Water-Supply and Irrigation Paper No. 151 Series L, Quality of T^ater, 11

DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

CHARLES D. WALCOTT, DIRECTOR

FIELD ASSAY OF WATER

BY

MARSHALL O. LEIGHTON

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1905

CONTENTS.

Page.

Letter of transinittal .---_...--......_........._.......-......----....-.- 7

Introduction_.-.._.-_.___.____.______.______.._________.-____.__.--_.--.--- 9

Sanitary analyses.,-.-_-_---'_--__--______-___ ________.-.- ---_-_-_.- 10

Inorganic analyses... -.-_-.----._--.___________-_._--___-..-----.--.._ 13

General observations.._. ......_................ J _......._............ 15

Field determinations.-_-..-_---.--_.-__ .__________-___-.___ ....-.-..-... 17

Suspended matter _.--_...__..._________________.__-____-_.__.--_---_- 18

Methods of determination ...-....................._....--.. ... _ - 18

Turbidity ...... ^...................................... ......... 22

United States Geological Survey turbidity rod..--..-._..-.-.. 23

Description---.--_------____-----___----_--.--. _-.-.----. 23

Objections. -----.-_-.-..-..-._-..--_._._____---.------ -_.- 25

Jackson's turbidinieter........_... __._____-___.- __----..._--- 26

Description ......._.... ^.............................. . 26

Tests ..-_-_._.__-_._.________.______.______..__..-._-..... 29

Probable error ______ .-___.___._____.__,-___-..-_---_----. 40

Color........ .__-__-_-..-_.-__..__.._._..____..__.____-_____-__-..-. 41

Occurrence --___---_-----_-...-- ____..___--._._---_---_-_._----. 41

Color standards..----_-.-.__..___....._........_..._.-_.---.----. 42

Geological Survey standard __.___._...___._.____......_.--._. 42

Field standards ._---..-...-......._........--.._---.-..-.--... 43

Description.-..--..---.-.._.__ ...---__.-_-.--.._----_-.- 43

Use ..................................................... 44

Iron -.-.-.----..------..--.--.-._-.-.-..._ ..__.-..__-._--...._---_.- 45

Chlorides.-------...- ......................... ..................... 47

Laboratory determination.--.--...._. ....._ _...---.----...-.-_.._ 47

Field determination.-------------- ........ _._. .----.-.--.-- .. 50

Standard silver-nitrate tablets-_...__.---...--.-----.-----.--- 50

Practical tests of method...-..........---..---.----.--_.-...- 53

Estimation of chlorine _______________________________________ 55

Hardness .........................................^.......... .-..-_.. 56

General statement --..-..-..._--._.__..___-..._-- ....__--__,--.__ 56

Field method of determination __.______-.-____-____.---_----_---- 57

Use of sodhim-oleate tablets. ................................. 57

Test of sodiuna-oleate tablets _......._ ___---___-_--___-.__--- 57

Estimation of hardness ---.-__-____-__---___----___----_--_-_ 61

Hardening constituents .-.-__--_____.___.__--_---__..--------.---- 62

Classes ......._......--.._.................--.......--.-....- 62

Carbonates ._.----.-.--..-._...........---_..---__---._-.--.. 63

Tests of sodium acid-sulphate tablets....-...---.--.--...- 63

Estimation of alkalinity....._.. __..-____--_.__-_-._-.---_ 66

Normal and acid carbonates...---...-....-.--------..-..- 66

Sulphates........................................ ............ 69

Determination by turbidinieter- -.-..--_.-.._.-.---.-----.- 70

Precautions --.._..........-_-...._..__._..._-..---..--.. 73

Calcium ....^................................................ 73

Instruments and reagents._--_--_----__....-----. ..---...-..---.----- 74

Index .................. ................................................ 77

ILLUSTRATIONS.

PLATE I. Jackson's candle turbidimeter__--__-_._.____-------_---------- 26

II. Tubes and disks for determining color of water _..___._____-.._- 46

III. United States Geological Survey tablet case _.._.--------------- 50

IV. United States Geological Survey field case ,_.___----.----------- 74

FIG. 1. Jackson's electric turbidimeter__ _--._-___._-_.--- _ - - - __-_____..-- 28

2. Logarithmic scale of turbidity. ................... ..----.-.-....- 38

3. Turbidity curve..-.-....-.--......,..--...---.--..-.-----.-----.- 39

LETTER OF TEANSMITTAL.

DEPARTMENT OF THE INTERIOR, 

UNITED STATES GEOLOGICAL SURVEY,

HYDROGRAPHIC BRANCH, 

Washington, D. 6'., June 9, 1905.

SIR : I transmit herewith a manuscript entitled u Field Assay of 

Water," by Marshall O. Leighton, and request that it be published as 

one of the series of Water-Supply and Irrigation Papers.

In this manuscript are described and discussed the method? which 

nave for some time been used with success in connection with the 

investigations into the quality of water in various parts of the United 

States carried on by the division of hydro-economics. As the methods have proved of value, it is believed that their publication in the 

form submitted will be of general interest.

Very respectfully, F. H. NEWELL,

Chief Engineer. 

Hon. CHARLES D. WALCOTT,

Director United States Geological Survey.

- 7

FIELD ASSAY OF WATER

By M. O. LEIGHTON.

INTRODUCTION.

A chemist aims to secure exceeding refinement in analytical methods and results. He seldom considers whether or not a method is 

sufficiently exact for certain broad purposes. The fact that it is 

incomplete, approximate, or susceptible of refinement is to him sufficient reason for improving or rejecting it at the first opportunity.

The scrutiny to which chemical methods have been subjected in 

the endeavor to secure exact results has led in many cases to processes 

so complicated and expensive that in commercial work the advantages do not compensate for the increased cost and delay which the 

methods involve. The result has been that the chemical profession 

distinguishes between two classes of chemical methods which differ 

in degree of accuracy. The first includes the exact methodr which 

afford results as nearly perfect as chemical procedure will permit. 

Such methods are used in all cases where minute differences in analysis would cause errors in interpretation or in subsequent chemical 

procedure. The second class consists of u commercial methods," so 

called because the results obtained by them, while departing from 

the actual truth, are sufficiently accurate to insure the profitable conduct of industrial chemical processes without appreciable error or 

waste. Methods of the first class are the product of .chemistry, 

while those of the second are used in response to the demands of 

expediency they are good enough for the purposes for which they 

are used.

In no branch of chemistry are approximate results more serviceable than in the analysis of water for hydro-economic surveys, or 

surveys made to determine the value of water and its applicability 

for use in domestic supply, boilers, industries, etc. Under th° conditions which generally prevail it is necessary to resort to long, tedious, 

and expensive processes in order to secure a determination of the 

character and amount of foreign constituents in water. It is the 

-practice in such cases to secure a sample of the water and transport
10 FIELD ASSAY OF WATER. INO. 151.

it to a laboratory, where, after conventional delays it is passed 

through the usual course of analysis.

There has in the past been surprisingly little discrimination used 

with reference to the selection of determinations for specific purposes, 

and as a general rule the same procedure has usually been followed 

without regard to the object of the particular investigation. If the 

purpose of the analysis is to determine the incrusting constituents, 

the course pursued has been to follow the entire analytical procedure. 

If, on the other hand, it is desired to determine the amonnt of organic 

pollution in a water and show its value for domestic use, the chemist 

forthwith begins the round of nitrogen determinations, and closes 

with a statement of the oxygen consumed and the number of bacteria 

per cubic centimeter. -In only a few well-known laboratories has 

this rule been violated, and such is the conservatism in the chemical 

profession that it will probably be largely followed in future. Conservatism is the safeguard of science and one of the most commendable qualities of a chemist, but an excess is sometimes almost as bad as 

a deficiency.

SANITARY ANALYSES.

The requisites to be met by a water in almost, every line of special 

development are broad and flexible. In the sanitary analysis certain 

results receive certain interpretations, which remain generally 

unchanged if the results are varied by 1, 2, 3, or sometimes even 10 

per cent. A strange feature in connection with sanitary analyses of 

water is that, in addition to insisting upon superrefinement, many 

chemists persist in making determinations that are admittedly to no 

purpose. It is a common thing to see an analyst's report of a water 

containing the results of determinations of albuminoid and free 

ammonia, nitrates, and nitrites, accompanied by a footnote stating 

that these results are unworthy of trust and mean very little, except 

to verify conclusions made from inspection of the territory from 

which the water was taken. In case such conclusions do not agree 

with the analytical evidence, the latter is invariably discredited.

It is to be hoped that some day the great and growing swarm of 

water analysts will awaken to the fact that sanitary analyses, as generally applied and interpreted, are but a succession of unrelated 

absurdities. Water experts, who encounter real problems, who must 

use analytical data as'a basis,for the design and construction of 

purification plants, and whose varied experience has taught them that 

in the United States the waters are as diverse in character as the 

climates, have learned a few things not taught in text-books nor anticipated in the beautiful theory of the oxidation of organic matter.

The occasional isolated sanitary analysis of water is positively without value. There are throughout the country numerous State, munic-
LEIGH-TON.] SANITARY ANALYSES. 11

ipal, and private laboratories in which sanitary analyses are carried on. The water analyzed to-day may be from a well, to-morrow 

from a brook, and the next day from a pond. From the results of a 

single analysis wise and ponderous verdicts are sent broadcast, and 

the eager, waiting public is duly impressed. No one understands 

how singularly misleading' a sanitary analysis of water can be until he 

has examined the results of such analyses of samples taken daily or 

hourly from the same source; then he sees that in general only a few 

single analyses in the group contain results which would admit of the 

interpretation that is finally placed upon the series.

If there is at hand a well-defined problem which involves the consideration of nitrogenous matter and the state in which it appears in 

a water, certain daily nitrogen determinations are of undoubted 

value; not, however, by reason of the absolute amounts which are 

revealed in each determination, but by reason of the daily relations 

and variations which appear in the successive analyses, and upon 

which interpretations can be placed. This statement, it should be 

emphasized, refers almost entirely to water slightly or moderately 

polluted, and does not include sewage. The organic matter normally 

occurring in a natural water, or what may be more accurately 

described as a highly dilute sewage, is, after all, practically infinitesimal in amount. The difficulties attendant upon a determination 

of nitrogen in its various forms and the true interpretation of the 

results, grow less and less as the amount of organic matter is increased. 

Yet, even with strong sewages some of the determinations, such as 

albuminoid ammonia and nitrites, are not usually productive of valuable information.

In an article entitled " The composition of sewage in relation to 

problems of disposal," ° Mr. George W. Fuller discusses in a characteristically clear manner an experiment which illustrates the apparent 

futility of the albuminoid-ammonia determination, as follows:

Illustrative of the varying relation of nitrogen in the form of albuminoid ammonia to the total organic nitrogen present in raw sewage, there are given 

below in a table the results of an experiment made in the Lawrence laboratory 

and published in the 1894 report of the Massachusetts State board of health, 

page 4G1. A bottle of fi'esh sewage was analyzed just after its collect'on and 

again at frequent intervals, allowing the natural decomposition processes to 

take place at room temperature. In this table it is seen that fresh sewage 

contains dissolved oxygen, coming, of course, from the water supply whic1! forms 

the principal portion of the sewage. It also contains nitrogen in the form of 

nitrates, as well as other salts which are completely oxidized. Throrgh the 

agency of the bacteria and the oxygen dissolved in the water and yielded by the 

oxidized salts, the carbon of the organic matter is oxidized and the organic 

nitrogen uniting with the hydrogen forms free ammonia.

0 Technology Quarterly, June, 1903, pp. 143-144.
Changes in composition occurring in fresh Lawrence sewage upon sta

[Parts per million.]

Date of examination.

Day.

March 11 ........................

Matfch 13 ........................

March 12 ........................

March 13 ........................

March 18 ........................

March 19 ........................

Hour.

10,30 a. m. 

13.30 p. m. 

3.00p.m. 

6.00p.m. 

8.00 a. m. 

12.00m...

5.00 p.m. 

10.80 a. m. 

10.30a.m. 

10.30a.m. 

10.30 a. m. 

10.30 a. m. 

10.30 a m.

Free 

ammonia.

18.5 

20.6 

21.0 

23.4 

40.7 

41.2 

41.2 

42.0 

41.2 

41.2 

41.2 

42.0 

43.8

Nitrogen asAlbuminoid ammonia.

Dissolved.

5.8 

5.8 

5.8 

5.6 

4.9 

4.9 

4 2 

4. 7 

3.3 

3.4 

3.5 

3.0 

3.0

Suspended.

2.1 

2.4 

2.5

X*. I

3.9 

4.4 

4 2 

3.5 

4.5 

4.3 

4.1 

3.8 

3.9

Total.

7.9

8. a

8.3 

8.3

8.8 

9.3

8.4

8.2 

7.8

7.6 

6.8 

8.9

Organic (Kjeldahl).

Dissolved.

31.4 

28.9 

28.9 

27.8 

11.6 

11.6 

11.6 

11.6 

9.4 

».3 

7.5 

7.4 

5.9

Suspended.

9.1 

11.4 

10.7 

9.9 

12.2 

8.2 

10.1 

8.2 

8.4 

8.3 

8.9 

6.9 

7.8

Tota

40.

40.

39.

37.

23.

19.

31.

19.

17.

17.

16.

14.

13.
LEIGHTON.] SANITARY ANALYSES. 13

Thus it is seen from the results in the table, page [12], that the dissolved oxygen and the nitrates gradually disappear, the bacteria for a time increase, the 

oxygen consumed (carbonaceous matter) decreases, the nitrogen as fre? ammonia increases, and the organic nitrogen (Kjeldahl) decreases. The nitrogen 

as albuminoid ammonia, however, remains approximately constant, notwithstanding that more than 20 parts of organic nitrogen are changed to free ammonia, and some 5 or 6 parts of free nitrogen escape into the atmosphere.

The nitrite determination, which has been regarded by rrany as 

one of the most valuable pollution indicators, fluctuates in a stream 

or reservoir according to the amount of available oxygen rathQ,r than 

the amount of organic matter undergoing oxidation. It will rise 

and fall in amount when there is a positive certainty that it can not 

be due to increase or decrease of organic pollution. Nevertheless, 

many an interpretation has been made largely on the evidence pre- - 

sented by this determination.

By far the greater number of sanitary water analyses reported 

include the determination of oxygen consumed, a test which is 

dependent upon so many features that as a whole the great, mass of 

determinations which have been made are valueless for purposes of 

comparison. The following table, compiled by Mr. George W. 

Fuller, shows clearly the relative results of the determination^ made 

according to different methods. In short, the only practical value of 

the " oxygen-consumed " determination is in its application to highly 

polluted waters of the same general character and origin, ard then 

only for purposes of comparison between the successive determinations made by absolutely the same method. In other word" it is 

essentially a sewage determination.

Approximate comparison of average amounts of oxygen consumed by sewage and 

sewage effluents as shown by different methods.

Method.

ally in America. 

Kubel, as practiced at Lawrence, Mass

English official tests .-.-.------......._...

Temperature 

of solution.

Boiling _ . _

.....do ....

.....do ....

r80°F______

_.-_do ....

I.. ..do ....

Period of contact.

5 minutes . . _

2 minutes

...--do ........

Relative 

results.

1.00

.65

1.25

.20

.35

.60

4.00

INORGANIC ANALYSES.

In the determination of inorganic constituents in a water it would 

make no difference, in the decision to accept or reject that water for 

boiler use, for irrigation, or for manufacturing, if the harmful constituents were contained, for example, in the proportion of 40, 44, 

or 48 grains per gallon. The lines dividing good and bad water for
14 FIELD ASSAY OF WATEE. [NO. 151.

boiler purposes are very broad. If a water contains a certain amount 

of iiicrusting constituents and a method used is inaccurate to a limit of 

5, or even 10, per cent, it would not lead to the acceptance of a bad 

water or the rejection of a good one. The " goocf " and " bad" 

provinces are approached too gradually to admit of such consequences.

Another error arises from the conventional methods of expression 

of results. If the analyst finds that a water contains certain amounts 

of calcium, magnesium, sodium, and potassium, and certain equivalents of the carbonate, sulphate, and chloride radicals, he unites these 

substances according to methods which are apparently not uniform 

and entitled to little scientific justification. It is a well-known fact 

that if several chemists, each independent of every o+her, analyze a 

certain water, there will almost invariably be wide differences in the 

expression of results.

Dr. F. W. Clarke, chief chemist of the United States Geological 

Survey, in a recent communication has given an excellent illustration 

of the various hypothetical combinations which may be made of the 

results of a single analysis of water. The statements are set forth in 

the following table. Each series of combinations is based upon a 

generally accepted hypothesis, and each represents r, water that is 

totally different from the others.

Analysis of water from artesian icell at Macoml), III.a 

[Grains per liter.]

Statement in ionic form.

SiO2 ..... 

A12 03 .... 

Fe2O3 . . - . 

SO4 . ....

C03 ......

Cl .......

Na. ______

K_. ......

Ca-.._.._

Mg ......

0. 0105 

.0013 

.0023 

. 9991 

. 3953 

. 5418 

.8086 

.0237 

.1581 

.0672

Statement according to hypothetical combinations.

KCL. .......

Nad... ......

CaCl2 _ ------

MgCL,--.---

K2S04 ..___--

Na.SO4 -----.

CaSO4 . ..... 

MgS04 ...

K2C03 ------

Na,CO3 ---..

CaCO3 ------

MgCO, ...

A1203 & ------

Fe3 03 & ------

SiO.,&. .......

0. 8968

.0538

.4649 

.5450 

.3360

.6983

. 0013 

.0020 

.0105

8. 0076

0. 0452

.8384

.0154

1.4781

.3952

.2215 

.0013 

.0020 

.0105

3. 0076

0. 0181 

.7164 

.0877 

. 0571 

.0211 

1.2495 

.1218 

.0711 

.0084 

.2793 

.2278 

.1355 

.0013 

.0020 

.0105

3. 0076

0.0211 

.8172 

. 0292 

. 0242 

.0246 

1.0642 

.2223 

.1357 

. 0028 

.3259 

.2076 

.1190 

.0013 

.0020 

.0105

3. 0076

"By George Steiger, laboratory of United States Geological Purvey. 

&AloO3, FegOg, SiO2, conventionally regarded as colloidal.
LEIGHTOX.] INOBGANIC ANALYSES. 15

The inorganic constituents of a water should invariably be expressed as positive and negative ions, and if so expressed tl Q result 

determined according to approximate methods is as valuable as the 

expression of precisely determined constituents united according to 

the individual ideas of the analyst.

GENERAL OBSERVATIONS.

A practical disadvantage in chemical water surveys arising from 

the insistence on refined methods of analysis and lack of discrimination in the choice of specific determinations is the delay which 

arises in securing valuable information with reference to wide areas. 

Months and even years have been spent upon water surveys covering 

only a comparatively small portion of the country. Two examples 

are here cited.

The most important chemical survey in the United States has been 

carried on since 1888 by the Commonwealth of Massachusetts. This 

survey work may safely be taken as the standard in this or any other 

country. During this period of sixteen years the appropriations for 

the work have been on an average about $30,000 a year, making a 

total cost of not far from $480,000. A large part of this sum has 

been used to pay expenses of experimentation and can not be charged 

to water survey. The work was confined to Massachusetts.

In the year 1898 tl^e Ohio State board of health commenced an 

examination of the principal streams of the State, making monthly 

analyses of samples of water taken from numerous points along 

the various streams. This work was continued five years before the 

State was covered, and there resulted merely a large number of periodical analyses in sets of twelve, showing the character of the 

stream water and its variation according to local conditions.

These two cases are typical. No one would claim that all the 

results could have been reached by the use of field methods. Undoubtedly a large part of them could have .been obtained far more 

cheaply and quickly, and there would have been no loss to tl °. cause 

of pure water, nor to science generally, had some of the determinations been omitted.

