David LQ Schemel, aged 7, of Denver, Colo., for his question:

What do they use to make bricks?

Men discovered how to make bricks many thousands of years ago. They used the soft mud from the floors of rivers. They patted this damp clay into brick‑shaped mud pie and let it dry in the sun. In the land of the Pharoahs they dug brick clay in and around the muddy Nile. The American Indians also knew how to make bricks from mud. We learned from them how to make houses of this adobe brick.

These sun‑baked adobe bricks are fine in warm climates. But adobe bricks tend to crack in frosty weather. This is because the sun does not dry out all the moisture from the clay. If the adobe brick freezes this moisture expands as it turns to ice. This is what cracks the bricks. So the people of colder climates needed tougher, drier bricks than the ones the old sun could bake for them.

All bricks are made of clay and other earthy materials. These things are plentiful and free for the taking. Almost any kind of fine clay can be made into bricks. You may wonder then why bricks for making buildings cost money. The answer is work. It takes hard work, special know‑.how, power driven machines and hot, hot fires to turn clay into sturdy bricks.

Steam shovels dig up the clay. Trucks tote it in loads to the brickyards. More machines chomp it and sift out the stoney lumps. Then comes a man with know‑how. He knows gust how much sand to mix with his brick clay. Too much sand, and his bricks will crumble. Too little sand, and they will crack. Maybe he adds powdered coal to his recipe. This burns out in the furnace and cooks the brick all the way through.

The muddy mixture is then squeezed through a machine. It comes out in a long slab. Another machine slices the slab into bricks ‑ 19 at a time. This machine may slice a quarter of a million bricks a day. Next, more men with know‑how load the damp bricks onto a wagon. This load is ready for its first baking.

There are several ways of baking bricks. Old fashioned methods may take six weeks. Modern methods can burn muddy clay into sturdy bricks in a few days. The trick is to raise the heat gradually and give the bricks plenty of time to cool off. The ovens for baking the bricks are called kilns. At some time during the cooking the bricks must reach a temperature of 2,100 degrees Fahrenheit.

By modern methods, the first baking takes about 24 hours The bricks pass through a tunnel of heated air.  Each brick looses about one pound of moisture.  If the temperature of this chamber is not kept just right, a scum will form on the finished brick. When the bricks cool off they are ready for the real hot furnace.

Some kilns can bake 3,000,000 bricks at a time. The cooking may last for six weeks. More modern kilns bake a million bricks in 72 hours. The heat builds up slowly and the bricks take two days to cool after the firing.