Part 2

Table 1.—GRADUATION OF TURBIDITY ROD.

───────────────────────────────────┬─────────────────────────────────── Turbidity │ Vanishing depth of wire (mm.). (parts per million). │ │ ───────────────────────────────────┼─────────────────────────────────── 7│ 1095 8│ 971 9│ 873 10│ 794 11│ 729 12│ 674 13│ 627 14│ 587 15│ 551 16│ 520 17│ 493 18│ 468 19│ 446 20│ 426 22│ 391 24│ 361 26│ 336 28│ 314 30│ 296 35│ 257 40│ 228 45│ 205 50│ 187 55│ 171 60│ 158 65│ 147 70│ 138 75│ 130 80│ 122 85│ 116 90│ 110 95│ 105 100│ 100 110│ 93 120│ 86 130│ 81 140│ 76 150│ 72 160│ 68.7 180│ 62.4 200│ 57.4 250│ 49.1 300│ 43.2 350│ 38.8 400│ 35.4 500│ 30.9 600│ 27.7 800│ 23.4 1000│ 20.9 1500│ 17.1 2000│ 14.8 3000│ 12.1 ───────────────────────────────────┴───────────────────────────────────

_Procedure._—Lower the rod vertically into the water as far as the wire can be seen and read the level of the surface of the water on the graduated scale. This will indicate the turbidity.

The following precautions shall be taken to insure correct results:

Observations shall be made in the open air, preferably in the middle of the day and not in direct sunlight. The wire shall be kept bright and clean. If for any reason observations cannot be made directly under natural conditions a pail or tank may be filled with water and the observation taken in that, but if this is done care shall be taken that the water is thoroughly stirred before the observation is made, and no vessel shall be used for this purpose unless its diameter is at least twice as great as the depth to which the wire is immersed. Waters which have a turbidity greater than 500 shall be diluted with clear water before the observations are made, but if this is done the degree of dilution shall be reported.

TURBIDIMETRIC METHOD.

Several forms of turbidimeter or diaphanometer[73] have been suggested for use. The simplest and most satisfactory form is the candle turbidimeter.[116] This consists of a graduated glass tube with a flat polished bottom, enclosed in a metal case. This is supported over an English standard candle and so arranged that one may look vertically down through the tube at the flame of the candle. The observation is made by pouring the sample of water into the tube until the image of the flame of the candle just disappears from view. Care shall be taken not to allow soot or moisture to accumulate on the lower side of the glass bottom of the tube so as to interfere with the accuracy of the observations. The graduations on the tube correspond to turbidities produced in distilled water by certain numbers of parts per million of silica standard. In order to insure uniform results it is necessary to have the distance between the top rim of the candle and the bottom of the tube constant, and this distance shall be 7.6 cm. or 3 inches. The observations shall be made in a darkened room or with a black cloth over the head.

It is allowable to substitute for the candle an electric light. Calibrate the apparatus to correspond with the United States Geological Survey scale. The figures in Table 2 on page 8 are believed to be approximately correct for the candle turbidimeter but should be checked by the experimenter. It is allowable to calibrate the tube of the instrument with waters of known turbidity prepared by making a series of dilutions of the silica standard with distilled water. From the figures obtained in calibrating plot a curve from which the turbidity of a sample may be read when the depth of water in the tube has been obtained.

Table 2.—GRADUATION OF CANDLE TURBIDIMETER.

───────────────────────────────────┬─────────────────────────────────── Depth of liquid │ Turbidity (cm.). │ (parts per million of silica). ───────────────────────────────────┼─────────────────────────────────── 2.3│ 1000 2.6│ 900 2.9│ 800 3.2│ 700 3.5│ 650 3.8│ 600 4.1│ 550 4.5│ 500 4.9│ 450 5.5│ 400 5.6│ 390 5.8│ 380 5.9│ 370 6.1│ 360 6.3│ 350 6.4│ 340 6.6│ 330 6.8│ 320 7.0│ 310 7.3│ 300 7.5│ 290 7.8│ 280 8.1│ 270 8.4│ 260 8.7│ 250 9.1│ 240 9.5│ 230 9.9│ 220 10.3│ 210 10.9│ 200 11.4│ 190 12.0│ 180 12.7│ 170 13.5│ 160 14.4│ 150 15.4│ 140 16.6│ 130 18.0│ 120 19.6│ 110 21.5│ 100 ───────────────────────────────────┴───────────────────────────────────