Among water analysts there seems to be a general tendency to attack 

every water problem as though the object were to prove its fitness or 

unfitness for drinking purposes. In many investigations it is well 

known at the outset that the water can not be used for domestic purposes and the problem is of quite another character. The conventional grind of nitrogen determinations has been made to do service 

in almost every conceivable water problem. It has been used frequently in investigating pollution problems in which organic matter 

had absolutely no part, A study of the results obtained in many
16 FIELD ASSAY OF WATER. [NO. 151.

laboratories will show that in the routine work a number of determinations could be omitted without detriment. These facts are 

mentioned in order to emphasize the point that if care and discrimination were used in the selection of tests the work necessary 

in carrying on chemical surveys might be decreased and the money 

available for such work might be distributed over a wider field; 

results of more immediate use might be secured and the completion 

of a chemical survey would not be postponed for the benefit of future 

generations. " Commercial methods " serve useful purposes in manufacturing; the success of enormous industrial plant? is dependent 

upon them, and in water surveys they would at least be businesslike.

It was these considerations, in connection with the knowledge of 

the vast areas covered by the United States, which led the United 

States Geological Survey, through its hydro-economic division, to 

investigate the practicability of employing field methods for the 

determination of important characteristics of water. It was realized 

that if there could be provided a few simple tests, the apparatus for 

which could be taken into the field and used on the spot, large areas 

might be covered in a short time, and if it were necessary for any 

reason to make periodical determinations the.cost of the work would 

still be small and the total would not run up into the large sums 

which have been spent in such investigations. In general, the testimony of a large number of approximate results is for more representative of actual conditions than that of one or two refined analyses.

The idea of testing waters in the field is by no means new. Very 

successful field tests have been carried on by numerous authorities. 

Probably one of the most successful systems now in use is that of the 

Bureau of Soils, Department of Agriculture. Another excellent field 

outfit for sanitary analysis has been devised and used with satisfaction 

by Mrs. Ellen H. Richards. Several others are noteworthy. They all 

involve the use of considerable apparatus and the carrying of standard solutions. Specially equipped wagons are necessary in some 

cases. In others the variety of determinations is limited or the 

equipment can not be used in an extensive circuit without renewal of 

reagents. The difficulty of carrying solutions and complex apparatus 

into the field is obvious. The ideal equipment is one which can be 

carried on journeys afoot or on horseback without much fatigue. 

The sources of useful or desirable water supply are not distributed 

with reference to the railroad or wagon routes and the field man must 

often climb mountains or trace obscure trails to accomplish his purpose. The outfit should contain a sufficient supply of reagents to 

serve for a large number of determinations without renewal. The 

processes should be rapid and the results fairly accurate and comprehensive. Finally, the equipment should be provided with material 

for ,so various a series of determinations that with proper discrim-
LEIGHTCN.] FIELD DETEEMTNATIONS. 17

ination the essential characteristics of a water may bs shown, whether 

the purposes be domestic or industrial water supply, irrigation, or 

any other special line of utilization. Volumetric methods requiring 

the use of burettes are objectionable; gravimetric methods are impossible. Therefore, in the Survey's study of field methods the whole 

matter developed into a question of choosing the most useful determinations and so modifying the volumetric methods that their use 

would be practicable, while at the same time they would give a degree 

of accuracy sufficiently close for all practical purposes.

To the methods hereinafter proposed the term " assay " readily 

lends itself. There is no attempt at water analysis. The plan contemplates the determination of ingredients which give to water certain 

well-known characteristics. The methods and the suggestions with 

reference to their application are only tentative and will be modified 

as experience may dictate. As they stand they are the result of 

extended experimentation, and the tests to which they have been put 

show that they are practicable. They have been found to b^ more 

nearly accurate than was at first anticipated, though this fact, it is 

believed, has not greatly increased their usefulness for the purposes 

in view. By their use, combined with a fair amount of common 

sense, the essential characteristics of waters can be ascertained at 

small expense. In almost every situation in which such determinations are significant they will afford sufficiently satisfactory data. 

In the case of finely balanced considerations of a purely physical, 

chemical, or geologic nature, however, they are practically useless. 

They are intended for practical purposes and have no place in pure 

science.

FIELD DETERMINATIONS.

The following determinations are described on subsequent p^ges:

1. Turbidity.

2. Color.

3. Iron.

4. Chlorine or total chlorides.

5. Total hardness.

6. Alkalinity.

7. Normal carbonates.

8. Bicarbonates.

9. Total sulphates.

10. Calcium.

It should be stated at the outset that the successful operation of 

these methods depends, as in all chemical procedure, upon the manner 

in which they are applied. A failure to insist upon strict compliance with the rules laid down may result in total failure,

IRR 151 05 2
18 FIELD ASSAY OF WATEE. [NO. 151. 

SUSPENDED MATTER.

The turbidity of water is that property which is imparted to it by 

substance carried in suspension. In many parts of the United States 

waters are often extremely muddy, and when this condition is maintained during long periods it becomes one of the most serious difficulties with which the water-supply engineer has to deal. Turbid 

water is objectionable for domestic use. In industrial operations, 

especially in those in which water enters into manufacturing processes, turbidity is a factor which, if not removed, may exert a harmful influence upon the manufactured products. It is rlso important 

in connection with irrigation works. One of the serious troubles in 

Western reservoirs is loss of storage capacity due to silt deposits. In 

the construction of irrigation canals the amount of turbidity usually 

carried by the water often determines the grade of the canal. Such 

canals must have grade sufficient to cause the flowing water to carry 

along suspended matter and not allow it to settle. If tl is is not taken 

into consideration, the maintenance of the irrigation system becomes 

extremely expensive, and cases have occurred where tl e canals have 

been practically filled by the deposits of suspended matter.

The suspended substances causing turbidity are of various characters. They are found often in a flocculent condition, settling 

readily when the water which carries them becomes quiescent. On 

the other hand, the turbid matter is often made up of minute particles of clay, so fine that they pass through certain filtering media. 

In some cases the problem of removing turbidity frori the water is 

so difficult that the process which may be successful is so radical that 

it will remove also dissolved organic material and ever a large number of the bacteria.

METHODS OF DETERMINATION.

There are several methods of estimating the proportion of suspended matter in a water, all but one of which have tl °ir particular 

fields of usefulness. The first is merely a statement of the observer's 

opinion of the degree of turbidity, such as u very slight," u slight," 

u distinct,' 1 or " decided." Although this method of estimation has 

no real value, it is used by many water chemists.

The second method is also based upon the appearance, of the water, 

but differs from the first in that a definite and fairly vrell-fixed basis 

of comparison is provided. A water containing no suspended matter 

is practically transparent, but matter in suspension intercepts the 

rays of transmitted light. An observer can see objects distinctly 

through a body of clear water, but as the water becomes more and 

more muddy the objects Qan be seen less and less distinctly until
LEIGHTON.] SUSPENDED MATTEE. 19

they are quite lost to view. Now, it has been found by experiment 

that there is a fairly definite relation between the prcDortion 

of light rays intercepted and the amount of matter in suspension. 

This relation varies somewhat with the character of the suspended matter and with the size of the particles, but for the purpose 

to which this method of measurement is applicable the variations do 

not often seriously affect the interpretations placed upon the results. 

The details of the method will be explained on later pages under the 

caption " Turbidity.' 1 For the present it will be sufficient to state 

that it has found its greatest usefulness in connection with the 

adaptation and operation of water-filtration plants and sewagedisposal works.

The third method of measuring the amount of suspended matter 

in water consists in separating it from a weighed portion o'f the fluid 

by filtration, weighing the filtered water, and stating the difference 

between the two weights as suspended matter. The form of statement commonly used is parts of suspended matter per million of 

water, milligrams per liter, or some other comprehensive proportion. 

This is undoubtedly the best method of determination, as it is relatively accurate and can be used in the study of all water problems. 

Its practical disadvantage is that the determination requires a large 

amount of time and can not be economically performed in serial 

investigations without considerable equipment and tecliour labor. 

It is also true that the processes for which a knowledge of suspended 

matter is necessary will generally in practical work be as well served 

by an approximate determination as by a precise one; therefore the 

cruder methods, based upon photometry, are more often used.

There is, however, no necessarily constant relation between the 

weight of suspended matter in a given volume of water and the 

turbidity produced. A certain weight of suspended substance of 

one kind does not usually produce the same degree of turbidity as 

a similar weight of another substance. In other words, the turbidity determination takes no account of the character, weight, or volume 

of the suspended matter. This has been clearly demonstrated by 

Mr. Robert Spurr Weston in the report on Water-Purification 

Investigation and on Plans Proposed for Sewerage and Waterworks 

Systems made to the sewerage and water board of New Orleans, 

La., pages 27 and 28. To overcome the errors above cited, Mr. Weston 

has proposed the use of a " turbidity coefficient," as follows:

All optical methods for the determination of turbidity are naturally compared 

with the gravimetric determination of the suspended matter which produces 

the turbidity. Equal weights of suspended matter do 'not necessarily produce 

the same turbidity. For example, waters which contain suspended silt or sand 

exhibit less turbidity per unit of suspended matter by weight than dt waters 

containing finely divided clay. Therefore the ratio between silica turbidity,
20 FIELD ASSAY OF WATER. [NO. 151.

determined optically, and suspended matter, determined gravimetrically, is 

most important, as it is an index of the character of the suspended matter producing the turbidity. To express this relation most conver'ently, the term 

" turbidity coefficient" has been adopted.

Turbidity coefficient equals Suspended matter.

Silica turbidity.

Naturally this coefficient varies with different waters, generally increasing 

with the size of the particles composing the suspended matter. Thus the 

samples of unsettled river water have the highest turbidity coefficient, while 

samples from the effluents of the three-day subsiding basins have the lowest, as 

the following table will show:

Table of average turbidity coefficients.

Turbidity

coefficient.

Mississippi River water____________________________ __ 1.68

Mississippi River water, after 6 hours' subsidence-___.____..__._..___ .00

Mississippi River water, after 12 hours' subsidence-____________ .87

Mississippi River water, after 18 hours' subsidence.____________ .80

Mississippi River water, after 24 hours' subsidence____________ .85

Mississippi River water, after 48 hours' subsidence-__________ _ .80

Mississippi River water, after 24 hours' subsidence and coagulrtion____ . 60

This table is very easy to understand, since the coarser particles of low 

turbidity-producing power and somewhat higher specific gravity gradually separate out according to their hydraulic values, the finer particles of high turbidity-producing power and somewhat lower specific gravity remaining longest 

in suspension.

The idea of Mr. Weston above set forth is an admirable one and 

should be utilized in connection with all water investigations.

The fourth method of determining suspended matter consists in 

measuring the cubical contents thereof after sedimentation. This 

method takes no account of the weight of the substance nor of the 

turbidity produced by it, and its particular value is confined to those 

highly turbid waters which it is proposed to conserve in storage 

reservoirs or to conduct in canals. In the preparation of reservoirs 

for irrigation and domestic uses in the arid and semiarid regions, one 

of the most troublesome features is the loss of storage capacity in the 

reservoir by reason of its filling up with matter deposited from suspension, and indeed it is necessary in the construction of these reservoirs to provide means whereby the silt can be. removed at proper 

intervals. The problem is, therefore, one of cubical contents and the 

observations are usually made by filling a 100 c. c. graduate with the 

turbid water, allowing the suspended matter to settl0, and reading 

the depth of the sediment and expressing it in percentage terms.

The results of such observations do not bear any mora, constant relation to the turbidity produced by the suspended matter than do the 

determinations of actual weight. An interesting series of observations upon this point has recently been compiled by the Geological.
LEIGHTON.] SUSPENDED MATTES. 21

Survey, the water being taken from Gila River at San Carlos, Ariz. 

This river is'probably the muddiest in the United States, and the 

observations represent extreme conditions. Turbidity measurements 

consume so small an amount of time in comparison with that necessary 

in the observation of per cent volume of total solids that an endeavor 

was made to determine whether or not turbidity measurements possess any constant relation to amount of matter. If such were found 

to be the case the work necessary in preparing plans for storage reservoirs would be considerably shortened.

Parallel determinations were therefore made of turbidity and per 

cent volume of sediment upon daily samples taken from Gila River 

from July 21 to October 24, 1904, the results of which are set forth in 

the following table. It will be noted in this table that the conversion 

factor, which should be constant if the hypothesis were correct, varies 

so widely as to indicate unmistakably the entire absence of pny constant relation between the two sets of observations:

Parallel observations of per cent 'volume of sediment and of turbidity, in terms 

of parts per million, of silica in water from Gila River at San Carlos, Ariz.

Date.

July 21..

22..

23..

24..

25..

26-_

27-

28--

29-.

30.-

31.-

Aug. 1--

2

3-.

4-_

51.

6-.

7-

8-_

9--

10.-

11-.

Per cent 

sediment 

volume.

12

16.5

19

18.5

21

18

16

9

21

19

12

13

23

20

19

15

. 15

14

15

14

14

13

Turbidity 

(silica parts 

per million).

27, 300

37. 800

43, 200

' 43, 200

44, 784

41,568

40, 572

40, 800

53, 000

64,000

64, 000

53,312

73, 536

67, 200

70, 368

63, 936

62, 400

62, 400

67, 200

63, 936

60, 768

62,400

Conversion 

factor.

2,280

2,290

2,280

2,340

2,140

2,310

2,540

4,530

2,530

3,370

5,330

4,110

3,340

 3, 350

3,680

4,260

4,160

4,460

4,480

4,560

4,340

4,800

Date.

Aug. 12.-

13.-

14..

15--

16..

17--

18.-

19..

20-.

21..

22..

23.-

24.-

25.-

26.-

27..

28..

29..

30..

31..

Sept. 1--

2

Per cent 

sediment 

volume.

15

10

11

17

18.5

15

13

9

12

15.5

13

10

13

8

9

8-

8

8

8

8

8.5

8.5

Turbidity 

(silica parts 

per million).

63, 936

57,600

33, 550

48,000

54,000

42, 000

39,000

33,000

39,000

36,000

36, 000

27, 000

39, 000

30, 000

30,000

27,000

24, 000

37, 000

27,000

21, 000

28, 500

30, 000

Conversion 

factor.

4,260

5,760

3,050

2,820

2,920

2,800

3,000

3,670

3,250

2,320

2,770

2,700

3,000

3,750

3,340

3,380

3,000

3,380

3,380

2,630

3,360

3,520
22 FIELD ASSAY OP WATER. [NO. 151.

Parallel observations of per cent volume r>f sediment and of turbidity, in terms 

of -parts per million, of xilica in water from Gila River, etc. Continued.

Date.

Sept. 3-

4_.

5_.

6_.

7.-

8..

9_.

10..

11..

12-

13..

14__

15..

16-

17-

18..

19-

20..

21-.

22-

23..

24_ .

25.-

26-

27__

28__

Per cent 

sediment 

volume.

9

8

13

15

11

10

6.5

3.5

1.5

1.5

5

7.5

4

6

6

5

5

4

2

1

3.5

14

17

3

g

1

Turbidity 

(silica parts 

per million).

33, 960

36, 000

40,980

42, 000

40, 980

31, 500

25, 200

9,200

4,200

3,150

14, 000

20, 000

13, 000

16, 000

16, 000

13, 000

11, 320

12, 000

6,300

5,500

8,000

30, 000

30, 000

7,000

8,000

1,000

Conversion 

factor.

3,770

4,500

3,150

2,800

3,730

3, 150

3,880

2,630

2,800

2,090

2,800

2,670

3,250

2,670

2,670

2,600

2,260

3,000

3,000

5,500

2,280

2,140

1,760

2,330

4,000

1,000

Date.

Sept. 29. _

30__

Oct. 1-.

2__

3_.

4..

5__

6__

7..

8__

9_.

10..

11..

12..

13-.

14.-

15.-

16..

17..

18..

19-.

20..

21--

22__

23__

24__

Per cent 

sediment 

volume.

0.5

.5

Trace.

2.5

Trace.

Trace.

Trace.

Trace.

2

10

13

12

13

9

5.5

3.5

2.5

2

1

7

2

1.5

.5

.3

.5

.5

Tr-bidity 

(sil'fja parts 

per million).

650

600

650

350

650

280

220

6,400

42, 000

42, 000

39, 000

36, 000

27, 000

18, 000

12, 000

8,000

4,400

3,800

3,750

36, 000

6,000

3,000

1,000

900

800

766

Conversion 

factor.

1,300

1,200

4,200

3,000

3,000

2,080

2,000

2,180

2,280

1,760

1,900

3,750

3,720

3,000

3,000

3,000

3,000

1,600

1,530

TURBIDITY.

As all the usual methods for the determination of turbidity are 

fairly familiar, having been repeatedly described in numerous scientific journals, no further statements are necessary here. It is customary at the present time to adopt as a basis for the scale of each an 

absolute turbidity produced by a definite amount of finely divided 

silica in a certain volume of water. The scale has been described 

by its originators, Messrs. George 0. Whipple and Daniel D. Jackson, 

in Technology Quarterly, Vol. XII, No. -1, December, 1899, pages 

283-287.
SUSPENDED MATTEE.

UNITED STATES fc!EOLO«ICAL SURVEY TURBIDITY BOD.

DESCRIPTION.

This rod, devised by Messrs. Alien Hazen and George C. Whipple, 

is a modification of the original Hazen rod, and is described in the 

following extract from circular No. 9 of the division of hydrography, 

United States Geological Survey:

Proposed turbidity standard. The standard of turbidity shall be a water 

which contains 100 parts of silica per million in such a state of fineness that a 

bright platinum wire 1 millimeter in diameter can just be seen when the center 

of the wire is 100 millimeters below the surface of the water and the eye of the 

observer is 1.2 meters above the wire, the observation being made in the middle 

of the day. in the open air, but not in sunlight, and in a vessel so large that the 

sides do not shut out the light so as to influence the results. The trrbidity of 

such water shall be 100.

The turbidity of waters more turbid than the standard shall be computed as 

follows: The ratio of the turbidity of the water to 100 shall be as the extended 

volume is to the original volume when the water is diluted with a cJear water 

until the mixture is of standard turbidity.

The turbidities of waters lower than the standard should be computed as follows : The ratio of the turbidity of the water to 100 shall be as the ratio of the 

original volume of water of standard turbidity is to the extended vol line when 

such water is diluted with clear water until its turbidity is equal to that of the 

water under examination.

This standard can be used in both field and laboratory. In the field the wire 

method will be employed as at present, except for a new graduation, while in the 

laboratory the methods of dilution and comparison now in use for the silica 

standard will be employed.

Method of application to the platinum-wire 'process. A rod with a platinum 

wire inserted in it at a fixed point and projecting from it at a right angle will 

be used, as at present. The graduation shall be as follows: The graduation 

mark of 100 shall be placed on the head of the rod at a distance of 100 millimeters from the center of the wire. Other graduations will be made, based on 

the best obtainable data, in such a way that when a water is diluted the readings will decrease in the same proportion as the percentage of the original water 

in the mixture. Such a rod, having the graduation shown in the table below, 

shall be known as the United States Geological Survey turbidity rol of 1902. 

When this rod is immersed in water, the visibility of the projecting platinum 

wire at the depth from the surface shown in the second column will determine 

the degree of turbidity, as indicated in the first column.
FIELD ASSAY OF WATER. 

Q-raduation of turbidity rod of 1902.

[NO. 151.

Turbidity.

7

8

9

10

11

12

13

14

15

16

17

18

19

20

22

24

26

28

30

35

40

45

50

55

60

65

Depth of

wire.

mm.

1,095

971

873

794

729

674

627

587

551

520

493

468

446

426

391

361

336

314

296

257

228

205

187

171

158

147

Corresponding 

value on 

reciprocal 

scale.

0.023

.026

.029

.032

.035

.038

.041

.043

.046

.049

.052

.054

.057

.060

.065

.070

.076

.081

.086

.099

.111

.124

.136

.148

.160

.172

Turbidity.

70

75

80

85

90

95

100

110

120

130

140

150

160

180

200

250

300

350

400

500

600

800

1,000

1,500

2,000

3,000

Depth of 

wire.

mm.

138

130

122

116

110

105

100

- 93

86

81

t*t& 

4O

72

68.7

62.4

57.4

49.1

43.2

38.8

35.4

30.9

27.7

23.4

20.9

17.1

14.8

12.1

CorreB"*onding 

ralue on 

reciprocal

scale.

0.184

.196

.208

.219

.230

.242

.254

.273

.295

.314

.334

.35

.37

.41

.44

.52

.59

.65

.72

.82

.92

1.09

1.21

1.49

1.72

2.10

This table is compiled from observations made at Cincinnati, St. Louis, New 

Orleans, Pittsburg, Brooklyn, Philadelphia, and Boston, for records of which 

we are indebted to several observers. The values of the turbidities by the reciprocal scale are included in the table for convenience, but they do not form a part 

of the standard.

