centrifuge

Apparatus that rotates containers at high speeds, creating centrifugal forces. One use is for separating mixtures of substances of different densities.

A laboratory centrifuge is used to separate small amounts of suspension. Test tubes of suspension are spun around very fast so that the solid gets flung to the bottom. The mixtures are usually spun horizontally in balanced containers (‘buckets’), and the rotation sets up centrifugal forces, causing their components to separate according to their densities. A common example is the separation of the lighter plasma from the heavier blood corpuscles in certain blood tests. The ultracentrifuge is a very high-speed centrifuge, used in biochemistry for separating colloids and organic substances; it may operate at several million revolutions per minute. The centrifuges used in the industrial separation of cream from milk, and yeast from fermented wort (infused malt), operate by having mixtures pumped through a continually rotating chamber, the components being tapped off at different points. Large centrifuges are used for physiological research – for example, in astronaut training where bodily responses to gravitational forces many times the normal level are tested.