The results of turbidity observations shall be expressed in whole numbers which correspond to parts per million of silica and recorded as follows:

Turbidity between │ 1│and│ 50│recorded to nearest│unit " " │ 51│ " │ 100│ " " " │ 5 " " │ 101│ " │ 500│ " " " │ 10 " " │ 501│ " │ 1000│ " " " │ 50 " " │1001│ " │greater│ " " " │ 100

COEFFICIENT OF FINENESS[80]

The quotient obtained by dividing the weight of suspended matter in the sample by the turbidity, both expressed in the same unit, shall be called the coefficient of fineness. If the quotient is greater than unity the matter in suspension is coarser and if it is less than unity it is finer than the standard.

COLOR.

The “color,” or the “true color,” of water shall be considered the color that is due only to substances in solution; that is, it is the color of the water after the suspended matter has been removed. In stating results the word “color” shall mean the “true color” unless otherwise designated.

The “apparent color” shall be considered as including not only the true color but also any color produced by substances in suspension. It is the color of the original unfiltered sample.

The platinum-cobalt method of measuring color shall be considered as the standard, and the unit of color shall be that produced by 1 part per million of platinum.

COMPARISON WITH PLATINUM-COBALT STANDARDS.[43]

_Reagents._—Dissolve 1.246 grams of potassium platinic chloride (PtCl_{4}2KCl), containing 0.5 gram platinum, and 1.00 gram crystallized cobalt chloride (CoCl_{2}.6H_{2}O), containing 0.25 gram of cobalt, in water with 100 cc. concentrated hydrochloric acid, and dilute to 1 liter with distilled water. This solution has a color of 500. Dilute this solution with distilled water in 50 cc. Nessler tubes to prepare standards having colors of 0, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, and 70. Keep these standards in Nessler tubes of such diameter that the graduation mark is between 20 and 25 cm. above the bottom and of such uniformity that they match within such limit 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. Protect the tubes from dust and light when not in use.

_Procedure._—The color of a sample shall be observed by filling a standard Nessler tube to the height equal to that in the standard tubes with the sample and by comparing it with the standards. The observation shall be made by looking vertically downward through the tubes upon a white or mirrored surface placed at such angle that light is reflected upward through the column of liquid.

Water that has a color greater than 70 shall be diluted before making the comparison, in order that no difficulties may be encountered in matching the hues.

Water containing matter in suspension shall be filtered, before the color observation is made, until no visible turbidity remains. If the suspended matter is coarse, filter paper may be used for this purpose; if the suspended matter is fine, the use of a Berkefeld filter is recommended. The Pasteur filter shall not be used as it exerts a marked decolorizing action.

The apparent color, if determined, shall be determined on the original sample without filtration. The true and the apparent color of clear waters or waters with low turbidities are substantially the same.

The results of color determinations shall be expressed in whole numbers and recorded as follows:

Color between 1 and 50 recorded to nearest unit " " 51 " 100 " " " 5 " " 101 " 250 " " " 10 " " 251 " 500 " " " 20.

COMPARISON WITH GLASS DISKS.[105]

As the platinum-cobalt standard method is not well adapted for field work, the color of the water to be tested may be compared with that of glass disks held at the end of metallic tubes through which they are viewed by looking toward a white surface. The glass disks are individually calibrated to correspond with colors on the platinum scale. Experience has shown that the glass disks used by the U. S. Geological Survey give results in substantial agreement with those obtained by the platinum determinations, and their use is recognized as a standard procedure.

COMPARISON WITH NESSLER STANDARDS.

Inasmuch as the Nessler scale[62] and the natural water scale[22][49] which agrees with it except for colors less than 20, have been largely used in the past, the old results may be converted[117] into terms of the platinum standard by means of the ratios in Table 3, but they must not be considered as universally applicable as the variable sensitiveness of the Nessler solution introduces an uncertain factor.