This graduation is subject to revision whenever additional data shall make 

it necessary and revised rods shall be designated by the same name, but with 

the year of revision substituted for 1902. The revisions shall have as their 

basis the 100 mark, 100 millimeters from the wire.

Near the end of the rod, at a distance of 1.2 meters from the platinum wire, 

a. wire ring shall be placed directly above the wire, through which the observer 

will look, the object of the ring being to control the distance from the wire to 

the eye.
LUIGHTON.] SUSPENDED MATTER. 25

When the turbidity is greater than 500 the water should be diluted before the 

observation is made. When the turbidity is below 7 this method can not be 

used, and comparison should be made with the silica standard property diluted 

in bottles or tubes, as described by Whipple and Jackson in Technology Quarterly, Vol. XII, No. 4, December, 1899.

The number obtained by dividing the weight of suspended matter in parts per 

million by the turbidity as obtained above shall be called the coefficient of fineness. If greater than unity it indicates that the matter in suspens'on in the 

water is coarser than the standard; if less than unity, that it is flne~ than the 

standard.

This standard is proposed with the idea of combining the best features of the 

platinum-wire and silica methods of measuring turbidities as commonly used, 

and of avoiding, as far as possible, the objections to each.

OBJECTIONS TO BOD METHOD.

The method of turbidity determination above outlined answers 

all purposes demanded in ordinary use. In field determinations it 

has many objections which are not easily overcome. It was readily 

observed in practice that the method is largely a test of the individual 

and that the point at which the wire disappears from view varies 

according to the eyesight of the observer. Under ordinary conditions this variation is not sufficient to influence the interpretations 

placed upon the results, but there are some conditions under which 

the variation would be large enough to cause considerable error.

Again, the method was found to be inaccurate and unsafe in determining turbidity above 100. It is also difficult to select the conditions 

prescribed in the directions above set forth. A person in the field 

is governed absolutely by the conditions which he meets, and it is 

exceptional when he is able to be at a desired point at a giT^en time. 

Therefore the observation, which must be made " in the middle of the 

day, in the open air, but not in sunlight, and in a vessel so large that 

the sides do not shut out the light," is in most cases an undertaking 

of extreme difficulty. Another observation is more important; it is 

necessary for the field man to take observations in the running stream. 

Obviously it would be impracticable to carry about a container large 

enough to meet these prescribed conditions, and in the majority of 

cases a turbidity reading must be taken at long distances from points 

at which such containers can be borrowed. It is well known that 

in many cases the suspended matter in running streams occurs' in 

clouds. In a certain section of the stream the turbidity at one 

moment may be high and at the next moment much reduced, or vice 

versa. Often the observer, after fixing the point at which the platinum wire disappears, finds that before he is able to read the scale 

the wire is either plainly in sight or has become submerged below the 

point of correct turbidity reading.
26 FIELD ASSAY OF WATER. [NO. 151.

All these objections make the use of the turbidity rod undesirable 

in general field work. While its value at selected stations is acknowledged, it has been found to be impracticable under less favorable circumstances; consequently a new method was sought.

JACKSON'S TllRBIDIMETER.

DESCRIPTION.

The needs of the Survey were found to be met in a satisfactory 

manner by the use of a turbidimeter devised by Mr. Daniel D. Jackson, chemist in charge of the Mount Prospect laboratory, department 

of water supply, gas, and electricity, city of New York. The following is a report by Mr. Jackson with reference to this instrument:

The suspended matter or turbidity in natural waters is the most important 

physical characteristic in many sections of the country. In ,»-uch sections the 

selection of new water supplies, as well as the improvement of existing supplies, rests, to a very great extent, upon a consideration of this particular 

feature. These milky or muddy waters are often quite variant in the amount 

and nature of their suspended matter, and, in case they an? to he purified. 

require considerable study to determine the proper treatment.

When the maximum and the average turbidity in a water are known, questions 

may be solved relating to the nature, size, and construction of settling basins, 

filter plants, and clear-water reservoirs, and, finally, in determining the effi 

ciency of the removal of suspended matter in such filter plants we must know 

the turbidity of the water before and after filtration.

The hydrographic branch of the United States Geological Survey is particularly interested in developing accurate and rapid methods for the determination of turbidity, both for data relating to water supplies as well as 

relating to the erosion and the carrying power of suspended matter by rivers 

and streams. It is necessary that the field methods should be comparable with 

those of the laboratory, that the work should be rapidly accomplished, and that 

the results should express, as nearly as possible, the actual weight of the 

suspended matter present.

If we determine the total solids in a water before and after filtration through 

a Berkfeld filter, the difference in the results obtained will give the weight of 

the suspended matter present, but this method is tedious in the laboratory and 

impossible in the field. It is evident that some photometric standard of comparison must be used, and extensive studies have shown th^t whatever the 

instrument employed for this purpose it should be graduated by a standard 

turbid water. The standard now employed is known as the " silica standard," 

and is made from diatomaceous earth."

This standard is preferable to all. others that have been u^'ed in that it is 

absolutely insoluble, has a very uniform size of particle, and, unlike clay, does 

not cake together on standing. The diatomaceous earth (infusorial earth) is 

found in natural deposits in many parts of the country. To prepare the 

standard this material is first washed and ignited to free it fror? organic matter. 

It is then ground to an impalpable powder in an agate mortar, put through a 200- 

mesh sieve to break up the lumps produced in grinding, treated with dilute 

hydrochloric acid, and the finest portion decanted. This fine portion is then 

dried at 100° C., cooled in a desiccator, and kept in a tightly stoppered bottle.

a Whipple, G. C., and Jackson, D. D., Silica standards for the determination of the 

turbidity in water: Techn. Quart., vol. 12, No. 4, Dec., 1899.
U. 8. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 161 PL.

JACKSON'S CANDLE TURBIDIMETER.
LE1GHTON.] SUSPENDED MATTER. 2 7

One gram of this material is weighed out and put into 1 liter of distilled water. 

The mixture represents a standard of 1,000 parts per million of silica turbidity, 

and dilutions may be made from this for comparison with natural waters. 

Readings made with this standard compare very well with the actual weight 

of the suspended matter in water, but it has been found that the standard as 

prepared varies slightly when made by different analysts. The author now proposes to make the standard absolute by making readings on the candle turbidirneter and so adjusting the mixture that the standard of 1,000 parts per million 

will always read 2.3 centimeters on the instrument.

THE CANDLE TURBIDI METER.

The original form of this instrument was first described by the writer in the 

Journal of the American Chemical Society, November, 1901, but since tlrt time 

it has been considerably improved upon. The accompanying illustration giyes 

a good idea of the present form of the instrument and its use. [See PL I.] The 

apparatus consists of a glass tube, closed at the bottom and graduated in centimeters and millimeters depth. This is surrounded by a brass holder, open at the 

bottom and supported by a stand, in the center of which is a standard English 

candle, so adjusted by means of a spring below that its top rim is always just 

3 inches below the bottom of the glass tube.

The water to be determined for turbidity is poured into the glass tube until the 

image of the lighted candle below just disappears.0 The depth of the water in the 

tube is then read (using the bottom of the meniscus), and this depth is compared 

with a table which gives the turbidity of the water in parts per million of 

silica. The tube itself may be graduated in turbidity as well as in mill?meters 

depth, thus dispensing with the use of the table. Between 5,000 and 100 parts 

per million of silica a tube 25 centimeters in length Is necessary, or a comparison 

with silica standards in tubes or bottles may be substituted. The candle instrument is very convenient in the laboratory, and as its source of light is the standard candle it is ready for use at all times. The candle must always be properly 

trimmed, and the determination must be made rapidly, so as not to Inat the 

liquid to any extent. The most accurate work is obtained in a dark room, and 

the candle should be so placed as not to be subjected to a draft of air. The 

latter necessity renders the instrument absolutely impossible for use in the 

field.

Several forms of field apparatus in which the candle was employed as a 

source of light were attempted, but were entirely unsuccessful, and it was found 

necessary to resort to the electric light for field use.

THE ELECTEIC TDRBIDIMETER.

This instrument was designed by the author for the use of the hydro.zraphic 

branch of the United States Geological Survey, and is intended for fi-?ld use 

only. Its construction is so regulated as to be exactly comparable with the 

candle turbidimeter, and the measuring tubes for each have been made interchangeable.

The electric turbidimeter as shown in fig. 1 consists of the same grrduated 

glass tube as described for the candle turbidimeter, inclosed in a similar manner

0 It has teen found in actual field work that the end point in the electric turbidimeter, 

viz, the disappearance of the cross of light, is generally sharper and less subject to personal errors than the end point above designated. This is especially true when the two 

instruments are used by the same person, i. e., a common end point is more satisfactory. 

The Geological Survey has therefore placed the glass plate and cross disk in tin candle 

turbidimeter.
28 FIELD ASSAY OF WATER. [NO. 151.

by a brass holder (A) open at the bottom. This holder is attached to the end of 

a brass cylinder (m) containing a 2.5-volt dry battery (C) and a 2.5-volt electric 

light (d). Above the electric-light bulb, at a distance of 1 centimeter, is a disk 

of glass (e) which is ground on the under side. Immediate'y above this is a 

brass disk (6) 1 millimeter thick, through the center df which a cross is cut (B). 

The lines in this cross are 0.5 millimeter wide. From the top of the brass plate 

to the bottom of the graduated glass tube the distance is just 1 centimeter.

To make a determination with the electric turbidimeter, first pour i the turbid 

water to be tested back and forth from the glass tube to arother vessel until 

it is thoroughly mixed, and then turn on the light by adjusting the screw (f) 

at the bottom of the instrument. Place the graduated glass tube in the holder, 

which has been screwed into place above the light, and pour the turbid water

into the tube until the c~oss of light just 

disappears. If the tube is not graduated 

directly in parts per million of silica, read 

the depth in millimeters of the water in the 

tube and refer to the table given later. In 

reading use the bottom of the meniscus as 

the reading point. In the lower part of the 

tube read past the disappearance of the 

sharp cross of light to the disappearance of 

the hazy cross of light. In this way the 

end point is the same as in the candle 

turbidimeter. Higher up in the tube there is 

only the sharp cross of light for an end point. 

If the turbidity is above 100 parts per 

million use the short tube (25 centimeters 

long). If the turbidity is between 100 parts 

and 25 parts per million the long tube (75 

centimeters) may be emp^yed, but at any 

point below 100 the gla«s tube and the 

holder may be removed and the instrument 

lowered directly into the turbid water by 

means of a steel millimeter tape. Any degree of turbidity may be read in this manner 

provided the water is sufficiently deep.

If the water is shallow and below 25 

turbidity, close estimations may be made 

by holding a bottle of the water toward the 

light and comparing it with the remembered appearance of standards of 5, 10, 15, and 20 parts per million in bottles 

of the same size.

In the determination of turbidity with Jackson's turbidimeter 

many of the objections to the use of the United States Geological Survey turbidity rod -are avoided. As the standard illumination is a 

part of the apparatus itself rather than the sun, none of the limitations which apply to the use of the rod, such as time of day, shade, 

etc., are necessary considerations. The instrument may be used at 

night if desired. As the sample to be tested is collected from the 

body of water under observation, inaccuracies due to moving water 

anr] xariations in turbidity caused thereby are avoided, and it is not

 * »* * «_*_ * .

FIG. 1. Jackson's electric turbidimeter.
LEIGHTON.] SUSPENDED MATTEE.

necessary to consider the depth of water in the river or lake under 

observation. In the use of the rod this is often a very troublesome 

feature, because, in case of low turbidity, there may not be water of 

sufficient depth to allow the rod to be submerged to the point of disappearance of the platinum wire. Another advantage is that th Q. end 

point in Jackson's turbidimeter is approached more sharply and the 

use of the instrument is not practically a test of the observer's eyesight, for the measurement of turbidity depends upon the obliteration 

of a beam of light, and not upon the definition of a certain object.

TESTS OF ELECTRIC TUBBIDIMETEB.

The Jackson electric turbidimeter is made up of several parts 

which it was necessary to test in order to determine their effect upon 

the accuracy of the instrument. These tests, made by Mr. R. B. 

Dole, assistant engineer, United States Geological Survey, under the 

direction of Mr. Daniel D. Jackson, are classified as follows:

1. Tests of the battery for current, electromotive force, and durability.

2. Tests of the electric bulb for intensity of light.

3. Test of the ground-glass plate for opacity.

4. Calibration of the tube with silica standard.

5. Determination of the probable error.

6. Calibration of the tube with a sulphate standard. This vdll be 

treated under the heading " Sulphates,111 on page 69.

Battery test. The " Reliable " 2-cell battery, 6 inches long, was 

selected and tested, first for constant current and then for recuperation, by running it for one minute, alternating with a rest of five 

minutes. These tests, applied to three cartridges selected at random, 

resulted as follows:

-. Results of tests of 6-inch 2-ceU "Reliable " battery.

BATTERY NO. 1.

At end of 

2 minutes. ..._._-...-....-----.-....

3 minutes. .......... ..............

4 minutes- .........................

6 minutes. .__. .--.--_-. .---.-.....

7 minutes. _--,-.------.----------.._

8 minutes.---------. _-.-_-._-.--____

9 minutes. ---._.--......---.--......

10 minutes. .... _ -.-----_--.---.....

Current.

Ampere. 

0.250

.245

.243

.242

.240

.240

.238

.236

.235

.235

.235

Loss.

Ampere.

0.005

.002

.001

.002

.000

.002

.002

.001

.000

.000

.015

E. M. P.

Volts. 

2.66

3.50

Light.

Bright.

Bright.
30 FIELD ASSAY OF WATER. [NO. 151.

Results of tests of 6-inch 2-cell "Reliable " battery- Continued.

BATTERY NO. 1 AFTER A REST OF 90 MINUTES.

At end of 

1 minute - ..__..__---_. .-._...-_-.

3 minutes- ... __..._.. .............

7 minutes ........ ......... . . . . .

lOminutes.-. ........ -.....-...--..

Current.

Ampere. 

0.250

.245

.243

.241

.239

.237

.236

.235

.235

.234

.234

Loss.

Ampere.

0. 005

.002

.002

.002

.002

.001

.001

.000

.001

.000

.016

E. M. F.

Volts. 

2.66

2.50

Light.

Bright.

Bright.

BATTERY NO. 2.

0 minute ........ . _ _ .......... . .

3 minutes. .............. ....... ....

4 minutes. .-____._.-__________ .....

5 minutes. ........-.--.--.-....---..

6 minutes, ................ .........

7 minutes. ....... . . .-----.-...- ..

10 minutes. . . . . . . . . . ... ... .

0.272

.268

.265

.263

.261

.258

.255

.253

.251

.250

.249

0.004

.003

.002

.003

.003

.003

.003

.002

.001

.001

.023

2.80

-

2.63

Bright.

Bright.

BATTERY NO. 2 AFTER A REST OF 90 MINUTES.

0 minute ........ . . . . .......

1 minute ... ...... ....______ ...

3 minutes . . . ... ...... . .........

5 minutes. ..... .... .... ...... ...

8 minutes. ......... ....... . . .. .

^0 minutes ....._. . ,.,.. ...... ...

0.263

.258

.253

.252

.250

' .248

.246

.245

.244

.243

.243

0.005

.005

.001

.002

.002

.002

.001

.001

.001

.000

.020

2.70

2 52

Bright.

Bright,
SUSPENDED MATTER.

t 

Results of t&sts of 6-inch 2-cell "Reliable " battery Continued.

BATTERY NO. 3.

31

At end of 

3 minutes ..___.-_._- . .-.-.-.-_-__-_

4 minutes _.___._.---_.-._ _....__ . . _

6 minutes . ..... ............. .__._

9 minutes -_._.-._-.__--------_-.-____

10 minutes. _ _____._.__.:..-.._ .....

Current.

Ampere. 

0.273

.270

.265

.262

.260

.258

.255

.253

.252

.251

.250

Loss.

Ampere.

0.003

.005

.003

.002

.002

.003

.002

.001

.001

.001

.023

E. M. F.

Volts.

2 82

2.60

Light.

Bright.

Bright.

BATTERY NO. 3 AFTER REST OP 90 MINUTES.

0 minute. ..._.._.__.___. ___________

2 minutes ...._...... .___-.-_._____ .

3 minutes ............ . . . - ..........

4 minutes . _____ __ .._._.._

5 minutes ________--__----__-__-.____.

6 minutes .................. .........

7 minutes ...... . . . . . ...... ....

8 minutes ------.-...-..---.-..-.

9 minutes . . . . : ......................

0.256

.252

.249

.246

244

.243

.242

241

.240

.239

.238

0. 004

.003

.003

.002

.001

.001

.001

.001

.001

.001

.018

2.70

2.50

Bright.

BrigEl.

The batteries were next tested for recuperation by alternatirg one 

minute of use with five minutes of rest, as follows:

BATTERY NO. 1.

Period.

First minute _...____..

Second minute _____ . .

Third minute __--___.--.-__ _

Fourth minute __....___...._.

Fifth minute . . . . . .._._.___..

Initial 

current.

Ampere. 

0.243

.242

.241

.240

.240

Final 

current.

Ampere. 

0.238

.237

.237

238

.236

Drop in 

current.

Ampere. 

0.005

.005

.004

.002

.004

Initial 

voltage.

2.60

2.56

2.56

2.56

2.57

Final 

voltage.

2.54

2.51

2.50

2. 5Q

2.50

Drop in 

^oltage.

0.06

.05

.06

.06

.07
32 FIELD ASSAY OF WATEE. 

BATTERY NO. 2.

[NO. 151.

Period.

First minute __------_._____.

Second minute . . .............

Third minute .................

Fourth minute -__.__-_-______

Fifth minute 1 ...........

Initial 

current.

Ampere. 

0.249

.349

.248

247

.247

Final 

current.

Ampere. 

0.245

.245

.245

.243

.243

Drop in 

current.

Ampere. 

0. 004

.004

.003

.004

.004

Initial 

voltage.

2.63

2.63

2.63

2.63

2.63

Final 

voltage.

2.56

2.56

2.56

2.56

2.60

Drop in 

voltage.

0.07

.07

.07

.06

.03

BATTERY NO. 3.

First minute . _ . . . . . .

Third minute. __-_.---....____

Fourth minute -__-..._... ...

Fifth minute ...--...--... .

0.260

.257

.255

.254

.253

0.255

.253

.251

.250

.249

0.005

.004

.004

.004

.004

2.7:

2.72

2.70

2 70

2 6:

2.66

2.66

2.63

2.63

2.60

0.10

.06

.07

.07

.06

Volts. 

Highest voltage observed ______________.._________________ 2.82

Lowest voltage observed_______ ____________________ 2.50

Extreme variation____________________ .____ .32

Reckoned on an average voltage of 2.66 volts, this is a variation of 

12 per cent.

Ampere. 

Highest amperage observed.____________'_____________ 0.273

Lowest amperage observed______________________________ .234

Maximum variation____________________________- ___ . 039

Reckoned on an average amperage of 0.248 ampere this is a variation 

of 1Q per cent in current. The drop in current averages 0.002. 

ampere per minute, or about 0.8 per cent.

It will be seen from these results that the battery is quick in recovery and that while in use the reduction in electromotive force 

is comparatively small. The change in current observed in the batteries tested does not cause any error in a turbidity estimation. 

Readings were made at different times with a standard of turbidity 

corresponding to 250 parts per million of silica, and in every case the 

variation in depth of liquid read in the graduated tube came within 

the probable deviation occurring in reading. The ordinary variation of current in the battery does not affect the accuracy of the 

instrument to a measurable degree.

This battery will remain effective under ordinary conditions from 

fifty to sixty days, at tlie epcl of which time it is advisable to change 

the cartridge,
LEIGHTON.] SUSPENDED MATTER. 33

Electric-bulb test. Several lights were tested to see if the^re were a 

noticeable deviation in the intensity of light produced. The test of 

four sample lights is here given:

Battery.

No. 1..... .......... ...

No. 3.. ........ ........

No. 3.. ........... ......

Lamp

No. 1.

8.7

8.6

8.9

Lamp 

No. 2.

8.5

8.6

8.5

Lamp

No. 3.

8.4

8.2

8.3

Lamp

No. 4.

