Many medicine bottles have cork stoppers to keep the medicine from spilling. Life preservers are filled with cork. Cork is used for hot-dish plates. It is used in the caps of soft-drink bottles. Coasters to put under glasses of ice water are often made of it. So are some of the helmets which explorers wear in hot tropical lands. Artificial arms and legs are made of cork, too. Ground-up cork is used in linoleum. The centers of baseballs are cork. Cork is also placed between the double walls of refrigerators and cold storage rooms.

   Cork is certainly very useful. Four things about it make it so. It is so light that it floats on water. It is waterproof. It is elastic. Heat cannot travel through it easily.

   Cork comes from the bark of one kind of oak tree. The tree is the cork oak. Most trees have cork in their bark. But no other tree has so much as the cork oak.

   A cork oak has to be 20 years old before its cork is worth cutting. If the cork is then cut off carefully, a new layer will grow. Every seven or eight years the cork can be cut again.

   One big oak tree may furnish as much as 500 pounds of cork at a time. But most trees furnish much less.

   The cork is boiled as a way of cleaning and softening it. The rough outer layer is then scraped off.
   More than half of all the cork in the world comes from Portugal and Spain.

   Ships sailing away from those countries very often carry cargoes of baled cork. Some cork is now raised in California, but the yields are not yet very large.

   Buyers cut up the cork into the sizes and shapes they want. Some cork is cut so thin that 500 sheets would make a pile only an inch thick.