ter Supplies Purification

HOUSTON^

MAIN LIBRARY-AGRICULTURE DE.I

RURAL WATER SUPPLIES AND THEIR PURIFICATION

BY

ALEXANDER CRUIKSHANK HOUSTON, M.B., D.Sc., F.R.S.ED.

Director of Water Examination^ Metropolitan Water Board

ILLUSTRATED

LONDON

JOHN BALE, SONS & DANIELSSON, LTD.

OXFORD HOUSE

i, GREAT TITCHFIELD STREET, OXFORD STREET, W.

1918

BY THE SAME AUTHOR : u STUDIES IN WATER SUPPLY."

(Messrs. MACMILLAN & Co.) 1913.

u RIVERS AS SOURCES OF WATER SUPPLY." (Messrs. JOHN BALE, SONS & DANIELSSON, LTD.) 1917.

MAIN LFBRARY-AGRICtlLTURE DEPT

THIS LITTLE BOOK IS, WITH PERMISSION,

RESPECTFULLY DEDICATED BY THE WRITER TO

SIR WILLIAM OSLER, BART., M.D., F.R.S.,' F.R.C.P.(LOND.);,

REGIUS PROFESSOR OF MEDICINE, OXFORD UNIVERSITY,

IN APPRECIATION OF

HIS INVALUABLE SERVICES TO MEDICINE, HIS HIGH LITERARY GIFTS AND HIS UNAFFECTED MANNERS AND SUNNY GENEROUS DISPOSITION ; QUALITIES WHICH ATTRACT HIS MANY FRIENDS AS FORCIBLY AS OPEN SPACES, GREEN FIELDS AND PLEASANT WATERS APPEAL TO LOVERS OF THE COUNTRY.

419832

PREFACE.

THE kindly reception given to the writer's previous books, " Studies in Water Supply " (Messrs. Macmillan and Co., 1913), and " Rivers as Sources of Water Supply " (Messrs. John Bale, Sons and Danielsson, Ltd., 1917), has led him to try and fulfil a want which has long been felt by rural dwellers.

Despite the enormous improvements in our public water supplies, not only as regards quality and quantity of water, but in respect of its availability to isolated communities, there remains a large, but scattered population, whose only source of a primary necessity of life is the utilization of rain-water, or the water from shallow wells, neigh- bouring rivers, streams, or lakes. These private isolated supplies, lying outside the direct control of Public Authorities, are frequently polluted and a source of potential danger to health. It is to be feared that in many of these cases there is a regret- table disregard of possible consequences, and although a minority of individuals remains anxious to remedy existing evils, adequate knowledge of

v.

PREFACE

how best to proceed is often lacking. Even those who are usually careless as regards water supply may soon learn wisdom, or prove amenable to friendly advice, but unfortunately their would-be advisers are themselves often at a loss what course to suggest.

The writer has always been glad to give his advice freely to professional men — for example, clergymen and doctors in the country concerned about the welfare, as regards water supply, of their parishioners and patients. In answering these appeals for help, which are often of a pressing and sometimes of a pathetic character, the writer has often felt how great the gulf is between theory and practice, how hopeless it is to attempt, within the limits of ordinary correspondence, to deal satis- factorily with so complex a subject, and how useless it is to give references to books which do not contain the exact kind of information really required.

A life-long experience of water questions has left the writer in the position of a learner, and in his spare time he has endeavoured to acquire a more practical knowledge of rural requirements. In trying to teach others, the would-be teacher speedily learns how much has to be self-learnt, but the writer's purpose will have been served, if, in this little book, he can usefully hand on to others the outcome of some of his own experiences (see p. 1 28).

vi.

PREFACE

The future of this country holds possibilities which can only be gauged by guess work. One effect of the War may be to increase enormously the number of people who like to do things well, and to decrease correspondingly the number of those who prefer to let things " slide." There has been un- questionably a great awakening, and amidst the excitement and sadness of a colossal war one sees everywhere signs of quickened interest. Beyond all doubt, in the ordinary affairs of life, there is a growing tendency to learn and work and succeed, not merely from recognition that ignorance and idleness and failure may spell disaster, but because, let psychologists explain it as they may, some influence is at work impelling people to adopt a saner outlook on life, which was not felt, or in much less degree, in pre-war days. One direction in which a change is noticeable is in the growing appreciation of the value of sanitary science, and in this connection the question of water supply will receive its full share of attention. The writer is of opinion, as already suggested, that in the future it will become, to a progressive extent, a pleasure and not a burden to do things efficiently (e.g., to take a homely illustration, cooking). So also is he optimistic enough to believe that " scamping" and ignorance in connection with water supply will largely disappear. It is true that pessimists declare that when the War is over there will be a rapid reversion to the old somewhat careless ways of

vii.

PREFACE

living. Others, however, hope and believe that the tendency will be quite the other way. Much depends on how we are taught to regard the ordinary affairs of life. Education, discipline, example, if not mere suggestion, can render our daily tasks almost pleasurably exciting. Speaking irrespective of any party the writer ventures to think that a little more imagination (the greatest gift on earth) on the part of our rulers is needed. Many hours are spent daily, and spent well, in cooking operations. Surely it is worth while to devote a few minutes, say in the morning and evening, to purifying water for domestic use.

Again, no one knows to what extent our mode of life may change. At heart we are all country- folk, and after the War there may be an unprece- dented rush for the peaceful country, stimulated, perhaps, by the standardization of houses, more equitable terms for the purchase of houses and land, war weariness, shattered nerves, reduced incomes, difficulty of soldiers reverting to town life after their experiences at the Front, successful results of allotment gardening, tariff on imported foodstuffs, improved railway facilities for the con- veyance of market produce and recognition of the value of co-operation, revived love of Nature, alarm at the falling birth-rate (for which town life is partly responsible), increasing distrust of over- centralization, simpler standards of living and dislike

VI 11.

PREFACE

of ostentation, growth of democratic (in the best sense of the word) ideas, reversion to more primi- tive (but perhaps saner) ideals, and other factors. Should these events come to pass, rural water supplies will become of enormous importance, and means of purifying contaminated water will be eagerly sought after. For it is hardly conceivable that a large, new and widely-scattered rural popula- tion can be supplied economically now (possibly not for many years to come) from the existing or even contemplated public sources of water supply. Moreover, this book will have failed in its object if it does not convince the reader that almost any water supply can be purified to any standard of safety required.

It would be a grave mistake to suppose that the writer is wavering in his allegiance to public water supplies — quite the contrary is the case — but com- plete belief in responsible control does not imply dis- belief in making the best of existing circumstances.

*

The writer feels that some words of explanation are needed to his potential readers. The actual expert will perhaps find little in these pages by way of instruction, unless, indeed, the writer's long experience as a bacteriologist and epidemiologist may here and there prove to be of some slight use. Next come those who by their capabilities and training (not necessarily technical) are admirably qualified, prospectively, if not immediately, to help

ix.

PREFACE

themselves, and others, as regards the safety of water supplies. These may possibly find this little book a useful stepping-stone to further progress. Lastly, but most importantly, come those who have grown a little rusty, those who are inexperienced but zealous to learn, and those who, whatever their limitations may appear to be, are determined to overcome all obstacles. These are the readers to whom the writer specially makes his appeal.

A moment's reflection will suggest the wide circle of country dwellers liable to be affected by non- public water supplies. The dreamy philosopher, the ascetic, the man of science, the millionaire, the sportsman, the invalid, the clergyman, the doctor, the farmer, the rich and the poor.

There is another aspect of the case which the writer feels deserves recognition.

The principles which underlie the choice and treatment of water supplies, be they public or private, are very much the same, and the writer in studying rural requirements has widened consider- ably the scope of his own knowledge of the subject of water supply generally.

Is it too much to hope then that the more fortunate and more numerous consumers of publicly controlled water supplies may find in this treatise some point of importance to stimulate their interest in a subject which may be as old as the hills, but

X.

PREFACE

which still possesses unexhausted fields of possibili- ties ? Even the partial realization of such a hope would far more than repay the writer for the time and labour he has devoted to the study of rural water supplies.

Perhaps the best years of the writer's life have been spent in the service of the Metropolitan Water Board ; his work has been rendered additionally pleasant for the reason that although primarily con- cerned with London's Water Supply, the policy of his Board has always been in the direction of improving knowledge of water supplies gener- ally. Not less grateful is the writer to the members of his staff, whose active co-operation and valuable help have been of so pleasant and intimate a character that he welcomes success more for their sakes than for his own.

Since writing these notes, the author has read in the Morning Post of November 9, 1917, a letter from Lord Sydenham, entitled " Home Settlement for Ex-Service Men."

The following extracts are of interest : —

" It has been said that few of our sailors and soldiers will wish to settle on the land, and that during the period of reconstruction after the War there will be an immense demand for labour. We cannot be certain as to what the extent and the

xi.

PREFACE

nature of the labour demanded will be. Nor can we assume that the men themselves will necessarily be willing to fall in completely with preconceived ideas. They have fought for our freedom, and saved the Empire from disaster. We must consider the effect that the War has had upon them. Their nerve-shaking experiences, and their altered outlook on life, are bound to make a certain number of them welcome the conditions of life on the land, instead of in urban surroundings. We must ensure that the necessary opportunities are provided."

"The Royal Colonial Institute has during the past two years issued and circulated some hundreds of thousands of leaflets in the endeavour to let our sailors and soldiers know what opportunities there are for them at Home and Overseas. The inquiries arising from these leaflets are extremely interesting, because they show that so far the number of men desiring to settle at home is equal to, if not greater than, that of those who wish to emigrate to the Dominions. This fact alone proves the urgent need for immediate action on the part of the Government."

In conclusion, the writer ventures to hope that this book may be of some little use in post-war settlement, so far as rural water supplies are con- cerned. (See offer of help on p. 128.)

January, 1918. A. C. HOUSTON.

xn.

CONTENTS.

The book is arranged as follows : —

The first three Chapters are devoted to the study of rain-water. All the chief methods for sterilizing and purifying waters are here dealt with in detail, and it is assumed that the reader will master their contents as the subsequent Chapters IV. and V., (well-waters, springs, rivers, brooks and lake-water) deal chiefly with generalizations.

In Chapters VI. and VII. the results of actual experiments are considered, and in Chapter VIII. a description of the apparatus required is given.

Next comes some miscellaneous information (nature of chemicals, symbols, atomic weights, weights and measures, conversions) notes on lime and chlorine, cost of chemicals, &c., which may

be useful to the non-expert reader.

• In advance of each Chapter there is a summary

of contents, and at the end a few concluding remarks.

The index is at the end of the book.

The non-expert reader should not be turned aside by the amount of technical matter necessarily included in this book. References to the concluding notes at the end of each Chapter (pp. 12, 34, 46, 56, 67, 88, 101, 113) and to Miscellaneous Information (p. 114) will simplify things considerably. See also conclud- ing remarks on p. 128.

xiii.

ILLUSTRATIONS.

PAGES

FIG. i. — Suspended matter in 0-5 c.c. of rain-water

collected from a roof in London ( x 50 diam.) 8, 9

FIG. 2. — Small conical flask ... ... ... 15

FIG. 3. — One hundred c.c. measuring cylinder ... 15

FIG. 4. — Burette ... ... ... ... 16

FIG. 5. — Burette stand ... ... ... ... 16

FIG. 6.— Small bottle ... ... ... ... 18

FIG. 7. — Cheap form of dispenser's hand balance ... 20

FIG. 8. — A more delicate balance ... ... ... 20

FIG. 9. — Suspended matter in 0-5 c.c. of a river water

during a flood (x 50 diam.) ... ... 60,6 1

FIG. 10. — (a) Anabsena x 400 ; (b) Eudorina x 400 ; (c) Sponge growth after treatment with acid to show spicules X 50 ... ... ...66,67

FIG. ii. — (a) Stephanodiscus x 400; (b) Glenodinium X 150 ; (c) Pandorina x 400 ; (d) Synura x 400 ... ... ... ... ...66,67

FIG. 12. — Mixing pan ... ... ... ... 103

FIG. 13. — Floating-arm method of drawing off clear

water ... ... ... ... ... 103

FIG. 14. — Screw clip ... ... ... ... 103

FIG. 15. — Rubber bung with distal connections ... 104

FIG. 16. — Cork floater at proximal end of rubber tube... 105

FIG. 17. — Rigid outlet method of drawing off clear water 106

FIG. 18. — Small sand and gravel filter ... ... 108

FIG. 19. — Plan of rain-water tank (Kershaw)... ... 125

The writer is greatly indebted to Mr. Kershaw for per- mission to quote his views on the utilisation of rain-water (with plan of rain-water tank, p. 125), and to Messrs. Baird and Tatlock (scientific instrument makers, laboratory fitters, chemical dealers, &c.), 14, Cross Street, Hatton Garden, E.G. i, for the loan of blocks in connection with Figures 2, 4, 5, 6, 7, 8, 12, and 14.

xv.

RURAL WATER SUPPLIES AND THEIR PURIFICATION.

CHAPTER I. RAIN -WATER.1

First Report (1916) of the Committee formed (1912) for the Investigation of Atmospheric Pollution — Composition of normal air — Gaseous and solid impurities of the atmo- sphere— Results of analyses of rain-water — Questions of taste — Physical appearances and chemical composition of rain-water — Health considerations — Sterilization and purification of rain-water — Concluding remarks (p. 12).

AS a result of a conference of delegates of municipal authorities and others held in con- nection with the Smoke Abatement Exhibition in 1912, a Committee was formed for the Investigation of Atmospheric Pollution. The Committee's first

1 The writer feels that he is justified in placing this source of water supply first, because it may be the sole refuge of dwellers in certain rural areas where there is neither a public water supply nor reasonable hope of providing at a non- prohibitive cost a private supply (superficial or deep). To this must be added the fact that a rain-water supply, although often impure and most difficult to render palatable, is prac- tically free from the possibility of human fa3cal pollution. (Set, however, qualifying remarks on p. 10.) Most of our

1

WATER SUX'PI.IES AND THEIR PURIFICATION

report1 was published in 1916 and contains a great deal of useful information, bearing directly or in- directly, on the quality of rain-water.

The following table, taken from the report, shows the composition of normal air : —

TABLE I.— COMPOSITION OF NORMAL AIR.

Oxygen 20-94

Nitrogen 78-09

Argon 0-94

Carbon dioxide 0-03

Helium, krypton, neon, &c traces

lOO'OO

Unfortunately, falling rain is not only affected by the presence of these gases, but also by the gaseous and solid pollutions of the atmosphere resulting from animal and vegetable life and the manifold operations of mankind.

Coastguard stations have rain-water supplies for domestic use. From a British point of view, one of the most interest- ing water supplies in the world is that of Gibraltar. For non-potable purposes (e.g., flushing) a brackish water is used. There is also an emergency distilling plant for furnish- ing, if required, a potable supply from sea-water, but the principal drinking supply is from the rain, which apparently is partly collected from a cemented rock surface, and also from corrugated iron sheets laid on sandy slopes. The rain falling on these surfaces is led into underground storage reservoirs, the locality of which is, of course, necessarily kept secret. (See " Water Supply," by Dr. W. P. Mason. John Wiley and Sons.) Information as regards the Bermuda rain-water supply will be found on p. 124.

1 Lancet, February 26, 1916. Offices of Committee, 47, Victoria Street, Westminster, London, S.W.

RAIN-WATER

The Committee give the results of the analysis of the solid matters intercepted by the ventilator filters of a large institution in London :—

TABLE II. — ANALYSIS OF SOLID MATTERS FROM VENTILATOR FILTERS.

Sodium chloride trace

Calcium carbonate ... ... ... 2*17 per cent.