7.7

8.0

7.9

The numbers given are the depths in centimeters produced by using 

a standard turbidity of 250 with different batteries and lights. The 

mean of these observations is 8.4, while the average deviation from the 

mean is 0.3, which brings three of the lamps within the limit allowed 

on individual readings under constant conditions; the fourth light, 

however, falls without the limit of error. The lamps were chosen 

at random from a stock of 2.5-volt lights. It is evident that here is a 

variation which must be overcome. It may be done by buying a 

large stock of lamps and selecting only such as come within the standard conditions, or by buying lamps of guaranteed candle power. 

In conclusion it may be said that it is well to test a new lamp with 

silica standard before using it in the field.

Glass-plate test. The glass diaphragm placed over the lamp is 

ground on one side in order to tone and diffuse the rays from the 

electric light. It also makes possible the use of a much shorter 

glass tube than would otherwise be necessary, and it reduces variation in candlepower in the effect thereof on turbidity determinations. It appears to be possible to procure glasses which are ground 

to the same opacity. Different glasses were tried in the instrument 

without any apparent effect on the depth of turbid liquid required 

to shut off the light. It may be said in connection with the ground 

glass that the cross slit of brass above it should be constant in width 

of aperture. As this offers no mechanical difficulties, no experiments were made to determine the effect of variation in tlie width 

of the slit.

Calibration for turbidity. When work was begun on the calibration of the instrument it was necessary to prepare a standard silica 

solution. The standard heretofore used has been very difficult to 

match on account of the difficulty of grinding the silica fine enough 

to reach the required turbidity. The standard is such that it gives 

a reading of 500 parts per million at a depth of 4.5 centimeters, 

while the standard prepared by ordinary grinding gives a reading 

of 500 parts per million at a depth, of about 5,7 centimeters. Several

IRK 151 05 3
FIELD ASSAY OF WATEE. [NO. 151.

careful grinclings failed to give the desired reading of 4.5 centimeters. It was therefore decided to make some very careful grindings 

and to select as a standard the one giving the lowest reading in 

depth with the turbidimeter. It was found that the particles ot 

silica need to be rubbed apart with the finger after being ground, in 

order to secure the maximum turbidity. It is of interest to note the 

various readings with the four standard solutions prepared.

Variations in turbidity readings with different degrees of fineness of siJica.

DEPTH, IN CENTIMETERS, PRODUCED WITH 500 STANDARD.

Standard 

No. 1.

5.7

5.6

5.6

5.7

a 5. 6

Standard 

No. 2.

5.3

5.4

5.3

5.2

«5.3

Standard 

No. 3.

4.4

4.6

4.5

4.4

«4.5

Standard 

No. 4.

6.1

6.0

6.1

6.1

«6. 1

DEPTH, IN CENTIMETERS, PRODUCED WITH 250 STANDARD.

10.2

10.2

10.1

10.2

«10.2

10.2

9.7

9.9

10.0

"10.0

8.6

8.5

8.6

8.7

«8.6

11.0

11. J

11.0

11.0

ffll.O

DEPTH, IN CENTIMETERS, PRODUCED WITH 125 STANDARD.

20.0

20.3

20.5

20.5

«20.3

19.8

19.6

19.9

20.1

«19.8

i

16.7

16.9

17.0

17.1

«16.9

21.7

21.5

22.0

21. f

«21.P

" Average.

According to these readings it was found that solution No. 3 practically coincides with the old standard and was therefore used as 

standard. It is believed that this choice will result in less confusion 

in the future when a new standard solution is desired, because this 

chosen turbidity represents the limit in grinding.

The work of calibration consisted in taking readings with different 

dilutions of the silica standard. After thoroughly shaking the stand-
LEIGHTON.] SUSPENDED MATTEE. 35

ard it was poured into the graduated tube until the depth was 

reached at which the cross of light disappeared. Precautions were 

taken to secure uniform conditions of light, and the battery was tested 

for current at frequent intervals. In the following tables the actual 

readings of the tube are given, after which the average and average 

deviation are stated. Observations deviating by more than the- average deviation are then discarded and the average of the remairder is 

taken to determine the resultant point on the curve wfyich represents 

the turbidity scale.

Calibration of turbidimeter for standard of 250 parts per million turbidity. 

[Centimeters. Excess of average deviation indicated by italic figures.]

Reading.

9.2

8.4

8.7

8.9

8.5

9.2

8.4

8.7

8.9

8.5

8.6

8.8

8.9

9.0

8.7

8.8

8.5

Deviation.

0.5

.3

.0

.2

.2

.5

.3

.0

.2

.2

.1

.1

.2

.3

.0

.1

.2

Beading.

8.6

8.4

8.8

8.4

8.4

9.2

8.4

8.7

8.9

8.5

8.8

8.9

8.7

8.5

269.9

Deviation.

0.1

.3

.1

.3

.3

.5

.3

.0

.2

.2

.1

.2

.0

.2

6.2

Mean=269.9-^ 31=8.7. Average deviation=6.2-^ 31=0.2.

It will be noted that 10 of 31 readings differ from the mean by an 

amount greater than the average deviation (0.2). Only 3 readings 

have a deviation greater than 0.3. It is therefore assumed that 

under ordinary conditions a variation of 0.3 centimeter at 250 

standard should be allowed.
36 FIELD ASSAY OF WATER. [NO. 151.

Calibration of turbidimeter for standard of 200 parts per million turbidity. 

[Centimeters. Excess of average deviation indicated by italic figures.]

Reading.

11.8

11.1

11.1

11.0

11.0

10.9

11.5

10.6

11.1

10.7

Deviation.

0.3

.1

.1

.0

.0

.1

.5

 4

.1

.3

Beading.

10.6

11.3

11.1

11.1

11.0

11.0

10.9

187.3

Deviation.

0.4

.3

.1

.1

.0

.0

.1

2.9

Mean=187.3-^17=11.0. Average deviation=2.9-=-17=0.2.

The deviation of 6 of the 17 observations exceeds 0.2 centimeter, 

the average deviation. Only 3 observations exceed 0.3 centimeter in 

deviation. Under ordinary circumstances we may consider 0.3 centimeter as the average deviation.

Calibration of turbidimeter for standard of 100 parts per million turbidity. 

[Centimeters. Excess of average deviation indicated by italic figures.]

Beading.

21.9

21.5

21.6

21.1

22.2

21.0

21.9

21.5

Deviation.

0.2

g

.1

.6

.5

.2

.2

Beading.

21.9

22.2

' 21.0

21.9

31.5

21.9

303.1

Deviation.

0.2

.5

.7

.2

.2

.2

4.7

Mean=303.1-M4=21.7. Average deviation=4.7-^ 14=0.3.

The deviation of 5 of the 14 observations exceeds 0.3 centimeter, 

the average deviation. Probably 0.4 centimeter would be the ordinary deviation. If we reckon 0.4 as the average deviation, mean = 

21.8. Probably 21.7 is correct.
LEIGHTON.] SUSPENDED MATTER. 37

Calibration of turMdimeter for standard of 125 parts per million turbidity. 

[Centimeters. Excess of average deviation indicated by italic figures.]

Beading.

17.3

16.7

17.2

17.4

17.3

17.6

Deviation.

0.0

.6

.1

.1

.0

.3

Beading.

17.2

17.5

17.4

155.6

Deviation.

.1

.2

.1

1.5

Mean = 155.6 -r 9 = 17.3. Average deviation = 1.5 -± 9 = 0.2.

The average deviation from 9 readings is 0.2 centimeter and is 

exceeded by only 2 readings. Probably more readings would give 

greater deviations and the average deviation would be increased.

Calibration of turbidimeter for standard of 500 parts per million turbidity. 

[Centimeters. Excess of average deviation indicated by italic figures.]

Beading.

4.4

4.6

4.5

4.4

4.4

Deviation.

0.1

.1

.0

.1

.1

Beading.

4.6

4.5

31.4

Deviation.

.1

.0

.5

Mean=31.4-r-7=4.5. Average deviation=0.5 7=0.1.

Though only 7 readings are here given, many more were taken 

without getting anomalous results. The probable deviation is 0.1 

centimeter and will not be exceeded. Mean=:4.5 centimeters.

Turbidity of 1,000 parts per million. From many observations 

at different times, 2.3 centimeters is the reading for 1,000 standard.

Average deviation=0.1 centimeter. 

Mean =2.3 centimeters.

We have, then, determined by actual experiment the depth corresponding to 6 turbidities <

Turbidity ________ 100 125 200 250 500 1,070 

Depth (centimeters) 21.7 17.3 11.0 8.7 4.5 2.3
38 FIELD ASSAY OF WATEE. [NO. 151.

These points are then plotted on logarithmic cross-section paper 

(fig. 2) and intermediate points determined by measurement on 

the plot.

Below 100, depths have been determined at 50 and p,t 25 by using a 

longer tube, with which the effect will be the same as lowering the 

light into the standard by means of a tape. The observations made

\

X

I

\

\

\.

ZOO 3OO 4OO 

Parts per million of silica

FIG. 2. Logarithmic scale of turbidity.

600 700 800 900 1000

at 50 and 25 seem to indicate that the curve begins to swing away 

from its course at 100. This change may be due to the fact that the 

distance between light and eye is increased. From 1,000 to 100 the 

light is 25 centimeters from the eye; at 50 it is 40 centimeters away, 

while at 25 the distance is 65 centimeters. The readings are as 

follows:
LBIGHTON.] SUSPENDED MATTEE. 39 

Calibration of turbidimeter for standard of 50 and 25 parts per million turbidity.

[Centimeters.]

60 parts.

36.1

34.0

34.5

34.4

35.3

35.0

34.3

34.1

33.9

35.2

346.8

[Centimeters.]

35 parts.

64

61

56

61

63

60

65

430

Mean=430-=-7=61.

Mean=346.8n-10=34.7.

400 500 600 

farts per million of silica

FIG. 3. Turbidity curve.
40 FIELD ASSAY OF WATEB. [NO. 151.

These readings may not be accurate. Further experiments may 

show that they are too low. At most, however, they are within 10 

parts per million of silica in their relation to the real values (fig. 3). 

The limit of accuracy between 100 and 1,000 is well defined from the 

points determined.

From the values heretofore determined the depths of liquid in the 

turbidimeter corresponding to a silica standard of turbidity are set 

forth in the following table:

Turbidity determ inations.

Depth.

Cm.

2.3

2.6

2 9

3.2

3.5

3.8

4.1

4.5

4.9

5.6

6.3

7.3

7.6

7.8

8.1

8.5

8.7

9.1

9.5

10.0

Silica.

Parts per 

million.

1,000

900

800

700

650

600

550

500

450

400

350

BOO

290

280

270

260

250

240

230

220

Depth.

Cm.

10.5

11.0

11.5

12.1

12.8

13.6

14.4

15.4

16.6

18.0

19.6

21.7

23.0

25.0

28.0

31.0

35.0

42.0

52.0

70.0

Silica.

Parts per 

million.

210

200

190

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

DETERMINATION OF THE PBOBAKLE ERROR.

Readings on the same standard solution with the same battery 

and light by the same person will vary within narrow limits. These 

limits have been determined for several points and calculated as 

average deviation.
LEIQHTON.] COLOE,

Limits of accuracy on duplicate readings.

41

Standard.

1,000

500

250

200

100 

50

30

Average deviationin centimeters.

0.1

.1

.3

. .3

.4

Limit of accuracy in parts per million.

Reading correct within 35 parts.

Reading correct within 15 parts.

Reading correct within 10 parts.

Reading correct within 8 parts.

Reading correct within 5 parts.

In other words, a turbidity between 500 and 1,000 parts can be 

measured accurately within 35 parts. Between 200 and 50') parts 

measurement can be made within 10 to 15 parts, and between 50 and 

200 within 5 to 8 parts per million.

The limit of accuracy is not changed by change of observers. Since 

the thing seen is a ray of light, it appears to be visible to any eye and 

appears to be shut off at the same depth for different observers.

The limit is greater than that change in depth caused by normal 

variations in the current. Therefore the limit of accuracy is not 

increased by variations in the battery within ordinary limits.

Changes in the electric bulb can introduce a constant error greater 

than the probable error in determination. Therefore only such 

lamps should be used as have been tested with a standard silica 

solution.

In the general field work of the hydrographic branch the field 

assistants and those cooperating are instructed to use the Jackron turbidimeter in connection with all waters having a turbidity of more 

than 100, while the turbidity rod could be used in waters having a 

lower turbidity. The objections mentioned in connection with the 

use of this rod are not so serious in the determination of low turbidities.

COLOR.

OCCURRENCE.

The term " color " as used in water chemistry should not be confounded with the term as ordinarily used. The streams of the Mississippi Valley, and indeed the great river itself, appear highly colored. 

One will find rivers which are habitually red, yellow, brown, or black 

in appearance. This color is not due to the water itself, but to the 

character of the matter which is carried in suspension. It is s, factor 

of the turbidity, and reveals the nature of the geologic formations 

eroded by the flowing water. On the other hand, waters may have a
42 FIELD ASSAY OF WATEE. [NO. 151.

color due to dissolved substances, and this is the feature referred to 

by the term as used in water analysis.

In those parts of the United States where the underlying rock is 

resistant that is, where it does not readily break up and disintegrate 

under the forces of erosion we usually find colored vr ater. At first 

sight it seems paradoxical that the clear waters of New England, 

many of which drain from granitic formations and hills of gravel, 

are colored, while those of the Central West, which carry large 

amounts of suspended matter eroded from the surface, are, when freed 

from turbidity, nearly colorless. In many cases this is due to the fact 

that the substances in suspension are of such nature tl at they absorb 

any color which might have been dissolved. On the other hand, in 

New England streams the color due to the decay of vegetable matter, 

such as peat or muck, remains in solution, and while tl ° water is generally very clear the color itself is apparent in varying degrees.

The importance of the color determination arises from the fact that 

in public supplies consumers demand a clear, colorless liquid, and 

are reluctant to accept any other. In manufacturing processes a 

colored water often works harm. In certain classes of waters the 

dissolved color is a fair index of the amount of organic matter contained. These facts pertain primarily to unpolluted water, for it is 

apparent that a water contaminated by wastes may have colors arising from sources such as dyes, sediments, etc. On the whole, the color 

of a natural water which can be applied to domestic and manufacturing purposes affects its value along economic lines. The periodical 

determination of dissolved color is necessary, as its intensity varies 

with the seasons and is influenced by sunlight, precipitation, and 

various other natural phenomena.

COLOR STANDARDS. 

GEOLOGICAL SURVEI STANDARD.

The standard of color determinations adopted by the United States 

Geological Survey is known as the platinum-cobalt method, devised 

by Mr. Alien Hazen, from whom so many practical and extremely 

valuable ideas with reference to the determination of quality of water 

have come.

The method is as follows :

A standard solution which has a color of 500 is made by dissolving 1.246 grams potassium-platinic chloride a (PtCl4 ,2KCl), 

containing 0.5 gram platinum, and 1 gram of crystallized cobalt 

chloride (CoCl2 ,6H2O), containing 0.25 gram of cobalt in water, with

" Potassium-platinous chloride is a salt that is often substituted by dealers in place of 

the potassium-platinic chloride. It is sometimes incorrectly labeled. The platinous salt 

has a reddish color, while the platinic salt has a yellow color. x
LEIGHTON.] GOLOK. 43

100 cubic centimeters concentrated hydrochloric acid, and maling up 

to 1 liter with distilled water. By diluting this solution, standards 

are prepared having values of 0, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 

and TO. The numbers correspond to the metallic platinum in the solutions in parts per million. These are kept in 100 c. c. Nessler jars 

of such diameter that the liquid shall have a depth between 20 and 25 

centimeters and shall be protected from dust. The color of a sample 

is observed by filling a similar tube with water and comparing it 

with the standards. The observation is made by looking vertically downward through the tubes upoji a white surface placed at 

such an angle that light is reflected upward through the column of 

liquid. The reading is recorded to the nearest unit. Waters that 

have a color darker than 70 are diluted before making the comparison, in order that no difficulties may be encountered in matching the hues. Water containing matter in suspension is filtered 

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 the Berkfeld filter is recommended. The use of a Pasteur filter is to be avoided, as it exerts a decolorizing action.

It is impracticable to carry the standard tubes above described into 

the field for observations, and yet field observations are of great convenience and value to the sanitary engineer, and in general to the 

investigations of the United States Geological Survey.

FIELD STANDARDS.

DESCRIPTION.

Disks of colored glass have been prepared by Mr. Alien H?,zen, in 

cooperation with the Survey, as standards for measuring color of water 

in the field.0 These disks have been rated by Mr. George C. Whipple 

to correspond with the platinum-cobalt standard. The color is measured by balancing the color of the water in a metallic tube with glass 

ends against the colors of glass disks of known value. The number 

on each disk represents the corresponding color of a water. This is 

not a new standard, but a new application of an old standard. The 

glass disks are rated to correspond with the platinum-cobalt color 

standard. The process bears the same relation to the usual laboratory process that an aneroid barometer bears to a mercurial barometer. 

The metallic* tubes and glass standards are more portable and better 

adapted to field use than the Nessler tubes and color solutions heretofore used. The standards are disks of amber-colored glass, mounted 

with aluminum. Each disk carries two numbers. One number is 

over 100, and is a serial number for the purpose of ide itif cation.

" Pressey, H. A., Observations on flow of rivers in vicinity of New York City : WaterSup, and Irr. Paper No. 76, U. S. Geol. Survey, 1903, 1*1. X.
44 HELD ASSAY OF WATEB. [NO. 151.

The other number is less than 100, and shows the color value of the 

disk; that is to say, the color of each disk is equal to the color of a 

solution of the designated number of parts per million of platinum 

with the required amount of cobalt to match the hue when seen in a 

depth of 200 millimeters. When a water comes between two disks its 

value can be estimated between them by judgment. Two or more 

disks can be used, one behind the other, in which case their combined 

value is the sum of the individual values. By combining the disks of 

a series in different ways a considerable number of values can be produced, allowing the closer matching of many waters.

USE OF FIELD STANDABDS.

Filling the tubes. The tube, having an aluminum stopper, is to be 

filled with water, the color of which is to be determined. Blnse the 

tube once or twice by filling and emptying it. The second tube, having the clips to hold the glass disks, is made much like the one holding 

the water, to facilitate comparison. Theoretically tl is tube should 

be filled with distilled water. Practically it makes very little difference whether it is filled with distilled water or empty. Use distilled 

water when it is convenient to do so, and when distilled water of 

unquestionable quality is at hand; otherwise wipe the inside of the 

tube dry to prevent fogging of the glass ends, and proceed with the 

tube empty.

Holding the tubes. Hold the tubes at such a distance from the eye 

that the sides of the tubes just can not be seen. This occurs when the 

near end of the tube is 8 or 9 inches from the eye. Hold the tubes at 

such an angle that both can be seen at once with one eye. Good 

results can not be obtained in any other way. Intercl <Mige the tubes 

once or twice, as sometimes the light on the right and left is not quite 

equal.

Background. There should be a clear white background. with a 

strong illumination. The best results can not be obtained with either 

too little or too much light. In a gray day look at tH sky near the 

horizon away from the sun. In a bright day look at a piece of 

white paper or tile upon which a strong light falls. The white surface may be vertical and the tubes held horizontally, or the tubes may 

be held at an angle directed downward toward a horizontal surface, 

as may be most convenient. Good results can not be obtained by 

artificial light.

Turbid water. The colors of very turbid waters can not be measured in this way. Slight turbidities do not interfere seriously with 

the results. Waters too turbid for direct observations should be 

filtered through thick filter paper before being testei; and in case 

the suspended matter causing the turbidity is fine in grain and large
LEIGHTON.l IRON. 45

in amount, even this method may fail. The turbidity of water should 

be tiSfen as far as possible in connection with color observations, 

except in cases where it is obvious from inspection that there is prafetically no turbidity. r

Highly colored ivaters. Some waters will be found having a 

higher color than can be matched by the standards. In general, 

waters with colors above 100 should not be matched in 200-millimeter 

tubes, and the results with waters having colors below 80 will be 

considerably more accurate than with more highly colored ones. 

