ABSORPTION OF SALTS 69 



(J?) Nitrate. — In order to compare the amount of 

 nitrate present in the original solution and that shaken 

 with soil, 5 c.c. of each liquid is evaporated nearly to 

 dryness, mixed with excess of pure strong sulphuric 

 acid and a drop of diphenylamine dissolved in sulphuric 

 acid. The depth of blue coloration produced in each 

 case may be used as an indication of the nitrate 

 present. 



{c) Potash. — Equal quantities of the two solutions 

 are acidified with acetic acid and tested with a fresh 

 solution of sodium cobaltinitrite, and the extent of 

 precipitation in each case noted. 



(</) Phosphate. — The amounts of phosphate present 

 in the original solution and in the soil filtrate are 

 compared by precipitating each with ammonium- 

 molybdate solution after acidification with a few 

 drops of dilute nitric acid. 



48. Absorption of Salts {Quantitative^ 



Into each of four stoppered bottles is placed 50 

 grams of good clay soil. To (i) is added 250 c.c. of 

 a I per cent, solution of ammonium sulphate; to (2), 

 250 c.c. of I per cent, sodium phosphate solution ; to 

 (3), 250 c.c. of 0-5 per cent, solution of potassium 

 chloride; and to (4), 250 c.c. of i per cent, sodium 

 nitrate. The bottles are then well stoppered, put on 

 one side for a week, and shaken occasionally. 



In the meantime the strengths of the various 

 solutions are estimated as follows : — 



{a) Ammonium Sulphate. — Two hundred and fifty 



c.c. of the solution are mixed with excess of caustic 



soda, and distilled in the Kjeldahl distillation apparatus, 



N 

 the distillate being collected in 20 c.c. of — acid, 



tinted with methyl orange. After half an hour the 



E 2 



