Daniel McGee, age 12, of Nampa, Ids., for his question:
HOW IS ICE MADE?
Ice is nothing more than frozen water. Pure water and moisture in the air form ice at a temperature of 32 degrees Fahrenheit. At this point the motion of the water molecules becomes so slow that the water crystallizes or freezes into ice.
When water freezes, it increases its volume by 1/11th. This means that when 11 cubic centimeters of water freezes, 12 cubic centimeters of ice form. Thus, ice is lighter than water and will float on it.
Almost 25 million tons of manufactured ice are sold in the United States every year. This ice is made by freezing water in ice plants.
Manufactured ice is produced in large blocks that weigh about 300 pounds.
Pure water is placed in a long rectangular metal can with an open top. The can is lowered into a solution of brine or salt water. The brine is kept at a temperature of from 6 to 18 degrees Fahrenheit by running ammonia through pipes in the brine. The ammonia is evaporated from the liquid in a gas to make it very cold. It takes heat from the brine.
The water in the cans freezes first around the sides, so that expansion occurs toward the top, which freezes last. Thus, expansion does not split the can open as it does a container of water left outside in the winter.
After the cakes of ice freeze solid, the metal containers are lifted from the brine by hoists and dipped into warm water to loosen the cakes. The entire operation of forming ice and loosening it from the containers takes from 20 to 26 hours, depending on the size of the blocks and the temperature of the brine.
Other methods have been developed to freeze ice in smaller pieces. One method freezes the ice on the outside of a turning cylinder. Then the ice is removed in small flakes. Another machine freezes ice on the inside of a cylinder with ridges on it.
In the United States, natural ice was once harvested from streams in many Northern states. The ice was first scraped clean of snow and dirt. Next, a machine called a marker cut a series of grooves about three feet apart up and down the stream. Then it was drawn across the stream, marking parallel grooves the same distance apart. This made blocks of ice.
Next, a plow that had a steel bar fitted with a set of sharp knives followed the marker. It cut the grooves even deeper, so that it was easy to pry the cakes of ice loose and float them to shore through channels in the ice.
Sometimes power saws were used instead of the plow. They had rotating wheels with saw toothed edges.
After the cakes had floated to shore, they were slid up slanting boards or troughs into an icehouse and packed in sawdust. The icehouse was insulated to keep out heat and reduce melting.
The first artificial ice plant was set up in 1868 at New Orleans. The same year, the first refrigerator car was built. This meant that meat animals could be killed and packed in Texas and shipped to the East Coast without spoiling.