330 SOILS: PROPERTIES AND MANAGEMENT 



An analysis by this method is supposed to show the 

 proportion of plant-food materials in a soil that are in a 

 condition to be ultimately used by plants at the time 

 when the analysis is made, and the plant-food materials 

 that are not dissolved by treatment with hydrochloric 

 acid are assumed to be in a condition in which plants 

 cannot use them. The difficulty with this assumption is 

 that, while treatment with hydrochloric acid of a given 

 strength marks a definite point in the solubility of the 

 compounds in the soil, it does not bear a uniform rela- 

 tion to the natural processes by which these compounds 

 become available to the plant. 



In the case of most soils a large proportion is not de- 

 composed by treatment with strong hydrochloric acid, 

 and the portion that is dissolved may contain a larger or 

 a smaller quantity of the agriculturally important ele- 

 ments, depending on the character of the soil. Thus if 

 calcium is present as a phosphate, a larger proportion 

 will be dissolved by the acid than if it is in the form of 

 silicate. The form in which potassium occurs also in- 

 fluences greatly the amount shown by analysis. 



Snyder * has analyzed a number of soils by means of 

 digestion with strong hydrochloric acid, and has then 

 decomposed the acid-insoluble residue by fusion and 

 determined its composition. Veitch 2 has analyzed soils 

 by the hydrochloric acid method and by means of com- 

 plete solution. A few examples are given below to show 

 how soils may vary in the solubility of their constituents 

 in strong hydrochloric acid : — 



1 Snyder, Harry. Soils. Minnesota Agr. Exp. Sta., Bui. 41, 

 p. 35. 1895. 



2 Veitch, F. P. The Chemical Composition of Maryland 

 Soils. Maryland Agr. Exp. Sta., Bui. 70, p. 103. 1901. 



