Questions 17-20 are based on the following passage.

    Cold Storage, refrigeration, is keeping food at temperatures between 32 and 45 degrees F in order to delay the growth of microorganisms— bacteria, molds, and yeast - that cause food to spail. Refrigeration produces few changes in food, so meats, fish, eggs, milk, fruits, and vegetables keep their original flavor, color, and nutrition. Before artificial refrigeration was invented, people stored perishable food with ice or snow to lengthen its storage time. Preserving food by keeping it in an ice-filed pities 40-year-old art. Cold storage areas were built in basements, cellars, or caves, lined. with wood or straw, and packed with ice. The ice was transported from mountains or harvested from. local lakes or rivers.

    Artificial refrigeration is the process of removing heat from a substance, container, or enclosed area, to lower its temperature. The heat is moved from the inside of the container to the outside. A refrigerator uses the evaporation of a volatile liquid, or refrigerant, to absorb heat. In most types of refrigerators, the refrigerant is compressed, pumped through a pipe, and allowed to vaporize. AS. the liquid turns to vapor, it absorbs heat because the molecules of vapor use energy to leave the liquid. The molecules left behind have less energy and so the liquid becomes colder. Thus, the air inside the refrigerator is chilled.

    Willem Cullen demonstrated artificial refrigeration in Scotland in 1748, when he let ethyl ether boil into partial vacuum. In 1805, American inventor Oliver Evans designed the first refrigeration ‘machine that used vapor instead of liquid. In 1842, physician John Gorrie used Evan'sdesignto create an air-cooling apparatus to treat yellow-fever patients in a Florida hospital. Gorrie’s basic principle of compressing a gas, and then sending it through radiating coils to cool it, is the one most often used. in refrigerators today. Gorrie later experimented with ice making, and in 1851 he has ranted the first US. patent for mechanical refrigeration. In the same year, an Australian printer, James Harrison, built an ether refrigerator after noticing that when he cleaned his type with ether it became very cold as the ether evaporated. Five years later, Harrison introduced vapor-compression refrigeration to the brewing and meatpacking industries.


The word "perishable" in paragraph 1 is closest in meaning to ....