36 



liifitriictluiLS to Field JPartles. 



Directions for estimating soluble salts in soils. — Take a known 

 volume (or weight) of saturated soil, wash into a 250 cc. tiask and 

 nil to the mark with distilled water, and filter if necessary. Take 

 50 cc. of the solution and titrate with N/20 acid potassium sul- 

 phate, containing 6.758 grams per liter, using phenolpthalein as 

 an indicator. This will represent the carbonates. Then add a 

 drop or so of methyl orange or congo red and again titrate with 

 N/20 acid potassium sulphate. Subtract an amount equal to the 

 first titration from the second, and the difference represents the 

 bicarbonates. Add a few drops of potassium chromate as an 

 indicator to the same solution and titrate with X/10 silver nitrate. 

 This will represent the chlorides. The salts are all to be estimated 

 as sodium salts, as follows: 



1 cc. N/20 HKSO4 is equivalent to 0.005266 gram Na-jCO^. 

 1 cc. N/20 HKSO4 is equivalent to 0.004172 gram NaHCOo. 

 1 cc. N/IO AgNOs is equi^^lent to 0.005806 gram NaCl. 



In areas where the amount and distribution of sodium carbonate 

 warrant it, construct the sodium carbonate map in the field from 

 the volume of solution used. Limiting values will be 0.3, 0.2, 0.1, 

 and 0.05 per cent of dry soil. The limiting values for each vessel 

 are found in the following way: Multiply the volume of saturated 

 soil, represented by the solution taken for titration, by the num- 

 bers in the following table: 



