H. A. Baker — Loose Arenaceous Sediments. 327 



In elutriation work on arenaceous sediments it is important for 

 the investigator to know accurately the rate of settling of quartz 

 grains between the limits of '01 mm. and about "4 mm. diameter. 

 This matter has recently been made the subject of careful investiga- 

 tion by another worker, who very kindly permitted the present 

 writer to make use of his results (which are as yet unpublished) in 

 the carrying-out of mechanical analyses. It is not fitting to discuss 

 here the unjoublished work of another, but the writer may, perhaps, 

 be 23ermitted to state that the behaviour of subsiding grains, between 

 the limits of "2 nmi. and '5 mm. diameter, shows no closer adherence 

 to the law of eddying resistance than does that of grains between 

 the limits of "01 mm. and '2 mm. diameter to the law of viscous 

 resistance. In fact, the rates of subsidence of grains between the 

 limits of "01 mm. and '4 mm. diameter vary in a definite way, 

 which is very clearly a compromise between these two laws. 



In the absence of ^^i^iblished information concerning this later 

 research, which is of fundamental importance to workers interested 

 in the mechanical analysis of sediments, it may be remarked that 

 the data are of such a character as to lend themselves to 

 mathematical expression in the form of formulae. A series of 

 formulcB, by means of which the rate of subsidence in water of a 

 quartz grain can be calculated, when the diameter of the grain and 

 the temperature of the water are known, has been worked out 

 by the present writer, who hopes, at a later stage, to collaborate 

 with the author of the research in discussing this point. 



(2) Conduct of Elutriation Experiments. 



The reasons for rejecting the rapidly working, two-tubed Crook 

 elutriator in favour of the more tedious Schoene single-tube process 

 may be stated. The Crook elutriator possesses the advantage of 

 effecting the separation of a sample into three grades in one operation. 

 The disadvantages, however, far outweigh this initial gain. The 

 Crook elutriator consists of a pair of tubes, one beloAv the other, 

 the water passing from the lower, smaller tube to the upper, wide 

 tube, and thence escaping from the jet-tube carried by the latter. 

 The diameters of the two tubes are adjusted to each other and to 

 the water-supply in such a way that the total sand-grade (>'l mm.) 

 in the sample under examination is retained in the lower tube, the 

 total silt grade (O'Ol to O'l mm.) is retained in the upper tube, 

 and the clay grade (<"01 mm.) is washed away. A practical 

 difficulty which meets one at the outset is the matter of adjusting 

 the diameters of the two tubes so as to preserve the correct ratio 

 between them. It is only by chance that tubes of precisely the 

 diameters required can be secured, and in the Crook elutriator, 

 as set up in laboratories, the adjustment is usually more or less 

 approximate. 



