Part 19

Table 13.—PREPARATION OF PERMANENT STANDARDS FOR CONTENT OF CHLORINE.

───────────────────────┬───────────────────────┬─────────────────────── 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.

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.

Collection of sample.—Collect the sample in a narrow-necked glass-stoppered bottle of 250 to 270 cc. capacity. The following procedure should be followed in order to avoid entrainment or absorption of atmospheric oxygen. In collecting from a tap fill the bottle through a glass or rubber tube extending well into the tap and to the bottom of the bottle. To avoid air bubbles allow the bottle to overflow for several minutes, and then carefully replace the glass stopper so that no air bubble is entrained. In collecting from the surface of a pond or tank connect the sample bottle to a bottle of 1 liter capacity. Provide each bottle with a two-hole rubber stopper having one glass tube extending to the bottom and another glass tube entering but not projecting into the bottle. Connect the short tube of the sample bottle with the long tube of the liter bottle. Immerse the sample bottle in the water and apply suction to the outlet of the liter bottle. To collect a sample at any depth arrange the two bottles so that the outlet tube of the liter bottle is at a higher elevation then the inlet tube of the sample bottle. Lower the two bottles, in any convenient form of cage properly weighted, to the desired depth. Water entering during the descent will be flushed through into the liter bottle. When air bubbles cease rising to the surface raise the bottles. Finally replace the perforated stopper of the sample bottle with a glass stopper in such manner as to avoid entraining bubbles of air.

Procedure.—Remove the stopper from the bottle and add, first, 0.7 cc. of the concentrated sulfuric acid, and then 1 cc. of the potassium permanganate solution. These and all other reagents should be introduced by pipette under the surface of the liquid. Insert the stopper and mix by inverting the bottle several times. After 20 minutes have elapsed destroy the excess of permanganate by adding 1 cc. of the potassium oxalate solution, the bottle being at once restoppered and its contents mixed. If a noticeable excess of potassium permanganate is not present at the end of 20 minutes, again add 1 cc. of the potassium permanganate solution. If this is still insufficient use a stronger potassium permanganate solution. After the liquid has been decolorized by the addition of potassium oxalate add 1 cc. of the manganous sulfate solution and 3 cc. of the alkaline potassium iodide solution. Allow the precipitate to settle. Add 2 cc. of the hydrochloric acid and mix by shaking.

The procedure to this point must be carried out in the field, but after the acid has been added and the stopper replaced there is no further change, and the rest of the test may be performed within a few hours, as convenient. Transfer 200 cc. of the contents of the bottle to a flask and titrate with N/40 sodium thiosulfate, using a few cubic centimeters of the starch solution as indicator toward the end of the titration. Do not add the starch solution until the color has become faint yellow, and titrate until the blue color disappears.

The use of potassium permanganate is made necessary by high nitrite or organic matter. The procedure outlined must be followed in all work on sewage and partly purified effluents or seriously polluted streams or samples whose nitrite nitrogen exceeds 0.1 part per million. In testing other samples the procedure may be shortened by beginning with the addition of the manganous sulfate solution and proceeding from that point as outlined, except that only 1 cc. of alkaline potassium iodide need be added.

Calculation of Results.—Oxygen shall be reported in parts per million by weight. It is sometimes convenient to know the number of cubic centimeters per liter of the gas at 0°C. temperature and 760 mm. pressure and also to know the percentage which the amount of gas present is of the maximum amount capable of being dissolved by distilled water at the same temperature and pressure. If 200 cc. of the sample is taken the number of cubic centimeters of N/40 thiosulfate used is equal to parts per million of oxygen. Corrections for volume of reagents added amount to less than 3 per cent and are not justified except in work of unusual precision. To obtain the result in cubic centimeters per liter multiply the number of cubic centimeters of thiosulfate used by 0.698. To obtain the result in percentage of saturation divide the number of cubic centimeters of thiosulfate by the figure in Table 14 opposite the temperature of the water and under the proper chlorine figure. The last column of Table 14 permits interpolation for intermediate chlorine values. At elevations differing considerably from mean sea level and for accurate work attention must be given to barometric pressure, the normal pressure in the region being preferable to the specific pressure at the time of sampling. The term “saturation” refers to a condition of equilibrium between the solution and an oxygen pressure in the atmosphere corresponding to 158.8 millimeters, or approximately one-fifth atmosphere. The true saturation or equilibrium between the solution and pure oxygen is nearly five times this value, and consequently values in excess of 100 per cent saturation frequently occur in the presence of oxygen-forming plants.

Table 14.—SOLUBILITY OF OXYGEN IN FRESH WATER AND IN SEA WATER OF STATED DEGREES OF SALINITY AT VARIOUS TEMPERATURES WHEN EXPOSED TO AN ATMOSPHERE CONTAINING 20.9 PER CENT OF OXYGEN UNDER A PRESSURE OF 760 MM.

(Calculated by G. C. Whipple and M. C. Whipple from measurements of C. J. Fox.)