Two procedures are possible with waters having higher colors; 

namely, to dilute with distilled water before measuring the color, or to 

use shorter tubes. The latter procedure'is the more convenient, but 

both are equally accurate. To measure the color with short tubes, 

put the highly colored water in a tube of one-half the usual length 

and match as usual. It is not necessary to have a short standard 

holder. The 200-millimeter tube can be used. After the r^ater is 

matched the result is multiplied by 2. In case the color is too high 

to be read in a 100-millimeter tube it can be put in a 50-millimeter 

tube, and the result multiplied by 4. When dilution is used the 

highly colored water is mixed with one or more volumes of distilled 

water, the color matched, and the result multiplied by a corresponding factor. The tube itself can be used for measuring the colored 

water and the distilled water, and the mixing can be done in a tumbler 

or any convenient clean vessel.

Cleaning the tubes. Always keep the tubes clean. Take particular care of the glass ends. All the ends are removable for the purpose 

of cleaning, and should not be screwed on too tightly. They should 

be water-tight when screwed up only loosely, for if screwed on hard 

they may stick so as to come off with difficulty.

IRON.

One of the important determinations which it is necessary to 

include in many special investigations is that of iron. Water containing an appreciable amount of this metal can not be used in many 

manufacturing processes. It is objectionable in domestic uses by 

reason of its taste and the discoloration of linen. Certain solutions 

of iron in boiler feed waters are particularly destructive. Iron in 

ground waters stimulates the growth of Grenothrix, which frequently 

clogs water pipes. On the other hand, iron has a certain medicinal 

value, and when it is in the form of sulphate has valuable coagulating properties. The last-named effect is well demonstrated in streams 

draining coal regions."

" Leighton, M. O., Quality of water in Susquehanna River drainage basin: Vater-Sup. 

and Irr. Paper No. 108, U. S. Geol. Survey, 1904, p. 36.
46 FIELD ASSAY OF WATER. [NO. 151.

Colorimetric methods are believed to be the simplest and best for 

the determination of iron in natural waters, and they readily lend 

themselves to modification for field purposes. That which involves 

the use of potassium ferrocyanide, described on page 226 of Button's 

Volumetric Analysis, ninth edition, was selected as best adapted for 

the purposes in view. The process involves the addition of acid and 

KCNS to the water under investigation or to the residual solution of 

that water, thereby producing a characteristic blood-red color. The 

depth of this color is absolutely fixed by the amount of iron in the 

water. It is then necessary to add to a similar mixture, made up with 

distilled water, such a quantity of standard iron solution as will produce in this solution exactly the same shade, of red as is shown in the 

water under investigation. Then from the amount of standard iron 

solution used to produce that shade of red the amount of iron in the 

water under investigation may easily be determined.

The modification of this method for field purposes consists of the 

use of fixed color standards, each having been previously rated to correspond with some known equivalent of iron. The apparatus used 

in the work is that already described for the determination of natural 

color. (PL II.) The color standards are red glass disks, rated and 

used in precisely the same way as the natural color standards. The 

colored light is transmitted directly through the disk tube, and the 

disks may be changed or combined until the color of the sample under 

examination is matched. Then from the rating of the disks the 

amount of iron may be stated.

A sample of the clear water to be tested is poured into a 50- or 100- 

c. c. graduate to the 45 c. c. mark, 2 cubic centimeters of concentrated 

nitric acid added, and the contents thoroughly mixed in order to convert all ferrous iron present into ferric iron. The fluid should then 

be allowed to stand about ate minutes.

The mixing and oxidation is preferably accomplished by pouring 

the solution from the graduate into another vessel, such as the glass 

turbidimeter tube, and vice versa, at least eight or ten times. To the 

acidified solution in the graduate is then added & cubic centimeters of 

a solution of potassium sulphocyanide containing j20 grams. E

TX ^ I-, v 1 ^ 1,1 " a***" fa&»$&iM*tr*.T. jer liter, and the liquids are thoroughly.niixe/iA.as^fd rjuTed 'lo sta - . , , - * J A .*f~lf/ -1 > ^_** * -* » J ^£P. ^-*J-* f ft uT m^ U

f'The solution is nowJransferred to the aluminum colorimeter tube, which has a capacity of about 45 cubic centimeters and is 

about 8 inches long.

Nitric acid is used in the above method instead cf hydrochloric 

acid, commonly employed, in the first place to avoid any corrosion of 

the aluminum tube, the desirability of the use of which will be explained later. With the employment of nitric acid instead of hydrochloric acid, moreover, it was discovered that the color produced in
U. S. GEOLOGICAL SURVEY

TUBES AND DISKS FOR DETERMINING COLOR OF WATER,
LEIGHTON.] CHLORIDES. 47

iron solutions by the addition of sulphocyanide is somewhat deeper 

and does not fade nearly so rapidly. Finally, the addition of nitric 

acid not only effects the required acidity of the solution essential to 

the test, but obviates the need of employing potassium permanganate 

in order to convert any ferrous iron present to the ferric state.

The aluminum tube is employed in the assay for iron in natural 

waters, because (1) it is light, (2) it can not be easily broken in 

transportation, like the glass tubes used in the water laboratories, (3) 

it is provided with a suitable spring for supporting the colored-glass 

disks, (4) it provides a suitable depth of column of the water for the 

iron determination, and (5) it is generally used by the hydrographic 

division in determining the natural colors of waters. The aluminum 

colorimeter tube thus serves a double purpose, and obviates the necessity of carrying special tubes in the field for the iron assay.

The results reached by this method of determination should be as 

accurate for practical purposes as those attained by the laboratory 

method.

CHLORIDES.

The determination of chlorides in water is significant in two general lines of investigation. In connection with sanitary analyses, it 

is in certain parts of the country a valuable index of sewage pollution. In analyses of water for boiler and industrial purpose? it is 

also important, as the chlorides of calcium and magnesium corrode 

boiler plates.

LABORATORY DETERMINATION.

With reference to the determination of chlorides from a sanitary 

 standpoint, the following article by Mr. Daniel D. Jackson, chemist 

in charge of the Mount Prospect laboratory, department of water 

supply, gas, and electricity, of New York City, is presented:

Chlorine, a constituent of common salt, is present in nearly all natural voters. 

Its original sources are mineral salt deposits and finely divided salt spray from 

the sea. This latter is carried with dust particles by the wind and precipitated 

with the rain. All salt found in waters not coming from these original sources 

comes from domestic drainage, and indicates that the water is at the present time 

polluted, or was polluted and has since been purified. By a comparison of the 

salt contents of any water under examination with the normal chlorine figure 

for that region, the extent of past or present pollution may be determined.

PHYSIOLOGICAL FUNCTIONS OF COMMON SALT.

Salt always occurs in drainage from animal sources because in all animal 

economy a certain fairly definite amount of common salt is eaten with the food 

daily and later expelled from the body in practically the same condition in 

which it was absorbed. That it plays an important role in the blood ij? indicated by the fact than on an average it constitutes about one-half of th^ total
48 FIELD ASSAY OF WATER. [NO. 151.

blood ash. It is also found that normal gastric juice can not be formed without 

the presence of salt, and that in many ether secretions of the body its presence 

is probably a necessity.

SALT AS AST INDICATION OF POLLUTION.

The amount of salt in a water is a valuable indication of pollution because 

of the following facts: The animal body expels the same amount of salt that it 

absorbs; this salt is unchangeable in the soil and is very soluble in water; it 

must eventually form a part of the drainage and become mixed with the general 

run-off of the region in which it is expelled. The average amount of salt entering the drainage of any particular district is so constant for each inhabitant 

that it has been claimed that the number of people living on a drainage area 

may be determined with a fair degree of accuracy from the average run-off and 

the excess of chlorine over the normal.« Stearns estimates the chlorine in the 

run-off of any drainage area not receiving factory waste to be increased about 

one-tenth of a part per million by every 2U inhabitants per square mile.

SALT IN THE WATERS OF INLAND STATES.

All sajt in natural unpolluted waters farther inland than Ohio comes from 

mineral deposits. The salt winds from the sea have no effect beyond this 

State, but, unfortunately, west of this State a large proportion of the natural 

waters are more or less affected by the salt deposits. Tto? underground salt 

seems to spread over a broad area, and exerts not only a vnde but a variable 

influence over most of the waters. In these inland States, while the " normal 

chlorine " would be practically zero, the value of the determination of chlorine 

is in most cases vitiated by the variable quantity of salt from mineral sources. 

Determinations of chlorine in samples of water taken above and below a city 

which runs its drainage into the stream examined may give the extent of pollution due to the city sewage, but the waters so far analyzed in the inland States 

give indications that the question of normal chlorine doe? not to any great 

extent enter into sanitary problems.

SALT IN COAST STATE WATERS.

On the other hand, the coast State waters are practically unaffected by this 

mineral salt, and while very extensive deposits exist, especially in the State 

of New York, they are in narrow pockets and exert an influence over a very 

limited area. Except in these pockets the mineral salt has apparently been 

washed into the sea.

It is found that in the coast States the salt in the natural waters which 

comes from original sources is practically all brought in by the sea winds, and 

that a certain normal amount is present in the waters of each locality.

The difference in the normal amount in different localities is due to variations in distance from the seacoast, in the amount of rainfall, in the rate of 

evaporation, in the amount of protection from ocean winds, and in the direction 

of the prevailing winds. In spite of the great variety of causes which affect 

the normal chlorine in natural waters, the normal for any particular region is 

surprisingly constant.

The chlorine decreases as waters farther and farther inland are tested, so 

that by connecting with lines 011 the map localities having the same normal we 

find that these lines of equal chlorine (isochlors) follow in a general way the

"Eept. Massachusetts State Board of Health, 1890, pt. 1, p. 680.
LEIGHTON.] ' CHLOEIDES. 49

coast lines, and as they extend inland are still more or less parallel to the coast. 

The distance of these lines from the coast depends chiefly upon the general 

direction of the wind and the protecting Influences of mountains on the coast 

or of islands near the mainland.

COLLECTION OF SAMPLES.

In order to obtain the normal chlorine lines for any State it is first necessary 

to collect a large number of analyses for chlorine in waters taken at different 

seasons over the entire area to be covered. It is evident that near the seacoast. 

where the variations in chlorine within a limited area are greatest, the largest 

amount of data must be collected. A large number of samples of water taken 

from surface and ground sources must be obtained. The pond waters usually 

give the best results, and careful inspection of the drainage area of sucl sources 

gives a good idea of whether or not the water is subject to pollution. Samples 

for analysis should be chosen as far from human habitation as possible.

SOLUTIONS BEQUIBED IN THE ANALYSIS OF WATEE FOE CHLOEINE.

The following solutions are employed in the analysis of water for chlorine:

Salt solution. A solution of chemically pure fused salt, containing 1 milligram of chlorine in each cubic centimeter, is made by dissolving 1.648 jrrdms of 

the fused sodium chloride in 1 liter of distilled water free from chlorine.

Silver-nitrate solution. Two and one-half grams of crystallized silve^ nitrate 

are dissolved in 1 liter of distilled, water free from chlorine. To this solution 

water or strong silver nitrate is added until by actual titration 10 cubic centimeters of it are equal to 5 cubic centimeters of the standard salt solution. 

One cubic centimeter of this solution is then equal to 0.5 milligram of chlorine.

Potassiiim-cJiromate solution. An indicator solution is made by adding 50 

grams of potassium chromate to 1 liter of distilled water and then adding sufficient silver-nitrate solution to .precipitate all the chlorine present and turn the 

precipitate slightly reddish. This is allowed to stand, and by filtering or decanting the clear solution is then obtained.

Emulsion of alumina. This is made by dissolving 125 grams of potassium or 

ammonium alum in 1 liter of water and precipitating the alumina froir boiling 

solution by ammonia. After precipitation the alumina must be washed free 

from chlorine, sulphate, and ammonia by successive treatments, settlings, and 

decantations with cold distilled water.

METHOD OF PBOCEDUEE IN THE ANALYSIS OF WATEE FOE CHLOEINE.

Pour 25 cubic centimeters of the water to be tested into a white porcelain 

dish. Add about one-half a cubic centimeter of chromate solution and run in 

standard silver-nitrate solution from a burette until the first faint reddish tint 

appears. This is more easily noted if for comparison a dish containing the 

same amount of water and chromate is kept beside the dish in which tin test is 

made.

If 1 or more cubic centimeters of silver nitrate are necessary to reacl an end 

point, the test may be made without evaporation, but if less is required then 

evaporate 250 cubic centimeters to 25 cubic centimeters volume before making 

the test. It may at times be necessary to evaporate more than this if the 

chlorine present is very close to zero in amount.

It is best to always titrate with 25 cubic centimeters of the water. In this 

case 0.1 cubic centimeter is subtracted from the results as an indicator error.

IEK 151 05 4
50 FIELD ASSAY OF WATER. [NO. 151.

.If more than this amount is used in titration, subtract 0.1 cubic centimeter for 

e'ach 25 cubic centimeters of the volume of water titrated.

If 250 cubic centimeters of water are taken, the number of cubic centimeters 

of silver-nitrate solution used to obtain an end point minus 0.1 cubic centimeter 

multiplied by 2, gives the chlorine in parts per million.

Example: 250 cubic centimeters are evaporated to a volume of 25 cubic centimeters and chromate solution added. In the titration 3.5 cuMc centimeters of 

silver nitrate are used. Then (3.5 0.1) X2 = 6.8. The water, then, contains 

6.8 parts per million of chlorine.

If the sample is highly colored and very turbid it may be necessary to clarify 

it by treating it with an emulsion of alumina. This is best accomplished by 

bringing the water just to the boiling point, and then adding alumina and 

shaking the emulsion. In a few minutes the clarified water may be decanted. 

This is allowed to cool and the required amount is measured out for titration.

OBSERVATIONS ON THE USE OP THE NORMAL CHLORINE MAP.

Having drawn a map of this character for any coast State, we are then able 

to estimate the pollution in any natural water by the amount of chlorine present 

over the normal. In some instances it is first.necessary to ascertain that the 

chlorine is not from mineral sources.

It will be seen that the normal chlorine lines are of great practical value, 

both to the chemist and to the engineer, as they give an inder from which may 

be estimated the sanitary quality of most waters analyzed within the coast 

States. The chlorine also furnishes information as to the source of deepseated springs or artesian wells.

While this chlorine in the general run-off is in direct proportion to the population on a drainage area, provided none of the sewage is carried outside of that 

area, yet waters in this region may have been purified before reaching tho 

source from which they are collected. The chlorine would still be present and 

it is necessary to find from other tests whether the pollution is present or past.

It will be noted in Mr. Jackson's discussion that the determination 

of chlorine for the location of isochlors should be made by very precise laboratory methods. In fact, such precision should be used in all 

cases in which it is necessary to decide whether or not a water in a 

country where normal chlorine is significant contains chlorides in an 

amount which corresponds to or approximates a normal for the 

country from which the water comes. In general water surveys, 

however, it is necessary to make such nice distinctions only in rare 

cases. In the determination of chlorides in a water which is to be 

used for boiler or industrial purposes this refinement is not necessary, 

and field methods will generally .suffice.

FIELD DETERMINATION. 

STANDARD SILVEB-NITBATE TABLETS.

The Geological Survey proposes to use a method for the rapid 

determination of chlorides which, from numerous experiments, seems 

to meet the conditions in a satisfactory manner. In place of the
U. S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 151 PL. Ill

UNITED STATES GEOLOGICAL SURVEY TABLET CASE.
LEIGHTON.] CHLOEIDES. 51

standard solution of silver nitrate, which must be measured in a 

burette when applied to a water under examination, there are used 

tablets of silver nitrate containing a known equivalent of this recent. 

These tablets are packed in tubes and carried in a leather cafe, the 

details of which are shown in PL III. This method of packing is 

well designed to avoid mechanical agitation of the tablets, which 

would result in their loss of active equivalent. The tablets are held 

securely in place by the stoppers, which are sufficiently small to be 

pushed through the lumen of the tube as fast as the tablets are used. 

This maintains a constant pressure against the tablets and prevents 

their agitation.

The manufacture of stable silver-nitrate tablets proved to be 

somewhat difficult. A number of pharmaceutical experts who were 

engaged at various times to prepare them failed to produce a tablet 

which was reasonably stable. Those which are now supplied to the 

Survey are made by the Kremers-Urban Company, of Milwaukee, 

Wis., and are of superior quality.

In connection with the determination of chlorides it is necessary 

to carry into the field only a small bottle of potassium-chromate crystals or solution and a heavy glazed porcelain mortar, together vdth a 

pestle of approved design. The tablets are dissolved in a measured 

quantity of water, a small amount of potassium chromate having first 

been placed in the solution. The end point is indicated by the change 

in color in the usual way and the number of tablets of known enuivalent indicates the amount of chloride in the water.

This method may be objected to by some chemists because it is 

generally believed that the results of a chlorine determination made 

on a water without first evaporating the same are too high. This 

is apparently true with waters like those of New England, which contain only minute quantities of chlorine, but in the waters of the 

greater part of the country the chlorides are so high in amount that 

the error which arises from direct titration is not large enough to be 

of significance in industrial work.

While the tablets may be manufactured to contain almos4: any 

reasonable amount of silver nitrate, it has been found that the most 

convenient equivalents for general field use are those of approximately 

\ and 10 milligrams of chlorine. In all special cases the strength of 

tablets should be adjusted to suit conditions. As it is practically 

impossible to manufacture tablets of the exact equivalent desired, it is 

necessary to determine the strength of each new supply and to make 

calculations of all field results accordingly.

The following statement includes various tests of a supply of 

tablets. Each tablet was made up to contain an equivalent of as near 

1 milligram of chlorine as possible. The purposes of the tests were
52 FIELD ASSAY OF WATEE. : 151.

to determine the variation in equivalent of single tablets and the 

combined equivalent of tablets in sets of 5 and 10, tb<3 actual values 

in milligrams of chlorine being determined by volumetric methods.

Tests to determine variation in silver-nitrate tablets. 

[Milligrams.]

Single tablets.

Equivalent of 

1 tablet.

0.96

.95

1.049

1.062

Mean.

1.005

Deviation 

from 

mean.

-0.045

- .055

+ .044

+ .057

Maximum 

deviation.

40.057

5 tablets.

Equivalent of 

5 tablets.

5.060

5.230

5.210

5.110

5.090

5.200

5.080

5.110

Mean equivalent of 1 

tablet.

1.013

1.046

1.042

1.022

1.018

1.040

1.016

1.022

Mean.

5.211 1.027

Deviation 

of 1 tablet from 

mean.

-0.015

+ .019

+ .015

- .005

- .009

+ .013

- .011

- .005

Maximum 

deviation.

+0.019

10 tablets.

Equivalent of 10 

tablets.

10.24

10.15

10.17

10,18

Mepn equi^alent of 1

tablet.

1.024

1.015

1.017

1.018

Mean.

10.185 1.018

Deviation 

of 1 tablet from 

mean.

+0.0055

- .0035

- .0015

- .0005

Maximum 

deviation.

+0.0055

It will be seen from the above results that the maximum variation 

in the equivalent of single tablets is 0.057 milligram of chlorine for 

each tablet. Therefore, considering the maximum variation shown 

in the single tablets and allowing, for purposes of illustration, that 

the maximum error may always be present in a determination, it 

would be necessary to use 18 tablets in a determination in order to 

reach an error equivalent to 1 milligram of chlorne. The mean 

value, however, of the single tablet is thoroughly representative of all 

the tablets tested, the variations lying above and below the mean value 

equally. It will be seen, further, that when the tablets are used in 

larger quantities and the combined equivalents of such quantities are 

compared, the deviations from the mean are.considerably less and the 

maximum deviation is practically negligible. This is shown especially well in the statement of the comparison of the ten tablets. It 

is therefore apparent that the tablets do not vary by an appreciable 

amount, and that having established their equivalent by taking the 

mean of several determinations, such mean can be used in connection 

with the field determinations of chlorine in natural waters.
MIGHTON.] CHLOEIDES.

PRACTICAL TESTS WITH TABLET METHOD.

Three chloride solutions were made up at random, which, when 

tested by precise methods, were found to contain 4,280, 12,9 ^0, and 

1,372 parts of chlorine per million, respectively. These solutions 

were titrated with tablets, -and the end points reached in tlr°, same 

manner as that used in the field. The results are set forth in the 

following table:

Tests of silver-nitrate tablets, with solutions of Jenown equivalent.

SOLUTION NO. 1. CHLORINE, 4,280 PAETS PER MILLION.

Volume of 

solution.

c. c.

