A centrifuge is a spinning device used to separate materials of different densities. Centrifuges are used industrially to separate impurities from products such as milk, lubricating oils, beer, and wine. They are also used in scientific research as a separation tool. In genetic research, for example, high-speed centrifuges are used to separate viruses, small cell components, and even individual protein and nucleic acid molecules.
Centrifuges work on the principle of centrifugal force and its counterpart, centripetal force. The relationship between these two forces can be demonstrated by considering the analogy of a person swinging a liquid-filled bucket on a rope. As the bucket is swung in a circle, it tends to pull outward, but the rope keeps it from flying away. The pull on the rope away from that person is called centrifugal force, and the tension of the rope that keeps the bucket from flying away is called centripetal force. When mixtures of materials are spun in this fashion, the heavier particles are driven outward, to the bottom of the container, and the lighter particles move less, staying on top.
The centrifuge was originally developed as a way to separate cream from milk. For centuries, farmers had simply allowed gravity to pull apart milk and cream; however, this process was extremely slow and inefficient. In 1877, a Swedish inventor, Carl Gustaf Patrik de Laval, introduced a device which could rapidly separate the two components. Laval invented a steam engine powered device which could spin a container of milk at 4,000 revolutions per minute in such a way that the heavier milk would sink to the bottom and the lighter cream would rise to the top. Over the next several years engineers made improvements in Laval's basic design and it began to be used in other areas of industry and science.
In 1923 a Swedish chemist, Theodor Svedburg, developed an faster centrifuge that could a force 100,000 times greater than normal gravity. By 1936, Svedburg had perfected an ultracentrifuge that spun at 120,000 times per minute and created a centrifugal force equal to 525,000 times that of normal gravity.
Using this state of the art technology, other scientists perfected centrifugation techniques used in biological sciences. Early pioneers in the field of biological centrifugation include Albert Claude, George Emil Palade, and Belgian biochemist Christian Rene de Duve. Claude was an expert in the use of the centrifuge, and Palade and de Duve developed advanced techniques to separate cell components. By applying differential centrifugation to ruptured cells, de Duve was able to collect different fractions of cells by centrifugation. Using these techniques he discovered two kinds of cell organelles: the lysosome and the peroxisome. The three men shared a shared the 1974 Nobel Prize for their work.
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