Part 5

EXPRESSION OF RESULTS.

Express the quality of the odor by a descriptive epithet like the following, which may be abbreviated in the record:

a—aromatic C—free chlorine d—disagreeable e—earthy f—fishy g—grassy m—moldy M—musty P—peaty s—sweetish S—hydrogen sulfide v—vegetable.

Express the intensity of the odor by a numeral prefixed to the term expressing quality, which may be defined as follows:

Numerical Term. Definition. value.

0 None. No odor perceptible.

1 Very An odor that would not be detected ordinarily by faint. the average consumer, but that could be detected in the laboratory by an experienced observer.

2 Faint. An odor that the consumer might detect if his attention were called to it, but that would not attract attention otherwise.

3 Distinct. An odor that would be detected readily and that might cause the water to be regarded with disfavor.

4 Decided. An odor that would force itself upon the attention and that might make the water unpalatable.

5 Very An odor of such intensity that the water would be strong. absolutely unfit to drink. (A term to be used only in extreme cases.)

CHEMICAL EXAMINATION.

EXPRESSION OF RESULTS.

The results of chemical analyses shall be expressed in parts per million, which in most analyses is practically equivalent to milligrams per liter. In some laboratories other forms of expression have been used. Results expressed in parts per 100,000 or in grains per gallon may be transformed to parts per million, or conversely, by the use of the following table:

Table 4.—FACTORS FOR TRANSFORMING RESULTS OF ANALYSES.

───────────────────────────────┬─────────────────────────────────────── Unit. │ Equivalent. ───────────────────────────────┼─────────┬─────────┬─────────┬───────── │ Grains │ Grains │ │ │per U.S. │ per │Parts per│Parts per │ gallon. │Imperial │100,000. │million. │ │ gallon. │ │ ───────────────────────────────┼─────────┼─────────┼─────────┼───────── 1 grain per U. S. gallon │ 1.000│ 1.20│ 1.71│ 17.1 1 grain per Imperial gallon │ .835│ 1.00│ 1.43│ 14.3 1 part per 100,000 │ .585│ .70│ 1.00│ 10.0 1 part per million │ .058│ .07│ .10│ 1.0 ───────────────────────────────┴─────────┴─────────┴─────────┴─────────

The following general rules shall govern the use of significant figures in the expression of results:

1. If the results show quantities greater than 10 parts per million use no decimals; record only whole numbers. If the quantities reach hundreds and thousands of parts record only two significant figures.

2. If the results are between 1 and 10 parts do not retain more than one decimal place.

3. If the results are between 0.1 and 1 part do not retain more than two decimal places.

4. Estimates of ammonia, albuminoid, and nitrite nitrogen alone justify the use of three decimals.

5. If the results of analyses are tabulated ciphers should not be added at the right of the decimal point to make the column uniform.

FORMS OF NITROGEN.

Nitrogenous organic matter passes through several intermediate compounds during its natural decomposition, and that which does not gasify ultimately forms nitrate. Nitrogen in organic matter is determined by the Kjeldahl process. An indication of the amount present is obtained by the albuminoid nitrogen determination. It has not been found possible to differentiate the nitrogen in the organic matter that readily decomposes from that in stable or non-putrescible compounds. Decomposition of organic matter produces nitrogen combined in ammonia, which is the first step between nitrogenous organic matter and the completely mineralized nitrate. Ammonia nitrogen may be determined by distillation and Nesslerization or by direct Nesslerization of the clarified sample. The next step is oxidation to nitrite, and the final step, oxidation to nitrate. It is recommended that all forms of nitrogen be reported as the element nitrogen (N).

AMMONIA NITROGEN.

There are two methods for estimating ammonia nitrogen—distillation and direct Nesslerization. Distillation is recommended for most waters and direct Nesslerization is recommended for sewages, sewage effluents, and highly polluted surface waters.

DETERMINATION BY DISTILLATION.

Procedure.—Use a metal or a glass flask connected with a condenser so that the distillate may drop from the condenser tube directly into a Nessler tube or a flask. Free the apparatus from ammonia by boiling distilled water in it until the distillate shows no trace of ammonia. After this has been done empty the distilling flask and measure into it 500 cc. of the sample, or a smaller portion diluted to 500 cc. with ammonia-free water. If the sample is acid or if the presence of urea is suspected add about 0.5 gram of sodium carbonate before distillation. Omit this if possible as it tends to increase “bumping.” Apply heat so that the distillation may proceed at the rate of not more than 10 cc. nor less than 6 cc. per minute. Collect the distillate in four Nessler tubes, 50 cc. to each tube, or if the nitrogen is high in a 200 cc. graduated flask. These receptacles contain the ammonia nitrogen to be measured as hereafter described.