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svedberg or Svedberg unit

A unit of time, = 0.000 000 000 000 1 second (10⁻¹³, ten trillionths of a second in American-style big numbers), used to measure the sedimentation velocity of colloidal solutions in an ultracentrifuge. Symbol, S. It was first used in 1942.¹

A related unit, the Svedburg flotation unit, has the same value but is used to describe molecules that float rather than sink in the centrifuge, such as lipoproteins. Symbol S_f.

The svedberg is named for T. Svedberg (1884–1971), the Swedish chemist who pioneered use of the ultracentrifuge.²

1. Wilbur B. Bridgman.
Some physical chemical characteristics of glycogen.
Journal of the American Chemical Society, volume 64, number 10 (October 1942).

Page 2350: “The average values of s₂₀ for these ten experiments varied from 60 to 70 S (one Svedberg unit, S, = 1 × 10⁻¹³ c.g.s. units).”

2. T. Svedberg and K. O. Pedersen.
The Ultracentrifuge.
New York: Oxford University Press, 1940.