Calibration of the - 8 - D. M. Poole and 



Emery Settling Tube W. S. Butcher 



for Sand Analysis 



difference in the individiial splitting errors from the mean of the scries. 

 Probably more complete data vrould haYc shor-m some correlation bctv;cen split- 

 ting method and splitting error. It is felt that the homogeneity of most 

 sands and the time saved by the loss complicated splitting procedure obviate 

 the necessity for the use of the procedure of combining alternate q_'uarters. 



All the samples (except as noted) used in determining the splitting error 

 were ubAo up from a mixture of sands from the beaches around La Jolla, Cali- 

 fornia. One-third of the sand \-ip.s from Cove Beach (Md 0.? mm.), one-third from 

 V/'indansea Beach (Md 0.35 nim.), and one-third from Scripps Beach (Md 0.1? mm.). 



Effect of SamT>lc Weight ; It v/as thought that some significant error 

 might be introduced in the settling tube analysis if the v;eight of the material 

 were not the same in each case. The error might come from the increase in 

 density of the medium and from the increased tendency to advection currents 

 with increased material. From Ov/cns' (19II) data, it c?-n be estimated that 

 5 grams of material in the 515 grams of water in the settling tube will affect 

 the settling time by about 2.5/^ di^e to increase in the density of the medium, 

 if the sand is considered to be in solution. As the sand is obviously not in 

 solution, the error introduced must be considerably reduced and probably can 

 be neglected. Calculations based on the formulas of Rubcy (1933) indicate 

 the same order of magnitude for the error introduced by incrcp.se of density 

 of the medium. It is of advantage to have the sample as large as possible 

 vrithin the capacity of the settling tube, because 3. large sample gives a 

 greater change in ciimulativc height for a given volume percentage of the 

 total sample. Most of the error introduced should be due to advection 

 currents rather th^.n to increase in density. 



