An equation is derived which gives the relation between the time required for sedimentary particles to settle out a specified distance in the tubes of a microcentrifuge and the radius of the particles. This is done by substituting into Stokes' Law the centrifugal force incurred by particles in the spinning microcentrifuge for the gravitational force incurred by particles falling freely through water. Several sediments with average sizes in the [1]/[16]-[1]/[8] mm. or [1]/[32]-[1]/[16] mm. Wentworth grade are analysed by the pipette method of Krumbein and Pettijohn. Then the remaining portions of dispersed sediments are analysed for the finer grades by the pipette method of size analysis for the centrifuge. As derived in this paper it consists of an application of the Krumbein and Pettijohn method on a smaller scale to a microcentrifuge, allowing it to spin for periods of time determined by the centrifuge equation. The results obtained by the pipette-centrifuge method are compared with the results obtained on the finer grades of the same sediments by the ordinary pipette procedure of analysis. A noticeable cheek is evident. A complete procedure for the size analysis of fine grained sediments is presented. The portion above [1]/[16] mm. is screened, the portion between [1]/[16] mm. and 1/256 mm. is analysed by the ordinary pipette method, and the grades below 1/256 mm. are analysed by the pipette-centrifuged method. In this way a great saving of time is obtained for the analysis of the finer grades of sediments.

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