H. A. Baker — Loose Arenaceous Sedimenits. 



329 



Clay. 



mm. 

 <-01 



Thanet Sand 

 (upper part), 

 Knee Hill, Abbey 

 Wood. 



Woolwich Beds 

 (basement loam) 

 Charlton Pit. 



% wt. 

 5-64 



5-23 



26-20 



26-45 



Silt. 



mm. 

 >-01 

 <-05 



% wt. 

 2-37 



mm. 

 >-05 

 <-l 



% wt. 

 12-10 



14-47 

 38-72 



Sand. 



50-56 



44-40 



By single-tube 

 method. 



By Crook 

 elutriator. 



By single-tube 

 method. 



By Crook 



elutriator. 



If the lower tube of the Crook elutriator were increased in diameter 

 the upper tube would assume very unwieldy proportions. 



Two other disadvantages of the Crook elutriator may be mentioned. 

 The sample is sejjarated into three grades only. Consequently, 

 when the attempt is made to express the result of a mechanical 

 analysis graphically, by means of a curve, the data are insufficient. 

 Further, the elutriation curves of arenaceous sediments are now 

 known to be of such a character that, for the purpose of obtaining 

 accurate and reliable curves, grade divisions are required to be 

 effected at points which this apparatus does not determine. In 

 attempting to overcome this by employing more than tM^o tubes, 

 the original difficulty of adjusting the required tube-diameters 

 correctly becomes insurmountable. In addition, it is not possible, 

 when using a Crook elutriator, to apply a correction for, or make 

 any adjustment to counteract, changes of temperature in the water 

 passing through the apparatus, although this can readily be done 

 when the single-tube method is employed. The temperature 

 correction is a large one, and the ignoring of it is liable to lead to 

 serious error, particularly in the case of the finer sediments. 



The mechanical analyses made by the writer were carried out 

 on samples of about 40 grammes weight, preliminary trials having 

 shown this quantity of sediment to be well suited to the capacities 

 of the tubes employed. The latter ranged in diameter from about 

 3"75 inches down to about 1 inch. Bearing in mind the value of 

 graphical representations of the analyses obtained, preliminary 

 experiments were made in order to ascertain the general character 

 of the curves given by arenaceous sediments, so that the separations 

 might be effected at points where the latter were most required 

 for curve-plotting purposes. 



The elutriator tubes employed by the writer are fitted with specially 