22

5

5

35

25

50

50

Number of 

tablets.

133.0

21.0

21.0

10.4

f 10.0 

X 3.0

20.8

20.0

5.0

1.0

Value of 

tablets.

1.052

1.05S

1.052

10.1

10.1 

1.052

10.1

10.1

1.052

.481

Parts chlorine, tablet 

method.

6,350

4,410

4,410

4,200

} 4, 160

4,200

4, 154

Deviation 

from actual 

value.

+2, 070

+ 130

+ 130

- 80

- 120

- 80

 126

Pel1 cent 

deviation.

48.4

3.04

' 3.04

1.87

2.80

1.87

2.44

15.06

Mean deviation (six results)=15.06-r-6=2.51 per cent. 

SOLUTION NO. 2. CHLORINE 12,940 PARTS, PER MILLION.

26

26

15

15

5

32.25

32.0

f 19.5 

I 1.0

i 18.5 

t 8.0

64.0

10.1

10.1

10.1 

1.052

10.1 

1.052

1.052

12,510

12,430

} 13, 200

| 13,020

13, 470

-430

 510

+260

+ 80

+530

3.32

3.94

2.01

.62

4.09

13.98

Mean deviation=13.98-r-5=2.80 per cent.
54 FIELD ASSAY OF WATER. [NO. 151.

Tests of silver-nitrate tablets, 'With solutions of known equivalent Continued. 

SOLUTION NO. 3. CHLORINE 1,372 PARTS PER MILLION.

Volume of 

solution.

c. c.

50

50

50

20

5

Number of 

tablets.

6.7

c 6.0 

I 7.0

6.0

6.0

2.0

f 26. 0 

I 1.0

(

6.0

1.0

2 « 4T:

Value of 

tablets.

10.1

10.1 

' 1.052

10.1

1.052

.481

1.052 

.481

1.052

.481

ORO 

. «OO

Parts chlorine, tablet 

method.

1,353

| 1,358

j

1 1,358

J

} 1,392

1,480

Deviation 

from actual 

value.

 19

- 14

- 14

+ 20

+108

 Per cent 

deviation.

1.38

1.02

1.02

1.46

7.80

12.27

Mean deviation= 12.27-=-5=2.45 per cent.

The first result in the table above set forth is so radically wrong 

that it is inserted to illustrate a condition which must always be 

a voided when this method is employed, viz, the use of a large number 

of tablets. It will be noted that a considerable ampunt of strong 

chloride solution was used with tablets of low equivalent, i. e., 1.052 

milligrams of chlorine. This made it necessary to use 133 tablets to 

reach the end point, with a result that is absurd. But 25 and 50 

cubic centimeters of the same solution are titrated vdth the tablets 

with only a small error when the tablets of larger equivalent, 10.1 

milligrams of chlorine, are used. On the whole, the results shown in 

the above table are very satisfactory, the error involved in the determinations averaging about 2.5 to 3 per cent, which is well within the 

limits of field work. Indeed^ when the method was designed it was 

believed that an error of 5 per cent would be as small as could be 

expected.

A very simple way of testing for small amounts of chlorine is 

afforded by cutting tablets into quarters with a jackknife. Only 

ordinary care need be used and the quarters may then be taken for 

analysis without extreme regard to the selection of large or small 

pieces. The following account of some experiments performed is 

submitted:

No. 1. Twenty tablets were cut into quarters. Each quarter should 

precipitate 0.25 milligram of Cl. To 100 cubic centimeters of water 

(blank = 0.13 cubic centimeter) 1 cubic centimeter of NaCl was
LEIGHTON.] CHLOBIDES. 55

added, making the actual value of the water = 1.13 milligrams Cl. 

Four quarters gave no end reaction, but five quarters did. This 

experiment was done fifteen times with the same results. Cie and 

one-fourth tablets are equivalent to 1.25 milligrams Cl.

No. 2. Twenty more tablets were cut up and added as above, except 

that 1.1 cubic centimeters of NaCl were used, making the value of 

water =1.23 milligrams Cl (blank-j-0.13 cubic centimeter). Five 

quarters used in eight out of twelve titrations. This shows a variation in quartering of possibly an equivalent of 0.02 milligram Cl, or 

0.2 part per million, an insignificant amount.

No. 3. Next 1 cubic centimeter of NaCl was used (=1.13 milligrams Cl). One whole tablet gave no end reaction, but one,whole 

tablet-fone quarter tablet gave a reaction in every case.

No. 4. The same was done with 0.9 cubic centimeter NaCl (=1.03 

milligrams Cl). One tablet, no end reaction; 1J tablets, end ruction.

No. 5. The same, using 1.2 cubic centimeters NaCl (=1.3? milligrams Cl). One tablet, no end reaction,=l milligram Cl; 1^ table.ts, no end reaction,=1.25 milligrams Cl; li tablets gave erd reaction,=1.50 milligrams Cl.

Nos. 3, 4, and 5 were each done ten times.

The value of these results and their accuracy are shown below:

No.

1

2

3

4

5

Milligrams chlorine.

Actual content.

1.13

1.23

1.13

1.03

1.33

Found by titration.

1.25

f 8 show 1.25 

I 4 show 1.50

1.25

1.25

1.50

This method comes within 0.25 milligram of the amount of chlo- \ 

rine present, or within 2.5 parts per million of chlorine. This pro- V 

cedure is recommended. If only ordinary care be used in cutting 

tablets, their value will be within 1 part in a million. ^J

ESTIMATION OF CHLORINE.

A known amount (about 50 c. c.) of the water to be tested is measured into a glazed porcelain mortar (4 inches diameter) and 5 drops 

of potassium chromate (5 per cent solution) added.

One silver-nitrate tablet is then cut into quarters, using ordinary 

care to get the quarters equal. Whole tablets are added to the water
56 FIELD ASSAY OF WATEE. [NO. 151.

till near the end point, when quarter tablets are used. The end point 

is the appearance of the red color of silver chromate.

* w =milfigrams per liter of chlorine, when W=cubic centimeters of water used, n = number of tablets used, and A = value 

of one tablet in milligrams of chlorine. Proper allowance should be 

finally made for the amount of silver nitrate consumed in the end 

reaction.

Each tube of AgNO3 tablets is marked with ite equivalent of 

chlorine.

NOTE. Silver-nitrate tablets should not be handled witf the fingers nor 

exposed to sunlight. Keep all tubes well stoppered.

HARDNESS. 

GENERAL STATEMENT.

A hard water is popularly recognized as a water with which it is 

difficult to obtain a soap lather. Strictly defined, it is that property 

imparted to water by the carbonates, sulphates, chlorides, and nitrates 

of calcium and magnesium. Chemical methods for the determination of hardness are not yet well defined; in fact, tlv. whole subject 

is somewhat chaotic. A method which may be satisfactory for the 

waters of one part of the United States may be of little value for 

those of another. Consequently there has developed a rude geographic distribution of methods, each being adapted to the peculiarities of the waters in the regions in which they are used. The result 

is that comparisons between hardness determinations made in different regions are somewhat uncertain and nearly always unsatisfactory.

The effect of hard water upon the lathering properties of sodium 

soap that is, the soap used for laundry and toilet purposes has 

been made use of in determining hardness. Indeed, the soap test 

was the earliest and is still the commonest of all those employed for 

this purpose. A standard solution of a pure soap, usually a highgrade castile, is standardized against a solution of calcium chloride, 

the equivalent of which has been determined in terms of calcium carbonate. The details of this process are too familiar to warrant further description. Practically, the principal weakness of the $est is 

the determination of the end point, which is not sharply defined. 

The sodium salts of oleic, palmitic, and stearic acids which compose a 

pure soap are definite chemical compounds, and their transformation 

into calcium and magnesium soaps should follow the usual course of 

chemical change, and therefore the soap test is not merely a test of the 

soap-consuming power of water, as maintained by some chemists.

In practice the soap test is limited in its usefulness, and its results 

are modified by many conditions. A few authorities who have 

made minute studies of the soap method are impressed with its pos-
LEIGHTON.] HARDNESS. 57

sibilities, but the modifications which they suggest are somewhat cumbersome, involve superrefinements, and in the end require so much 

time that the importance of the results is not commensurate. In 

those parts of the country where soft waters abound and where it is 

known that magnesium salts are not abundant the test has great 

value. Its usefulness is limited in the waters of the Mississippi 

basin, and it fails entirely when applied to western waters.

FIELD METHOD. 

USE OF SODIUM-OLEATE TABLETS.

The soap test has been modified for field use by the substitution of 

tablets of pure sodium oleate for the soap solution. Sodium oleate 

can be obtained in pure form and readily divided in tablets, erch containing a known amount of the reagent. The tablets used by the 

Geological Survey in field work are made by the Kremers-Urban 

Company, of Milwaukee, Wis. They are of three grades, " full," 

u half," and " quarter," or, as they are Usually denoted, " F," " H," 

and " Q," according to their content of 10, 5, or 2.5 milligrams of 

sodium oleate, respectively.

. In using these tablets, 100 cubic centimeters of the water to be 

tested are placed in a specially designed bottle (Emil Greiner) 

having a heavy semispherical bottom. Tablets are then added one at 

a, time and dissolved in the water. 'This process is greatly hastened 

by trituration of the tablets in the bottle with a blunt glass rod. 

After each tablet is dissolved the bottle should be shaken and laid 

upon its side, and the determination conducted in precisely the same 

manner as that prescribed in the case of the soap solution. From 

the number of tablets used and their equivalent the hardness may be 

determined.

The facility with which this determination may be carried on is 

largely determined by practice. When first attempted it seens awkward, but after a few trials the operator finds that it can be readily 

performed. The proper way is to start with the F tablets until near 

the end point, then apply the H, and finally the Q tablets. This-of 

course may become a method of u trial and error," but the skilled field 

man will seldom add tablets beyond the end point. The appearance 

of the lather at various stages is characteristic and affords a g lide for 

the operator. In order to show certain characteristic feature? in the 

tablet method for the hardness determination the following results 

of a test made of a supply of tablets are set forth:

TEST OF SODIUM-OLEATE TABLETS.

For a standard of hardness, 0.2 gram of Iceland spar was dissolved 

in HC1, evaporated to dryness three times in HC1 and twice with 

water. Finally the residue was dissolved and diluted to one liter
58 FIELD ASSAY OF WATER. [NO. 151.

with redistilled water. Five cubic centimeters of this solution of 

CaCl2 is equivalent to 1 milligram CaCO3 .

The tablets used in the work are of three equivalents, and are 

designated as follows:

One F tablet contains an approximate equivalent of 0.0014 gram calcium 

carbonate.

One H tablet contains an approximate equivalent of 0.0007 gram calcium 

carbonate.

One Q tablet contains an approximate equivalent of 0.00">3 gram calcium 

carbonate.

The first test was to determine the amount of sodium-oleate tablet 

reacted with 100 cubic centimeters distilled water. In the following tabulated statement the sign -j- denotes a permanent foam or 

satisfactory end point, while denotes no end point

Standardization of sodium-oleate tablets against 100 cubic centimeters distilled water.

F. H. Q- 3Q

Results in the above series of experiments indicate that 100 cubic 

centimeters distilled water requires about 0.005 grrms of sodium 

oleate.

To reduce this to terms of calcium carbonate experiments were 

made with 100 cubic centimeters distilled water containing varying 

amounts of calcium chloride. It was found by repeated trial that 

where two H tablets were used it required 3.2 cubic centimeters of the 

CaCL solution in 100 cubic centimeters of distilled water to react 

exactly. Consequently, as the 100 cubic centimeters distilled water 

required one H tablet, the remaining H tablet was ec^iivalent to the 

CaCL. Therefore the distilled water is equivalent in tiH soap reaction 

to 3.2 cubic centimeters of CaCL, or 0.64 milligram CaCO3 .

The first experiments in standardizing the tablets vere made with 

the standard CaCL solution diluted with 100 cubic centimeters distilled water against one F tablet, with results as follows:
LEIGHTON.] HAEDNESS. 

Standardisation of sodium-oleate tablet F.

59

CJaCls against 

1 F tablet.

c. c. 

3.0-_._--.

3.5--.----

3. 6- ......

3.7------.

8.7.... ...

8.7....... 

8.7-..-.-.

3.8-______

8.8.-....-

4.0-....-.

Result.

Foam.

Foam.

Foam.

Foam.

Foam.

Foam.

No foam.

No foam.

From the above it appears that one F tablet is eqtiivalert to 3.7 

cubic centimeters CaCl2 solution with 100 cubic centimeters distilled 

water, or actually equivalent to 6.9 cubic centimeters (3.7-f-F,2 cubic 

centimeters), which expressed in terms of CaCO3 is equal to 1.38 

milligrams.

Using seven F tablets in 100 cubic centimeters distilled water against 

different amounts of the CaCL solution the following results were 

reported:

CaClo against 

1 F tablets.

c. c.

41.7

41.5

42.5

44.9

45.0

45.9

46.0

Result.

Foam.

Foam.

Foam.

Foam.

Foam.

No foam.

No foam.

From the above results it appears that the end point is practically 

reached with 45 cubic centimeters CaCl2 solution. With the amount 

for 100 cubic centimeters distilled water added, seven tat lets are 

therefore equivalent to 48.2 cubic centimeters CaCL, or 9.64 milligrams CaCO3. This allows for one tablet an equivalent of 1.37 

milligrams CaCO3 , which agrees with the previous determinations 

within the limit of experimental error.
60 FIELD ASSAY OF WATEE. [NO. 151.

Experiments were made with various combinations of tablets as 

follows:

Caca2.

c. c.

3.2

3.2

3.0

3.0

2.8

2.9

45.0

45.9

45.9

45.0

45.0

45.0

45.0

Tablets (number 

and value).

4Q

5Q

5Q

5Q

4Q

4Q

7F

7F

7F + 1Q

14 H

15 H

6F + 3H

6F + 2H

Result.

No foam.

Foam.

Foam.

Foam.

Foam.

Foam.

Foam.

No foam.

Foam.

No foam.

Foam.

Foam.

Foam.

Analyzing the results above given we have:

i.

CaCl»+100 c. c. 

distilled 

water.

c. c.

3.2 

3.2

3.0

2.8

2.9

Tablets 

(number and 

value).

4Q 

5Q

5Q

4Q

4Q

Result.

No foam. 

Foam.

Foam.

Foam.

Foam.

Therefore four Q tablets are equivalent to an amount of CaCO8 

lying between 1.28 milligrams and 1.22 milligrams, or one Q tablet to 

an amount lying between 0.32 and 0.30. Using either as the value, 

the error will not be significant. 0.31 milligram is probably the most

accurate factor.

2.

CaCljj+100 c. c. 

distilled 

water.

c. c.

45.0

45.9

45.9

Tablets 

(number and 

value).

7F

7F

7F+1Q

Result.

Foam.

No foam.

Foam.
LHIGHTON.] HARDNESS. 61

Therefore seven F tablets are equivalent to an amount of CaCO3 

lying between 9.82 and 9.64 milligrams, or one tablet to an amount 

lying between 1.40 and 1.38 milligrams. The error introduced

if either 1.40 or 1.38 is used as a factor will be less than ^ and

theref ore insignificant.

3.

CaClu-f-lOOc. c. 

distilled 

water.

c. c.

45

45

45

Tablets 

(number and 

value).

14 H

15 H

6F+2H

Result.

No foam.

Foam.

Foam.

Therefore the equivalent of 9.64 milligrams CaCO3 lies between the 

value of 14 and 15 H tablets, or one tablet is equivalent to an amount 

of CaCO3 between 0.69 and 0.64 milligram. But from the third 

experiment it is seen that two H tablets are equivalent to 1.36 milligrams (9.64 [6X1-38]), or one tablet to 0.68 milligram.

., ESTIMATION OF HARDNESS.

*

The directions for using these tablets should be followed absolutely. 

The end-point foam should be permanent for at least five minutes, 

the bottle lying upon its side. The smallest number of tablets possible should be used; for example, if the hardness of a water is 120 

parts per million on direct titration without correction, the best 

procedure assuming the given value of the tablets used would be as 

follows:

Milligrams CaCO,.

8 F tablets equivalent to____________u_______________ 11.04 

1 H tablet equivalent to______________________________ .68 

1 Q tablet equivalent to ______________________________ . 31

Total _________________________ _ ___________ 12. 03 

Subtracting 0.64 milligram CaCO, for distilled water____________ . 64

Hardness expressed by tablets___________________ 11.39 

Or in parts per million________________________________ 113. 9

In this case the error would be equivalent to 0.03 milligrams CaCO3 , 

an amount unimportant in practical work.

The end point can be approached in the manner above described 

after the operator has had a short experience with the method. The 

comparative permanence of the preliminary foam pellicles which do 

not remain unbroken for the entire five minutes is a guide.

*If the total hardness of the water exceeds 

150 parts per million, this method has the same 

inaccuracies as the ordinary laboratory method 

in which a solution of soap is used*
62 FIELD ASSAY OF WATER. [NO. 151.

HARDENING CONSTITUENTS.

CLASSES.

It is customary to distinguish between temporary and permanent 

hardness. Temporary hardness is due to the carbonates (and bicarbonates) of calcium and magnesium. Calcium and magnesium carbonates are not readily soluble in water unless accompanied by carbon 

dioxide. Under such circumstances it is supposed that the carbonates 

become bicarbonates, although the bicarbonates of there two elements 

have never been isolated. When waters containing calcium and magnesium bicarbonates are boiled the carbon dioxide is driven off and the 

normal carbonates of calcium and magnesium ar? precipitated. 

Therefore, the properties which they impart to the water are designated temporary hardness. Permanent hardness, on the other hand, 

is that property which is imparted to waters by the sulphates, chlorides, and nitrates of the alkali earths. They are not precipitated by 

ordinary boiling, and therefore their effects are regarded as permanent. The usual method of determining temporary and permanent 

hardness by the soap test consists in making the test on a sample of 

water before boiling, and another on a similar sample after boiling; 

the difference in the two results representing the temporary hardness.

Temporary and permanent hardness are often expressed as al^alinity and incrusting constituents, respectively, and it is common to 

see, even in analytical reports of well-informed chemists, the expression " alkalinity or temporary hardness." This expression is 

misleading. It is approximately correct when the waters of New 

England and certain other portions of the country ere referred to, 

but as a general statement concerning the majority of waters nothing 

could be more inaccurate. There are abundant instances in which 

waters are alkaline to an extraordinary degree, and yet are widely 

known as soft waters, giving little or no reaction with the soap test. 

The alkalinity in such cases is due to the carbonates of sodium and 

potassium, which, while they impart a truly alkaline reaction, have no 

hardening effect. The majority of the waters of the United States 

contain alkali carbonates, and therefore any interpretation of alkalinity as being equivalent to temporary hardness with such waters is 

erroneous.

If the alkalinity found in a water is the result of the carbonates 

of the alkali-earth elements, its industrial significance is considerably different from that of the carbonates of the alkalies. For example, calcium carbonate forms soft scale when u^ed in boilers, 

while sodium carbonate forms no scale, but presents a much less 

important difficulty, that of foaming. If, however, a water containing calcium carbonate were used for irrigation purposes, it
LEIGHTON.] HABDNESS. 63

would not damage crops unless it were present in extremely high 

proportions higher, in fact, than it is almost ever found in nature. 

On the other hand, a small amount of sodium carbonate is destructive to crops. It is as desirable to know whether the sulphates and 

chlorides which are found in the water are of the alkali earths or 

the alkalies, for they present variations in usefulness with reference 

to industries similar to those above described in the case of tl^ carbonates.

It has been the endeavor of the Geological Survey to so modify 

the methods by which the various determinations of the hardening 

constituents of water may be made that they can be used in the field. 

These methods are set forth in subsequent pages. They do not include all of the determinations desirable for some classes of work, but 

sufficient to allow of a very comprehensive interpretation concerning 

the quality of any water under investigation.

CARBONATES.

The determination of alkalinity or carbonates is a simple volumetric process. It requires only a standard solution of ar acid, 

preferably a mineral acid, with accurate means for measuring, the 

same, and a proper indicator solution. On account of the carbon 

dioxide set free by the determination, methyl orange is the indicator 

in commonest use. The objections already cited to carrying standard 

solutions and burettes in the field led to an attempt to adopt an 

acid which could be preserved in tablet form. Many organic acids 

were tried, but is was found that they were either too weak to 

afford a definite end point or were of so deliquescent a character 

that they could not be made to form stable tablets. It was finally 

decided to adopt the use of sodium acid sulphate. Tablets made 

from .this reagent are easily regulated in equivalent and are of an 

extremely stable nature. The results whiclj can be procured tl rough 

their'use are very satisfactory.

