There is provided a new method for analysis of the size and/or distribution of particles emanating from a mother liquid by sedimentation in a rotating disc centrifuge, particularly a photosedimentometer. The method is characterized in that the spin fluid or medium is formed externally of the disc as distinct from being formed within the disc while it is rotating. The externally prepared spin medium is formed from at least two miscible liquids of different densities for example, methanol and water, in a manner such that they are substantially incompletely mixed whereby a density gradient is established in the spin medium. Thereafter the spin medium is injected into the disc while spinning at a given speed, and later the mother liquid is injected. Results are closely comparable to the buffered line start method described in U.S. Pat. No. 3,475,968.
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