74 SOILS AND FERTILIZERS 



into an insoluble part, and the acid solution which 

 contains the soluble compounds of the various elements. 

 The table on page 73 gives a general idea of the 

 process of soil analysis. One-half of the acid solu- 

 tion is used for obtaining the metals as noted 

 on page 73. The second half is divided into two 

 portions. The first portion is used for the deter- 

 mination of phosphoric acid, which is precipitated 

 with ammonium molybdate. The second portion is 

 used for the determination of sulphuric acid, which is 

 precipitated as barium sulphate. Carbon dioxide 

 is determined in a fresh portion of the original soil j 

 the acid is 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 chemistry, a discussion of which would 

 not be germane to this work. 



94. 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 

 soluble in hydrochloric acid and produce good crops. 

 While these facts are frequently true, it does not 

 necessarily follow that the chemical analysis of a soil 



