A vacuum, in theory, is a space entirely devoid of matter. But no method has been devised for producing one. In practice, therefore, a vacuum in an enclosed space from which air or other gasses have been expelled to such an extent that the pressure inside is below that of the atmosphere. There are partial vacuums and high vacuums, according to the proportion of air pumped put of the container.
Vacuums can be put to a wide variety of uses, thanks largely to the truth of the old saying, “Nature abhors a vacuum”. The tendency of air to rush into empty spaces under pressure from the atmosphere provides vacuums with suction power. This can be used to operate vacuum cleaners, Pumps, milking machines and powerful brakes for heavy vehicles. Vacuums speed up evaporation and are, therefore, used in refrigeration and the dehydration of drugs and food.
High vacuum processes are used to produce extra hard steel, blend new materials and make components for radio and television sets. Perhaps the best known vacuum is the electric light lamp in which the glowing wires are deprived of the oxygen which would cause them to burn up almost immediately.