Calibration of the - 10 - D. M. Poole and 



Sncry Settling Tube W. S. Butcher 



for Sand Analysis 



and to the total error. The difference betvreen the cuiaulative curves of the 

 sieve and settling tube analyses for the sanple having the coarse fraction 

 renoved, is within the limit of error of the nethod. 



The conclusion reached in this test of coarse na-terial is that the 

 r)articlcs coarser than 1 nrn. should bo sieved out before attcnroting a settling 

 tube analysis in order to obtain accurate results. 



Influence of Particles Finer than I/16 nm. 

 on the Medican Dianeter 



The influence of fine material (less than I/16 mm.) in the sanple run 

 through the settling tube has been investigated by a series of test sairiples 

 containing varying amounts of fine material. A graph of the percentage 

 variation of the median diameter for a given percentage of fine material and 

 a graph of the percentage variation of sorting for a given percentage of fine 

 np.terial are sho',<m in figures 9a and 9b respectively. The scatter of the 

 points on these graphs is so great that it does not seem profitable to draw 

 a best-fit cm-vc. It seems probable that if fine material in the sample 

 exceeds a total of 57J, the error in the cumulative curve due to the presence 

 of the fine material may be greater than the total error. It is therefore 

 advisable to sieve off all material finer than I/16 mm. unless the amount of 

 such mcatcrial is less than approsima.tcly 5"^ of the total. An esanplo of the 

 similarity of I'uns with a small percentage of fine material is given in 

 figure 10a, and of the dissimilarity with a large pcrccntp.ge of fine material 

 in figure 10b. 



