2O SOILS AND FERTILIZERS 



remain in the sieve, and after drying and igniting, are 

 weighed. The contents of the flask c, containing the 

 particles less than 0.5 mm., are now passed through a 

 sieve having holes 0.25 mm. in diameter. 



The fine sand and silt are separated by gravity. The 

 fine sand with some silt and clay are read- 

 ily deposited and the water containing the 

 suspended clay is decanted into a second 

 glass vessel. The residue is treated with 

 f- b more water and allowed to settle, this opera- 

 tion being repeated until the microscope 

 shows the soil particles to be nearly all 

 of one grade. The separation of silt 

 and clay is facilitated 

 by the use of a centri- 

 fuge. 9 _ 



"FKT7. It is often difficult to F IG - * 



secure even an approximate separation of sand, silt, and 

 clay particles, because the finer particles tenaciously ad- 

 here to the larger ones. 



The clay is obtained by evaporating an aliquot por- 

 tion of the washings or by determining the total per 

 cent of the other grades of particles and the volatile 

 matter and subtracting the sum from 100. This is the 

 modified Osborne sedimentation method. 10 



By means of Hilgard's elutriator 7 a more extended sep- 

 aration of the soil particles is effected. For detailed direc- 

 tions for making mechanical analyses of soils the student 

 is referred to Wiley's " Agricultural Analysis," Vol. I. 



