It was made as early as in the 19th Century in the United States. It consisted of an insulated cabinet into the top of which a block of ice was placed. Modern refrigerators, which are automatic, first appeared in 1918. They use one of two methods-technically known as absorption and compression-to keep foods at, temperatures near freezing point, 0° Centigrade (320 Fahrenheit). The period during which foods can be preserved at this temperature is limited to a few days, but in freezers, at temperatures of -18°C (O°F) and lower, they can be stored indefinitely.