate glass and the glass used to make mirrors must be given a very high glass. They are put through extra polishing processes.