Ferric oxide ... ... ... ... 2-44 „

Calcium sulphate ... ... ... ... 5-09 „

Alumina ... ... ... ... ... 834 ,,

Magnesium carbonate 0-33 „

Sand 37-99 „

Carbon ... ... 35-48

Ammonium sulphate ... ... ... 5-77 tt

Tar (extracted by CS2) 1-49 „

Fibrous matter ... ... ... ... 0-95 ,,

100-05 »

The large proportion of carbon, together with sticky tarry matter, explains why the surface of all solids, both inside and outside buildings, are coated with filthy sooty material in large towns. Not less important in relation to destructive effect on stone buildings is the presence of sulphur compounds.

One of the chief sources of these suspended impurities in the air is the imperfect combustion of bituminous coal, and the analyses of samples of the sooty matters produced are given in the report. (See Table III.)

These are the matters which cling to the walls of the chimneys and also pass in the form of smoke into the atmosphere accompanied by many noxious

RURAL WATER SUPPLIES AND THEIR PURIFICATION

gases, e.g., formaldehyde, sulphuretted hydrogen, carbonic oxide, carbonic dioxide, sulphur oxides, ammonia, &c.

TABLE III. — ANALYSES OF SOOTY MATTERS.

Sample No. I Sample No. 2

SO8 6-2 percent. ... 5-8 per cent.

H2O ... ... 4-4 „ ... 4-0

CaO ... ... 1-4 „ ... 2-5 „

Fe2O3 2-2 „ ... 2-5 „

Cl ... ... 77 „ ... 7-9 „

Ether extract (tar) ... 28-6 ,, ... 17-7 „

NH3 (combined) ... 4-7 „ ... 3-8 ,,

Other constituents ... 44-8 ,, ... 55*8 „

The oxides of sulphur and ammonia, whether existing separately as gases or combined to form the soluble solid ammonium sulphate, appear to exercise a most destructive action on buildings.

The report sets forth very clearly the advantages of gas and electric heating and cooking stoves over coal fires, so far as atmospheric pollution is con- cerned.

" The products of combustion from a gas fire consist mainly of CO2 and water vapour, together with a minute quantity of sulphur oxides. There is a total absence of those tarry and carbonaceous substances that are produced by the use of raw coal, and as the sulphur is so exceedingly small in amount the gaseous method of heating is compara- tively innocuous. As regards heating capacity, a coal fire consuming 2 1 Ib. of coal per day would be

4

RAIN-WATER

about equal to a gas fire consuming 200 cubic feet of gas per day, but whereas the coal would evolve about 1,500 grains of sulphur in various forms, as well as tar, carbon, &c., already alluded to, the gas would contribute only 50 or 60 grains of sulphur in the form of sulphur oxides. Electric stoves do not evolve products of combustion, and therefore their use also tends to a cleaner air.

" Apart from the polluting effect of the 20 to 30 Ib. of sulphur for each ton of coal consumed, it is regrettable that this valuable material should be wasted. Its total amount must be huge. The Committee recognizes that much of this waste of material is avoided when coal is utilized in the gasworks.''

In view of what has been said, it is small wonder that rain-water is apt to be seriously contaminated, especially near large towns and manufacturing centres. Rain literally washes the air, and so inevitably contains, either in solution or suspension, many impure substances which are really foreign to a non-vitiated atmosphere.

On the other hand, the reader must preserve a sense of proportion and remember that the impurities which contaminate rain-water (collected over a clean area) are drawn into the respiratory passages with every breath we take, and yet town dwellers seem to thrive on the respiratory " capture" (potentially) of substances which mixed with or dissolved in rain- water appear to be of almost poisonous significance.

5

RURAL WATER SUPPLIES AND THEIR PURIFICATION

No doubt the respiratory tract is a purifying and filtering agency, but so, to some extent, is the alimentary tract. At all events, the amount of rain- water we require for drinking purposes is small and the contained impurities relatively slight when compared with the huge volume of air which we breathe and the aggregate amount of apparently deleterious substances liable to be absorbed or retained in the process of respiration. Of course, when rain is collected from areas which concentrate, so to speak, past atmospheric pollutions and add to them other contaminations, which are not truly of aerial origin, the case may be different.

The Committee in seeking to investigate the pollution of the atmosphere adopted the expedient of collecting, at a number of centres, the total rainfall for each month of the year in a standard circular gauge vessel of four square feet superficial area, and submitting the liquid to special analysis.

The results are expressed as metric tons (2,205 1°-) per square kilometre (about 250 acres).

There may be many advantages in expressing the results in this way, but it would be a great convenience if, as well, they were expressed as parts per 100,000 or grains per gallon of rain-water. As the volume of water collected is always measured, this could readily be done.

A useful table of the deposit per acre per month is given on p. 31 of the report.

It should be noted that the nine columns are not

RAIN-WATER

independent of each other. The tar, carbonaceous matter and ash come under the heading of insoluble matter. The loss on ignition and ash refer to the soluble matter, and included in this are the sulphates, chlorine, and ammonia.

TABLE IV. — DEPOSIT PER ACRE PER MONTH (RAIN-WATER).

Carbon-

-

aceous

Loss

Tar

other than

Ash

on ignition

Ash

Total solids

S04

Cl

NH,

tar

Ib.

Ib.

Ib.

Ib.

Ib.

Ib.

Ib.

Ib.

Ib.

CLASS A

0-23

4'5

9

3'4

6-8

23

4*5

I '4

0-23

(The Malvern

type)

CLASS B

0-9

18

36

I3-5

27

90

18

5'4

0-9

(The Ravens-

court Park or

Cheadle type)

CLASS C

1-8

36

72

27

54

180

36

10-8

1-8

(The Liverpool

or Embank-

ment Gar-

dens type)

CLASS D

Over

Over

Over

Over

Over

Over

Over

Over

Over

(The Old ham

2-25

45

90

34

68

225

45

14

2-3

type)

One inch of rain per acre is equal to 22,622 gallons (about 101 tons, say 100 tons), and 2 to 3 inches of rainfall per month is a good average figure to take. Adopting 2*5 inches, 250 tons, or 2,240 x 250 = 560,000 Ib. of rain-water contain the number of Ibs. of the constituents given in the table. On this basis the relatively pure Malvern type of rain-water yields, in parts per 100,000 and grains per gallon, the following results : —

7

RURAL WATER SUPPLIES AND THEIR PURIFICATION

TABLE V.— ANALYSIS RELATIVELY PURE RAIN WATER.

Parts per Grains per

100,000 gallon

Insoluble matter: —

Tar 0*041 ... 0*0287

Carbonaceous (other than tar) 0*8 ... 0*56

Ash 1*6 ... ri2

Soluble matter : —

Loss on ignition o'6 ... 0*42

Ash 1*21 ... o'847

Total solids 4-1 ... 2*87

Included in soluble matter: —

Sulphur as SO* 0*8 ... 0-56

Chlorine as Cl 0-25 ... 0*175

Ammonia as NH 0*041 ... 0*0287

For present purposes the Malvern (comparatively pure) type is best chosen as an example, because in the vicinity of tqwns Public Water Supplies are nearly always available, and in such cases it is quite unnecessary, if not indefensible, to use rain-water for drinking purposes.

The gauge vessel used by the Committee is enamelled, and there is a device to safeguard it, as far as possible, against the " droppings" of birds.

When rain is collected from roofs, the roof surfaces, and more especially the gutters, harbour all sorts of accumulated filth (e.g., manure, dust, grit, decaying vegetation, " droppings " of birds and small animals, &c.).

It follows that the first " washings," after the cessation of a period of fine weather, are apt to be very foul, and 4< separators " (see p, 126) are often provided which reject this portion and allow of

8

FIG. i. — Shows the suspended matter in 0-5 c.c. of a sample of rain-water collected in London (x 50 diam.)-

RAIN-WATER

the collection only of rain-water after this pre- liminary scouring has taken place.

In considering the possibility of using rain- water for potable purposes, regard must be had to questions of taste, chemical composition, physical qualities, and, most important of all, considerations of health.1

Speaking generally, there is nothing in the chemical composition of rain-water to preclude its use for drinking purposes apart from its physical qualities and taste.

As regards taste, even pure rain-water is apt to have a flat, insipid taste, and impure samples are so objectionable as almost to create feelings of nausea (see p. 63).

The physical appearances of rain-water are often most uninviting. It is frequently highly coloured and contains much suspended matter.

The analysis of a town collected sample of rain- water gave results (in grains per gallon) as follows : —

1 The writer feels that he labours under the disadvantage of trying to appeal both to the expert and non-expert reader. For the former, advice is hardly needed unless indeed the writer's experience as an epidemiologist and bacteriologist may prove to be of some little value. As regards the latter, an endeavour will be made to show that the ordinary man of affairs is quite competent to safeguard the purity of any ordinary rural water supply, although he may have at the outset to seek expert help.

RURAL WATER SUPPLIES AND THEIR PURIFICATION

TABLE VI.— ANALYSIS OF TOWN RAIN-WATER.

Ammoniacal nitrogen 0*14

Albuminoid nitrogen ... ... ... ... 0*015

Chlorine 0*45

Oxygen absorbed from permanganate ... 0*22

Total hardness 37

Colour (m.m. brown, 2-ft. tube) 160

The high figures for ammoniacal nitrogen, oxidizable matter and colour are especially note- worthy.

It is of interest to give for comparative purposes the corresponding figures (grains per gallon) for the raw Thames and Thames-derived filtered waters for the ten-year period ended March 31, 1916.

TABLE VII. — ANALYSIS OF Raw THAMES AND THAMES Filtered WATER.

Raw Thame water

Ammoniacal nitrogen 0*005 Albuminoid nitrogen o-oii

s Thames-derived filtered water

0'OO02 ... 0-0043

PIS

Oxygen absorbed from permanganate 0-147 Total hardness 16-3 Colour (m.m. brown, 2-ft. tube) ... 71

J

... 0-059 ... 15-6 ... 19

From a health point of view, rain-water has the advantage that it is practically free from the possibility of human excremental pollution. That is, of course, excluding those cases where the rain-water is stored in pervious underground tanks, unfavourably situated as regards drains, cesspools, and other sources of dangerous contamination. On the other hand, roof collected rain-water may be

10

RAIN-WATER

contaminated by the "droppings" of birds, the excreta of rats, mice, and other lower animals, and a multitude of flies, insects, &c. Some diseases of the lower animals are communicable to man, and it would seem not unwise to regard unpurified rain-water as potentially unsafe, if not actually dangerous.

The first thing to consider then is how rain-water can be best sterilized, and, secondly, how it can be so purified as to be physically free from objection as regards colour, suspended matter and taste. It is assumed in what follows that the rain-water has been collected in bulk in storage cisterns, tanks or butts and all that is needed is to periodically purify such proportion of the bulk quantity as will meet the daily requirements of the household. It would obviously be out of place to encroach on the domain of the architect or the engineer and describe methods of separating the first "washings" and the best means of collecting and storing rain-water in bulk (see, however, notes under Miscellaneous Information, p. 126). It is, however, taken for granted that the expert in these matters has pro- vided against the possibility of the stored rain- water becoming contaminated from outside sources. For example, a pervious underground tank, badly situated as regards external sources of pollution, should, as already suggested, at once be condemned.

In conclusion, the chief points to be noted are as follows : —

11

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Putting on one side the dirty discoloured appear- ances of rain-water, its unpleasant taste, and the presence of sulphur compounds and tarry matters, there is nothing chemically objectionable in its use for drinking purposes.

On the other hand, if the mode of collection of rain-water is open to criticism (as it usually is), many undesirable impurities may be added to its normal composition.

Bacteriologically it is potentially unsafe, or at least open to suspicion, as, under ordinary con- ditions, it is liable to be polluted with excrementitious matter. On the other hand, it is practically free from the possibility of the worst kind of contamina- tion, namely, the discharges of human beings (see^ however, qualifying remarks on p. 10).

Assuming it to be possible to remove, or reduce satisfactorily, the taste,1 suspended matter and colour, and to kill all harmful microbes without leaving in the water any noxious substance, rain-water is perfectly safe for drinking purposes.

The methods of rendering rain-water safe and palatable will next be described.

1 The question of taste is fully considered on p. 63. The non-technical reader may find it convenient to concentrate attention on this page (12) and pass over lightly the preceding technical paragraphs.

12

RAIN-WATER

CHAPTER II.

RAIN-WATER— (Continued).

Excess lime method of sterilization — Determination of dis- solved carbonic acid gas, &c., in rain-water — Estimation of sulphates or permanent hardness — 10 gallons taken as the unit — Straining necessary — Amount of lime to be used — Eight to twelve hours' contact — Neutralization of the excess lime — Sodium phosphate and sodium bi- carbonate method — Aluminium sulphate and sodium carbonate method — " Carbonic acid water " method — Summary — Simpler "blind " methods — Questions of duration of contact — Acids as neutralizing agents — Concluding remarks (p. 34).

EXCESS LIME METHOD.1

Rain-water is very soft and normally contains so few substances capable of combining with lime that the use of this substance as a sterilizing agent is specially attractive in view of its cheap and innocuous character. In the doses about to be recommended, a lime-treated water has no taste (due to lime) and the use of lime is " hallowed by precedent." From a purely scientific point of view, these matters may seem to be relatively un-

1 For fuller information the reader is referred to p. 78 of the author's little book " Rivers as Sources of Water Supply " (Messrs. John Bale, Sons and Danielsson, Oxford House, 83-91, Great Titchfield Street, Oxford Street, London, W.i).

13

RURAL WATER SUPPLIES AND THEIR PURIFICATION

important, yet the average person may consider that they dominate the whole position.

The first thing to determine is how much of the lime is used up and therefore rendered non- bactericidal by the dissolved carbonic acid, bicarbonates, magnesium salts, &c., in the rain- water. It is well worth acquiring this knowledge (despite its technical character) because once it has been mastered all lime sterilization processes become matters of extreme simplicity and certainty.

Add 20 c.c. of standard lime water (i c.c. = O'ooi gramme CaO)1 to 700 c.c. rain-water (= 2 grains per gallon) in a stoppered bottle, shake and allow any precipitate formed to settle.

Rinse out a small flask and 100 c.c. (cubic centimetres) measuring cylinder (see figs. 2 and 3) respectively with the settled liquid.

In all chemical operations " rinsing " is of vital importance, and if the point is not pressed hereafter, it is assumed that this warning will not be neglected.

Measure out 70 c.c. (cubic centimetres) of the settled liquid, pour it into the flask, and add a few drops of phenol phthalein solution (see p. 115); the liquid ought to turn bright pink. If it does not do

1 Any first class firm of chemical dealers employing well- trained chemists can supply the standard or other solutions or chemicals mentioned in this treatise. On p. 114 will be found a few elementary notes on the various chemicals, materials, &c., mentioned in this little work. No apology is needed to the expert if the non -expert reader finds them of some little use.

14

RAIN-WATER

so, repeat the experiment using more lime water (in measured amount).

It should perhaps be explained here that standard solutions are made up on the metric gramme and

FIG. 2.

c.c.

80

70

60

(about '/s***) (about fufl size)

FIG. 3. — 100 c.c. measuring cylinder.

cubic centimetre basis. If one uses 100 c.c. (100,000 milligrammes) of water for analysis the results read as parts per 100,000 parts ; if 70 c.c.

15

RURAL WATER SUPPLIES AND THEIR PURIFICATION

{70,000 milligrammes) the results read as grains per gallon, because a gallon weighs 70,000 grains.

Rinse out a burette (see fig. 4) fixed in a burette stand (see fig. 5) with a little standard sulphuric acid (i c.c. = O'ooi gramme CaO) and. fill up to the 0*0 c.c. mark with the acid.

FIG. 4,

FIG. 5.

Add the acid, a few drops at a time, to the contents of the flask until the pink colour just dis- appears on shaking, and then take the reading (say, 4 c.c. of acid used).