─────────────┬────────────────────────────────────────────┬─────────── │ │Difference Temperature. │ Chloride in sea water (milligrams per │ per 100 │ liter). │ parts of │ │ chloride. ─────────────┼────────┬────────┬────────┬────────┬────────┼─────────── │ 0. │ 5000. │ 10000. │ 15000. │ 20000. │ ─────────────┼────────┴────────┴────────┴────────┴────────┼─────────── °C. │Dissolved oxygen in milligrams per liter. │Parts per │ │ million. 0│ 14.62│ 13.79│ 12.97│ 12.14│ 11.32│ 0.0165 1│ 14.23│ 13.41│ 12.61│ 11.82│ 11.03│ .0160 2│ 13.84│ 13.05│ 12.28│ 11.52│ 10.76│ .0154 3│ 13.48│ 12.72│ 11.98│ 11.24│ 10.50│ .0149 4│ 13.13│ 12.41│ 11.69│ 10.97│ 10.25│ .0144 5│ 12.80│ 12.09│ 11.39│ 10.70│ 10.01│ .0140 │ │ │ │ │ │ 6│ 12.48│ 11.79│ 11.12│ 10.45│ 9.78│ .0135 7│ 12.17│ 11.51│ 10.85│ 10.21│ 9.57│ .0130 8│ 11.87│ 11.24│ 10.61│ 9.98│ 9.36│ .0125 9│ 11.59│ 10.97│ 10.36│ 9.76│ 9.17│ .0121 10│ 11.33│ 10.73│ 10.13│ 9.55│ 8.98│ .0118 │ │ │ │ │ │ 11│ 11.08│ 10.49│ 9.92│ 9.35│ 8.80│ .0114 12│ 10.83│ 10.28│ 9.72│ 9.17│ 8.62│ .0110 13│ 10.60│ 10.05│ 9.52│ 8.98│ 8.46│ .0107 14│ 10.37│ 9.85│ 9.32│ 8.80│ 8.30│ .0104 15│ 10.15│ 9.65│ 9.14│ 8.63│ 8.14│ .0100 │ │ │ │ │ │ 16│ 9.95│ 9.46│ 8.96│ 8.47│ 7.99│ .0098 17│ 9.74│ 9.26│ 8.78│ 8.30│ 7.84│ .0095 18│ 9.54│ 9.07│ 8.62│ 8.15│ 7.70│ .0092 19│ 9.35│ 8.89│ 8.45│ 8.00│ 7.56│ .0089 20│ 9.17│ 8.73│ 8.30│ 7.86│ 7.42│ .0088 │ │ │ │ │ │ 21│ 8.99│ 8.57│ 8.14│ 7.71│ 7.28│ .0086 22│ 8.83│ 8.42│ 7.99│ 7.57│ 7.14│ .0085 23│ 8.68│ 8.27│ 7.85│ 7.43│ 7.00│ .0083 24│ 8.53│ 8.12│ 7.71│ 7.30│ 6.87│ .0083 25│ 8.38│ 7.96│ 7.56│ 7.15│ 6.74│ .0082 │ │ │ │ │ │ 26│ 8.22│ 7.81│ 7.42│ 7.02│ 6.61│ .0080 27│ 8.07│ 7.67│ 7.28│ 6.88│ 6.49│ .0079 28│ 7.92│ 7.53│ 7.14│ 6.75│ 6.37│ .0078 29│ 7.77│ 7.39│ 7.00│ 6.62│ 6.25│ .0076 30│ 7.63│ 7.25│ 6.86│ 6.49│ 6.13│ .0075 ─────────────┴────────┴────────┴────────┴────────┴────────┴───────────

Footnote F:

Under any other barometric pressure, B, the solubility can be obtained from the corresponding value in the table by the formula:

S´ = S(B/760) = S(B´/29.92) in which S´ = Solubility at B or B´, S = Solubility at 760 mm. or 29.92 inches, B = Barometric pressure in mm., and B´ = Barometric pressure in inches.

ETHER-SOLUBLE MATTER.

Evaporate 500 cc. of the sample in a porcelain evaporating dish to a volume of about 50 cc. By means of a rubber-tipped glass rod remove to the bottom of the dish the solid matter attached to the sides, and add normal sulfuric acid to neutralize the alkalinity. Do not use an excess of acid. Then evaporate the contents of the dish to dryness. Treat the dry residue with boiling ether, rubbing the bottom and sides of the dish to insure complete solution of fat. Three extractions with ether are required. Filter the ether solution through a 5 cm. filter into a weighed flask having a wide mouth. Evaporate the ether slowly, and dry the flask at 100° C. for 30 minutes. The increase in weight of the flask gives the amount of fats, or, in more precise language, the ether-soluble matter.

An excess of acid gives too high results because of the formation of fatty-acid residues.

RELATIVE STABILITY OF EFFLUENTS.

Reagent.—Methylene blue solution. A 0.05 per cent aqueous solution of methylene blue, preferably the double zinc salt or commercial variety.

Collection of sample.—Collect the sample in a glass-stoppered bottle holding approximately 150 cc. If the dissolved oxygen is low observe precautions similar to those used in collecting samples for dissolved oxygen (p. 66).