───────────────────────┬───────────────────────┬─────────────────────── Chlorine. │ Solution of copper │ Solution of potassium │ sulfate. │ bichromate. ───────────────────────┼───────────────────────┼─────────────────────── _Parts per million._ │ _cc._ │ _cc._ │ │ 0.01│ 0.0│ 0.8 .02│ .0│ 2.1 .03│ .0│ 3.2 .04│ .0│ 4.3 .05│ .4│ 5.5 .06│ .8│ 6.6 .07│ 1.2│ 7.5 .08│ 1.5│ 8.7 .09│ 1.7│ 9.0 .10│ 1.8│ 10.0 .20│ 1.9│ 20.0 .30│ 1.9│ 30.0 .40│ 2.0│ 38.0 .50│ 2.0│ 45.0 ───────────────────────┴───────────────────────┴─────────────────────── DISSOLVED OXYGEN.[16][65][68][71b][99][100c][120] _Reagents._—1. Sulfuric acid, concentrated. (Sp. gr. 1.83–1.84.) 2. Potassium permanganate. Dissolve 6.32 grams of the salt in water and dilute the solution to 1 liter. 3. Potassium oxalate. A 2 per cent solution. 4. Manganous sulfate. Dissolve 480 grams of the salt in water and dilute the solution to 1 liter. 5. Alkaline potassium iodide. Dissolve 700 grams of potassium hydroxide and 150 grams of potassium iodide in water and dilute the solution to 1 liter. 6. Hydrochloric acid. Concentrated (Sp. gr. 1.18–1.19). 7. Sodium thiosulfate. A N/40 solution. Dissolve 6.2 grams of chemically pure recrystallized sodium thiosulfate in water and dilute the solution to 1 liter with freshly boiled distilled water. Each cc. is equivalent to 0.2 mg. of oxygen or to 0.1395 cc. of oxygen at 0°C. and 760 mm. pressure. Inasmuch as this solution is not permanent it should be standardized occasionally against a N/40 solution of potassium bichromate. The keeping qualities of the thiosulfate solution are improved by adding to each liter 5 cc. of chloroform and 1.5 grams of ammonium carbonate before diluting to the prescribed volume. 8. Starch solution. Mix a small amount of clean starch with cold water until it becomes a thin paste and stir this mass into 150 to 200 times its weight of boiling water. Boil for a few minutes, then sterilize. It may be preserved by adding a few drops of chloroform.