Next add a very few drops of methyl orange solu tion (see p. 115) and proceed with the titration until the yellow colour begins to change to pink. This

16

RAIN-WATER

requires a little practice, and it is desirable for com- parative purposes to add the same amount of methyl orange to 70 c.c. of rain-water contained in a separate flask and compare the tints during titration. Now take the final reading, that is, the total number of cubic centimetres of acid used up (say, 7 c.c. required altogether). Then multiply the first phenol phthalein reading by 2, and subtract the total methyl orange reading from it 14x2 ==8 — 7==!. Now as 2 were added (see p. 14) and i remains, the CaO used up (i.e., rendered inoperative) is equal to i grain per gallon and this must be allowed for in calculating the dose of lime required for sterilization purposes. For example, if the dose for sterilization purposes is 3 grains, then 4 grains would be required for each gallon. Should the phenol phthalein reading doubled be less than the total reading (methyl orange), this shows that there is no excess of lime (CaO), and the operation must be repeated and more lime-water used.

If it is proposed to remove the permanent hard- ness (due to sulphates, not affected by boiling) as well as to sterilize the rain-water, the sulphates present should be determined. This, however, involves precipitation with baric chloride (using and therefore wasting at least 1,000 c.c. of rain-water) and the very accurate weighing of the precipitate of barium sulphate produced. Another and simpler

* For further information see table on p. 55. 2 17

RURAL WATER SUPPLIES AND THEIR PURIFICATION

plan is to estimate the permanent hardness by means of the soap test and allow i *o6 (anhydrous) or 2*86 (crystals) grains of sodium carbonate for every degree of hardness. The procedure is as follows : —

Measure out (fig. 3) 70 c.c. of the rain-water, pour the liquid into a small flask (fig. 2), and boil until the volume of the water has been reduced about one-half. Add 25 c.c. of previously boiled and cooled distilled water and transfer contents to a measuring cylinder (fig. 3) and, when cool, add more distilled water so as to bring the volume of liquid back to the original 70 c.c. Transfer this to a small bottle (fig. 6) and from a burette (figs. 4 and 5) run in a few drops of standard soap solution (i c.c. = i grain per gallon CaCO3) at intervals, shaking vigorously after each addition until a lather which remains "unbroken" for a few minutes is obtained. The number of cubic centimetres of soap used represents the de- grees of permanent hardness (grains per gallon) of the water. Suppose 4 c.c. are needed, then 4 x 2*86 = n*44 grains of soda crystals per gallon are required. Although a useful chemical exercise the determination of the permanent hardness with a view to its removal is usually not a matter of great importance.

18

RAIN-\VATER

Let it be supposed that 10 gallons is the amount of water to be dealt with.

Ten gallons of rain-water are transferred from the rain-water tanks or butts into a suitable vessel.

In Chapter VIII. will be found a description of the vessel recommended, but the writer feels that his purpose will have failed if it does not stimu- late others to improve greatly on the tentative suggestions here offered.

The water should be strained through wire gauze, having a sufficiently fine mesh to hold back all but microscopic objects, and if it is passed through clean linen or fine muslin as well so much the better.

The lime should not be added as calcium oxide or quicklime (CaO), but as slaked lime or hydrate of lime (CaO, H2O). The latter contains theoreti- cally over 75 per cent, of oxide of calcium (CaO), but as it is practically impossible to get it absolutely pure, 60 per cent, (factor 1*67) would be a much safer figure to adopt.

It will be remembered that 4 grains of calcium oxide (CaO) were needed, so 4 x 1*67 x 10 = 66'8 grains (say, i drachm, 7 grains) are required.1 It is best to weigh out this amount, mix it into a

1With a small Apothecaries' balance (having a pan of 2 1 in. diam.) the maximum amount of substance (say, of calcium hydrate) that can be conveniently " massed " on the pan is about 100 grains. For larger amounts, a letter weight balance, or for still larger amounts a kitchen balance may be used. Figs. 7 and 8 represent a cheap dispenser's and a more delicate balance, respectively.

19

RURAL WATER SUPPLIES AND THEIR PURIFICATION

paste with a little rain-water in a small cup and transfer the mixture to the 10 gallons of rain-water, rinsing the cup out several times afterwards to ensure that all the lime has been washed out. Then stir

FIG. 7.

FIG. 8.

thoroughly for five to ten minutes and leave for eight to twelve hours to allow of sterilization taking place.

Of course, if preferred, the lime may be added as

20

RAIN-WATER

" milk of lime." Weigh out ij oz. (Imperial) of slaked lime on an ordinary letter weight balance, and, if accuracy is aimed at, add to it 1 2 grains of lime weighed on Apothecaries' scales. Transfer the lime to a 12 oz. bottle, having a mark at 10 oz. capacity and containing, say, 5 oz. of water. Shake vigorously for several minutes, then make up with water to the 10 oz. mark. One oz. of the shaken mixture, measured quickly, will be the correct dose, approximately, for TO gallons.

Another method is to use lime-water. The solubility of CaO is nearer i in 900 than i in 1,000 but having regard to loss of strength on keeping, the latter is the safer figure to adopt. Further, for the sake of simplicity, the dose may be taken at 70 instead of 66*8 grains per 10 gallons. Then the proportions are 0*9 gallon (=7 pints, 4 oz.) of lime-water to 9 gallons of rain-water. The lime-water may be prepared in bulk as follows : Fit a barrel, capable of holding rather more than 30 gallons, with a stopcock, about 3 inches from the bottom. Raise a foot or two from the ground for " drawing-off" purposes. Pour 2 or 3 gallons of rain-water into the barrel and add an excess (say, i Ib.) of slaked lime (CaO, H2O), mixing the lime and water very thoroughly. Then bring up to 30 gallons, stirring all the time and place a tightly fitting lid on the mouth of the barrel. The clear liquid drawn off from the tap will be approximately of the strength of i in 1,000.

21

RURAL WATER SUPPLIES AND THEIR PURIFICATION

The next stage is neutralization of the excess lime. Rinse out a 100 c.c. measuring cylinder and small flask with the liquid. Then measure out 70 c.c. and transfer to flask and estimate the calcium oxide (CaO), using phenol phthalein and methyl orange in the way indicated previously (p. 16). Suppose the phenol phthalein and methyl . orange " readings " are 3*5 and 4 respectively ; then 3-5 x 2 = 7-4 = 3 x I0 (f°r 10 gallons) = 30 is the number of grains of calcium oxide (CaO/ which require neutralization. There is a con- siderable number of ways of effecting this object. (See, however, first paragraph, p. 31.)

(i) Sodium hydrogen phosphate (Na2 HPO4, 12 H2O)1 may be used, the practically insoluble calcium phosphate being precipitated as a flocculent white deposit and sodium hydrate being left in solution. (See Table XVII., p. 92.)

1 68 716 (factor 4*26)

3 CaO + H20 + 2 Na2HP04, 12 H2O = Ca3 (PO4), + 4NaHO+ i2H20.

The amount required is obviously 30 x 4*26 = 127*8 grams (say, 2 drachms, 8 grains)2 of sodium phosphate.

1 The writer has purposely chosen, as far as possible, pre- parations which are used medicinally and are to be found in the British Pharmacopoeia.

2 Weights may be purchased from 10,000 grains down to T^j grain which avoid all the complications of scruples,

22

RAIN-WATER

As it is perhaps undesirable to leave sodium hydrate (NaHO) in solution, sodium bicarbonate (NaHCO3) may be added to change it into carbonate of soda (Na2CO3), which in its turn will act on the calcium sulphate (CaSO4 permanent hardness).

1 60 336 (factor 2-0).

4 NaHO + 4 NaHCO3 == 4 Na.2 CO3 + 4 H,O.

The amount required is 30 x 2*0 = 60 grains (i drachm) of sodium bicarbonate (NaHCO3), which theoretically would produce about 76 grains of sodium carbonate (Na2CO3) or enough to remove about 7 degrees of permanent hardness.

This is in excess of the permanent hardness of country rain-water, but sodium carbonate in small doses is quite innocuous.

Na.2CO3 + CaSO4 = Na2SO4 + CaCO8.

The sodium sulphate (Na2SO4) produced is soluble, innocuous and does not cause curdling of soap. The calcium carbonate (CaCO3) is soluble only to the extent of about 1*4 grains per gallon.

127*8 grains (say, 2 drachms, 8 grains) of sodium phosphate are therefore added to the excess-limed rain-water and the mixture stirred for a few minutes,

drachms and ounces (Apothecaries' weights) and ounces and pounds (Imperial weights). Both as regards weights and measures it seems a great pity that we do not finally adopt the simple and scientific systems practised by Continental nations.

23

RURAL WATER SUPPLIES AND THEIR PURIFICATION

and then 60 grains (i drachm) of sodium bicarbonate added as well and the mixture again stirred.

After settlement, preferably for eight to twelve hours, the clear liquid is ready for domestic use.

(2) Alternatively, Aluminium sulphate crystals (A12 (SO4)3, 1 8 H2O) may be used to neutralize the excess lime. (See p. 78.)

1 68 666 (factor 3*96)

3 CaO + A12 (S04)3, 1 8 H2O = A12O3 + 18 H2O + 3 CaSO4.

The amount required is thus 30 x 3*96 = 118*8 grains (nearly 2 drachms) of crystallized sulphate of alumina. As this would not remove the permanent hardness formed (CaSO4 being soluble), it may be desirable to add subsequently carbonate of soda (crystals).

408 858 (factor 5'ii).

3 CaSO4 + 3 Na2CO3, 10 H2O = 3 Na2SO4 + 3 CaCO3 + 30 H2O.

Hence 30 X 5*11 = 153*3 grains (2j drachms, 3 grains) of sodium carbonate are required.

If it is required as well to remove the original permanent hardness of the rain-water, an additional 28*6 grains of sodium carbonate (crystals) for each degree of hardness is required per 10 gallons.

1 1 8* 8 grains (say, 2 drachms) of aluminium sul- phate are therefore added to the excess-limed rain-

24

RAIN-WATER

water, the mixture stirred for a few minutes and then 153*3 grains (2^ drachms, 3 grains, or more if the original permanent hardness has to be removed) of sodium carbonate added as well and the mixture again stirred.

Unfortunately, sodium carbonate has a solvent action on aluminium hydrate, and instead of acting on the sulphates may have a tendency to interfere with the coagulating effect of the aluminium sul- phate. In the case of lime-treated peaty waters, at all events, the writer has obtained better clarification by its omission.

After settlement, preferably for eight to twelve hours, the clear liquid is ready for domestic use.

(3) Instead of the phosphate or aluminium sul- phate methods, the excess CaO could be neutralized directly and simply with sodium bicarbonate (NaH CO3), although the clarifying action is apt to be much less satisfactory (see p. 96).

1 68 504 (factor 3). 318 (factor '63).

3 CaO + 6 NaHCO3 = 3 Na2 CO3 + 3 CaCO3 + 3H20.

30 x 3 = 90 grains (\\ drachms) of sodium bicarbonate (NaHCO3) required which by producing 56*7 grains of Na2CO3 (90 x "63 = 56*7) would remove about 5 to 6 degrees of permanent hardness.

Na2CO3 + CaSO4 = Na2SO4 + CaCO3.

This is about the hardness of a town rain-water,

25

RURAL WATER SUPPLIES AND THEIR PURIFICATION

but country rain-water would be softer. Any slight excess of Na2CO3, however, is, as already suggested, harmless, possibly even beneficial.

Another plan would be to place the 90 grains of sodium bicarbonate (NaHCO3) in a flask with a little water, fit the neck with a rubber bung and bent glass tube, one end of which is placed in the lime-treated water. With a spirit lamp heat the contents of the flask and boil briskly for a few minutes ; the carbonic acid gas (CO2) will be driven off and combine with the CaO to form the relatively insoluble carbonate of lime.

6 NaHCO3 = 3 Na2CO3 + 3 H2O -f 3 CO2 3 C02 + 3 CaO = 3 CaCO3.

Speaking of the first named plan, 90 grains (ij drachms) of NaHCO3 are added to the excess- limed rain-water and the mixture stirred for several minutes. After settlement, preferably for eight to twelve hours, the clear liquid is ready for domestic use.

(4) Another very convenient way of neutralizing the excess CaO is to prepare carbonic acid water (see p. 99). For this purpose Gasogene or Sparklet Syphons may be used. Full instructions are issued with the apparatus and all that need be said here is that the water used should be above suspicion. Perhaps the simplest way is to bring 30 oz. of rain-water to the boil and add to it 10 oz. of non- 26

RAIN-WATER

boiled rain-water. When cool, the mixture will be free from the germs of water-borne epidemic disease, and suffice in volume for the 2 -pint size of apparatus. After the water has been charged with carbonic acid gas, a portion of the excess-limed rain-water (say, 2 oz.) is placed in a small bottle or flask and phenol phthalein added, when the liquid will turn bright pink. A little of the carbonic acid water is run into any convenient vessel and 10 c.c. of it drawn up into a graduated 10 c.c. pipette, and this is added very gradually to the liquid in the flask until the pink colour disappears. Half the amount used multiplied by Soo1 gives the volume, in cubic centimetres, required to neutralize 10 gallons of the excess limed rain-water.

CaO + CO2 = CaCO3.

After settlement, preferably for eight to twelve hours, the clear liquid is ready for domestic use.

An excess of carbonic acid water should prefer- ably not be added as then the relatively insoluble carbonate of lime (CaCO3) is re-dissolved, forming bicarbonate of lime, thus hardening the water.

CaCO3 + H2O, CO2 = CaCO3, H2CO3.

There would, of course, be no objection to adding an excess of carbonic acid water subse- quently, that is, after the clear liquid has been separated from the deposited carbonate of lime.

1 Because 2 oz. = ^J^ part of 10 gallons. 27

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Indeed, such a procedure would give "bite" and flavour to the final product.

SUMMARY AT THIS STAGE. Ten gallons of rain-water require to be treated.

(a) Determine, in the way already described, the amount of CaO used up by the CO2, &c., in the rain-water (p. 14).

(b) Determine the permanent hardness (see p. 18).

(c) Sterilize with 30 x 1*67 (+ grains of CaO found under (a) x 1*67) grains of calcium hydrate (CaO, H2O). (See p. 19.)

(d) Estimate, in the manner previously set forth, the amount of CaO left over after sterilization per 10 gallons (p. 22).

(e) For sodium phosphate and sodium bicarbonate treatment, multiply figure obtained under (d) by 4*26 and 2*0 respectively (p. 22).

For aluminium sulphate and sodium carbonate (see, however, remarks on p. 25) treatment, multiply figure obtained under (d) by 3*96 and 5*11 (4- 28*6 for every degree of permanent hardness) respectively (p. 24).

(g) For direct sodium bicarbonate method, multiply figure obtained under (d) by 3 (p. 25).

28

RAIN-WATER

(h) For carbonic acid water method use a Gasogene or Sparklet apparatus and add a neutralizing quantity of the CO2 charged water to the excess-limed rain-water (p. 26).

The purification processes here described offer to the student of chemistry no difficulties either in principle or practice. Nevertheless, there are many persons who will be discouraged by the technical terms used, and by the apparent complexity of the procedure. For these some simpler (although admittedly " blind ") methods may be described.

A fairly safe figure for the amount of oxide of lime (CaO) used up by the dissolved carbonic acid gas, &c., in freshly collected samples of rain-water would be one grain per gallon. Sixteen samples of freshly collected samples of town rain-water gave an average of 0*8. Of course, in the case of rain- water stored for a long time in tanks containing much decomposing organic matter the water might be almost saturated with CO2, and, if the tanks were made of concrete, bicarbonates would be formed which would also use up a certain pro- portion of the lime (CaO). In these cases actual tests ought certainly to be made.

