88 SOILS AND FERTILIZERS 



contents of the flask are transferred to a filter and sepa- 

 rated into the insoluble part, and the acid solution which 

 contains the soluble compounds of the various elements. 

 The table on page 89 gives a general idea of the 

 process of soil analysis. One half of the acid solution 

 is used for obtaining the metals as noted on page 89. 

 The second half is divided into two portions, the 

 first portion to be used for the determination of phos- 

 phoric acid, which is precipitated with ammonium 

 molybdate, and the second portion to be used for the 

 determination of sulphuric acid, which is precipitated 

 as barium sulphate. The carbon dioxide is determined 

 in a fresh portion of the original soil, the acid being 

 liberated with hydrochloric acid and the carbon dioxide 

 retained by absorbents and weighed. The nitrogen 

 and humus are determined in separate portions of the 

 original soil. The analysis of soils involves the use of 

 accurate and well-known methods of analytical chem- 

 istry, a discussion of which would not be germane to 

 this work. 



103. Value of Soil Analysis. Opinions differ as to 

 the value of soil analysis. It is claimed by some that 

 a chemical analysis of a soil is of no practical value 

 because it fails to give the amount of available plant 

 food. A soil may have, for example, 0.4 per cent of 

 potash soluble in hydrochloric acid and still not con- 

 tain sufficient available potash to produce a good crop, 

 while another soil may contain 0.2 per cent of potash 



