RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 199 



APPENDIX C. 



STANDARD TITRATION METHODS FOR SOIL ACIDITY AND FOR CARBONATES 



("BLACK ALKALI"). 



The following procedure in titration for the alkalinity and acidity tests is practically 

 that followed by the Bureau of Soils, and a number of soil departments in the agricul- 

 tural experiment stations: 



The equipment required x is two 50-cubic centimeter burette titration apparatuses, 

 one 50-cubic centimeter graduate, one 250-cubic centimeter graduate, two 50-cubic 

 centimeter Xesslar tubes, 1-liter flask, four 100-cubic centimeter beakers, two 50-cubic 

 centimeters Royal Berlin porcelain evaporating dishes, one 50-cubic centimeter 

 pipette, two ordinary pipettes or droppers, bottles and jars for reagents, analytical 

 balance, numerous quart jars with screw caps or stoppers, and reagents as indicated 

 by the procedure. The necessary reagents are prepared as follows: 



(1) Standard potassium hydrogen sulphate solution: 



The average single test will not require over 5 cubic centimeters of this solution. 

 Dissolve 5.58 grams of pure KHS0 4 in 1 liter of water, and dilute 100 cubic centi- 

 meters of this solution to 1 liter. Place the dilute solution in burette jar Xo. 1, 

 for alkalinity titrations. 



(2) Phenolphthalein indicator: 



A drop or two for each alkalinity and acidity test is required. Dissolve 1 gram 

 of phenolphthalein in 100 cubic centimeters of 50 per cent alcohol. Neutralize 

 by adding a few drops of centinormal alkali, until faintly red, then add a drop 

 of centinormal acid, which should remove the color. 



(3) Methyl orange indicator: 



A drop or two for each alkalinity test is required. Dissolve 1 gram of methyl 

 orange (indicator) in 1 liter distilled water. 



(4) Normal alkali is prepared by dissolving 39.96 mams of NaOH in 1 liter of water. 

 Since only a few drops of the centinormal solution are needed in preparing the 



phenolphthalein indicator, and the exact strength is unimportant, use in about 

 the proportion of 0.04 gram per 100 cubic centimeters of water. 



(5) Centinormal acid (HCl): 



Exact strength unimportant. About 2 drops in 100 cubic centimeters of water 

 give approximately correct strength. 



(6) Standard sodium hydroxide solution: 



Compute quantity required at rate of one-half to 1 cubic centimeter per acidity 

 test made. The solution is not normal, but is computed so that 1 cubic centi- 

 meter will have the equivalent value of 4 mg. of calcium. Dissolve 6.4 grams of 

 pure NaOH in 1 liter of freshly boiled distilled water. Place this in burette jar 

 Xo. 2, for acidity titrations. Exclude air from the jar as far as possible and make 

 up fresh solution frequently. 



(7) Normal potassium nitrate solution: 



Use 250 cubic centimeters for each soil examined for acidity. Dissolve 100.93 

 grams of pure KN0 3 in 1 liter of distilled water. 



Alkalinity Test. 



Place 100 grains of air-dried soil of the sample to be examined in a quart jar; add 

 200 cubic centimeters of distilled water: shake occasionally during 12 hours and allow 

 to settle. The test may best be started early in the day, shaking jars occasionally dur- 

 ing the day and leaving them to settle overnight. Turbidity of the solution is difficult 

 to eliminate in this test, but time is saved if complete settling occurs. 



Draw off with pipette 50 cubic centimeters of the supernatent liquid; filter, if 

 not fairly clear, into an evaporating dish; and evaporate over Bunsen flame, continu- 

 ing the drying almost to red heat, so that residue is devoid of humus and will cling 

 together in flakes when the dish is scraped. When dish is cooled add 50 cubic centi- 

 meters of distilled water: allow to stand for two hours; then pour half of solution into 

 each of two 50-cubic centimeter Xesslar tubes. If fusing of residue has been complete, 



1 The special equipment required to conduct the work at experiment stations should cost approximately 

 J20 to S2.i. 



