Maureen Johns, age 12, of Wilkinsburg, Penn., for her question:

WHEN WAS REFRIGERATION FIRST USED?

Refrigeration today keeps food from spoiling before you buy it in a supermarket and before you eat it at home.  Refrigeration process prevents spoilage by keeping foods at temperatures near or below freezing until you are ready toss them. These low temperatures slow down or completely stop the growth of microorganisms that can quickly ruin food.

Refrigeration is the process of producing low temperatures.  You can cool with ice or by machines.

Refrigeration takes place when heat is removed from a substance.

Perhaps the most important use of refrigeration today is with the preservation of food. In addition, however, refrigeration is used to cool homes, offices, stores and cars. It is also used for the storage of medicines and in cold vaults where furs are stored. Florists use refrigeration and so do the industries involved in the processing of rubber, lubricants and steel. It is also vital in producing frozen fruit juices, candy, photographic films and ice cream.

Refrigeration is based on the second law of thermodynamics. This law states that heat flows only from warmer bodies to colder bodies, or from a substance at a certain temperature to a substance at a lower temperature.

Ice is one of the oldest methods of refrigeration. As far back as 1000 B.C. the Chinese were cutting and storing blocks of ice which they used to keep food cold. The ancient Chinese discovered that ice absorbs heat as it melts.

Ice was the only form of home refrigeration used until mechanical refrigeration came along during the 1920s. The iceman would deliver a block of ice which was placed in the upper part of the icebox. The ice absorbed the heat from the warm air, and the cool air then increased its weight. The heavier cold air flowed downward to the food compartments. The air became lighter as it absorbed heat from the food. The warmer, lighter air then went up to the upper compartment where it again lost its heat to the cake of ice.

Using chemicals to reduce temperatures is another method of refrigeration that is not new. About 1550 the Italians found that a mixture of potassium nitrate and water could be used to cool bottled liquors.

A Massachusetts inventor named Jacob Perkins developed the first compression refrigeration machine in 1834.

A French engineer named Ferdinand Carre developed the first absorption refrigeration system during the 1850s while a German inventor named Carl von Linde introduced the first successful compression system using ammonia between 1873 and 1875.