If some expression is desired of the size of a particle settling at 

 terminal velocity, such as nominal diameter d n , one can solve for particle 

 radius : 



2 



9 H 



- 4P f (P . 



P*) 



C D R 



24 



(14) 



All of the values for settling velocity and particle size reported in 

 this study are based upon settling analyses run with a copy of the Woods 

 Hole Rapid Sand Analyzer, WHRSA (Whitney, 1960; Zeigler, et al. 1960), and 

 upon values found in tables published by Zeigler and Gill (1959). The 

 Woods Hole settling tube (Figure 4) measures fall rates of all immersed 

 sand grains over a 1-meter distance by sensing the changes of pressure 

 produced by the sand suspension as a function of time. Electronics of the 

 system used were identical to those published by Whitney (1960, Plate 4), 

 with the exception that the bellows, pressure case, and the differential 

 transformer were replaced with a Sanborn bidirectional, differential gas- 

 pressure transducer (Figure 4). A resume of the reliability and precision 

 of the analyzer is presented by Zeigler, et al. (1960). Reproducibility 

 of results is excellent. 



Prior to analysis, samples were dried and split with a micro splitter. 

 Because a few shell fragments larger than 4 mm. in diameter occurred in 

 some of the samples, they were picked out of each of the sample splits. 

 Final splits of 8- to 10-gm. weight were introduced into the analyzer. 



It was assumed that there was no interparticle interference and no 



particle -wall interference during the sediment analyses. It was also 



assumed that surface roughness of the grains had a negligible effect on 

 the measured fall velocities. 



An output curve from a typical settling analysis performed on the 

 analyzer is shown in Figure 5. By using a Gerber variable scale, it is a 

 simple matter to scale off the height of a given curve into 100 equal 

 divisions. If, then, one desires to estimate the median settling velocity 

 of the sample he refers to the 50th percentile of the curve of pressure 

 versus time. In the case of Figure 5, one obtains 24.2 seconds for the 

 1-meter fall, or a fall velocity of 4.2 cm/sec (at 24.2 seconds, 50 per- 

 cent of the sample has settled one meter, as indicated by the pressure- 

 time curve). 



Zeigler and Gill (1959) developed a very useful set of tables for 

 the conversion of particle settling velocity to particle diameter. Their 

 tables express the solution of Equation 14 in terms of nominal diameter 

 d n , and are formulated for pure water at various temperatures over the 

 range 20-27° C. The tables assume a particle density of that of quartz 