A reasonably safe figure for bactericidal purposes would be about 3 grains per gallon of lime (CaO) with about twelve hours' contact. Very impure samples may possibly require a larger dose, or more prolonged contact. On the other hand, the dose suggested is in excess of ordinary requirements.

29

RURAL WATER SUPPLIES AND THEIR PURIFICATION

The reason for giving about twelve hours for sterilization and about twelve hours for subsequent neutralization, clarification, &c., is that the first part of the process may conveniently be started in the morning and the final part in the evening, the com- pletely treated water being ready for drinking on the following morning. This involves, of course, the tanks or vessels for treatment being in duplicate. The important point is that rapid chemical steriliza- tion processes labour, in the writer's experience, under the serious disadvantage of ^/^r-dosing, that is, of using far more of the chemical than is actually required owing to the duration of contact being unduly curtailed. This is apt to be specially true when the water to be sterilized is at a low tempera- ture. Under abnormal conditions short contact may be absolutely unavoidable, but, generally speaking, the practice is to be condemned.

Slaked lime or hydrated lime (CaO, H2O) con- tains nominally over 75 per cent, of oxide of lime (CaO), but 60 per cent, would be a safer figure to adopt (factor 1*67).

Hence (i + 3) x 1*67 = 6*68 grains (i drachm, 7 grains) per gallon is the amount of slaked or hydrated lime (CaO, H2O) required to sterilize rain-water within twelve hours.

Dealing in round numbers, 67 grains (i drachm, 7 grains) of slaked lime are therefore added to 10 gallons of rain-water, the mixture stirred for five to fifteen minutes and then left for twelve hours to

effect sterilization.

30

RAIN-WATER

Such a water could be drunk with perfect safety without any further treatment, the amount of excess lime being too small to give rise to any taste of lime, or to produce any injurious effects when ingested.

On the other hand, .the process is incomplete and might be considered to call for neutralization of the excess lime, with, perhaps as well, clarification by coagulants.

Hence, the following additional processes are put forward tentatively.

For the sake of simplicity it is assumed that, after sterilization, the excess lime (CaO) is equal to 30 grains per 10 gallons.

Add to the sterilized 10 gallons of rain-water one or other of the following substances : —

Sodium hydrogen Aluminium sul- Sodium bi- Neutralizing

phosphate, 128

phate, 119 grains

carbonate,

quantity of

grains (2 drachms,

(about 2 drachms).

90 grains

carbonic

8 grains). Then

Then (see, how-

(l£ drachms).

acid water.

sodium bicarbo-

ever, remarks on

nate, 60 grains

p. 25) sodium car-

(i drachm).

bonate, 153 grains

(2\ drachms, 3

grains).

The first two processes aim not only at neutraliza- tion, but clarification and softening. The last two exercise a softening influence, but their clarifying effect is negligible.

In provisionally fixing the bactericidal dose of excess CaO at 3 grains per gallon, regard has been had to the duration of contact (eight to twelve hours), providing a wide margin of safety, and the

31

RURAL WATER SUPPLIES AND THEIR PURIFICATION

variable quality of the rain-water. With a contact of one to seven days the dose may safely be reduced from three (assuming this to be sufficient with eight to twelve hours' contact) to from about two to mere traces. The matter requires furthur study, but the doses about to be suggested probably err on the side of safety, as the beneficial effect of storage would be (so to speak) superimposed on the germicidal action of the lime. Say, 2, i, 0*5, 0-25, 0*125, 0*0625 and 0*03125 grains of CaO per gallon for one, two, three, four, five, six, and seven days' contact (plus i grain per gallon in each case for CO2, &c., see p. 29).

Putting on one side questions of clarification, &c., the "rain-water purifier" might perhaps not un- reasonably prefer to rely on time rather than on dose, and have tanks in duplicate for alternate use to hold either seven, six, five, four, three, two or one days' supply. (See Table XVI., p. 86.)

Working on a ten-gallon a day basis the dose and tankage accommodation would, if the fore- going assumptions are sound, be approximately as shown in Table VIII.

Of course, especially with the smaller doses here given, it is desirable first to determine accurately the amount of CaO used up by the dissolved CO2, &c., in the rain-water, and then calculate the amount of hydrate of lime to be added so as to give an excess of CaO of 2, i, 0*5, &c., &c.

Indeed, having regard to the innocuous, if not

32

RAIN-WATER

beneficial, effect of minute doses of lime, a minimum dose of 0*25 excess CaO, with not less than four days' contact, would seem to be the wisest course to pursue.

TABLE VIII.— LIME, TIME AND TANK CAPACITY IN RELATION TO STERILIZATION.

Ten Gallons a Day Basis, Tanks being in Duplicate and used Alter- nately. (Doses based partly on experimental data, and partly on empirical grounds?)

Hydrate of lime (CaO, H2O) <* parity

<Srains> (gallons)

1 day's contact 50'!, say 50 (approximately 2 CaO in excess) 10

2 » 33'4 » 33 j» i »> i« 20

25-05 „ 25 „ 0-5

20-875 », 21 „ 0-25 „

18788 „ 19 „ 0-125 »»

17744 „ 1 8 „ 0-0625 „

17-222 „ 17 „ 0-03125 „

30 40

50 60

70

For health or taste purposes, and putting on one side questions of clarification or hardness, water treated in this manner could be safely drunk without any further treatment.

Some reference should perhaps also be made to the use of acids for neutralization purposes. The writer sees no objection to the use of either mineral or organic acids in this connection, provided the treatment rests in safe hands. Of the mineral acids, phosphoric acid (the dilute phosphoric acid of the Pharmacopoeia, acidum phosphoricum dilutum may be used), has the advantage of producing the practically insoluble calcium phosphate, and so re- ducing the hardness of the " lime-treated " water. 3 33

RURAL WATER SUPPLIES AND THEIR PURIFICATION

On the other hand, the organic citric or tartaric acids are crystalline, and so can be added by weight. They are medicinal preparations and practically non-poisonous. In combination with lime, the salts produced have an anti-scorbutic tendency, and, in the amounts involved, are perfectly innocuous. Each grain per gallon of excess CaO requires 1*24 and 2*66 grains of citric and tartaric acids respectively.

In conclusion, the chief points to be noted are as follows : —

Rain-water can be sterilized successfully with an innocuous dose of lime, say, 67 grains of slaked lime per gallon of water. (See also Tables XL, XIV., XVI. and XVII.)

If questions of neutralization of the excess lime and of clarification and softening are considered necessary or desirable, these results can be achieved by comparatively simple means.

Granting the approximate accuracy of certain assumptions, the processes involved require no chemical knowledge, and become a matter of mere simple weighing of the necessary ingredients.

The non-expert reader may find it desirable to pay most attention to pp. 29 to 34.

Consideration may next be given to the steriliza- tion of rain-water by means of heat and by the use of chlorine compounds.

34

RAIN-WATER

CHAPTER III.

RAIN-WATER (Continued).

Sterilization by means of heat — three parts boiled, one part not boiled method — Clarifying methods — Sterilization by means of chlorine — Bleaching powder — " Chloros " — Electrolytic compounds — Prejudice against "doping" waters — Doses of chlorine — How administered — Use of sodium sulphite — Combination with clarification methods — Combined lime and chlorine methods — How best applied — Neutralization of the proportion treated with lime — Less chance of taste — Liquid chlorine — Electro- lytic compounds — Ozone — Ultra-violet rays — Household devices—" Halazone " — Concluding remarks (p. 46).

STERILIZATION BY MEANS OF HEAT.

This method does not aim directly at clarifying a water, or eliminating taste, or purifying it chemically.

Nevertheless, from the point of epidemic water- borne disease, it has no equal, and it differs from all other kinds of treatment, inasmuch as it is applicable to every kind of water (rain-water, river-water, surface-water, spring- water, well-water, &c.).

The old rule was to boil a water violently for at least five minutes ; this procedure was based partly on empiricism, and partly on a knowledge of the limitations of human nature.

It has the disadvantage of robbing a water of

35

RURAL WATER SUPPLIES AND THEIR PURIFICATION

most of its dissolved gases, and therefore rendering it less palatable.

A perfectly safe rule to adopt is to bring three parts of water barely to boiling point (212° F. ; 1 00° C.), and add one part of " unboiled" water. The mixture within five minutes will be innocuous, whatever the temperature of the water was ante- cedently, and the dissolved gases will only be partly dissipated. For example, even with water initially at the freezing point, the temperature of the mixture would be 167° F. (75° C.), a temperature more than sufficient to kill the typhoid bacillus within five minutes (see Miscellaneous Experiments, p. 98).

Of course, if it is desired as well to reduce the colour and precipitate the bulk of the suspended matter, heat may be used for sterilization purposes, and aluminium sulphate as a coagulant. About 3 to 6 grains of aluminium sulphate and 3-9 to 7*8 grains of sodium carbonate crystals may be used for this purpose per gallon of rain-water.

Perhaps a few words should be added as regards distillation processes. Practically any water may be used for distillation purposes, and distilled water is absolutely safe from a bacteriological point of view. Most people dislike the taste of distilled water, but the writer disagrees with those who consider it actually injurious to health. Dr. W. P. Mason1 quotes Surgeon-General W. C. Braisted, of the U.S. Navy, as saying: —

1 " Water Supply," by Dr. W. P. Mason (John Wiley and Sons).

36

RAIN-WATER

" The use of distilled water on ships of the Navy has always tended to the very best of health condi- tions. In my opinion the use of distilled water offers the ideal drinking fluid for human con- sumption."

Of course, unless the water is brackish, or con- tains an injurious proportion of salts, or for some other reason cannot be drunk directly, there is no occasion to distil it, heating in the way already described being all that is required. As distillation is only required in quite exceptional circumstances, and as the provision of a still and condensing and heating apparatus is a mere matter of purchase, involving no special knowledge, the matter need not be considered further. Any responsible firm dealing in laboratory apparatus can supply full information on the subject.1

STERILIZATION BY MEANS OF CHLORINE.* There are at least four ways of utilizing this method : —

(1) Bleach solution. Bleaching powder or chloride of lime should contain about 33 per cent, of avail- able chlorine.

(2) Chloros (solution of sodium hypochlorite) contains 10 to 15 per cent, of available chlorine.

1 For large plants to deal with sea-water, p. 1820 of " Kelly's London Directory" (1917), may be consulted.

2 Bromine and Iodine have also been employed for sterili- zation purposes, but their use cannot be considered here.

37

RURAL WATER SUPPLIES AND THEIR PURIFICATION

(3) Liquefied chlorine gas (100 per cent, value).

(4) Electrolytic compounds. These are prepared electrolytically from various chlorides (e.g., sea- water), and the percentage of available chlorine depends on the concentration of salt and other factors.

It seems a great pity that so much prejudice surrounds the use of chlorine for sterilization pur- poses.1 As a pioneer (Lincoln Water Supply, 1905) on this subject, the writer has had to contend with a great deal of well-meant criticism. After all, it is only natural to look with suspicion on what many persons regard as a "doped" water. It is foolish to try and ride roughshod over the opinions of others merely because they do not coincide with our own. Yet if this War has taught us anything, it is the triumph of expediency over sentimentality. When all has been said, the safety of a water supply comes first, and if this end can only be achieved by chemical treatment, all other considerations should occupy a secondary position.

Rain-water varies so much in chemical composi- tion that it is difficult to suggest a dose of chlorine suitable for all, or, perhaps, even a majority of, cases. For example, unless suitably protected from outside sources of contamination, rain-water may contain much decomposing vegetable matter, many insects, and even the bodies of mice, rats, and birds.

JSee Chapter V., "Studies in Water Supply," and Chapter IV., " Rivers as Sources of Water Supply."

38

RAIN-WATER

Strictly speaking, the strength of the bleaching powder and chloros in terms of available chlorine should always be determined. But as this involves skilled chemical knowledge, experience and tech- nique, it has been assumed in what follows that bleaching powder contains 33 per cent, (factor 3), and chloros 12 per cent, (factor 8*3) of available chlorine.

On the whole, it would seem wisest to employ a somewhat larger dose than is actually required, and to counteract the effect of this by prolonged contact, and, if necessary, the final use of an " anti-chlor."

A dose of 0*5 part of available chlorine per million parts of water (i in 2 millions) with twenty- four hours' contact, and then the addition (if found desirable) of a de-chlorinating dose of sodium sulphite is recommended. This corresponds with 1*05 grains of bleaching powder or 0*00664 oz. of chloros per 10 gallons of water.

As these are inconveniently small amounts to deal with (by liquid or measure) it is desirable to work with standard solutions, as follows : —

Weigh out 1 0*5 grains (breaking up any lumps) of bleaching powder and transfer to a small bottle containing 2 oz. of rain-water and some lead shot. Shake thoroughly for several minutes, allow to settle and pour the more or less clear liquid into a 10 oz. measuring glass. Add another 2 oz. of rain-water to the small bottle, shake vigorously,

39

RURAL WATER SUPPLIES AND THEIR PURIFICATION

allow to settle and pour the clear liquid into the measuring glass. Repeat this procedure twice more so as to ensure that practically all of the active part of the bleaching powder has been extracted, and then finally make up the measuring glass to 10 oz. with rain-water ; stir, allow to settle, and transfer the clearer portion to a stoppered bottle. The dose is now obviously i oz. for every 10 gallons of rain-water.

Alternatively, the 10-5 grains may be put in a mortar and mixed repeatedly with rain-water, the clearer portion being transferred each time to a 10 oz. measuring cylinder, Finally, rain-water is added up to the 10 oz. mark, the mixture stirred, then allowed to settle, and the clear portion poured into a stoppered bottle.

As regards the chloros, if this is diluted with 19 volumes of rain-water ( = i in 20), then 1^0624 (say i) drachm of the mixture per 10 gallons gives a dose in available chlorine of 0*5 per million.

Ten gallons of rain-water are placed in a suitable vessel and either i oz. of bleach solution or i drachm of diluted chloros added, and the mixture stirred for a few minutes.

After twenty-four hours, measure out 8 oz. of the now-sterilized rain-water into a convenient bottle or flask. Take the temperature of the liquid, if it is below 10° C. add a little freshly prepared potassium iodide and starch solution (see p. 116). If above 10° C., the liquid should, before testing, be

40

RAIN-WATER

cooled, if practicable, with a mixture of ice and salt to below 10° C., as otherwise the delicacy of the test is much impaired.

If there is no blue reaction, or only the very faintest tint, no sodium sulphite need be added and the liquid may be drunk with impunity. On the other hand, if there is a decided blue reaction, sodium sulphite solution (o'i percent.) should be run in from a burette and the number of cubic centimetres needed to remove the blue colour " read off." Obviously, this amount X 200 will give the dose of sodium sulphite required. Those who are averse to making actual tests might proceed on the basis that each part of available chlorine requires about 3-5 parts of sodium sulphite. With the dose here suggested (0*5 per million) 1*225 grains of sodium sulphite would be required. As, however, all, or nearly all, the available chlorine is likely to have been used up at the end of twenty-four hours, it is probable that about J grain of sodium sulphite would be sufficient. It is perhaps unnecessary to warn the reader that on no account must the sodium sulphite be added until the chlorine has exercised its sterilizing action. This, of course, would have the effect of destroying the bactericidal effect of the chlorine.

The chlorine treatment may be combined with clarification, but if aluminium sulphate is used, care must be exercised not to add more than will be neutralized by the alkalinity of the rain-water.

41

RURAL WATER SUPPLIES AND THEIR PURIFICATION

For example, after the addition of the bleach or chloros solution add from 30 to 60 grains (per 10 gallons) of aluminium sulphate according to the quality of the rain-water, and then, to avoid any risk of acidity, from 39 to 78 grains of sodium carbonate crystals.

