316 Mechanical Analysis of Soils and other Dispersions 



i -50 530 



Depth t3 cm. 1 100 51-5 



Time 100 mins. 'i 200 52-2 



1 400 490 



„ .,1- (100 450 



Depth lo cm. 2-00 44-2 



T.mr 240 mms. ] g.^,, ^g.3 



,, ,, , f 100 37-5 



Depth 7 cm. \ gg.^, 



T,.ne 27 hours | g.^^ ^,._ 



The variations in the results obtained with varyin<; concentrations 

 are not serious when the nature of mechanical analysis and the nature 

 of the material under examination is taken into account. In the standard 

 Phighsh method the concentration used is about 2 per cent. In \'iew of 

 the small weights to be dealt with in very dilute suspensions and the 

 consequent magnification of weighing errors, it was decided to use 

 2 per cent, suspensions as a general rule and in the comparisons given 

 later of the results by the new method with those by the old method, 

 this concentration was used. 



(h) Diameter of column. The diameter of the column may be ex- 

 pected to have some effect on the result obtained since, apart from any 

 boundary effect, the fall in height due to the removal of liquid will be 

 greater in narrow columns. The following experiment senses to test 

 this point. 



Chiy suspension 25 %. Time 19-5 hrs. Dejjth 9 em. 



Diameter of cvlinder Weight of ignited material 

 7-7 cm. -102 gm. 



60 -101 



4-6 102 



3-4 098 



The last cylinder was an ordinary 250 c.c. measuring cylinder. It 

 would appear that with J litre, litre and 2 litre cylinders consistent 

 results may be obtained and that the diameter of the cylinder is im- 

 material. In general, a litre or \ litre cylinder was used. 



(c) Equivalence of Depth/Time ratio. Theoretically the same con- 

 centration should be obtained for different times and depths provided 

 that the ratio depth/time, i.e. the hmiting velocity is constant. This 

 point is investigated in the following experiments. 



Kaolin. 2-5 % suspension in -025 "„ sodium carbonate. 



Weight of ignited 



Depth Time material 



cm. hours gra. 



5 5 -165 



19-5 19-5 169 



Clay. 2-5 % suspension in -025 % sodium carbonate. 



4 1 -254 

 12 3 253 



5 18-75 -178 

 18 68 177 



