AVAILABILITY OF PLANT NUTRIENTS 329 



the total quantity of the plant-food materials except 

 nitrogen, which is never determined in any of the acid 

 solutions but by a separate process. 1 A deficiency of 

 any particular substance may be discovered in this way, 

 but nothing can be learned as to the ability of the plant 

 to obtain nutriment from the soil. A rock may show as 

 much mineral plant-food material as a rich soil. This 

 method of analysis is used only to ascertain the ultimate 

 limitations of a soil or its possible deficiency in any essen- 

 tial constituent. Results of such analyses are to be found 

 in paragraphs 46, 48, 52, 53 of this text. 



231. Partial solution with strong acids. While sul- 

 furic, nitric, and hydrochloric acids have all been used as 

 solvents, 2 the one most commonly employed is hydrochloric 

 acid of 1.115 specific gravity. 3 It has been used to such 

 an extent that it may be considered the standard solvent, 

 and a statement of a chemical analysis of a soil in this 

 country may be considered as based on this solvent unless 

 otherwise stated. 



1 Official and Provisional Methods of Analysis. U. S. D. A., 

 Bur. Chem., Bui. 107 (revised), p. 19. 1908. 



2 Analyses using concentrated mineral acids on the same soil. 

 From Snyder, Harry. Soils. Minnesota Agr. Exp. Sta., Bui. 

 41, p. 66. 1895. 



3 Official and Provisional Methods of Analysis. U. S. D. A., 

 Bur. Chem., Bui. 107 (revised), pp. 14-18. 1908. 



