Part 6

Use Nessler tubes of such diameter that the graduation mark is between 20 and 25 cm. above the bottom and of such uniformity of diameter that the distance from the bottom to the graduation mark of the longest tube shall not exceed that of the shortest tube by more than 6 mm. The tubes must be of clear white glass with polished bottoms.

MEASUREMENT OF AMMONIA NITROGEN.

The amount of ammonia in the distillates may be measured either by (1) comparison of the Nesslerized distillates with Nesslerized solutions containing known quantities of nitrogen as ammonium chloride, or by (2) comparison of the Nesslerized distillates with permanent standard solutions in which the colors of Nesslerized standard ammonia solutions are duplicated by solutions of platinum and cobalt chlorides.

COMPARISON WITH AMMONIA STANDARDS.

Reagents.—1. Ammonia-free water.

2. Standard ammonium chloride solution. Dissolve 3.82 grams of ammonium chloride in ammonia-free water and dilute to 1 liter; dilute 10 cc. of this to 1 liter with ammonia-free water. One cc. equals 0.00001 gram of nitrogen.

3. Nessler reagent. Dissolve 50 grams of potassium iodide in a minimum quantity of cold water. Add a saturated solution of mercuric chloride until a slight precipitate persists permanently. Add 400 cc. of 50 per cent solution of potassium hydroxide, made by dissolving the potassium hydroxide and allowing it to clarify by sedimentation before using. Dilute to 1 liter, allow to settle, and decant. This solution should give the required color with ammonia within five minutes after addition and should not produce a precipitate with small amounts of ammonia within two hours.

Procedure.—Prepare a series of 16 Nessler tubes containing the following amounts of the standard ammonium chloride solution, diluted to 50 cc. with ammonia-free water, namely: 0.0, 0.1, 0.3, 0.5, 0.7, 1.0, 1.4, 1.7, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and 6.0 cc. These solutions will contain 0.00001 gram of nitrogen for each cubic centimeter of the standard solution.

Nesslerize the standards and the distillates by adding approximately 1 cc. of Nessler reagent to each tube. Do not stir the contents of the tubes. The temperature of the tubes should be practically the same as that of the standards; otherwise the colors will not be directly comparable. Allow the tubes to stand at least 10 minutes after Nesslerizing. Compare the color produced in the tubes with that in the standards by looking vertically downward through them at a white or mirrored surface placed at an angle in front of a window so as to reflect the light upward.

If the color obtained by Nesslerizing the distillates is greater than that of the darkest tube of the standards, mix the contents of the tube thoroughly, pour out half of the liquid, and dilute the remainder to the original volume with ammonia-free water; then make the color comparison and multiply the result by two. If the color is still too dark after pouring out half the liquid, repeat this process of division until a reading can be made. The process of dilution may be shortened by mixing together the distillates from one sample before making the comparison and comparing an aliquot portion with the standards.

After the readings have been recorded add the results obtained by Nesslerizing each portion of the entire distillate. If 500 cc. of the sample is distilled this sum, expressed in cubic centimeters and multiplied by 0.02, will give the number of parts per million of ammonia nitrogen in the sample. If x cc. of sample is used multiply the sum of the readings by 10/x.

If the ammonia is known to be high the distillate may be collected in 200 cc. flasks and an aliquot part Nesslerized.

COMPARISON WITH PERMANENT STANDARDS.

Reagents.—Platinum solution. Dissolve 2.00 grams of potassium platinic chloride (PtCl_{4}.2KCl) in a small amount of distilled water, add 100 cc. of strong hydrochloric acid, and dilute to 1 liter.

Cobalt solution. Dissolve 12 grams of cobaltous chloride (CoCl{2}.6H{2}O) in distilled water, add 100 cc. of strong hydrochloric acid, and dilute to 1 liter.

Prepare standards by putting various amounts of these two solutions into Nessler tubes and diluting to the 50 cc. mark with distilled water as indicated in Table 5. These standards may be kept for several months if protected from dust.

Table 5.—PREPARATION OF PERMANENT STANDARDS FOR THE DETERMINATION OF AMMONIA.

───────────────────────┬───────────────────────┬─────────────────────── Value in standard │ Solution of platinum. │ Solution of cobalt. ammonium chloride. │ │ ───────────────────────┼───────────────────────┼─────────────────────── cc.│ cc.│ cc. 0.0│ 1.2│ 0.0 .1│ 1.8│ .0 .2│ 2.8│ .0 .4│ 4.7│ .1 .7│ 5.9│ .2 │ │ 1.0│ 7.7│ .5 1.4│ 9.9│ 1.1 1.7│ 11.4│ 1.7 2.0│ 12.7│ 2.2 2.5│ 15.0│ 3.3 │ │ 3.0│ 17.3│ 4.5 3.5│ 19.0│ 5.7 4.0│ 19.7│ 7.1 4.5│ 19.9│ 8.7 5.0│ 20.0│ 10.4 │ │ 6.0│ 20.0│ 15.0 7.0│ 20.0│ 22.0 ───────────────────────┴───────────────────────┴───────────────────────

The amounts in Table 5 are approximate, and the actual amount necessary will differ with the character of the Nessler solution, the color sensitiveness of the analyst’s eye, and other conditions. The final test of the standard is best obtained by comparing it with Nesslerized standards and modifying the tint accordingly. Such comparison should be made for each new batch of Nessler solution and should be checked by each analyst.

Procedure.—In comparison with permanent standards, Nesslerize the distillates in the manner above described and compare the resulting colors at the end of about 10 minutes with the permanent standards. The method of calculating results is precisely the same as with the ammonia standards.

MODIFICATION FOR SEWAGE.

Ammonia nitrogen and albuminoid nitrogen in sewages, soils, and other materials of high nitrogen content may be satisfactorily determined by diluting the sample with ammonia-free distilled water and proceeding as described in the preceding sections, but it is permissible to distill with steam.

Procedure.—Use a 200 cc. long-necked Kjeldahl flask connected with a condenser so that the distillate may drop from the condenser tube directly into a Nessler tube or a flask. Connect the Kjeldahl flask with a steam generator by a tube reaching almost to the bottom of the flask.

After the apparatus is freed from ammonia put the sample to be tested into the flask. Use 10 to 100 cc. of the sample according to its ammonia content. Pass ammonia-free steam through the liquid in the Kjeldahl flask and collect the distillate in the usual way. It is usually convenient to collect the distillate in a 200 cc. flask and to take an aliquot part of it for Nesslerization. Compare with standards and calculate the nitrogen content in the usual manner.

This method has the advantage, when the sample is treated with an alkaline solution of potassium permanganate, of avoiding bumping, permitting the assay of solid matter, and yielding the ammonia more rapidly than by the ordinary process of distillation.

DETERMINATION BY DIRECT NESSLERIZATION.

Reagents.— 1. Ten per cent solution of copper sulfate (CuSO{4}.5H{2}O).

2. Ten per cent solution of lead acetate (Pb(C{2}H{3}O{2}){2}.3H_{2}O).