666 858 (factor about i -3)

A12 (S04)3, 1 8 H20 + 3 Na2 CO3, 10 H2O -* A12 O3 + 3 Na2 SO4 + 3 CO2 + 28 H2O.

If this method is adopted, it is best to do without the sodium sulphite, as its addition at the end of the twenty-four hours necessarily means disturbing the precipitate produced by the aluminium sulphate.

Of course, if it is added as a solution, it might be possible to stir so gently and superficially as to secure fair mixing without appreciable disturbance of the precipitate.

Alternatively and preferably, the clear liquid might be " run " into another vessel and the sodium sulphite added to it. Speaking generally, the non- expert use of sodium sulphite is almost contra- indicated, unless in infinitesimal doses, or in those cases where the excess of chlorine is so marked as to impart a chlorinous taste to the treated water. In passing, the writer is prone to admit that it is not always easy for the non-expert worker to steer between the Scylla of an impure water, and the Charybdis of an imperfectly treated supply. Never- theless, "microbial" safety stands first, and even

42

RAIN-WATER

gross blunders with the chemicals here recom- mended could hardly render a water actually injurious to health.

Yet another alternative plan may be suggested. The dose of chlorine may be doubled, the duration of contact halved, and then wood charcoal (say 20 to 200 grains per gallon, according to the impurity of the water) added together with aluminium sulphate and a neutralizing quantity of sodium carbonate. The charcoal interferes, but not seriously, with precipitation and it has the effect of removing the chlorinous and the sooty taste.

COMBINED LIME AND CHLORINE METHODS.

It is obvious that these two processes may be combined in a variety of ways.

For example, 5 gallons of rain-water may be placed in each of two vessels (A) and (B).

(A) receives 33 grains (| drachm, 3 grains) of hydrate of lime.

(B) receives f oz. of bleach solution (10*5 grains of bleaching powder in 10 oz. of water). This equals a dose of 075 in i million (instead of 0*5 per million) as the duration of contact is only twelve hours.

After twelve hours (B) receives an anti- chlorinating dose of sodium sulphite, say 0*4594

43

RURAL WATER SUPPLIES AND THEIR PURIFICATION

grain, allowing for about half the chlorine having been used up.

The contents of (A) and (B) are then poured into a third vessel (C) capable of holding 10 gallons, and 45 grains (2 scruples, 5 grains) of sodium bicarbonate added to neutralize the lime and remove (as carbonate) the permanent hardness, and the mixture left to settle for twelve hours.

Alternatively (C) may be treated as follows: — (a) With 64 grains (i drachm, 4 grains) of

sodium phosphate and 15 grains (4 scruple, 5 grains)

of sodium bicarbonate, or,

(6) With 60 grains (i drachm) of aluminium sulphate and 77 grains (i drachm, £ scruple, 7 grains) of sodium carbonate, or,

(c) With a neutralizing quantity of "carbonic acid water."

There is less chance of a chlorinous taste with this combined method, although it loses a little in point of simplicity.

As regards the use of liquid chlorine, special apparatus has to be provided, and although the writer has had, on the whole, a favourable expe- rience of its use on a large scale, he is inclined to think that for very small volumes of water some of the other processes here described are for the present to be recommended. It is quite possible,

44

RAIN-WATER

however, that some ingenious inventor will design a form of apparatus which will sterilize even small volumes of water simply, cheaply and effectively.

Little need be said about electrolytic compounds. Where electric current is available, it may be used either in connection with an ozonizing apparatus to produce ozone (a most powerful bactericidal agent), or with an elect rolyzer to form hypochlorites from salt solution, or else with a quartz-mercury lamp to yield ultra-violet rays. The forms of apparatus on the market, however, for fulfilling these objects are usually designed for dealing with larger volumes of water than are being considered in this treatise. Waters containing much suspended matter should be filtered before being exposed to sterilization by means of ultra-violet rays. The writer, however, is rather trying to avoid purification processes which require filtration.

The fact that there has been no wide-spread adoption of any household device for sterilization purposes seems to point to inventors having failed to convince the public, or their advisers of the cheap- ness and "fool-proof" efficiency of the apparatus on the market.

As regards dose, enough has already been said to indicate the probable amount of active substance required for sterilization purposes.

Before closing this section, reference should

45

RURAL WATER SUPPLIES AND THEIR PURIFICATION

perhaps be made to a new chlorine compound, p-sulphondichloraminobenzoic acid (called kalasone] recommended by Dakin and Dunham (British Medical Journal, May 26, 1917) for sterilizing small quantities of water. Halazone can be made up in tablets, and to sterilize a quart of water one or two tablets, according to its quality, are said to be required. Apparently sterilization takes place within thirty minutes (see also Halazone for Water Sterili- zation, British Medical Journal, August n, 1917).

In conclusion, the chief points to be noted are as follows : —

Rain-water can be sterilized by means of heat (3 pints boiling, i pint unboiled) and clarified with coagulants (e.g., aluminium sulphate). (See also

P. 98.)

Various chlorine preparations (e.g., bleaching powder) may be used successfully for sterilization purposes (say, 0*105 grain per gallon), and any excess of active chlorine removed by means of an "anti-chlor. " (e.g., sodium sulphite). Aluminium sulphate may be employed as well for clarification purposes. (See also Chapters VI. and VII.)

The lime and chlorine methods may be combined with some advantages.

Household devices for sterilizing waters by means of ultra-violet rays, ozone, &c., have not achieved wide popular success.

46

RAIN-WATER

A substance termed " Halazone " has recently been introduced in tablet form for household sterilization purposes.

The diligent and intelligent reader will, no doubt, by this time have come to the conclusion that, although the purification of rain-water may be a complex process, putting on one side com- plicating questions (e.g., turbidity, taste, &c.), safety may be secured always by adding 3 parts of boiling to i part of unboiled water, and usually by adding either 67 grains of £&£**/ lime, or i "05 grains of bleaching powder to 10 gallons of rain-water.

In the remaining chapters, other sources of water supply will be briefly dealt with, but, to save repetition, it will be assumed that the sterilization and purification processes (see also Actual Experi- ments, Chapters VI. and VII.) described under rain- water have been carefully studied. The necessity for sterilization has, so far, been assumed, but, of course, there are waters which are pure, bacterio- logically, but unsatisfactory as regards colour, suspended matter, &c. In these cases, the addition of from 3 to 6 grains per gallon of aluminium sulphate is usually found to be most satisfactory, but in the case of soft water an alkali should be added as well — say 3*9 to 7*8 grains of sodium carbonate per gallon. The precipitate must be given time to settle and the clear liquid decanted for domestic use.

47

RURAL WATER SUPPLIES AND THEIR PURIFICATION

CHAPTER IV. WELL-WATER AND SPRING- WATER.

Well-water — Shallow wells usually impure and often hard — Excess lime method — Determination of hardness — Trial experiments — Estimation of alkalinity — Practical difficul- ties— Neutralization of the excess lime — Citric and tartaric acid — Duration of contact — Heat, chlorine, electrolytic compounds, ozone and ultra-violet rays — Combined lime and chlorine method — Relative volumes — Trial experiments — Springs — Often very pure — Caution, however, necessary — Methods of treatment (when required) broadly comparable with those already described — Usually tasteless and palatable — Concluding remarks (p. 56).

WELL-WATER.

Shallow1 wells are so often contaminated in the neighbourhood of dwellings, that their probable impurity should be taken almost for granted.

Such waters, despite their unsafe character, are frequently bright, clear and sparkling, and pleasant to taste.

Their topographical relation to drains and cess-

1 Deep wells, especially if sunk through impervious strata, are usually perfectly safe sources of water supply. Owing to the excessive and speculative cost of sinking they are seldom found in connection with private individual supplies. In any case the purity of the water is usually beyond question.

48

WELL-WATER AND SPRING-WATER

pools is most important. Hardly less vital is the kind of soil in which they are sunk (a good filtering- medium or otherwise), the nature of their lining (pervious or impervious), and the possibility or probability of surface impurities reaching the supply. For example, a leaking or overflowing cesspool, situated at a higher level than, and not far distant from, a well, the intervening soil being highly porous or fissured, and the well itself shallow and unpro- tected either laterally from the surface downwards or vertically from below upwards from the rapid ingress ofunpurified water, is an extreme illustration of obvious dangers not unfortunately always avoided. Medical officers of health in particular, but medical men generally, are specially trained in these matters, and if any doubt exists, their advice should be sought and taken, especially as it usually errs on the side of " safety."

The principles of purification remain much the same whatever class of water is dealt with, but the details require modification.

As a rule, well-waters are hard and not infre- quently much of the hardness is what is known as *' temporary," that is, it can be removed by boiling.

It is assumed in what follows that the preceding chapters have been carefully studied.

EXCESS LIME.

Here, consideration must be given not only to dissolved carbonic acid gas (CO2) but to bicarbon- 4 49

RURAL WATER SUPPLIES AND THEIR PURIFICATION

ates, which may be present in considerable amount ; otherwise all the lime added may be neutralized and rendered non-bactericidal.

The first step is the determination of the total hardness of the water.

Pour 70 c.c. of the water into a small bottle and from a burette " run " in a few drops of standard soap solution (i c.c. = i grain per gallon CaCO3) at intervals, shaking vigorously after each addition until a lather which remains unbroken for a few minutes is obtained. The number of c.c. used gives the total hardness of the sample. The permanent hardness is estimated in the way explained on p. 1 8. The difference between the two is the "temporary" hardness and is commonly due to calcium bicarbonate. The action of lime (CaO) on calcium bicarbonate is as follows : —

100 56 (factor '56)

CaCO3, H2CO3 + CaO « 2 CaCO3 + H2O.

Suppose the temporary hardness was found to be 12, then 12 x 0*56 = 672 grains per gallon of CaO would be required. Add, say, 1*0 for dissolved carbonic acid and, say, 3*0 for bactericidal purposes (=1072).

It will be remembered that this must be multiplied by 1*67 if hydrate of lime is used (1072 x 1*67

= I7'9).

In order to obtain a more reliable figure, it is desirable to add this amount to a gallon (or, say,

50

WELL-WATER AND SPRING-WATER

one-tenth of it to one -tenth of a gallon) and then estimate the excess CaO with phenol phthalein and methyl orange in the way described on pp. 14 to 16.

Suppose the phenol phthalein reading is 5 and the methyl orange reading 7, then 5 x 2 = 10 — 7 = 3 grains per gallon of excess CaO, or the correct dose.

If found to be less or greater than 3, an obvious calculation will determine the correct amount to add.

Another way of estimating the dose of CaO required for sterilization purposes is to estimate the alkalinity. Seventy c.c. of the water are placed in a small flask, methyl orange added and then standard acid (i c.c. =cvooi gramme CaO) run in slowly from a burette until the yellow tint is beginning to change to pink (see p. 116). The number of cubic centimetres of standard acid solu- tion used gives the number of grains per gallon of CaO likely to be needed to combine with the bicar- bonates in the sample of water. To this must be added say i grain for dissolved CO2 and 3 grains for bactericidal purposes.

Of course, the matter may be much more complex than is here indicated. For example, lime acts on magnesium salts as well as on bicarbonate of lime, and magnesium salts are not uncommon constituents of water.

Only a complete analysis by a highly skilled analyst could be expected to yield the fullest infor- mation, but determination of the alkalinity or the

51

RURAL WATER SUPPLIES AND THEIR PURIFICATION

temporary hardness, is an approximate guide to the amount required. Then one or more trial experi- ments with calculated amounts of lime, with subse- quent estimation of the excess of lime actually left in the water, leaves no doubt as to the actual amount of lime required.

Unfortunately, most well-waters vary in com- position from time to time, and this circumstance can only be met by checking the results periodically, or adding such an excess of lime as will cover all variations, so far as sterilization is concerned.

With waters having a very high temporary hardness, the excess lime should be considerable, as a relatively slight increase in the hardness might use up all the caustic alkalinity and destroy the bactericidal action.

Those who do not feel wholly competent to carry out these tests are advised to send a sample of the water in question to a skilled analyst and ask him to determine what amount of lime it is necessary to add to it, so as to leave 3 grains of lime (as CaO) per gallon in it in excess.

The fact is that with rain-water and very soft moorland waters the excess lime method may be used almost " blindly," because nearly all the lime is available for bactericidal purposes. With hard waters the case is widely different, most of the lime being exhausted in precipitating carbonates from bicarbonates.

For the sake of description, let it be assumed

52

WELL-WATER AND SPRING-WATER

that 1 8 grains (J scruple, 8 grains) of hydrate of lime per gallon have to be added so as to leave an excess of 3 grains of CaO.

Working as before with a 10 gallon unit, 180 grains (3 drachms) of hydrate of lime are added to the water, the mixture well stirred and left to sterilize for eight to twelve hours.

As regards subsequent treatment, it should be remembered that well-waters do not usually require clarification, and so the sodium phosphate and aluminium sulphate methods are hardly needed.

Neutralization of the excess lime should be effected by means of sodium bicarbonate, the amount required being 30 x 3 = 90 (ij drachms). This would produce 567 grains of sodium carbonate or enough to remove five to six degrees of per- manent hardness. This is not at all an unlikely amount for a well-water, but even if it were less, the presence of a small excess of sodium carbonate would be of no importance.

Alternatively, "carbonic acid water" might be used to neutralize the excess of CaO in the way already explained under rain-water.

In either case, after addition of the sodium bicarbonate or the "carbonic acid water," the water should be left, preferably for eight to twelve hours, so as to allow the precipitate produced to settle to the bottom of the vessel.

As explained under rain-water, citric or tartaric acid might be employed for neutralization purposes,

53

RURAL WATER SUPPLIES AND THEIR PURIFICATION

the amounts required being 37*2 (J drachm, 7 grains), and 79*8 grains (i drachm, i scruple) respectively.

The sodium bicarbonate method, however, seems most suitable as producing a beautifully soft water.

As described under rain-water, the bactericidal dose of lime (CaO) is largely governed by the time it is allowed to act. Hence, by using tanks capable of holding one to seven days' supply (in duplicate) the dose could be so reduced that no neutralization of the excess of lime (CaO) would be really re- quired, or, if needed, the amount of sodium bicar- bonate necessary would be reduced proportionately.

On the other hand, as rain-water is usually very soft and well-water often very hard, the utmost care would have to be taken in the latter case to avoid any risk of all the lime being used up by the bicar- bonates, &c., in the water. This, of course, would have the effect of robbing the lime of its bactericidal power.

As regards heat, chlorine and electrolytic com- pounds, ozone and ultra-violet rays, the remarks made under rain-water apply broadly to other sources of supply.

The combined lime and chlorine method is well suited for well-waters, having a high temporary hardness as perhaps as much as one-half or more may be sterilized by means of lime, the subsequent mixture of the limed and chlorinated waters pro-

54

WELL-WATER AND SPRING-WATER

ducing a sterile soft and tasteless water. Theo- retically, whatever the number of grains per gallon of temporary hardness was found to be, roughly one-half (56 to 100), that amount of CaO would be required for neutralization purposes. For example, if the excess lime were equal to 3 grains per gallon, 6 grains of temporary hardness would be removed by it. Hence, if the temporary hardness were 12, one gallon of the limed water would be neutralized by 0*5 gallon of the chlorinated water (i.e., say 66 to 33 per cent.).

Obviously, the temporary hardness in grains per gallon, divided by twice the number of grains per gallon, of excess CaO gives the divisor for ascer- taining the proportion of i gallon which i gallon of limed water will neutralize.

In practice, it is best to mix the water in the amounts as calculated, and then determine the alka- linity with phenol phthalein and methyl orange as previously described (p. 14). Where pp = the phenol phthalein reading and mo = = the methyl orange reading, the following results may be obtained : —

TABLE IX. — ESTIMATION OF BICARBONATES, CARBONATES AND HYDRATES (BASED ON A.P.H.A. TABLE).

