174 § 99. ANALYSIS OF SOILS AND ROCKS. 



mus, it will be safer to add 0.2-0.4 grm. of pure cane 

 sugar to the sample in which nitrogen is determined; 

 otherwise some of the nitrogen may escape conversion 

 into ammonia; a small portion of the sugar should be 

 ignited by itself with soda-lime, cither to determine the 

 amount of nitrogen it contains, or to be sure of its free- 

 dom from that impurity. 



d. In order to determine the solubility of the various 

 elements of plant-food in the soil, it is necessary to treat 

 it successively with different solvents, and with these of 

 various degrees of strength ; in order that the results ob- 

 tained by different chemists may be compared with each 

 other, it is absolutely essential that these solvents should 

 be applied in the same order and in the same manner. 



A convenient and useful order is the following : 



1. Cold, distilled water, '|^ saturated Avith carbonic 

 acid. 



2. Cold concentrated liydrochloric acid (Sp. Gr. = 1.15). 

 8. Boiling concentrated hydrochloric acid of the same 



strength. 



4. Hot concentrated sulphuric acid, 



5. Hydrofluoric acid. 



The solutions obtained by the treatment of the soil 

 with these agents in succession will be found to differ 

 very much in their composition, and to yield data for 

 very interesting deductions in regard to its natural fer- 

 tility. 



Unless, however, a very complete analysis is desired, 

 but one of these solutions, viz., that in cold concentrated 

 hydrochloric acid, need be examined quantitatively ; next 

 to this, the solution in hot hydrochloric acid is of great- 

 est importance ; we shall, therefore, consider the treat- 

 ment of these first of all. 



Solution in Cold Concentrated Hydrochloric Acid. 



99. Put 450 grms. of air-dried soil in a large, glass- 