TESTS OF SODIUM ACID-SULPHATE TABLETS.

For use in titrating against sodium acid-sulphate tablets a fiftieth 

normal solution of sodium carbonate was made, in which each cubic 

centimeter equals 1.06 milligram NaCO3 . Six sets of five sodium acidsulphate tablets each were then dissolved in 50 cubic centimeters of 

distilled water and each solution was titrated with the standard 

sodium carbonate. The results of these titrations are shown in the 

following table:
FIELD ASSAY OF WATER. 

Standardisation of sodium acid-sulphate tablets.

[NO. 151.

NaHSO4.

c. c. 

10.60

10. 15

10.85

10.30

10.10

10.10

NaaCOa.

c. c. 

2.15

2.05

2.20

2.10

2.05

2.05

Value of 1 tablet.

MgCaCOg. 

3.03

3.02

2.03

2.04

2.03

2.03

Assuming these final reactions,

Na2CO3 + 2NaHSO4 = 2Na2SO4 + H2O + CO2 , 

and CaCO3 + 2NaHSO4 = CaSO4 + H2O + CO2 + Na?SO4 ,

then for the expression of the value of our tablet in milligrams of 

CaCO3 we have the following proportion:

Na2CQ3 106 

CaCO3 ~ 100*

The experiments above described were made with solutions of the 

acid-sulphate tablets, and the results show the constancy of the reaction between the normal carbonate and the sulphate. They do not 

show, however, the variations which would occur in the practical 

use of the tablets applied directly to the alkaline solution, as would 

be done in the field. Therefore the following tests are submitted to 

{ how the deviations which may arise in successive tablets or successive sets of tablets. The tablets used were marked " Lot 715, sodium 

acid-sulphate equivalent to 1.995 milligrams calcium carbonate." 

These tablets had been in stock for several months, had r< eeived some 

rough handling, and were in poor condition. In fact, they represented the most unfavorable conditions that might be supposed to 

occur in connection with the field use of tablets, and the variations 

which are shown may be accepted as the extreme variations which 

are likely to occur in common use.

In testing and standardizing the sodium acid-sulphate tablets normal solutions of sulphuric acid and sodium carbonate were used. 

Tests were made as follows:

Solutions of unknown strength of sodium carbonate Were made up 

and the alkalinity was determined volumetrically with standard sulphuric acid solution. Following this, determinations of the same 

unknown solutions were made with the tablets. Varying amounts 

of the solution were used, with a corresponding variation in the number of tablets.
BRIGHTON.] HAEDNESS. 65

Comparative determinations of alkalinity in carbonate solutions with standard 

sulphuric-acid and sodium acid-sulplfate tablets.

CARBONATE SOLUTION NO. 1. ALKALINITY, 5,764 PARTS PER MILLION IN 

TERMS OP CALCIUM CARBONATE.

Amount of 

solution.

c. c.

1.9

3.5

7.0

11.0 

10.5

17.5

46.5

Number of

tablets.

5

10

20

32 

30

50

135

Parts per 

million.

5,225

5,674

5,674

} 5, 726

5,674

5.767

Deviation 

in parts per 

million.

-539

- 90

 90

- - 38

- 90

+ 3

Per cent deviation.

9.3

1.56

1.56

.66

1.56

.05

CARBONATE SOLUTION NO. 2. ALKALINITY, 2,312 PARTS PER MILLION IN 

TERMS OP CALCIUM CARBONATE.

4.5

10.0

15.0

21.0

19.0

25.5 

25.0

51.0 

50.5

5

12

 18

25

23

.30 

30

60 

59

2,207

2,383

2, 384

| 2,359

1 2, 328

 105

+ 71

+ 72

+ '47

+ 14

4.55

3.1

3.1

2.0

.61

The figures of the above tables show that when a large number 

of tablets are used to determine alkalinity the results are more 

nearly correct than when a few are used. This is especially noticeable in the first entries in the two tables, where the small amount 

of the alkaline solution used requires only five tablets. The error 

in each of these cases is larger than is permissible even in field 

work. In the remainder of the tests, however, the variation is not 

sufficiently great to be appreciable, especially in the weaker carbonate solutions, where it is shown that the use of a larger number 

of tablets involves a minimum error. This suggests that in connection with the field determination of carbonates it is advisable, 

wherever waters of a low alkalinity are tested, to use a large amount 

of the water in order that a large number of tablets can. be ured to 

neutralize the alkalinity, and thereby avoid the error arising from 

the variation which occurs in the single tablets.

IRR 151 05 5
66 FIELD ASSAY OF WATEE. [NO. 151. 

ESTIMATION OF ALKALINITY.

Measure 100 cubic centimeters of water to be tested into a glazed 

porcelain mortar (4 inches diameter). Add two drops methylorange indicator. Add NaHSO4 tablets till an acid reaction is 

reached. Then add some of the original water that is being tested, 

drop by drop, till an alkaline reaction is exactly reached. Measure 

the liquid in the mortar and to the amount of the reading add 1 cubic 

centimeter for the wetted interior of the dish. Th? following formula is convenient for use in making calculations of alkalinity: .

1,000 n A

 ^ equals milligram per liter of CaCO3 .

When W equals cubic centimeter of water used; 

n equals number tablets used; 

A equals value of 1 tablet in milligrams' of CaCO3 . 

Each consignment of tablets is marked with its value in equivalent 

of CaCO3 .

NORMAL AND ACID CARBONATES.

It is nearly always of value to determine the proportion of normal 

and acid carbonates in a water, for it affords a fairly good index to 

the character of the base with which the carbon dioxide is united. 

It is a generally accepted idea that the carbonates of the alkalineearth metals are, when in solution in water, in the form of bicarbonates. For the general purposes of field work it mr.y be considered 

that all bicarbonates occurring in natural waters are alkaline-earth 

carbonates and may conveniently be calculated PS CaCO3 . All 

normal carbonates, on the other hand, must be alkali carbonates,' 

conveniently calculated as Na2CO3 . This generalization is not 

uniformly true, especially in certain classes of westeri waters. It has 

been plainly shown, by the work of Messrs. Frank K. Cameron and 

Lyman J. Briggs, of the Bureau of Soils, United States Department 

of Agriculture, that there is considerable complexity in the occurrence and equilibrium of carbonates and bicarbonates in waters. 

There are, however, few practical water problems occurring outside 

of the alkali-desert regions in which the interpretation of bicarbonates as alkaline-earth carbonates and normal carbonates as alkali 

carbonates would lead to erroneous results. The f Q,ld men of the 

United States Geological Survey are therefore instructed to report 

bicarbonates as CaCO3 and normal carbonates as Na2CO3 , in the 

absence of data which will allow of other interpretations.

The method of determining carbonates and bicarbonates in aqueous 

solution is discussed by Mr. Frank K. Cameron, chemist of the Bureau 

of Soils, in Bulletin No. 18 of the United States Department of Agriculture, Bureau of Soils, pages 77-89. The method depends upon the
LEIGHTON.] HAKDNESS. 67

fact that while phenolphthalein reacts with the normal carbonates of 

the alkali and alkaline-earth metals and not with the bicarbonates, 

methyl orange reacts with either. The water under investigation 

is titrated with a standard solution of potassium acid sulphate, 

using phenolphthalein as an indicator, the first end point being the 

complete disappearance of the red color. Methyl orange is then 

added to the solution, and the titration is continued with the same 

standard until a pink acid reaction is obtained. The amount of 

standard solution used to reach the first end point is a measure of 

the amount of normal carbonates, while the total amount u?ed in 

securing both end points, less twice that for the first end poirt, is a 

measure of the bicarbonates.

The reaction taking place before and up to the total neut^alization of the phenolphthalein is a conversion of carbonates into bicarbonates and can probably be expressed as follows:

2KHSO4+2Na2CO3 =Na2SO4+K2SO4+2NaHCO3 

or

2KHSO4+2MgCO3 =MgSO4+K2SO4+Mg(HCO3 ) 2.

The neutralization of bicarbonates probably takes place in this 

manner:

2KHSO4+2NaHCO3 =Na2SO4+K2SO4+2H2Q+2CO2 

or

2KHSO4+Mg(HCO8 ) 2 =MgSO4+K2SO4+2H2O+2COa .

It is evident that when the end point with phenolphthalein has 

been reached there remains as a product of the first reaction, ir addition to the bicarbonates originally present, an amount of bicarbonates equal in reacting power to the reaction shown by the phenolphthalein. In other words, double the amount of potassium acid 

sulphate required to convert the carbonates to bicarbonates, and so 

destroy the color of the phenolphthalein, is necessary to completely 

neutralize the normal carbonates as indicated by methyl orange. 

This must be taken into consideration in computing the results from 

the titration.

Inasmuch as the reactions taking place when sodium acid sulphate 

is used must be similar to those with the use of potassium acid sulphate, there is no reason to believe that the tablets now in use in this 

division may not be substituted for the standard solution suggested by. 

Mr. Cameron. Experiments have been made to determine the accuracy of the results obtainable and are discussed in the following 

paragraphs.

An unknown amount of thoroughly fused Kahlbaum's eodium 

bicarbonate was dissolved in distilled water that had previously been 

boiled to drive out carbonic acid. Twenty-five cubic centimeters of
68 FIELD ASSAY OF WATEE. [NO. 151.

»

this solution, which should contain only sodium carbonate, was tested 

by adding phenolphthalein, triturating and dissolving standard tablets of sodium acid sulphate till decolorized, adding methyl orange, 

and continuing the trituration until the methyl-orange end point was 

reached. Another equal portion of the solution was tested by adding 

methyl orange alone and dissolving tablets until the end point was 

reached. The results in the two cases were as follows:

1. Necessary for phenolphthalein end point________________ 9 tablets. 

Excess necessary for methyl-orange end point____________ 9 tablets.

2. Total necessary for methyl-orange end point______________ 18 tablets.

Two solutions were then made, one similar to the first, of sodium 

carbonate in boiled distilled water, the other of supposedly pure 

Kahlbaum's sodium bicarbonate in distilled water, also boiled. These 

were tested by solution of tablets, using first phenolphthalein and 

then methyl orange as an indicator, as in the first case.

Sodium carbonate solution ____________ _____ 25 cubic centimeters.

Necessary for phenolphthalein end point________ 27 tablets.

Necessary excess for methyl-orange end point____ 27 tablets. 

Sodium bicarbonate solution ________________ 2" cubic centimeters.

Necessary for phenolphthalein end point_________ 15 tablets.

Necessary excess for methyl-orange end point-_-_ 57 tablets.

It is evident that the solution of bicarbonate was impure, 30 tablets 

out of a total of 72 being required for the neutralization of the normal 

carbonate. A mixture of these two solutions wae then made, as 

follows:

Cubic centimeters.

Sodium carbonate solution____________________________ 100 

Solution containing bicarbonate____________________________ 100 

Distilled water (boiled)_________________________________ 200

It is evident that the number of tablets required by this solution, if 

the method is reliable, will be equal to one-fourth of the sum of all 

the tablets used to neutralize the two original solutior s, 25 cubic centimeters being taken in each case. This should be true, not only of 

the whole determination, but of each part. Tests made of the mixture resulted as follows:

Necessary for phenolphthalein end point_________________ 10i tablets.' 

Necessary excess for methyl-orange end point___________ __ 21 tablets.

Inspection of these figures and comparison with those preceding 

indicate that, in so far as it is possible to judge unde^ the conditions, 

the method is accurate and reliable.

To make the determination, measure a convenient quantity of the 

water to be tested into a porcelain mortar and add 4 drops of 

phenolphthalein (1 per cent). Triturate the standard NaHSO4 tablets in the mortar, one at a time, until the color disappears. Note the
MIGHTON.] HARDNESS. 69

number of tablets and then add 4 drops of methyl orange (1 per cent) . 

Continue the titration with the tablets until the orange color cf the 

solution changes to a faint pink. Then note the total number of' 

tablets used in both titrations. The equivalent of the sodium acid-j 

sulphate tablets is usually given in terms of calcium carbonate. 

Therefore the amount of bicarbonates in the water may be calcuated directly from this valuation. In order to calculate the normal 

carbonates as Na2CO3 , it will be necessary to multiply the valuation 

of the sodium-sulphate tablets given by 1.06, the conversion factor of 

^aCO3 to Na2CO3 .

For computation of the normal carbonates in parts per million, 

double the number of tablets used for the decolorization of phenolnhthalein, multiply by the equivalent of each tablet in milligrams 

Na2CO3. Then multiply this product by 1,000 and divide the whole by 

^he number of cubic centimeters of the sample tested. To find bicar- 

'xmates in parts per million, subtract from the total number of tablets 

 ised in the two titrations twice the number required for the phenolohthalein end point and multiply this difference by the equivalent of 

3ach tablet in terms of calcium carbonate. Then multiply this prodMct by 1,000 and divide by the number of cubic centimeters of water 

^ested.

For the convenient expression of the above in formulas, assuire the 

following symbols :

A equivalent of NaHSO4 tablets in terms of milligrams of Cr.CO3 . 

B= equivalent of NaHSO4 tablets in terms of milligrams of Na2CO3 .

The conversion factor being 1.06, we have

JL wO

n = number of tablets used to reach first or phenolphthalein end point." 

AT = number of tablets used to reach second or methyl-orange end point. 

'V= amount in cubic centimeters of water tested.

Then for the determination of normal carbonates we have the formula

2,OOOnB,-

W 

ind for the determination of bicarbonates

l,000(N-2n)A . 

W

The results of the two above equations will be the expression of parts 

~>er million.

SULPHATES^

Water generally contains either one or more of the sulphates of 

sodium, potassium, calcium, magnesium, and iron. If present in 

'irinute amounts the effect of any or all of them is negligible, b^it if
70 FIELD ASSAY OF WATEK. [NO. 151.

they appear in large proportions they do damage in every branch of 

science or industry in which it is necessary to use y^ater. Calcium, 

magnesium, and iron sulphates damage boilers, textiles, soaps, malt 

liquors, paper, and many other manufactured products, while they 

render water undesirable for domestic purposes. The sulphates of 

sodium and potassium are troublesome in boilers, and damage crops 

when water containing large amounts is used fo~ irrigation. A 

knowledge of the amount of sulphates in a water is of great importance.

The determination of sulphates, as it is usually performed in the 

laboratory, is a slow, laborious, and expensive process. A field 

method has, however, been devised by which the sulphates can be 

determined in a few minutes and with a degree of accuracy sufficient 

for all practical purposes. The determination involves the use of 

the Jackson turbidimeter, described on previous pages. In the following paragraphs the determination of sulphates is described by 

the originator of the method, Mr. Daniel D. Jackson:

DETERMINATION BY TUBBIDIMETEB.

Knowledge of the amount of sulphates in a water to be used for industrial 

purposes is especially important. The scale which is most troublesome to remove 

from boilers is produced by the precipitation of sulphate of lime. If the amount 

of sulphate is considerable the determination of lime may be made by the 

turbidimeter with a fair degree of accuracy. The method is as follows :

To 100 cubic centimeters of water to be tested add 1 cubic centimeter of hydrochloric acid (1-1) and 1 gram of solid barium-chloride crystals. If the amount 

of sulphate is low, 200 or 300 cubic centimeters of water must be treated in 

order to fill the longer tube employed. In this case add 1 cubic centimeter of 

acid and 1 gram of barium chloride for each 100 cubic centimeters of water 

taken.

ohould bo 'froc[uontlr..ahalion. It is best to employ a bottle fgp <v 1 

Treating the water in the cold with solid barium chloride V' K^jA^* ^wn "h 

sulphate to be precipitated in a finely divided state, and \y "Cr ,, & " T 4 

may then be read by either the candle or the electric tuX £ £**), <2K +r&

In the lower part of the tube the end point is ta> £$' -K> $ ^ 

light disappears. This is a higher reading \\y £** ^V j^O ~ -* 

cross disappears. Higher up in the tube ther*'^© /\Q^ & vV^ *V^* « *v 

end point is the disappearance of the sh" ^ -. ^^ -\*>* *V' 'V^'x®'^ - 

is obtained, remove the glass tube and -SQ^ ^£ -vV £»^* * ® >^ A ^e 

bottom of the meniscus in reading^ » * ^ ^* 6» *i ^5* *^ -'^ytag 

table to obtain the parts per milK £**$' V* K»® ft^X ^* ijl>esentThe readings of these inst' ^.p ^0 * > v^. *Cr * ^^" "t^ ^tent affected 

by the amount of light us^" $> Q> 'x^- -X> O >** -Cw ^nis respect

little or no error in tJ" v \®a.® ^ nations in the color

of different natura^ £*~<f>V * "^'o°^ ^T* XVV ?vy *^ the fact that the end

point is not to ' ^V "yj j^- .^^a *Q^«a «.Cr ^ amount of light cut out, 

but to the cc^^a Ov^1 *C^ *O^* *V, '^t by the particles in suspension. It '#*> 4^> . **.^iS? ^* "0$. ft^* xttion of disks, even of highly .colored *"' ^V eip*'^P' V"1" A*^. Q*V, the end point.
LEIGHTON.] HAKDNESS. 71

In using the electric turbidimeter, if the image becomes perceptibly dim the 

battery is replaced by a fresh one, but if the analyst is careful to keep the light. 

turned off except when actually making readings the batteries will last for a considerable period of time. Fresh electric bulbs and batteries may be obtained 

from the Howard Electric Novelty Company, 221-227 Canal street, New York 

City, or 183 Lake street, Chicago. If any parts of the instrument are lost or 

broken they may be replaced by Baker & Fox, 83 Schermerhorn street, Brooklyn, N. Y.

Table for converting readings in depths by the turbidimeter into parts per million or grains per gallon of sulpfiate.

Beading in 

centimeters.

i.o

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

Parts per 

million,

. S03.

522

478

442

410

383

359

338

319

302

287

273

261

250

239

230

221

213

205

198

191

185

179

173

168

164

159

155

151

147

Grains per 

United 

States gallon, SO3.

30.5

28.0

25.8

24.0

22.4

21.0

19.8

18.6

17.7

16.8

16.0

15.3

14.6

14.0

13.5

12.9

12.4

12.0

11.6

11.2

10.8

10.5,

10.1

9.8

9.6

9.3

9.1

8.8

8.6

Beading in 

centimeters.

3.9

4.0

4.1

4.2

4.3

4.4

, 4.5

4.6

4.7

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

5.9

6.0

6.1

6.2

6.3

6.4

6.5

6.6

6.7

Parts per 

million,

S03.

144

140

137

133

131

128

125

122

119

117

115

113

110

108

106

104

103

101

99

97

96

94

93

91

90

88

87

86

84

Grains per 

United 

States galktft, SO3 .

8.4

8.2

8.0

7.8

7.7

7.5

7.3

7.1

7.0

6.8

6.7

6.6

6.4

6.3

6.2

6.0

6.0

5.9

5.8

5.7

5.6

5.5

5.4

5.3

5.2

5.1

5.1

5.0

4.9
72 FIELD ASSAY OF WATEE. [NO. 151.

Table for converting readings in depths "by tJie tur'bldimeter into parts per million or grains per gallon of sulpJiate Continued.

Reading in 

centimeters.

6.8

6.9

7.0

7.1

7.2

7.3

7.4

7.5

7.6

7.7

7.8

7.9

8.0

8.1

8.2

8.3

8.5

8.6

8.7

8.8

9.0

9.1

9.3

9.5

9.7

9.8

10.0

10.2

10.4

10.6

10.8

11.0

11.2

11.4

11.6

11.8

12.0

Parts per 

million, 

S03.

83

82

81

80

79

78

77

76

75

74

73

72

71

70

69

68

67

66

65

64

63

62

61

60

59

58

57

56

55

54

53

52

51

50

49

48

47

Grains per 

United 

States gallon, SO3.

4.9

4.8

4.8

4.7

4.7

4.6

4.5

4.4

4.4

4.3

4.3

4.2

4.2

4.1

4.0

4.0

3.9

3.9

3.8

3.8

3.7

3.7

3.6

3.6

3.5

3.4

3.3

3.3

3.2

3.2

3.1

3.1

3.0

3.0

2.9

2.8

2.7

Reading in 

centimeters. .

