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Joel Grossman, ago 13, of Bridgeport, Conn., for the question:

How do they make bricks?

Old Mother Earth provided us with plenty of material to make bricks. For bricks are made from mud, or rather from clay, which is a form of mud, Just the right amount of sand is added to the recipe and heat is needed to bake it. Brick making is the adult version of making mud pies.

The simplest bricks are, in fact no more than mud pies. The wet clay or mud, is packed into molds and lift to dry in the sun. The result is a row of sturdy adobe bricks. Adobe buildings are fine in warm, dry climates. But these glorified mud pies tend to crack in the frost and melt in the rain.

Mankind learned how to improve his bricks by baking them at least 6,000 years ago. When the mud bricks are baked for a long time in a very hot oven the soft clay does through chemical changes. It turns into hard, solid brick, a substance which refuses to melt and will not crack from the frost. Some of the oven‑baked bricks made in old Babylon 6,000 years ago are still in existence.

Clay for making bricks is composed of aluminum and silicates. These substances are very plentiful, indeed. The clay needs to be fairly fine and there are usually impurities which add color to the finished product. When iron is Present in the clay the baked bricks have a rosy color. Limo or chalk add yellow or saffron to the bricks.

The clay is sifted to remove pebbles and debris. Sand is added or the bricks would be weak and crumble. Sometimes anthracite coal dust is added to help the burning process. Finally the wonderful ingredients are mixed with water and kneaded into a stiff paste.

The individual mud pies are male by a machine. The stiff paste is squeezed into columns and the columns are sliced by wires. A big brick making machine can slice 300,000 bricks a day.

The bricks arc then stacked onto wagons and sent through a drying tunnel. This takes a day and a night, during which time each brick loses a pound of moisture. Now the little mud pies are ready to be baked in an oven called a kiln. This process takes many days and thousands, perhaps millions, of bricks are baked together. The heat is built up slowly over several days.

The kiln must reach a temperature of at least 2,000 degrees Fahrenheit. Then the heat is lowered gradually, for the cooling process is slow. It is several days before the bricks are ready to come out of their oven.

Bricks may be piled around a fire to form their own kiln. This is a very slow job and may take as long as six weeks. A permanent kiln is oval or circular to allow the heat to curve up, over and around all sides of the bricks. Some plants are so large that a million bricks may be piled to fire at one time. Heat is provided by burning oil. Some kilns are over 400 feet long. The bricks pass through on trolleys while the heat around them builds up and cools.

The finished brick is no longer a mud pie. It is a sturdy building stone, able to withstand the weather for hundreds, maybe thousands, of years.

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