i6 



SOILS AND FERTILIZERS 



nected with the filtering flask c by means of the tube 

 l>, and the flask is connected at point d with a suction- 

 pump. Ten grams of soil, after soft pestling with 

 boiling water, are placed in the sieve. Water is passed 

 through until the washings are clear. All particles 

 larger than 0.5 mm. remain in the sieve and, after dry- 

 ing and igniting, are weighed. The contents of flask c, 

 containing the particles less than 0.5 mm. are then 

 passed through a sieve having holes 0.25 mm. in 

 diameter. Finally a o.io mm. diameter sieve is used. 



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 more water and allowed to settle ; 

 this operation is repeated until the micro- 

 scope shows the soil particles to be nearly 

 all of one grade. The separation of silt 

 and clay is facilitated 

 by the use of a centrifu- 

 gal. 9 



The clay is obtained Figs. 8 and 9. 

 by evaporating an aliquot portion 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 sed- 

 imentation method. 10 



Hilgard's elutriator" is a valuable apparatus for 

 separating the soil particles. 