12.4

12.6

12.8.

13.0

13.5

14.0

14.5

15.0

15.5

16.0

16.5

17.0

17.5

18.0

18.5

19.0

20.0

21.0

22.0

22.5

23.0

24.0

25.0

26.5

28.0

29.0

31.0

33.0

35.0

 37.5

40.0

43.0

46.5

50.0

55.5

62.0

68.0

Parts per 

million, 

S03.

46

45

44

43

42

41

39

38

37

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

15

14

13

 12

11

10

9

Grains per 

United 

States gallon, SO3.

2.7

2.6

2.6

2.5

2.5

2.4

2.3

2.3

2.2

2.1

2.0

2.0

1.9

1.9

1.8

1.8

1.7

1.7

1.6

1.6

1.5

1.4

1.3

1.3

1.2

1.2

1.1

1.1

1.0

1.0

.9.

.9

.8

.7

.6

.6

.5
LEIGHTON.] HAEDNESS. 73 

PRECAUTIONS IN USE OF INSTRUMENT

1. The same care should be taken as in measuring turbidity to have the turbidiineter in good running order. 2. Always shake the solution until all the 

barium chloride is dissolved. Otherwise a flaky precipitate may be obtained. 

?>. Since the barium-sulphate precipitate is very heavy, the solution should be 

mixed frequently by pouring and shaking while readings ar§ being made. 4. 

Only sufficient hydrochloric acid should be added to make the water acid.

 &- 

CALCIUM.

The determination of calcium is made by means of the turbidimeter, the method being similar to that described in the chapter on 

sulphates. It is the latest, and therefore the least known, of all the 

determinations here described. While the results which have been 

reached by this method appear to be satisfactory, no particular plan 

has yet been offered to determine certain necessary facts with reference to the behavior of precipitated calcium oxalate. The method 

depends upon the turbidity produced by the precipitation of. calcium 

oxalate upon the addition of ammonium oxalate to the water under 

investigation. Whether or not the variations which occur in the 

character of this precipitate under different conditions are sufficient 

to affect appreciably the degree of turbidity produced is a matter 

which is yet to receive attention.

The test is made in the following manner: To 100 cubic centimeters 

of the water to be tested add a. few drops of ammonium hydroxide, 

NH4OH. The amount added should be barely sufficient to impart to 

the water a perceptible ammoniacal odor. Then add crystals of ammonium oxalate. The amount of crystals to be added depends, of 

course, upon the amount of lime in the water. As this is yet undetermined, care should be taken to add an excess of ammonium oxalate. 

Mix thoroughly and allow the solution to stand for ten or fifteen 

minutes. Then determine the turbidity with the Jackson turbidiineter precisely as described in previous pages in the case of sulphates, 

and state the amount of calcium according to the table given below.

The treatment above described will precipitate materials oth^r than 

calcium, but they are usually in so small a proportion in natural 

waters that they do not often give trouble. The most frequent complication arises from the precipitation of magnesium on the addition 

of ammonia. If the precipitate is sufficient in amount to materially 

affect the degree of turbidity it should be filtered before the addition 

of ainmonium oxalate.

*It has been found by two or three hundred 

field tests and by laboratory experimentation 

sinoe this Bulletin was published that this 

method for calcium is not reliable,.the results frequently being as much as 50$ from the 

correct ones. This trouble is due to variation 

in the size of the calcium oxalate crystals under different conditions of concentration, temp-
74 FIELD ASSAY OF WATER. [NO. 151.

The table given below for the determination of calcium is less satisfactory than that for sulphates, and it will probably be found that 

corrections must be made as future experience dictates.

Table for determining calcium witJi Jackson's tur'bic'imeter.

Reading in centimeters.

1.0

1.1

1.2

1.8

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

Parts per 

million.

1,150

1,000

890

795

715

650

595

550

505

470

435

410

380

360

340

320

305

288

274

261

248

238

238

218

209

200

194

186

179

173

Beading in centimeters.

4.0

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

5. 7

5.8

5.9

6.0

6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

Parts per 

million.

167

162

156

151

146

142

137

133

130

126

123

119

116

113

110

107

105

103

100

98

96

94

92

90

88

87

85

84

82

81

Reading in centimeters.

7.0

7.1

7.2

7.3

7.4

7.5

7.6

7.7

7.8

7.9

8.0

8.1

8.2

8.3

8.4

 8.5

8.6

8.7

8.8

8.9

9.0

9.1

9.2

9.3

9.4

9.5

9.6

9.7

9.8

9.9

Parts per 

million.

80

78

77

76

' 74

73

72

71

70

69

68

67

66

65

64

64

63

62

61

60

60

59

58

57

57

56

55

55

54

54

Reading in centimeters.

10.0

10.2

10.4

1C. 6

1C. 8

11.0

11.2

11.4

11.7

11.9

12.2

IS. 4

13.7

13.0

13.3

13.7

14.0

14,4

14.8

15.3

15.7

16.2

16.7

17.3

17.9

18.5

19.2

20.0

21.7

22.7

Parts per 

million.

53

52

51

50

49

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

32

31

30

29

28

27

26

24

23

INSTRUMENTS AND REAGENTS.

The field case (see PI. IV) contains the instruments and reagents 

described below:

1. A Berkfeld army filter for removing suspended matter from 

water under investigation. The porous stone in this filter should
U. S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 151 PL. IV

UNITED STATES GEOLOGICAL SURVEY FIELD CASE.
LEIGHTON.] INSTETJMBNTS AND EEAGENTS. 75

be removed from the tube frequently and thoroughly cleansed with 

the small stiff brush provided for this purpose. If it is desired to 

secure sterile water, or if the only water available is knov^n to be 

polluted and a supply for drinking purposes is desired, the filter stone 

should be boiled or baked frequently. Watch the filter stone closely 

for cracks and imperfections. When water is pumped through the 

filter, care should be taken that the suction end does not rest on 

sand or mud; such materials, if drawn into the buckets of tH pump, 

are troublesome and materially shorten the term of usefulness of the 

filter.

2. One or more leather cases containing tubes of reagent tablets. 

The equivalent of each tablet of the various reagents should be noted 

on a slip pasted upon the inside of the case.

The tablets are packed in tubes to prevent mechanical agitation. 

This is highly important, because if the tablets are loosely packed 

a loss of active chemical reagent is inevitable. Tablets which show 

signs of extraordinary wear should be rejected. In using a tube 

one of the cork stoppers should be removed and the tablets poured 

out as needed. When the end point is reached the cork should be 

replaced and the stoppers in the opposite end of the tube should be 

pushed through the lumen until the tablets remaining in the tube are 

projected against the opposite stopper, thus holding them securely.

Sodium-oleate tablets are packed in unmarked transparent glass 

tubes. Two grades of silver-nitrate tablets are usually issued. The 

tubes containing tablets of the higher equivalent have a crops etched 

on the glass, while those with the lower equivalent are etched with 

a single transverse line. The sodium acid-sulphate tablets are packed 

in transparent glass tubes, upon each of which is etched the symbol 

NaHSO4.

3. One case containing four aluminum tubes for natural color and 

for iron determinations. There will also be provided brown-glass 

disks for the color determination or red-glass ones for the iron, or 

both. The equivalent of each disk in terms of parts per irillion is 

engraved on the aluminum rim.

4. One Jackson candle or electric turbidimeter with two graduated 

cylinders for same. An extra electric bulb, a ground-glass1 disk, a 

brass cross disk, a standard English candle, and a dry battery will be 

provided with each turbidimeter. The field observer should not use 

any dry battery which has been in his possession over sixty days, 

irrespective of the intensity of the light produced by it. Candles 

other than the standard English sperm should not be used.

The candle turbidimeter should be used in preference to the electric 

whenever possible, as the former is the more steady instrument and 

insures uniformity of results. If, however, it is necessary to make
76 FIELD ASSAY OF WATER. " [NO. 151.

determinations in exposed places when the wind is blowing, the electric turbidimeter must be used, as the slightest flickering of the candle 

flame will introduce errors in the determinations. Whenever possible, 

water samples should be carried to a convenient shelter and assayed.

5. Seven special dropping bottles containing the following reagents: Concentrated nitric acid (HNX)3 ) ; concentrated hydrochloric^ 

acid (HC1) ; concentrated ammonium hydroxide (NH4OH) ; two per 

cent solution of potassium sulphocyanide (KCNS) ; five per cent solution of potassium chromate (K2OO4 ) ; one per cent solution of 

phenolphthalein; one-tenth per cent solution of methyl orange.

Care should be taken to close the stoppers in these dropping bottles 

where they are packed in the cases.

6. Two salt-mouth bottles containing pure crystals of barium 

chloride and ammonium oxalate.

All bottles containing chemicals have etched labels, except the 

indicators, the colors and odors of which are sufficiert for identification.

7. One heavily glazed porcelain mortar and pestle.

8. One round-bottom glass bottle, with glass pestle, for hardness 

determination.

9. One small horn spoon for handling crystals noted in section 6.

10. One 5 c. c. pipette in case for general use in measuring small 

amounts of liquid.

11. One centigrade thermometer in brass case.

12. One loose-leaf notebook. This notebook is made up of printed 

cards, with every alternate leaf a blank.

*Instead of carrying concentrated hydrochlori 

aoid in the oase it is advisable to carry 1-1 ao 

The concentrated acid corrodes the inside of the 

case "badly and by its fumes contaminates the pot 

sium chromate indicator used in the chlorine det 

mination. This is not so likely to happen if di 

ted acid is carried.
INDEX.

Page.

Agricultural Department, field assay of water by........................... 1&

Alkalinity, determination of............... 66

discussion of............................ 62-63

Analysis, methods of..................... 9,13-15

Analysis, commercial, character of ........ 9

Analysis, sanitary, requirements of .7...... 10

Assay, definition of......................... 17

Battery of turbidimeter, tests of............ 29-32

Bicarbonates, determination of............ 66-69

Boiler water, quality of ................. 13-14,62

Bulbs, electric-light, for tnrbidimeter, tests

of............................... 33

Calcium, determination of................. 73-74

Calcium carbonate, effect of ............... 62-63

Candle turbidimeter, description of........ 27

view of................................. 26

Carbonates, determination of .............. 63-69

Chemicals, list of, in Survey outfit......... 74-76

Chlorine, determination of, ia field ..... 48,50-56

determination of, in laboratory........ 47-50

occurrence of........................... 47-49

Chlorine maps, construction and use of.... 50

Clarke, P. W., on water analysis ........... 14

Color of water, definition of................ 41-42

determination of....................... 44-46

' tubes and disks for, plate showing ............................... 46

standards of............................ 42-44

Conservatism, abuse of..................... 10

Crenothrix, growth of...................... 45

Electric turbidimeter, description of....... 27-28

view of................................. 28

Filtration, determination of turbidity by.. 19 

Fuller, George W., on nitrogen determination............................. 11-13

Geological Survey, field case of, description

of......................:.. 16-17,74-76

field case of, view of.................... 74

tablet case, description of .............. 75

view of............................. 50

Gila River, Arizona, turbidity of........... 21-22

Glass plate for turbidimeter, tests of....... 33

Hardening constituents, classes of......... 62-63

Hardness, permanent, definition of........ 62

determination of....................... 70-74

Hardness, temporary, definition of......... 62

determination of....................... 63-69

Hardness, total, definition of............... 56-61

determination of.................... 56-57,61

Hazen, Alien, turbidity rod of ............. 23

Hypothetical combinations, unreliability

of....................................... 14

Incrusting constituents, determination of,

accuracy of.....:............... 13-14

Instruments, list of, in Survey outfit....... 74-76

Page. 

Iron in water, determination of............ 45-47

effects of................................ 45

Isochlors, determination of ................ 50

Jackson, D. D., on chlorides ............... 47-50

on sulphates............................ 70-73

on turbidity............................ 22

Jackson's turbidimeters, description of..... 26-28

tests of ................................. 29-41

views of..............................:. 26,28

Macomb, 111., well at, water of, analyses of. 14 

Massachusetts, water survey in ............ 15

Nitrites, determination of, futility o*. in

sanitary analysis............... 11-13

Ohio, water survey in...................... 15

Oxygen, relation of nitrites and ........... 13

Platinum-cobalt method of color determination .......................... 42-43

modification of, in field ................ 43-44

use of................................... 44-45

Reagents, list of, in Survey outfit.......... 74-76

Richards, Ellen H., field assay outfit of .... 16

Sewage, analysis of, interpretation of...... 11-13

Silica, standard solution of, preparation of. 33-34 

Silver-nitrate tablets, manufacture and use

of......................... 50-51,55-56

tests of ................................. 51-55

Soap test for hardness, use of............... 56

Sodium acid sulphate tablets, tests of...... 63-65

use of................................... 66

Sodium carbonate, effect of................ 62-63

Sodium-oleate tablets, tests of.............. 57-61

use pf................................... 57,61

Sulphates, determination of................ 70-73

Tablet case, description of ................. 75

view of................................. 50

Turbidimeters, Jackson's, description of... 26-28 

testsof.................................. 29-41

use of............................. 27-28,70-71

views of ................................ 26,28

Turbidity, curves of, figures showing ...... 38,39

definition of............................ 18

determination of, methods of .......... 18-41

Geological Survey rod for detenrinationof................................ 23-26

relation of volume of suspended matter

and............................. 19-20

relation of weight of suspended matter and......................... 20-22

standard of....................... 22-23,33-40

Turbidity coefficient, definition of......... 19-20

Water, analysis of, interpretations of ...... 13-15

methods of............................. 9-10

Water surveys, chemical, slowness of ...... 15-16

Water surveys, field, speed of .............. 16

Weston, R. S., on turbidity................. 19-20

Whipple, G. C., on turbidity scale......... 22-23

77

o
PUBLICATIONS OF UNITED STATES GEOLOGICAL SURVEY.

[Water-Supply Paper No. 151.]

The serial publications of the United States Geological Survey consist of (1) Annual 

Eeports, (2) Monographs, (3) Professional Papers, (4) Bulletins, (5) Mireral Besources, (6) Water-Supply and Irrigation Papers, (7) Topographic Atlas of United 

States folios and separate sheets thereof, (8) Geologic Atlas of United States folios 

thereof. The classes numbered 2, 7, and 8 are sold at cost of publication; the others 

are distributed free. A circular giving complete lists may be had on application.

Most of the above publications maybe obtained or consulted in the following ways:

1. A limited number are delivered to the Director of the Survey, from wl om they 

may be obtained, free of charge (except classes 2, 7, and 8), on application.

2. A certain number are allotted to every member of Congress, from wl om they 

may be obtained, free of charge, on application.

3. Other copies are deposited with the Superintendent of Documents, Washington, 

D. C., from whom they may be had at practically cost.

4. Copies of all Government publications are furnished to the principal public 

libraries in the large cities throughout the United States, where they may be consulted by those interested.

The Professional Papers, Bulletins, and Water-Supply Papers treat of a variety of 

subjects, and the total number issued is large. They have therefore been classified 

into the following series: A, Economic geology; B, Descriptive geology; C, Systematic geology and paleontology; D, Petrography and mineralogy; E, Chemistry and 

physics; F, Geography; G, Miscellaneous; H, Forestry; I, Irrigation; J, Water storage; K, Pumping water; L, Quality of water; M, General hydrographic investigations; N, Water power; O, Underground waters; P, Hydrographic progress reports. 

This paper is the eleventh in Series L, the complete list of which follows. 

(PP=Professional Paper; B=Bulletin; WS=Water-Supply Paper.)

SERIES L QUALITY OP WATER.

WS 3. Sewage irrigation, by G. W. Rafter. 1897. 100 pp., 4 pis. (Out of stock.)

WS 22. Sewage irrigation, Pt. II, by G. W. Rafter. 1899. 100pp., 7 pis. (Out of stock.)

WS 72. Sewage pollution near New York City, by M. O. Leighton. 1902. 75 pp., 8 pis.

WS 76. Flow of rivers near New York City, by H. A. Pressey. 1903. 108 pp , 13 pis.

WS 79. Normal and polluted waters in northeastern United States, by M. O. Leighton. 1903. 192 pp.,

15 pis. 

WS 103. Review of the laws forbidding pollution of inland waters in the United States, by E. B.

Goodell. 1904. 120 pp. 

WS 108. Quality of water in the Susquehanna River drainage basin, by M. O. Leighton, with an

introductory chapter on physiographic features, by G. B. Hollister. 1904. 76 p">., 4 pis. 

WS113. Strawboard and oil wastes, by R. L. Sackett and Isaiah Bowman. 1905. 52 pp., 4 pis. 

WS 121. Preliminary report on the pollution of Lake Champlain, by M. O. Leighton. 1905. 119 pp.,

13 pis. 

WS 144. The normal distribution of chlorine in the natural waters of New York and Ne"F England,

by D. D. Jackson. 1905. 31pp., 5 pig. 

WS 151. Field assay of water, by M. O. Leighton. 1905. 77 pp., 4 pis.

Correspondence should be addressed to

THE DIRECTOR,

UNITED STATES GEOLOGICAL, SURVEY,

WASHINGTOIT, D. C. 

OCTOBER, 1905.

I
LIBRARY CATALOGUE SLIPS.

[Mount each slip upon a separate card, placing the subject at the top of the 

second slip. The name of the series should not be repeated on the series 

card, but the additional numbers should be added, as received, to the first 

entry.] v

Leighton, Marshall O[ra] 1874-

. . . Field assay of water, by Marshall O. Leighton. 

Washington, Gov't print, off., 1905.

77, iii p. illus., IVpl., diagrs. 23om. (U. S. Geological survey. Watersupply and irrigation paper no. 151)

Subject series: L, Quality of water, 11.

1. Water analysis.

Leighton, Marshall O[ra] 1874-

*s ... Field assay of water, by Marshall O. Leigh ton. 

f Washington, Gov't print, off., 1905.

9£

77, iii p. illus., IV pi., diagrs. 23cm. (U. S. Geological survey. Watersupply and irrigation paper no. 151)

Subject series: L; Quality of water, 11.

1. Water analysis.-

U. S. Geological survey. 

g Water-supply and irrigation papers. 

I no. 151. Leighton, M. O. Field assay of water. 1905.

£ U.S. Dept. of the Interior.

1 see also

| U. S. Geological survey.

IRE 151 05 6 Hi
RTD-MLF 

Correct ions 

Pa6e i§* Jjpo J§: In place of the words "and

allowed to stand 10 minutes, * read and comparison made immediatelj.

Page 61, Estimation ot Hardness: If the total hard 

ness of the water exceeds 1.^0 parts per million, 

this method has the same inaccuracies as the ordinary laboratory method in which a solution of 

soap is used.

Page 70, line SO; In place of "The mixture should 

He "allowed to stand for 10 minutes and in this 

time it should be frequently shaken,* read The 

mixture should be shaken until the barium ohloriqe crystals are completely dlssolyed, for if 

the mixture^ is allowed to stancf without" 'scaling 

jftie Gonoentr'aTeTliol'ution of "barium chloride 'in 

the bottom causes preclpftafion oj the

sulphate in ft jlaky form instead of jffie semipolloldal condition that is deslr^U

Page 75, Calcium: It has been found by 2 or 5 hundrei 

HeTS tests and by laboratory experimentation 

since this Bulletin was published that this method for calcium is not reliable, the results frequently being as much as 50$ from the correct one 

This trouble is due to variation in the size of 

the calcium oxalate crystals under different conx ditions of concentration, temperature and the 

presence of other salts.

Page 76, line g: Instead of carrying concentrated 

hydrochloric acid in the case it is advisable 

to carry 1-1 acid. The concentrated acid corrodes the inside of the case badly and by its 

fumes contaminates the potassium chroxr ate indicator used in the chlorine determination. This is 

not so likely to happen if diluted acid is used.

It is preferable to make determinations with the 

turbidimeter in the dark, or at any r^*4 no^* 

direct sunlight, because the outside light ^^& 

the eye, so that lower readings than the correct 

ones are obtained. The batteries in the ©lectric 

turbidimeter will last with moderate use from 50 

to 60 days in a moderately humid climate, in aria 

regions, they dry up so fast that it is preferable 

thou h not so convenient to use the candle turfci-