Metaphosphoric acid, combination with

Place the other vegetable sample in a beaker containing 25 mL of water. Heat the water to boiling and continue to boil for 10 minutes. Pour off and save the water, cut vegetable into small pieces, and transfer to a mortar. Grind with three 25-mL portions of metaphosphoric acid solution as before. Combine all the metaphosphoric acid extracts in a 100-mL volumetric flask. Filter the extract and titrate with DCIP as before. Mix 5.0 mL of the cooking water with 5.0 mL of metaphosphoric acid solution. Titrate with DCIP. 

Phosphorus pentoxid—Phosphoric anhydride Phosphoric oxid —PaOj—142—is formed when P is burned in an excess of dry O. It is a white, flooculent solid, which has almost as great a tendency to combine with HjO as has P2O3. It absorbs moisture rapidly, deliquescing to a highly acid liquid, containing, not phosphoric, but metaphosphoric acid. It is used as a drying agent. 

Shake a weighed quantity of the liquid expressed from the sample, equivalent to about 75 mg of ascorbic acid with 25 ml of freshly prepared 20 per cent metaphosphoric acid solution until completely dispersed, centrifuge and filter. Wash the residue with successive portions of a 5 per cent solution of trichloroacetic acid until the volume of the combined filtrate and washings is exactly 100 ml. Titrate a 2-5-ml aliquot of this solution with 2,6-dichlorophenolindophenol solution (as used for Syrup of Black Currant), avoiding oxidation by air. 

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