314 Mechanical Analysis of Soils and other Dispersions 



into the diagram, their velocity values were calculated on the assump- 

 tion that they obey Stokes' law and that the diameter of particle repre- 

 sented by the upper limit of the silt is -04 mm. The lines thus obtained 

 are D, E, and F, respectively and are inserted for the sake of com- 

 pleteness. By taking into account the coefficient of viscosity and using 

 glycerine-water mixtures, these points on the di.stribution curve might 

 be obtained by the above method. It is however simpler to use the 

 sieve method to fill in the right hand portion of the curve. It may be 

 added that the data of an ordinary mechanical analysis are given 

 graphically by the difference between successive intercepts on the 

 ordinates A, B, C, etc. For example the fine silt is given by the difference 

 between the intercept on B and the intercept on A, the silt by the differ- 

 ence between the intercept on C and the intercept on B and so on. 



By suitable choice of depths and times any required degree of detail 

 can be secured in any part of the curve. If a large number of points 

 are required it is convenient to prepare a large volume of suspension 

 and work with a number of separate cyhnders. The details may be left 

 to the convenience and ingenuity of individual operators. Possibly a 

 more convenient, though scarcely less expensive, method of sampling 

 may be devised. Any measurable physical property of dispersions which 

 depends on concentration may be considered in this connexion. For 

 very dilute suspensions it is possible that a nephelometric method might 

 be devised. 



The method may find its best use as a substitute for the present 

 standard method of mechanical analysis. The suggested procedure in 

 this case is as follows. The air dried sample is treated with A'jb hydro- 

 chloric acid exactly as in the ordinary method, using however 20 grams 

 instead of 10 grams of soil. The fine gravel and coarse sand are separated 

 in the ordinary way and the finer material passing the 100 mesh sieve 

 is shaken with 600-700 c.c. of water and 50 c.c. of 10 per cent, ammonia 

 in an end over end shaker for two to four hours, the longer period being 

 necessary in the case of soils with much organic matter. After shaking, 

 the suspension is made up to one Utre, which is equivalent to 2 per cent., 

 reckoning on the original material. The following determinations are 

 then made successively by the method described above. 



