Mffkamctii Anaift^is of Soil 



15 



\ 



/ 



CH. 11 J 



The large ooai-i^e particles reaoli tie boTTom of the iiibe 

 very quickly and form a little layer there, or. if the tube 

 is left open, they caii be coUecieii in a small dish. Next 

 come the small but still coarse psxtioles. Alter these the 

 tine particles begin to come down and at the end the 



linest of all settle as a light mud, 



More refined methods ai^e in use in 

 analytical laboratories. The hmips of 

 soil are lirst broken down by a wooden 

 j^estle and then by treatment with v^r>- 

 vlilute acid followed by ammonia. Xext 

 I he soil is passed through sieves of known 

 dimensions which sort out the jvarticles 

 of a certain size. Finally it is stirred 

 up in a column of water of measurcii 

 height and ailowied to seitle for a certain 

 time. The detiiils oi the methvvi an^ 

 giv^n in the Appendix, and the student 

 is advisevi to carry out an analysis of a 

 soil with which he is famih.ar. It can be 

 sliown mathematically that the speev\ 

 with which a jw^rticle sink^ through the 

 column of water is proportional to the 

 squart^ of its radius, hence the metho^i 

 enables us to grade the particles a<WTvi- 

 ing to their siffc. Numejvus investiga- 

 tions have brought out the remarkable fact that the 

 soil vx>ntains maaiy particles as small as y^hf? i^*-^^ 

 in diameter, while the lai^>e^t particleis in the iii^ 

 earth art^ only some ^ inch in diameter. Siill more nc^ 

 markable }vrha|v< is the fact that no natural divisivxn 

 usually occtirs K^twtvn the various eonstiment*; the 

 jv^rticles merge by imperceptible i:: i^ns m>m the 