(< = less than ; > = greater than).

(a) pp = 0 -«,

bicar bonates

mo

Carbonate 0

tlydrates 0

(£) 2 pp < mo

mo - 2 pp

2PP

0

(c) 2 pp = mo

o

2Pp

o

(d) 2 pp > mo

0

2 (mo - pp)

2 pp — mo

(e) pp = mo .

0

0

mo

55

RURAL WATER SUPPLIES AND THEIR PURIFICATION

A (d) or (e) result implies that more chlorinated water is needed. A (c) result points to perfect neutralization. An (a) or (b) result indicates that the chlorinated water is in excess. Practically, under the conditions of experiment, results (a) and (e) could not possibly be obtained, as the former would mean that no lime had been added and the latter that carbonate of lime is absolutely (not merely relatively) insoluble.

SPRINGS.

Spring-water is often very pure, as the source of supply may be far distant and the passage of the water through the soil tends to rob it of any im- purities. This, however, is not always the case, and if any doubt exists on so important a matter, a sample, or samples, should be sent to a competent expert, accompanied with any topographical or other notes which may assist in the interpretation of the results obtained.

If impure, its treatment may be carried out on lines broadly parallel with those suggested under well-waters. Putting on one side the so-called " ochre " and medicinal springs and other excep- tional cases, the water from springs is usually bright, clear, sparkling, and most pleasant to drink.

In conclusion, the chief points to be noted are as follows : —

56

WELL-WATER AND SPRING-WATER

The principles of purification remain the same for all kinds of water, but in the treatment of well- water it should be remembered that the question of sterilization is frequently the most important factor to decide upon, clarification and removal of taste being seldom required.

Well-waters are often so hard that a sterilizing process, which involves softening as well, has many advantages (see Table XIX., p. 98). On the other hand, many persons may consider chlorine sterilization simpler (for dose, see p. 122).

Spring-water is often as pure as shallow well- water is impure, but when polluted, the treatment in the two cases may, as a rule, be carried out on broadly parallel lines.

The topographical surroundings of wells and springs are always of great importance.

The next chapter deals with the sterilization and purification of river, brook and lake-water for domestic use, and with questions of taste.

57

RURAL WATER SUPPLIES AND THEIR PURIFICATION

CHAPTER V. RIVERS, BROOKS, AND LAKE-WATER.

(THE TASTE OF WATERS.)

Rivers, brooks, and lakes — Usually agreeable to taste — Very variable as regards colour, physical appearances, chemical composition, and bacteriological qualities — Pollutions known and unknown (accidental) — Comparison between waters impure but purified, and initially pure but liable to chance contaminations — Soft waters and metallic poisoning — Topographical survey essential — Suggestions for treating different kinds of impure water — A few words of advice — The taste of water — Concluding remarks (P. 67).

RIVERS, BROOKS, AND LAKE-WATER (natural or artificial).

These supplies present the widest variations in quality, both chemically and bacteriologically. They usually have an agreeable taste, in the absence of excessive algal growths, although the taste of very soft peaty waters, in the case of per- sons used to a very hard water, is at first considered mawkish. When the conditions are reversed, the hard water, to begin with, seems to grip the mucous membrane of the mouth and to have almost a metallic taste. These sources of water supply may be so pure as to be absolutely safe for drinking pur- poses (excepting accidents) without any purification

58

RIVERS, BROOKS AND LAKE-WATER

whatsoever. On the other hand, they may be grossly polluted with excremental matters and so be extremely dangerous sources of supply. The com- paratively recent (1905) typhoid epidemic at Lin- coln should be a warning of the potential danger attached to surface water supplies. Here, with a population of about 50,000 there were over 1,000 cases of typhoid fever and over 100 deaths. Surface waters vary greatly in chemical composition and physical qualities, and some are as hard as others are soft.

The mere fact that they are surface sources (in greater or less measure) of supply suggests caution, as, even if normally pure, they are always exposed to chance contaminations.

The purest burn in the lonely Highlands of Scotland may be fouled by a chance and reckless wayfarer. Should such a vagrant be a typhoid " carrier," the burn water will, for the time being, be infinitely more dangerous than an initially impure supply which has been subjected to adequate purifi- cation processes. Indeed, it might be argued, with some show of reason, that uniformly well purified waters of doubtful or even dangerous antecedents, may be safer than non-purified supplies of happier origin, if the latter are ever exposed to accidental pollutions of specific sort. As an example of the former, an adequately stored and efficiently filtered initially impure river-water might be taken, and, for the latter, a pure Highland burn in the track of

59

RURAL WATER SUPPLIES AND THEIR PURIFICATION

shooters and beaters, some of which might be irresponsible and conceivably at the same time diseased.

When peaty water is piped to a house, it should be remembered that these waters are often acid and act energetically on lead, and that lead is a cumu- lative and dangerous poison. In such cases, the water should be rendered alkaline by means of lime or soda before passing through lead pipes, or the pipes used (owing to their composition, or their internal coating) should preclude the possibility of metallic poisoning.

It is most important that these surface sources of supply should be carefully surveyed to see whether there is any possibility or probability of excremental pollution between their areas of origin and points of abstraction for domestic use.

The mere fact, let us say, of your having found it convenient to fix your residence near a stream should suggest the probability of others having been similarly influenced. If the habitations are situated higher up on the water-shed the danger is yours, if lower down, it is your bounden duty to see that the danger is not theirs.

Impure soft, peaty and discoloured waters may well be treated with lime, aluminium sulphate and sodium carbonate, in the way described under rain- water, and the treatment, if properly carried out, sterilizes and clarifies the water and leaves it very soft.

60

FIG. 9. — Suspended matter in 0-5 c.c. of a river water during a flood

(X 50 diam.)

RIVERS, BROOKS AND LAKE-WATER

For contaminated hard waters which are not highly coloured, lime and bicarbonate of soda treat- ment yields satisfactory results.

Instead of lime, chlorine may be used as the sterilizing agent, and here it should be remembered that peaty discoloured waters contain much oxidiz- able matters, which may use up a considerable proportion of the chlorine.

River-waters are usually very turbid in flood-time and the use of lime, aluminium sulphate and sodium carbonate is attended with excellent results. Fig. 9 (for description see p. xv.) shows the sus- pended matter in o'5 c.c. of a sample of river-water during a flood.

The lime and chlorine methods may also be combined in a variety of ways according to the particular requirements of the case.

Careful consideration of the suggestions made under rain-water and well-water will enable the reader to decide which is the best course to adopt.

Important points to be considered are : —

(a) What is the source of the supply ; is it uniformly contaminated, or are chance accidental pollutions the only danger to health ? In this connection, remember that although the excreta of the lower animals is a most undesirable form of contamination, the greatest danger lies in the dis- charges of human beings, particularly those who

61

RURAL WATER SUPPLIES AND THEIR PURIFICATION

have the misfortune to be typhoid " carriers" (3 per one thousand according to some authorities).

(b) What is the character of the supply? Hard or soft, clear or discoloured, free from suspended matters or otherwise, rich in organic matter or the reverse, &c.

(c) If the verdict is unfavourable, questions of economy, sentiment and trouble must be ruthlessly set aside and the safety of the supply secured by sterilization at all costs. Absence of taste, freedom from colour and suspended matter, softness and reduction in the amount of oxidizable matter are less important than the destruction of all the germs of disease.

(d) If in doubt, sterilize the water or secure an alternative supply, or consult a competent expert.1 If the suggested methods of sterilization and puri- fication appear too complex, seek the advice of some person of experience in these matters. Never adopt a laissez faire attitude in the matter of water supply.

Before closing this chapter some reference may be made to questions of taste, as this is a subject

1 Readers who are ambitiously inclined, and desire to test for themselves the bacteriological qualities of water supplies are referred to pp. 138 to 188 of the author's little book, " Studies in Water Supply " (Messrs. Macmillan and Co., St. Martin's Street, London).

62

RIVERS, BROOKS AND LAKE-WATER

which is too often neglected ; yet to many persons it is so important that they prefer to drink a pleasant flavoured water although it is known to be exposed to pollution, rather than a bacteriologically " safe " water which has an unpleasant taste or smell.

The Taste of Water. — This is a fascinating but difficult study, and the number of persons with a discriminating and reliable taste is comparatively few.

Rain-water has a peculiar, mawkish, unpleasant, sooty taste, and in the neighbourhood of towns may be almost undrinkable. One can recall the taste vividly to the remembrance of most persons, however old, by reminding them of the days of their childhood when, if they really were children, they sucked icicles broken off from roofs, gutters, waterspouts, &c. It is a faint but unforgettable taste and one most difficult to eliminate. Rain- water shaken vigorously with air in a partially filled bottle for hours retains it almost, if not quite, unimpaired. None of the chemical processes of purification previously described appear at all satisfactory. Permanganate of potassium is most disappointing in this connection. If enough is added to give a faint pink tinge persisting for several minutes, the taste is seldom abolished and may hardly be even modified. If more is added, a permanganate taste is acquired which is, if any- thing, worse. Even when a large excess is added

63

RURAL WATER SUPPLIES AND THEIR PURIFICATION

and then after twenty-four hours' contact the excess removed by means of sodium sulphite, the results are disappointing. Slow sand filtration may improve matters very slightly, but slow filtration through charcoal is much more effective. Al- ternatively, wood charcoal powder may be added to the water, the mixture well stirred and then aluminium sulphate added as a coagulant. Both the charcoal and alumina are precipitated. As regards amounts, 20 grains per gallon of wood charcoal powder may suffice, but in obstinate cases it may be necessary to increase the dose greatly — it may be even tenfold. The aluminium sulphate, if lime has been used as the bactericidal agent, may be added in amount sufficient to neutralize the excess CaO (3*96, say 4, grains of aluminium sulphate for each grain of CaO). If this does not produce a good precipitate, more may be used up to a total of say 6 grains per gallon, care being taken to add sodium carbonate as well in the proportion of 1*29 (say 1*3) grains of sodium car- bonate crystals for each grain of aluminium sulphate used in excess of that portion required for neu- tralization of the excess lime (CaO). If the settled liquid is unsightly, due to imperfect settlement of the charcoal, it should be filtered. In the writer's experience, the worst cases of taste can be cured by the foregoing method. If a slight super-dose of chlorine (say i in i million) is added to rain- water, the liquid usually acquires a chlorinous taste

64

RIVERS, BROOKS AND LAKE-WATER

which may mask the sooty flavour, but is perhaps equally if not more unpleasant. If enough sodium sulphite is added to remove the excess of chlorine, the chlorinous taste may disappear, but the sooty flavour is apt to become again noticeable. The 1 ' after-taste " of stale chlorinated waters does not seem to lend itself readily to remedial treatment.

If a very strong super-dose of chlorine is tried and then the excess chlorine removed by means of sulphites, the chlorinous taste vanishes but the sooty taste still persists.

Wells and Springs. — These waters are usually highly palatable, although in the former case the water may be derived from most doubtful sources of supply. Slow passage through the soil, oxi- dation processes, and solution of various soluble salts and gases give to well waters a most acceptable "bite" and flavour.

Brooks and Burns. — These are usually well flavoured, although when very soft and peaty, the taste is an acquired one.

Rivers. — Much the same may be said of rivers, although in stagnant " reaches " a great develop- ment of plant and animal life may occur. These, by their decomposition and the setting free of oily matters and offensive gases, may give rise to a variety of most unpleasant tastes and odours.

5 65

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Lakes, Lochs and Reservoirs are generally pleasant to drink, but are liable, seasonably or occasionally, to active algal growths which may render the water temporarily almost undrinkable. It is curious that potassium permanganate, so disappointing in the case of rain-water, is almost a specific1 for this trouble in doses of 0*5 part per million parts. The writer has not found chlorine preparations satisfactory in this connection. Some aquatic plants (e.g., chara) give rise to most offen- sive tastes and odours as do some animals (e.g., the sponges). Figs. 10 and u (for description, see p. xv.) illustrate some of the growths associated with taste troubles.

Of course, the writer is here dealing with ordinary, not exceptional supplies.

Deep wells may sometimes have a most un- pleasant taste due to the presence of iron and sulphuretted hydrogen. Aeration and filtration usually remove these troubles. Some springs contain so much iron as to be called "ochre springs." Again, some surface and deep supplies may contain so high a proportion of chlorides, sulphates, &c., as to be practically undrinkable. Lastly, there are medicinal springs which, owing to their taste and purgative action, could only be tolerated for curative purposes. These, however,

1 See p. 100, " Studies in Water Supply" (Messrs. Macmillan and Co.).

66

(A) Anabaena, x 400.

(B) Eudorina, x 400.

(c) Sponge spicules, x 5°- FIG. 10.

(A) Stephanodiscus x 400.

(B) Glenodinium, x 150.

(c) Pandorina, x 400. (D) Synura, x 400.

FIG. n.

RIVERS, BROOKS AND LAKE-WATER

are exceptional waters, which lie outside the purview of this treatise.

In conclusion, the chief points to be noted are as follows : —

All surface sources of water supply, even if normally free from the taint of sewage pollution, are open to accidental contamination.

In selecting a method of treatment, consider in the first place safety from disease and then questions of clarification, softening, taste, &c. (see Tables XII., XV., and XVI. and Miscellaneous Experiments,

P. 98).

Never forget the importance of a topographical survey of the source of any water supply.

It is sometimes easy, at other times very difficult, to remove the taste from waters having an un- pleasant flavour. Aeration, filtration and the use of permanganate of potassium and charcoal (see p. 64) are all of value in particular cases. A chlorinous taste, due to active chlorine, may be removed by means of sulphites, &c., but the after- taste of a stale chlorinated water is less amenable to treat- ment. If strong doses of either permanganate or chlorine are added to rain-water, the excess being subsequently neutralized, the permanganate or chlorinous taste may disappear, but the sooty flavour is apt to become prominent again.

67

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Consideration will now be given to the results of actual experiments on the sterilization and purification of rain-water, &c. The reader will thus be able to judge how far practice agrees with theory. It is hoped that the examples given will stimulate the novice to become, if not a water expert, at all events a convert to the belief that nearly all waters may be purified to any standard of safety required.

The writer obviously cannot hope to render matters which are intrinsically difficult to the trained expert transparently simple to the average reader. His hope lies in stimulating interest, and in affording information to those who, with or without further advice, are determined to advance their knowledge of rural water supplies. (See con- cluding remarks on p. 128.)

68

THE RESULTS OF ACTUAL EXPERIMENTS

CHAPTER VI. THE RESULTS OF ACTUAL EXPERIMENTS.

Series I. Sterilization of rain-water with bleach solution. — Series II. Sterilization of rain-water by means of lime — Series III. Purification, clarification and softening of impure river- water by means of lime, aluminium sulphate and sodium carbonate. — Series IV. (I., II., and III.). Experiments in Series I., II., and III. repeated on a confirmatory B. coli basis. — Series V. Lime, time and sterilization. — Concluding remarks (p. 88).

There is nothing quite so convincing as the results of actual experiments, and the following notes are given as examples of the sterilization and purification of various kinds of water by one or other of the methods previously described.

SERIES I.1

The Sterilization of Town Rain-water by means of Bleaching Powder Solution.

The dose, in terms of available chlorine, was (a) i in i million, (b) i in 2 millions, and (c) i in

1 In Series I., II., III., a war brand of bile-salt medium was used which proved unsatisfactory from the point of view of presumptive B. coli results. In all the other experiments confirmatory tests were applied.