Table 3.—VALUES FOR CONVERTING COLORS BY THE NATURAL WATER SCALE INTO COLORS BY THE PLATINUM STANDARD IN PARTS PER MILLION.[B]

───────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬───── Modified │ │ │ │ │ │ │ │ │ │ Nessler or │ │ │ │ │ │ │ │ │ │ natural │0.00.│0.01.│0.02.│0.03.│0.04.│0.05.│0.06.│0.07.│0.08.│0.09. water │ │ │ │ │ │ │ │ │ │ standard. │ │ │ │ │ │ │ │ │ │ ───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴───── Platinum-cobalt standard color. 0.00│ 0│ 2│ 4│ 6│ 8│ 9│ 11│ 13│ 15│ 17 .10│ 18│ 19│ 20│ 20│ 21│ 22│ 23│ 24│ 24│ 26 .20│ 26│ 27│ 27│ 28│ 29│ 29│ 30│ 31│ 32│ 32 .30│ 33│ 34│ 34│ 35│ 35│ 36│ 37│ 37│ 38│ 38 .40│ 39│ 40│ 40│ 41│ 42│ 42│ 43│ 44│ 45│ 45 .50│ 46│ 47│ 47│ 48│ 48│ 49│ 50│ 50│ 51│ 51 .60│ 52│ 53│ 53│ 54│ 54│ 55│ 56│ 56│ 57│ 57 .70│ 58│ 58│ 59│ 59│ 60│ 60│ 61│ 61│ 62│ 62 .80│ 63│ 64│ 64│ 65│ 66│ 66│ 67│ 68│ 69│ 69 .90│ 70│ 71│ 72│ 73│ 74│ 75│ 77│ 78│ 79│ 80 1.00│ 81│ 82│ 82│ 83│ 84│ 84│ 85│ 86│ 87│ 87 1.10│ 88│ 89│ 89│ 90│ 91│ 91│ 92│ 93│ 94│ 94 1.20│ 95│ 96│ 96│ 97│ 98│ 98│ 99│ 100│ 101│ 101 1.30│ 102│ 103│ 103│ 104│ 105│ 105│ 106│ 107│ 108│ 108 1.40│ 109│ 110│ 110│ 111│ 112│ 112│ 113│ 114│ 115│ 115 1.50│ 116│ 117│ 117│ 118│ 118│ 119│ 120│ 120│ 121│ 121 1.60│ 122│ 123│ 123│ 124│ 125│ 125│ 126│ 127│ 128│ 128 1.70│ 129│ 130│ 130│ 131│ 132│ 132│ 133│ 134│ 135│ 136 1.80│ 136│ 137│ 137│ 138│ 139│ 139│ 140│ 141│ 142│ 142 1.90│ 143│ 144│ 144│ 145│ 146│ 146│ 147│ 148│ 149│ 149 2.00│ 150│ │ │ │ │ │ │ │ │ ───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────

Footnote B:

Zero on the true Nessler scale is about 15 on the platinum scale.

LOVIBOND TINTOMETER.

The value of the readings of tint and shade by the Lovibond tintometer[66][82][83] has not been commensurate with the labor involved, but it is necessary to make a record of the reflected tint and shade[50] of some waters. The standard color disks used in teaching optics may be used for the purpose.

_Procedure._—The white disk supports three movable standard color sectors, red, yellow, and blue, and one movable black sector. All are mounted on a device which can be revolved rapidly, blending the colors into a uniform tint or shade. A scale around the circumference of the disk is used to indicate the percentage of each color or white or black in the blend.

Place the sample in a battery jar on a white ground; adjust the sectors so that when blended the tint or shade will match the reflected tint or shade of the sample. Report the percentages of red, yellow blue, white, and black in the blended tint or shade.

ODOR.[4][14][53][72][92][114][115][121c]

The observation of the odor, cold and hot, of samples of surface water is important as the odors are usually indicative of organic growths or sewage contamination or both. The odor of some ground waters is caused by the earthy constituents of the water-bearing strata. The odor of a contaminated well water is often contributory evidence of its pollution. A study of the organisms as directed under Microscopical Examination (p. 90) is a valuable adjunct to physical and chemical examination of water. Certain odors distinguish or identify certain organisms, as, for example, the “fishy” odor of _Uroglena_, the “aromatic” or “rose geranium” odor of _Asterionella_ and the “pig pen” odor of _Anabaena_. Observe and record the odor, both at room temperature and at just below the boiling point, as follows:

COLD ODOR.

Shake the sample violently in one of the collecting bottles, when it is half to two-thirds full and when the sample is at room temperature (about 20° C.). Remove the stopper and smell the odor at the mouth of the bottle.

HOT ODOR.

Pour about 150 cc. of the sample into a 500 cc. Erlenmeyer flask. Cover the flask with a well-fitting watch glass. Heat the water almost to boiling on a hot plate. Remove the flask from the plate and allow it to cool not more than five minutes. Then agitate it with a rotary movement, slip the watch glass to one side, and smell the odor.

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.