20 METHODS OF ANALYSIS. 



14. Soil Acidity. Provisional. 



Place 100 grams of soil in a 400 cc wide-mouthed bottle, add 250 cc of normal 

 potassium nitrate solution, stopper, and shake continuously for three hours in 

 a shaking machine, or every five minutes by hand, Let stand over night. Draw 

 off 125 cc of the clear supernatant liquid, boil ten minutes to expel carbon 

 dioxid, cool, and titrate with standard sodium hydroxid solution. One cubic 

 centimeter is equivalent to 4 mg of calcium carbonate, using phenolphthalein as 

 indicator. 



The acids and acid salts of the soil are difficultly soluble in water, but by 

 treating with a salt solution, such as sodium chlorid or potassium nitrate, a 

 double decomposition takes place, rendering them soluble. An equilibrium is 

 reached, however, before this reaction runs to an end, and if, after having drawn 

 off 125 cc to titrate, 125 cc of fresh potassium nitrate are added to the bottle and 

 the bottle again shaken for three hours, 125 cc drawn off will give a titration 

 which is more than one-half of the first. By continuing this process until the 

 last 125 cc shows practically no acidity, a series of titrations is obtained the 

 sum of which represents the total acidity of the 100 grams of soil. It has been 

 found by working with a number of different soils that as an average the sum 

 of such a series is 2.5 times the first titration. 



Consequently when the sodium hydroxid is made up so that 1 cc is equivalent 

 to 4 mg of calcium carbonate and 125 cc (which represents 50 grams of soil) 

 are titrated, each 0.1 cc required to neutralize corresponds to 1 mg of calcium 

 carbonate required by the 100 grams of soil, or to 0.001 per cent of calcium 

 carbonate required by the soil tested. 



15. Statement of Results. Official. 



Calculate all results of soil analysis as per cent of the soil dried to con- 

 stant weight in the water oven (see "3. Moisture," p. 14) and state in the 

 following order : 



Insoluble matter 



Soluble silica 



Potash (K 2 O) 



Soda (Na 2 O) 



Lime (CaO) 



Magnesia (MgO) 



Manganese oxid (Mn 3 CM 



Ferric oxid (Fe 2 O 3 ) 



Alumina (A1 2 O 3 ) 



Phosphorus pentoxid (P 2 O B ) 



Sulphur trioxid (SO 3 ) 



Carbon dioxid (CO 2 ) 



Volatile matter. _ 



Total 



Humus 



Ash 



Phosphorus pentoxid. 

 Silica 



Nitrogen (organic) 



Hygroscopic moisture. 



Moisture absorbed at t_ 