69

RURAL WATER SUPPLIES AND THEIR PURIFICATION

4 millions. This is equal in grains per gallon to (a) 0*07, (&) 0*035, and 00 0*0175. With bleaching powder of 33 per cent, strength the amount of actual substance would be (a) o'2i, (b) 0*105, and (c) 0*0525. The rain-water was first purposely inoculated with a little fresh human faeces and then examined bacteriologically for B. coli ; 500 c.c. (17*65 ozs.) of the sample were next poured into each of three stoppered bottles and chlorine added in the doses already stated. It may be desirable to explain to the non-expert reader the reason why the B. coli test is applied in these cases. Excremental matters contains B. coli in enormous numbers, and although the ordinary faecal type of B. coli is believed to be relatively or absolutely harmless, its presence in any number in a water is presumptive evidence of potential danger to health, because, if the pollution is of human origin, B. coli is liable at any time to be accompanied by bacteria which are unquestionably pathogenic (e.g., the typhoid bacillus). Add to this the fact that B. coli is a more hardy germ than the typhoid bacillus and it becomes at once apparent that a sterilization process which rids a water of B. coli is unquestionably safe as regards the microbes of epidemic water-borne disease (e.g., typhoid fever).

Experiment i. — After inoculation, the rain-water contained B. coli in o'oi, but not in o'ooi c.c.

70

THE RESULTS OF ACTUAL EXPERIMENTS

After eight and twenty-four hours, B. coli tests were again made with the following results : —

After eight hours.

(a) + 100 - IOG.C. (£) + 100 - IOC.G. (c) + 100 - 10 c.c.1

After twenty-four hours. (a) - 100 c.c. (b) - 100 c.c. (c) + TOO- loc.c.

It is apparent that after eight hours the improve- ment, bacteriologically, was 10,000 times even with the smallest dose (i in 4 millions).

In twenty-four hours, the improvement was at least 100,000 times in (a) and (b) and 10,000 times in (c).

Experiment 2. — After inoculation, the rain-water contained B. coli in 0*01, but not 0*001 c.c. The results, after eight and twenty-four hours, were exactly the same as in Experiment i except that in twenty-four hours (b) as well as (c) contained B. coli in 100 c.c.

Experiment 3. — After inoculation, the rain-water contained B. coli in 0*000 1, but not 0*0000 1 c.c.

1 Note that + = positive result (or present in), and — = negative result (or absent from), the amount of water stated.

71

RURAL WATER SUPPLIES AND THEIR PURIFICATION

After eight hours.

(a) + 10 c.c. (6) + 10 c.c. (c) + i c.c, — i c.c. — i c.c. — 0*1 c.c.

(Improved 100,000 (Improved 100,000 (Improved 10,000

times) times) times)

After twenty-four hours.

(a) - 100 c.c. (b) + 100 c.c. (c) + 10 c.c. — 10 c.c. — i c.c.

(Improved at least (Improved I million (Improved 100,000

10 million times) times) times

Experiment 4. — After inoculation, the rain-water contained B. coli in o'oi, but not o'ooi c.c. The results, after eight and twenty-four hours, were exactly the same as in Experiment 2.

Experiment 5. — After inoculation, the rain-water contained B. coli in o'oi, but not o'ooi c.c. The results, after eight and twenty-four hours, were exactly the same as in Experiment i except that in twenty-four hours (c) as well as (a) and (b) contained no B. coli in 100 c.c.

Experiment 6. — After inoculation, the rain-water contained B. coli'm o* i, but not o'oi c.c. The results, both after eight and twenty-four hours, were the same in each case, namely, 10 c.c. — i c.c. The improvement was thus 100 times.

72

THE RESULTS OF ACTUAL EXPERIMENTS

Experiment 7. — After inoculation, the rain-water contained B. coli in o'oi, but not o'ooi c.c.

After both eight and twenty-four hours, the results were : —

(a) + 100 — 10 c.c. ; (ft) + i — o'i c.c.; (c) + 0*1 - 0*01 c.c. The improvement was (a) 10,000 times; (b) 100 times, and (c) 10 times.

Experiment 8. — After inoculation, the rain-water contained 13. coli in o'oi, but not o'ooi c.c. The results, both after eight and twenty-four hours, were as follows : —

(a) - 100 c.c.; (b) + 10 - I c.c.; (c) -f I - o'l c.c.

The improvement was thus (a) at least 100,000 times ; (b) 1,000 times ; and (c) 100 times.

Experiment 9. — After inoculation, the rain-water contained B. coli in o'ooi, but not o'oooi c.c. The results were as under : —

After eight hours.

(a) + 100 - 10 c.c. ; (b) + 10 - i c.c.; (c] + 10 — i c.c. The improvement was thus (a) 100,000 times; (b) and (c) 10,000 times.

After twenty-four hours.

(a) - 100 c.c. ; (b) + 100 - 10 c.c.; (c) + 100 - 10 c.c. The improvement was thus (a) at least i million times, (b) and (c) 100,000 times.

73

RURAL WATER SUPPLIES AND THEIR PURIFICATION

It is worth noting that the samples of rain-water in Experiments 6 and 7 were, quite apart from the artificial faecal contamination, extremely dirty.

A parallel series of experiments were carried out, but without the addition of faeces, for judging questions of taste.

All the samples had a sooty taste before the addition of the bleach solution.

After twenty-four hours they either had a chlorinous or a combined chlorinous and sooty, or a sooty taste only. The addition of sodium sulphite to those giving a chlorinous taste was of use inasmuch as it removed the chlorinous taste, but the sooty taste remained quite appreciable.

The chief bacteriological results are set forth in the table on next page.

The results show that with a very dirty sample of rain-water a dose of i in i million with twenty- four hours' contact is hardly sufficient (on a pre- sumptive basis), but with a very good sample i in 4 millions may actually suffice. Practically, a dose of i in 2 millions would probably be ample in the great majority of cases.

It should also be noted that the positive B. coh results were based on a presumptive basis.1 Ex- perience has shown that presumptive results may be sometimes misleading, because the positive

1 Presumptive = acid and gas formation in the lactose bile- primary medium. Confirmatory = isolation of a " lactose + indol + " microbe.

74

THE RESULTS OF ACTUAL EXPERIMENTS

TABLE X. — THE STERILIZATION OF RAIN-WATER WITH BLEACH SOLUTION. DOSE : (a) i IN i MILLION, (b) i IN 2 MILLIONS,

(<r) I IN 4 MILLIONS, IN TERMS OF AVAILABLE CHLORINE.

Smallest

amount (in

Same as Ccl. 2,

Same as Col. 2,

Experi- ment

c.c.) of water yielding a positive B. colt result after inocula- tion, but

but after eight hours of chlorine treat- ment. (See, however, remarks at

Improve- ment after eight hours (times)

but after twenty-four hours' chlorine treatment (See, however, remarks at end

Improve- ment after twenty-four hours (times)

before addition

end of Series I.)

of Series I.)

of chlorine

Cols, i

2

3

4

5

6

la

+ O'OI

+ IOO

10,000

None in 100

100,000

(at least)

ib

II

M

> J

,,

100,000

1C

»

»

"

+ IOO

10,000

2a

+ O'OI

+ IOO

10,000

None in 100

100,000

(at least)

2t>

II

J>

M

+ IOO

10,000

2c

II

ft

»'

»

it

3*

+ O'OOOI

+ 10

100,000

None in 100

10,000,000

(at least)

3*

M

II

II

+ IOO

1,000,000

y

•J

+ I

10,000

+ 10

100,000

40

+ O'OI

+ IOO

10,000

None in 100

100,000

(at least)

4b

H

il

II

+ IOO

10,000

4C

"

"

it

»

it

5"

-f o-oi

+ IOO

10,000

None in loo

100,000

(at least)

5t>

n

»>

II

ii

100,000

5f

"

it

"

it

ii

6a

+ O'l

+ 10

IOO

+ 10

IOO

66

H

it

6c

II

»

'»

M

it

7<*

+ O'OI

+ IOO

10,000

+ IOO

10,000

76

}J

+ 1

IOO

+ I

IOO

V

»

+ O'l

10

+ O'l

IO

8a

+ O'OI

None in 100

100,000

None in 100

100,000

(at least)

(at least)

S/>

,,

+ 10

1,000

+ 10

1,000

8<r

"

H- i •

IOO

-f- i

IOO

ga

+ O'OOI

+ IOO

100,000

None in 100

1,000,000

(at least)

9*

,,

+ 10

10,000

+ IOO

100,000

II

+ 10

"

"

"

75

RURAL WATER SUPPLIES AND THEIR PURIFICATION

result obtained may be more apparent than real. That is, that acid and gas may show in the primary bile-salt medium1 and yet on subculture no growths occur, or a growth of microbes other than B. coli. It is possible or even probable that the results would have been completely satisfactory2 if they had been based on confirmatory instead of pre- sumptive evidence. These remarks also apply to Series II. and III.

SERIES II.

The Sterilization of Town Rain-water by means of Lime.

The rain-water was first purposely inoculated with a little fresh human faeces and then examined bacteriologically. Then 2 grains of hydrate of lime (CaO, H2O) were added to 48 ounces (= about 6*7 grains per gallon) of the faecally contaminated water and cultures made after eight and twenty- four hours on the shaken sample. Before shaking, however, a little of the clear liquid was withdrawn to estimate the amount of lime (CaO) left over in excess.

1 This remark, however, does not apply, or only to a very modified extent, to the bile-salt media of pre-war days. Then a presumptive result (if at all decided) was nearly always confirmed on subculture. Now with the current brands of bile-salt, the results, in the writer's experience, are much less to be trusted.

3 Reference to Series IV. (I., II., and III.) will show the correctness of this assumption.

76

THE RESULTS OF ACTUAL EXPERIMENTS

The method of determining the excess lime has already been described (see pp. 16, 55).

The chief results are set forth in the accompanying table : —

TABLE XL— THE STERILIZATION OF RAIN-WATER WITH LIME. Two GRAINS OF HYDRATE OF LIME (CaO, HaO IN 48 oz. (= ABOUT 67 GRAINS PER GALLON).

Experi- ment

Smallest amount (in c.c.) of water yielding a posi- tive B. coli result after inoculation, but before addition of lime

Same as Col. 2, but after eight hours of lime treatment. (See, how- ever notes at end of Series I.)

Improvement after eight hours. (Times)

Same as Col. 2, but after twenty-four hours of lime treatment. (See, however, notes at end of Series I.)

Improvement after twenty-four hours. (Times)

Actual excess of caustic lime (CaO) in the water in grains per gallon

Cols, i

2

3

4

5

6

7

!

+ O'OOI

+ 10

10,000

+ 100

100,000

2-4

2

+ O'OI

+ 10

1,000

+ 10

1,000

3'5

3

+ 0*01

+ 100

10,000

+ 100

10,000

4'3

4

+ o-ooo i

+ 10

100,000

+ 10

IOO,OOO

3'4

5

-f O'OI

+ 10

1,000

+ 10

1,000

4'5

6

+ O'OI

-f 100

10,000

+ 100

10,000

4'5

7

+ O'l

+ 10

100

-f- 100

I,OOO

3*5

8

+ O'OI

+ 10

1,000

+ 100

10,000

3-2

Average

about 3 7

It is apparent from the table that a dose of 6 to 7 grains per gallon of hydrate of lime (CaO, H2O), leaving in the water an excess of caustic lime (CaO) of about 3 to 4 grains, can improve to a remarkable extent bacteriologically, in from eight to twenty- four hours, an artificially fsecally contaminated rain-water. A somewhat larger dose than was here employed is needed to sterilize the water absolutely (as judged by presumptive results), but

77

RURAL WATER SUPPLIES AND THEIR PURIFICATION

it is obvious from the table that the results obtained were so good as only to miss perfection by a narrow margin.

The bacteriological cultures were made on 44 shaken" samples (i.e., so as to include the sediment).

In practice, however, the deposit would not be drunk, and human faecal contamination of rain- water is most unlikely to take place, and never to the extent here artificially produced. See, however concluding remarks under Series I., which indicate that much better results would probably have been obtained if confirmatory tests had been applied, or a pre-war brand of bile-salt used in preparing the medium.

SERIES III.

The Purification, Clarification, and Softening of an Impure River Water by means of Lime> Aluminium Sulphate and Sodium Carbonate,

The water was first examined for B. coli and for hardness and colour. Then 9 grains of calcium hydrate (CaO, H2O) were added to 80 ounces contained in a stoppered bottle, this being judged to be about the amount necessary to neutralize the dissolved CO2 and bicarbonates in the water and yet leave enough caustic lime (CaO) in excess to effect sterilization. After vigorous shaking the mixture was left for twelve hours. Next, a little

78

THE RESULTS OF ACTUAL EXPERIMENTS

was withdrawn and used to estimate the excess lime (CaO). The bottle was then shaken and further B. coli cultures made so as to estimate the improvement bacteriologically. Then 40 ounces were poured into a bottle and first 3 grains of aluminium sulphate and then 7*5 grains of sodium carbonate were dissolved in the water, it being judged that these amounts would serve to neutralize the excess of lime and clarify and soften the water. After settlement the clear liquid was examined for colour and hardness.

The chief results are shown in the accompanying table (Table XII.).

It will be seen that the chemical results were very satisfactory, the colour and hardness being reduced on the average 65 per cent, and 79 per cent, respectively.

Bacteriologically, a great improvement was effected, although evidently a slightly larger dose of lime, or a longer contact, was required to produce entirely satisfactory results (on a presumptive basis). See, however, concluding remarks under Series I., which indicate that much better results would probably have been obtained if confirmatory tests had been applied, or a pre-war brand of bile-salt used in preparing the medium.

SERIES IV.

In order to clear up the point as to whether the results in Series I., II., and III. would not have

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80

THE RESULTS OF ACTUAL EXPERIMENTS

been still better if confirmatory B. coli tests had been applied, a further set of experiments were undertaken.

RAIN-WATER. — SERIES IV. (I.).

This corresponds with Series /., except that the B. coli results were based on confirmatory evidence.

TABLE XIII.— COMPARE WITH TABLE X.

DOSE (a) I IN I MILLION, (b) I IN 2 MILLIONS, (f) I IN 4 MILLIONS, IN TERMS OF AVAILABLE CHLORINE.

Experi- ment

Smallest amount (in c.c.) of water yielding a positive B. coli result, after inoculation, but before addition of chlorine

Same as Col. 2, but after eight hours of chlorine treatment

Same as Col. 2, but after twenty-four hours of chlorine treatment

Cols, i

2

3

4

ia

\b

1C

-f O'OI C.C. » »

+ 10 c.c.

+ I „

+ o-i ,,

-f- IOO C.C.

+ I „

+ o-i „

za 2b

2C

-f O-OI C.C. » II

+ O*I C.C. M

II

+ I C.C.

+ o-i „ + o-i „

3<* 3*

y

+ O-OI C.C.

J> »

+ 10 C.C.

+ I „

+ O'l „

+ IO C.C.

+ o-i „ + o-i „

4<* 4b

4<r

+ O'OOI C.C. »» »

— IOO C.C.

M

+ IOO C.C.

— IOO C.C.

— loo „ + loo „

5* 5* 5'

+ O'l C.C.

II II

— IOO C.C. II

»

— IOO C.C. »»

II

The first three samples of rain-water, as it turned out, happened to be very dirty, and, although an improvement was effected even with the minimum 6 81

RURAL WATER SUPPLIES AND THEIR PURIFICATION

dose, the maximum dose failed to produce complete sterilization.

With the last two samples completely satisfac- tory results were obtained with the middle dose of i in 2 millions in the first experiment and with the minimum dose of i in 4 millions in the last experi- ment. For all ordinary samples of rain-water a dose of i in 2 millions would probably be quite safe.

SERIES IV. (II.).

This corresponds with Series //., except that the B. coli results were based on confirmatory evidence.

