The Determination of Iodine in Natural Waters.

Abstract

A large dishpan is filled with the water, 1 gram of sodium hydroxide is added and evaporated over a stove or gas burner. As the water evaporates, more is added until 100 litres have been added and evaporated to about 1 litre. After the addition of 2 drops of 60 per cent NaOH solution, it is filtered into a porcelain evaporating dish, evaporated to dryness, and heated to burn the organic matter, either over a free flame or in a furnace.∗ The temperature should not rise enough to make the dish luminous. It is cooled, 25 cc. of absolute alcohol added, and the residue rubbed with a pestle. The alcohol is decanted through a filter and 10 cc. more added. The process is repeated until 100 cc. have been added. The filtrate is evaporated in a porcelain dish after the addition of 1 drop of 60 per cent NaOH solution, and enough water to keep it in solution. When the volume has reached a convenient size, it is transferred to a platinum or nickel dish or crucible, and evaporated to dryness. The residue is dissolved in 2 cc. of distilled water, transferred to a small beaker, and after the addition of two drops of 0.1 N sulfuric acid, it is neutralized with phosphoric acid, using an indicator paper made by drying an alcoholic solution of brom-phenol-blue or methyl orange on ash-free filter paper. The solution is boiled to remove the CO₂ and SO₂, and cooled. The volume is made up to 10 cc. in transferring to a 12 cc. separatory funnel having a 10 cc. graduation mark. One cc. of purified carbon tetrachloride, and 1 or 2 mg. of sodium nitrite are added, and the separatory shaken 200 times.†