LaMotte STH Series - Manual (Page 10)

Procedure:
1. Use a transfer pipet (0364) to fill a Potash “A” Tube (0245) to
the lower mark with the general soil extract.
2. Add one *Potassium Reagent B Tablet (5161). Cap and shake
until dissolved.
3. Add *Potassium Reagent C (5162) until the Potash “A” Tube
is filled to the upper mark. Allow the *Potassium Reagent C
(5162) to run slowly down the side of the tube. Swirl the tube
to mix. A precipitate will form if potassium is present.
4. Stand the empty Potash “B” Tube (0246) on the Potassium
Reading Plate (1107), a rectangular piece of white plexiglass
with a solid black line down the middle. Place the tube
directly over the black line.
5. Fill a transfer pipet (0364) with the test sample from the
Potash “A” Tube.
6. Slowly add the test sample to the Potash “B” Tube, allowing it
to run down the side of the tube. Observe the black line down
through the Potash “B” Tube. Continue to add the test sample
until the black line just disappears.
7. Record as pounds per acre Available Potassium where the
level of the liquid meets the scale printed on the side of the
Potash “B” Tube.
8. If the test result is equal to or greater than 400 pounds per
acre, repeat the test on a diluted test sample as follows:
A. Fill a Potash “C” Tube (0247) to the lower mark with the
general soil extract.
B. Add *Universal Extracting Solution (5173) to the upper
mark and mix.
C. Using this diluted extract follow Steps 1 through 7 above.
Multiply the test result by 2 to obtain pounds per acre
Available Potassium.
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