High ultracentrifugal sedimentation

In the sedimentation velocity method a high ultracentrifugal field (up to about 400 OOOg) is applied and the displacement of the boundary set up by sedimentation of the colloidal particles is measured from lime to time. In the sedimentation equilibrium method, the colloidal solution is subjected to a mueh lower centrifugal field, until sedimentation and diffusion (mixing) tendencies balance one another and an equilibrium distribution of particles throughout the sample is attained. 

These solutions have been examined in sedimentation velocity runs on the analytical ultracentrifuge (31). Beyond 0.5 base equivalent per mole of iron a fairly narrow sedimentation peak developed. The sedimentation coefficient, 7 1 S, was essentially constant up to 2.5 base equivalents per mole of iron, although the area under the peak increased with increasing degree of hydrolysis. Apparently, then, hydrolysis of ferric nitrate beyond the reversible equilibrium region produces increasing amounts of a fairly discrete high polymer whose size is constant. 

The ultracentrifuge is an instrument in which a cell is rotated at very high speeds in a horizontal position. As we see below, the gravitational acceleration is easily increased by a factor of 105 in such an apparatus. Accordingly, the particle size that may be studied by sedimentation... 

An ultracentrifuge is a high-speed centrifuge equipped with a suitable optical system (usually schlieren or interference optics, the latter being particularly useful when low concentrations are involved) for recording sedimentation behaviour and with facilities for eliminating the disturbing effects of convection currents and vibration. The sample is contained in a sector-shaped cell mounted in a rotor (usually c. 

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