Angie Beck, age 11, of East Peoria, I11., for her question:
HOW DOES ICE FORM?
When the temperature of the air reaches 32 degrees Fahrenheit, pure water and moisture will turn into ice. Ice is nothing more than frozen water.
At this low temperature, the motion of the water molecules becomes so slow that water crystallizes or freezes into ice. Impurities will lower the temperature at which water freezes. It takes a temperature of 28.5 degrees Fahrenheit, for example, to freeeze seawater because of the salt content.
When water turns into ice because of low temperatures, it increases its volume by one eleventh. This means that when 11 cubic centimeters of water freeze, 12 cubic centimeters of ice form. Thus, ice is lighter than water and it will float in it.
An icicle forms on a roof's edge sometimes as water melts from snow or as rain drips. When the temperature drops low enough, the drops of water form a tapering mass of ice. As more water hits the icicle and freezes, the longer the shaft of ice will grow.
Ice now adds to our comfort and health. Our refrigerators produce ice which helps to keep our fruits, vegetables and meats from spoiling.
Ice plants in the United States make about 21 million tons of ice each year for commercial purposes. Pure water is put into rectangular metal cans with open tops. The cans are then lowered into a solution of salty brine which is kept at a temperature between 6 and 18 degrees Fahrenheit. The water in the cans freezes first around the sides, so that expansion occurs toward the top, which freezes last. The open top prevents the cans from splitting.
After the cakes of ice freeze solid, the containers are lifted from the brine by hoists and dipped into warm water to loosen the cakes. The entire operation takes from 20 to 26 hours, depending on the size of the blocks and the temperature of the brine.
Sometimes commercial ice is made on the outside of a turning cylinder to produce small pieces.
For many years, natural ice was harvested in the United States from streams in many Northern states. The ice was first scraped clean of snow and dirt and then a machine called a marker cut a series of grooves about three feet apart up and down the stream, with parallel grooves then made across the grooves to mark blocks.
A plow then followed with a steel bar fitted with a set of sharp knives. The cakes of ice were next pried loose and floated to shore where they were put into icehouses and packed in sawdust.
Natural ice was first transported in the United States in 1799 when ice blocks were shipped from New York City to Charleston, S. C.
By 1870, refrigeration machines had been built using four different principles: cold air, vacuum, absorption and compression.