(4. W. Robinson 315 



Lastly to determine the tine sand, the suspension remaining after 

 the last sampUng is poured away to about 200 c.c. without shaking up 

 the sediment. The remaining suspension and sediment are then washed 

 into a beaker and the fine sand determined by the ordinary method, 

 using the 10 cm. and 100 seconds, or 7-5 cm. and 75 seconds sedimen- 

 tation. 



The following figures are the results of an actual determination on 

 a Pennant Grit soil from CTlamorganshire : 



By ordinary method Fiue gravel ... ... ^'6% 



Coarse sand ... ... 20-1 



Moisture ... ... 4-2 



Organic matter ... ... 10-2 



Total 391 



So that fine sand + silt + fine silt + clay should = 100 - 39'1 =60-9 (1). 



By new method, using 2 "(, suspension. 



For 5 mins. and 30 cm., weight of ignited material iu 20 c.c. = -112 gm. 

 Therefore concentration =5 x -112 = -560 %. 



Therefore silt + fine silt + clay = '^-^^''-^-°^ = 28-0 % (2). 



Similarly for 20 mins. and 12 cm., ignited material = -065 gm. 



Concentration = -325 % and fine silt + clay = =16-25 % (3). 



Similarly for 20 hrs. and 7-2 cm. ignited material = -019 gm. 



Concentration =-095 % and clay = ," =4-75 % (4). 



Subtracting (4) from (3). fine sat = ll-5 %. 



Subtracting (3) from (2). silt =11-7.5 "o- 



Subtracting (2)from (1) fine sand = 32-9 %. 



By direct sedimentation at end of e.xperiment, tine sand = 32-5 %. 



Effect op Variations in Conditions of Working. 



In order to form some idea as to the latitude allowable in the con- 

 ditions of working the following points were investigated. 



(«) Effect of concentration. A number of determinations were made 

 on a clay suspension of varying concentrations. Results are given for 

 different times and depths. 



Depth 6 cm. 

 Time 10 mins. 



