G. W. Robinson 



:n7 



{d) Errors Id Depth of Saniplijuj. Tlie effect of errors in depth of 

 sampling may be best demonstrated by considering the nature of the 

 vertical concentration gradients in a column of suspension after varying 

 times. A series of curves showing the relation between depth and con- 

 centration for different times can readily be derived from the summa- 

 tion curve for the material under consideration. For example if it be 

 known from the summation curve that 50 per cent, of the material has 



100 



Fig. 4. Concentratiiin Gradients at Different Ueptlis. 



a limiting velocity less than -01 cm. per second (log v = 2-0000), then 

 at depth 10 cm. after 1000 seconds, the concentration will be 50 per 

 cent, of the original concentration. A series of concentration gradients 

 for a clay is shown in Fig. 4. AB is the summation curve and the 

 curves I. II, III, IV, and V give the percentages of the original concen- 

 tration at different depths for 10 sees., 1 min., 10 mins., 100 mins., and 



