EARLY USES OF LOW TEMPERATURES
Very early in his history man discovered fire, learned how to kindle it and how to use it for his good. That discovery placed him immediately on a level far above the beasts. However, it is only in comparatively recent times that he has learned the uses of low temperatures. Nature’s stores of ice were drawn upon, and methods of preserving ice through warm weather were discovered in ancient times. Nero had ice houses built for him in Rome, but he could stock these buildings only with the ice that nature furnished him. Freezing mixtures of salt and ice, such as we use in our ice-cream freezers to-day to obtain temperatures far below the freezing point of water, were probably known in early times, but the ancients did not know how to produce ice.
Artificial ice was probably first made in India, where it has long been the practice to produce ice by evaporation. Water is placed in shallow pans and then dry air is circulated over it, causing so rapid a vaporization as to cool the water to the freezing point. The idea of cooling water by evaporation belongs to very ancient times. Water placed in porous earthen vessels was found to be cooler than water kept in water-tight jars. The moisture that escaped through the vessel would evaporate, and in so doing draw heat out of the vessel and its contents. To-day campers keep water cool by putting it in canvas buckets and hanging the buckets in the wind, so that the moisture oozing through the canvas will evaporate quickly.
It was not until 1755 that a mechanical means of producing low temperatures was developed. The inventor was Dr. Cullen, and he used an evaporation system, expediting the evaporation by producing a partial vacuum over the water. But nearly a century elapsed before the first commercially successful refrigerating machine was built. Even then the advantages of artificial refrigeration were not fully realized, and it was not until late in the last century that real progress was made. Since then the development of artificial refrigeration has been truly remarkable.