RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 133 



3. One hundred eubic centimeters for determining P 2 5 (phos- 

 phorus pentoxide) . 



In order to determine the presence of phosphorus pentoxide 

 (P 2 5 ), 100 cubic centimeters of the solution is neutralized with 

 ammonia until an odor is perceived, the solution is made acid by 

 the addition of weak nitric acid (HN0 3 ), and to such acid solution 

 there is added from 10 to 15 cubic centimeters of molybdic acid 

 (H 2 Mo0 4 ) . 



A qualitative test for ferric oxide can be made in the water solu- 

 tion of the soil by hydrochloric acid. Some hydrochloric acid is 

 added, together with several drops of potassium sulplio cyanide 

 (KSCX). A pink, or often bright red, color will indicate the pres- 

 ence of ferric oxide in the solution. When the soil is rich in ferrous 

 oxides, their presence can be readily acertained by dropping directly 

 upon the soil some of the potassium ferricyanide (K 3 Fe(CN) 6 ) solu- 

 tion which with the ferrous oxides gives a blue color. 



The form for the "Summary of Physical and Chemical Properties 

 of Soil' is provided with a number of blank spaces in which the 

 results of qualitative or quantitative tests for various salts may be 

 entered. 



