| Bricks or blocks, however you call it, are a | | | | exactly this size. |
| common, cheap, and very useful building material | | | | Bricks range in color from nearly white, through |
| made of baked clay. Blocks are one of man's | | | | tan, red, and red-brown, to dark purple and blue. |
| oldest permanent building materials. Bricks are | | | | The color is determined by the amount of iron |
| durable, easy to build into walls, and cost little to | | | | and other impurities in the clay and by the |
| make. Ordinary brick can stand the direct flames | | | | method of baking, or firing, the brick. Usually the |
| of a fire with little damage, and firebrick (a special | | | | higher the baking temperature used, the darker |
| brick used for lining furnaces) can stand | | | | the brick will be. Bricks may also be glazed in |
| temperatures as high as 4000 degrees Fahrenheit. | | | | various colors, like pottery. |
| The clay in brick is highly resistant to acids, so | | | | The strength of brick also varies a great deal. |
| that brick walls can withstand the smoky, | | | | Brick has high compressive strength; that is, it can |
| corrosive air of cities better than some kinds of | | | | withstand forces that press in on it. But brick |
| stone and painted metal. | | | | does not have tensile strength -it cannot |
| Bricks have been made in many sizes and shapes | | | | withstand forces that tend to pull it apart. The |
| since they were first used over 5,000 years ago. | | | | average brick can take a load of about 5,000 |
| At the present time the standard brick in the | | | | pounds a square inch before it is crushed. Several |
| United States is a rectangular block measuring | | | | types of brick can stand a load as high as 10,000 |
| about 21.25 by 3.75 by 8 inches. Most bricks | | | | pounds a square inch. |
| shrink a little during baking, so that few are | | | | |