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The overall problem involves the development of a suitable method of obtaining the active material in solution, the development of the optimum phosphor, and the development of appropriate
instrumentation.
IV. DEPARTMENT OF AGRICULTURE
A. Procedure for the extraction of exchangeable calcium in soils:
1. General Statement:
The soil sample is leached with ammonium acetate and the filtrate evaporated to dryness.
The salts are dehydrated and the residue ashed at 600°C. The ashed residue is taken up in
HCl, and iron and aluminum are removed by precipitation as the hydroxides. The filtrate is
acidified and calcium precipitated as the oxalate at pH 6.2.
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2. Reagents;
Normal ammonium acetate, pH 7.0.
Hydrogen peroxide, 30-35 percent.
Hydrochloric acid, concentrated.
Ammonium hydroxide, 1:1.
Ammonium chloride, 2 percent aqueous solution.
Methyl red, 0.1 percent aqueous solution.
Oxalic acid, C.P., crystal.
3. Procedure:
Crush the air-dry sample with a wooden rolling pin and pass the sample through a 2 mm
sieve. Place 7-10 pounds of the prepared sample in a 4-liter beaker and add sufficient ammonium
acetate to cover. Stir the suspension well and let stand overnight. Fit an 18-liter carboy with
a 10-inch Buchner funnel and vacuum tube. Place two thicknesses of coarse filter paper in
the funnel, moisten, and apply suction. Transfer the contents of the beaker to the funnel and
leach the soil with ammonium acetate until a total of 1 liter of leachate for each pound of soil
is obtained. Transfer the leachate to large beakers (3 or 4 liter capacity) and evaporate almost
to dryness at 90-95°C. Combine the residues in a 2-liter beaker and take to complete dryness.
Loosen as much of the dry residue as possible with a large spatula and transfer to an
evaporating dish (or dishes). To the small amount of residue remaining in the beaker add
200 ml of water and 10 ml of H.O,. Cover and boil for 15-20 minutes. Place the evaporating
dish (containing the residue) in a muffle at about 150°, heat to 600°C, and hold this tempera-
ture for about 1 hour. Remove the dish from the muffle and cool.
and the peroxide treated residue.
Combine the ashed residue
Add small portions of MCl with stirring until all of the carbonates are decomposed; add
10-15 ml of HCl in excess.
Heat the solution to about 90°C and add 1:1 NH,OH with stirring until a faint odor of
ammonia persists. Boil for 2-3 minutes to coagulate the precipitate and filter through coarse
filter paper. Wash the filter well with 200 ml of hot NH,Cl. Add 20 drops of methyl red and
acidify with HCl. Add 5-10 ml excess HCl. Heat to 90°C and add 50 grams (25 gms.if soil is
low in calcium) of oxalic acid with stirring until the solution turns a light yellow. Digest at
90-95°C for 1-2 hours. Collect the precipitate on a Buchner funnel, wash 5 times with cold water
and dry.
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