PRACTICE XXVI 



FIXATION OF BASES IN SOILS 



1. Place a small bunch of glass wool in a percolator, cover with 

 1 cm. of clean sand, and add 100 g. of clay soil. Upon this carefully 

 pour 250 cc. of dilute ammonium sulfate solution (50 cc. of the solu- 

 tion prepared in Practice XIII, plus 200 cc. of ammonia-free water). 

 When percolation ceases, mix the percolate thoroughly and deter- 

 mine nitrogen in two 50-cc. portions. 



Titrations (1) cc. NH 3 



(2) cc.NH 3 



Av cc. NH 8 



N per cc. in solution used mg. 



N per cc. in percolate mg. 



Per cent N fixed by soil 



2. Kepeat the experiment, using 200 g. of the same soil. 



Titrations (1) cc. NH 3 



(2) CC.NH, 



Av cc. NH 3 



N per cc. in solution used mg. 



N per cc. in percolate mg. 



Per cent X fixed by soil 



3. Kepeat the experiment, using 200 g. of sand^soil. 



Titrations (1) cc. XH 3 



(2) cc.XH 8 



Av cc. NH 3 



N per cc. in solution used mg. 



N per cc. in percolate mg. 



Per cent X fixed by soil 



What class of soil components bring about the fixation of bases ? 



Give the general reaction, and explain fully. What chemical 

 elements that are important in soil fertility may be retained in 

 this way ? 



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