LaMotte DCL-20 Colorimeter - Manual (Page 10)

SOIL COLORIMETER TESTS
INSTRUCTIONS
pH and Lime Requirement are determined by means of the pH meter. The conductivity meter is used for determining
soluble salts. Calcium, Magnesium and Chlorides are determined by titration. All of the other readings are made on the
colorimeter.
EXTRACTION
The following method of extraction is employed for obtaining the soil filtrate for the tests for Nitrate Nitrogen,
Phosphorous, Potassium, Calcium, Magnesium, Ammonia Nitrogen, Nitrite Nitrogen, Manganese, Copper, Zinc, and Iron.
Separate extractions are required for the Chloride and Sulfate tests. Consult the LaMotte Soil Handbook for information
on sampling and preparation of sample for testing.
PROCEDURE
1. Use the 1 mL pipet (0354) to add 5 mL of the *Acid Extracting Solution (6361) to the 100 mL graduated cylinder
(0419). Add deionized water to 75 mL graduation.
2. Pour this solution into the 100 mL bottle (0990).
3. Use the Soil Measure (1165) to add 15 g (one level measure) of the soil sample to the bottle.
4. Cap the bottle and shake for a period of 5 minutes.
5. Use the funnel (0459) and filter paper (0463) to filter and collect all of the soil filtrate in a 100 mL bottle (0990).
6. The soil filtrate is used for all of the tests listed above, except Chloride and Sulfate.
SINGLE TEST PROCEDURE
1. Use the 1 mL pipet (0354) to add 1 mL of the *Acid Extracting Solution (6361) to the graduated vial (0989), then
add deionized water to the graduation.
2. Use the 1.0 g spoon (0697) to add 3 grams of soil to the extracting solution in the vial.
3. Cap the vial and shake for a period of 5 minutes.
4. Filter, using the funnel (0459) and filter paper (0463) and collect all of the soil filtrate.
5. The soil filtrate is used for all of the tests except Chlorides and Sulfates.
NEUTRALIZATION OF SOIL FILTRATE
In the tests for Calcium, Magnesium, Ammonia Nitrogen, Manganese, Copper, Zinc, and Iron the acidity of the soil filtrate
must be neutralized before proceeding with the test. This is done by treating the measured soil filtrate with *Sodium
Hydroxide, 15% (7886) until the solution shows a green or blue color when spotted on a strip of Bromthymol Blue Test
Paper (2931). This is done by adding the *Sodium Hydroxide, 15% (7886) solution to the soil filtrate, one drop at a time
while stirring with the plastic rod (0824). The stirring rod is touched to the Bromthymol Blue test paper after the addition
of each drop of *Sodium Hydroxide, 15% (7886), until the color changes from yellow to green or blue.
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1985-01 • 10/01