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9h.EXTRACTION OF PHOSPHORUS BY WATER
1. SCOPE
This method is for the determination of water-soluble phosphorus.
2. FIELD OF APPLICATION
All fertilisers, including compound fertilisers, where water-soluble phosphorus is to be determined.
3. PRINCIPLE
Extraction in water by shaking under specific conditions.
4. APPARATUS
500 ml graduated flask (for example Stohmann).
Rotary shaker, 35 — 40 turns per minute.
5. PREPARATION OF THE SAMPLE
See Method 1.
6. PROCEDURE
Extraction
Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a 500 ml graduated flask (4.1). Add to the flask 450 ml of water, the temperature of which must be between 20° and 25°C. Shake on the rotary shaker (4.2) for 30 minutes. Then make up to the mark with water, mix thoroughly by shaking and filter through a dry fluted filter, into a dry container.
Determination
Determine the phosphorus according to Method 10, on an aliquot part of the clear filtrate.
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