TABLE XIV.— COMPARE WITH TABLE XI. RAIN-WATER. Two GRAINS OF HYDRATE OF LIME (CaO, H2O) IN

48 OZ. (= ABOUT 6'7 GRAINS PER GALLON).

Experi- ment

Smallest amount (in c.c.) of water yielding a positive B. coli result, after inoculation, but before addition of lime

Same as Col. 2, but after eight hours of lime treatment

Same as Col. 2, but after twenty-four hours of lime treatment

Actual excess of caustic lime (CaO) in the water in grains per gallon

Cols, i

2

3

4

5

I

+ O'OI C.C.

+ 100 C.C.

— IOO C.C.

3-0

2

-fo-ooi „

- loo ,,

M

2-3

3

4- o-i „

- 100 „

If

2'5

The results seem to show conclusively that a dose of about 6*7 grains of calcium hydrate (CaO, H2O) per gallon of rain-water would be perfectly safe as regards sterilization.

82

THE RESULTS OF ACTUAL EXPERIMENTS

SERIES IV. (III.).

This corresponds 'with Series III., except that the B. coli results were based on confirmatory evidence, and questions of hardness and colour were not again considered,

TABLE XV.— COMPARE WITH TABLE XII. RIVER-WATER. HYDRATE OF LIME (CaO, H2O) 9 GRAINS PER

80 OZ. (= l8 GRAINS PER GALLON.)

Experi- ment

Smallest amount of water (in c.c.) yielding a positive B. coli result, before addition of lime

Same as Col. 2, but after twelve hours' lime treatment

Actual excess of caustic lime (CaO) in the water in grains per gallon

Cols, i

2

3

4

I

... -f- O'l C.C.

— 100 C.C.

I '4

2.

... +0-1 „ ...

II

2'8

3

... + O'OI „

kl

j>

The results show clearly that a dose sufficient to leave less than 3 grains of excess lime (CaO) in the treated water is more than enough for sterilization purposes.

Speaking generally, the assumption that the good results obtained in Series I., II., and III. would have been better still if confirmatory B. coli tests had been applied is completely borne out by the results set forth in Series IV. (I., II., and III.).

83

RURAL WATER SUPPLIES AND THEIR PURIFICATION

SERIES V. Lime, Time and Sterilization.

It will be remembered that in Chapter II. it was pointed out that the dose of lime for sterilization purposes could be very greatly reduced by pro- longing the contact for several days.

The following experiments serve to emphasize this point : —

Experiment i. — Rain-water : Lime added in such proportion as to leave an excess (CaO) of 2*1 grains per gallon. Inoculated with fresh human faeces. Initial B. coll determination (+ o'ooi c.c.) After twenty-four hours, no B. coli even in 100 c.c.

Experiment 2. — Same as Experiment i. Initial B. coli determination (+ 0*0 1 c.c.). Excess lime (CaO) 1*9 grains per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment 3. — Same as Experiment i. Initial B. coli determination (+ o'oi c.c.). Excess lime (CaO) 2 '6 grains per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment 4. — Same as Experiment i. Initial B. coli determination (+ o'oooi c.c). Excess lime (CaO) 0*7 grain per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment 5. — Same as Experiment i. Initial B. coli determination (+ o'ooi c.c.). Excess lime

84

THE RESULTS OF ACTUAL EXPERIMENTS

(CaO) 0*4 grain per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment 6. — Same as Experiment i. Initial B. coli determination (+ o'ooi c.c.). Excess lime (CaO) 0*3 grain per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment 7. — Same as Experiment i. Initial B. coli determination (-f o'ooi c.c.). Excess lime (CaO) o'i grain per gallon. After twenty-four hours, B. coli present in 10 c.c. After forty-eight hours, no B. coli even in 100 c.c.

Experiment 8. — Same as Experiment i. Initial B. coli determination (+ 0*001 c.c.). Excess lime (CaO) 0*2 grain per gallon. After twenty-four hours, B. coli present in 100 c.c. After forty-eight hours, no B. coli even in 100 c.c.

Experiment 9. — In this experiment an impure river-water (no artificial contamination was made) was substituted for rain-water. Initial B. ^/^deter- mination (+ 0*0 1 c.c). Lime added in such proportion as to leave an excess of 2*4 grains (CaO) per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment 10. — Same as Experiment 9. Initial B. coli determination (+ 0*1 c.c.). Excess lime (CaO) 1*2 grains per gallon. After twenty-four hours, no B. coli even in 100 c.c.

Experiment n. — Same as Experiment 9. Initial B. coli determination (+ o'oi c.c.). Excess lime

85

RURAL WATER SUPPLIES AND THEIR PURIFICATION

(CaO) o'6 grain per gallon. After twenty-four hours, B. £0/2* present in 100 c.c. After forty-eight hours, no B. coli even in 100 c.c.

Experiment 12. — Conditions same as in Experi- ment i (rain-water). Initial (i.e., after inoculation) B. coli determination (+ 0*1 c.c.). Excess lime (CaO) 0*1 grain per gallon. After twenty-four hours, B. coli present in i c.c. After forty-eight hours, B. coli present in 100 c.c. After seventy-two hours, no B. coli even in 100 c.c.

Experiment 13. — Conditions same as in Experi- ment i. Initial B. coli determination (+• 0*1 c.c.) Excess lime (CaO) cri grain per gallon. After twenty - four hours, B. coli present in TOO c.c. After forty-eight hours, B. coli present in 100 c.c. After seventy-two hours, no B. coli even in 100 c.c.

TABLE XVI. — LIME, TIME AND STERILIZATION.

Experi- ment

Excess lime (CaO) in grains per gallon

Initial B, coli result

When B. coli was killed

I

2'I

+ 0-001 C.C.

Within twenty-four hours

2

I'9

-|- O-OI

» >!

3

2'6

-j- O-OI

» »

4

07

-j- O'OOOI

»> >»

5

o*4

+ O'OOI

» J»

6

0-3

-j- O'OOI

>» »*

7

O'l

-j- O'OOI

Within forty-eight hours

8

0*2

+ 0-COI

>» 11

9

2 -4

+ o-oi ,

Within twenty-four hours

10

I '2

+ 0-1

>» »

ii

0-6

+ o-oi ,

Within forty-eight hours

12

O'l

+ 0-1

Within seventy-two hours

13

o-i

+ o-i ,

»> >»

14

O'2

+ 0-1

5> J>

86

THE RESULTS OF ACTUAL EXPERIMENTS

Experiment 14. — Conditions same as in Experi- ment i. Initial B. coli determination (4- o'l c.c.). Excess lime (CaO) 0*2 grain per gallon. After twenty-four hours, B. coli present in 10 c.c. After forty-eight hours, B. £0/z present in 100 c.c. After seventy-two hours, no B. coli even in 100 c.c.

The chief results are tabulated in Table XVI.

It is apparent that some waters at all events may be sterilized with very minute traces of lime (in excess) provided the contact is not less than from one to three days. It does not follow, however, that all waters will behave in a precisely similar manner (especially as some absorption of CO2 from the air would take place), and in practice it would be unsafe to rely on these fractional doses, unless the treatment was kept under scientific observation. Nevertheless, the results do indicate that if rain- water is so reasonably free from colour, taste and suspended matter as not to call for any special treatment, and if it can be stored for several days, lime treatment presents remarkable advantages. For example, the dose required for sterilization pur- poses is so small as not to require any neutralization subsequently, and, of course, a water treated in this way could not possibly have any taste of lime and would be innocuous in all respects. In the case of really hard waters, however, this " small dose and long contact" method of treatment is less attrac- tive, for the reason that any slight increase in the

87

RURAL WATER SUPPLIES AND THEIR PURIFICATION

temporary hardness might more than rob the treated water of any excess of lime (CaO), and in so doing destroy its bactericidal action.

In conclusion, the chief points to be noted are as follows : —

With reasonably pure samples of rain-water a dose of i in 2 millions (in terms of available chlorine), acting for eight to twenty-four hours, is amply sufficient for sterilization purposes (Series I., also Series IV. (I.)).

Rain-water may be effectively sterilized with a dose of slaked lime (calcium hydrate) of, say, 67 (to provide a margin for safety) grains per gallon acting from eight to twenty-four hours (Series II., also Series IV. (II.)).

Hard impure river-water may be readily sterilized by means of lime if enough is added to leave over an excess of, say, 3 (to provide a margin for safety) grains of CaO per gallon. The excess lime (CaO) may be neutralized, and the water softened (reduction 79 per cent, in the experiments) and rendered less brown (reduction 65 per cent, in the experiments) by the addition subsequently of aluminium sulphate and sodium carbonate (Series III., also Series IV. (III.)).

Extremely small doses of lime (CaO) in excess (considerably less than i grain per gallon) are

88

THE RESULTS OF ACTUAL EXPERIMENTS

capable of sterilizing rain-water and other waters, if the duration of contact is prolonged over several days (Series V.).

In the next chapter (so as to avoid over- burdening the present one) the results of further experiments on the purification of water will be given.

89

RURAL WATER SUPPLIES AND THEIR PURIFICATION

CHAPTER VII.

THE RESULTS OF ACTUAL EXPERIMENTS—

(Continued).

Series VI. Lime and phosphate method of sterilization. — Series VII. Sterilization and clarification of soft peaty waters. — Series VIII. Lime and sodium bicarbonate method of treatment. — Series IX. Miscellaneous experi- ments.—Concluding remarks (p. 101).

SERIES VI.

Excess Lime and Sodium Hydrogen Phosphate Method of Purification.

Experiment i. — Forty-eight ounces of rain-water were inoculated with fresh human faeces. The initial B. coli determination was + 0*01 c.c. The colour was 80 and the hardness 4*4 grains per gallon. Three grains (= 10 grains per gallon) of calcium hydrate (CaO, H2O) were then added, the mixture well shaken and the precipitate allowed to settle. After twelve hours a little of the clear liquid was withdrawn and the excess lime (CaO) determined. It was equal to 7*2 grains per gallon. After shaking, B. coli tests were made, but no B. coli could be found even in 100 c.c. of the water.

90

THE RESULTS OF ACTUAL EXPERIMENTS

Next, 24 ounces of the mixture were treated with 2-5 grains (= about 17 grains per gallon) of sodium hydrogen phosphate and then with i grain (= about 7 grains per gallon) of sodium bicarbonate. When the copious precipitate produced had been allowed to settle, the colour and hardness were found to be 50 (reduction about 37 per cent.) and 5*2 respectively.

Experiment 2. — Same as Experiment i. Initial B. coli determination (+ o'ooi c.c.), colour 150 and hardness 3*9 (grains per gallon). Three grains of calcium hydrate added to 48 ounces as before. After twelve hours, excess lime (CaO), 6*8 grains per gallon ; no B. coli even in 100 c.c. To 24 ounces of mixture 4*5 (= 30 grains per gallon) and 2*2 (= about 15 grains per gallon) of sodium hydrogen phosphate and sodium bicarbonate added, respec- tively. After settlement, colour and hardness 60 (reduction 60 per cent.) and 4*8 respectively.

Experiment 3. — Same as Experiment i. Initial B. coli determination (+ i c.c.). Colour 84 and hardness 5*8 (grains per gallon). Here only 2 grains of calcium hydrate were added to 48 ounces of water (= about 6*7 grains per gallon). After twelve hours, excess lime (CaO) 1 7 grains per gallon ; no B. coli even in 100 c.c. To 24 ounces of mixture added ri grain of sodium hydrogen phosphate and then 0*5 of sodium bicarbonate. After settlement,

91

RURAL WATER SUPPLIES AND THEIR PURIFICATION

colour and hardness determined and found to be 45 and 5*2 (grains per gallon) respectively.

The chief results may be tabulated as follows : —

TABLE XVII. — RAIN-WATER. LIME AND SODIUM PHOSPHATE TREATMENT.

Experi- ment

Initial B. coli result

Initial colour

Initial hard- ness

Excess lime (CaO)

Final B, coli result

Final colour

Final hard- ness

,

+ O'OI C.C.

80

4 '4

7-2

— 100 C.C.

50

5'2

(about 37 per

cent, reduc-

tion)

2

+ o-ooi „

ISO

3'9

6-8

II

60

4'8

(60 per cent.

reduction)

3

+ 1

84

5-8

17

»

45

5'2

(about 46 per

cent, reduc-

tion)

It will be seen that an excess of lime (CaO) of less than 2 grains per gallon (Experiment 3) sufficed for sterilization purposes. The colour was also considerably reduced. The hardness was higher in the first two experiments, where the dose of lime was somewhat large, but in the last experiment there was a slight reduction in the hardness as a result of the treatment.

Some authorities object to the use of phosphates as precipitants, as phosphates tend to encourage bacterial growths. The writer thinks that the importance of this matter has been exaggerated, as the only microbes likely to be affected would be harmless water bacteria.

92

THE RESULTS OF ACTUAL EXPERIMENTS

SERIES VII.

The Sterilization and Clarification of a Soft Peaty Moorland Water.

As a matter of fact, the water in question con- tained very few B. coli, so it was first inoculated with a trace of fresh human faeces, so as to see what would take place in the case of peaty waters ex- posed to excremental pollution. The B. coli, colour, and hardness results were then determined.

(A) Eighty ounces then received 3*35 grains (= 67 grains per gallon) of calcium hydrate (CaO, H2O). The mixture was well shaken and then allowed to settle. After twelve hours, a little of the clear liquid was withdrawn for estimation of the excess lime (CaO). After shaking, B. coli cultures were made. Then 40 ounces of the mixture were treated with aluminium sulphate and sodium carbonate, and the colour and hardness results re-determined.

Five hundred cubic centimetres (about 17*65 ounces) of the water were placed in each ot three bottles, and these received bleach solution in doses (in term^ of available chlorine) of (a) i in i million, (b) i in 2 millions, and (c) i in 4 millions. After seventeen hours, B. coli cultures were made.

Experiment i. — Initial B. coli result ( + cri c.c.). Colour 1 20. Hardness 3*4 (grains per gallon).

93

RURAL WATER SUPPLIES AND THEIR PURIFICATION

(A) Excess lime (CaO) 3*1. B. coli result, after twelve hours (— 100 c.c.). Forty ounces received 3*1 grains of aluminium sulphate and 4 grains of sodium carbonate. After settlement, colour 40, and hardness 8*0 (grains per gallon).

(B) After seventeen hours of chlorination, the results were as follows : (a) — 100 c.c. ; (b) — 100 c.c. ; (c) + 10 c.c.

Experiment 2. — Same as Experiment i, except that less lime (2*5 grains) was used. Initial B. coli result (+ 0*001 c.c.). Colour 114 ; hardness 273.

(A) Excess lime (CaO) 2*0. B. coli results, after twelve hours (— 100 c.c.). Forty ounces received 1*96 grains of aluminium sulphate and 2 '55 grains of sodium carbonate. After settlement, colour 60 and hardness 7*0.

(B) After seventeen hours of chlorination, the results were as follows : (a) + 100, not 10 c.c. ; (6) 4- 100 and 10, not i c.c. ; (c) + 100, 10 and i, not 0*1 c.c.

Experiment 3. — Same as Experiment 2, 2*5 grains of lime being used. Initial B. coli result (+ o'oi c.c.). Colour no; hardness 2-5.

(A) Excess lime (CaO) 2*2. B. coli results after twelve hours ( — 100 c.c.). Forty ounces received 2*18 grains of aluminium sulphate and 2*8 grains of

94

THE RESULTS OF ACTUAL EXPERIMENTS

sodium carbonate. After settlement, colour 90 and hardness 8*26.

(B) After seventeen hours of chlorination, the results were as follows: (a) — 100 c.c. ; (6) + 100 - 10 c.c. ; (c) +' i c.c. — cri c.c. The chief results may be tabulated as follows : —

TABLE XVIII. — STERILIZATION AND CLARIFICATION OF MOORLAND WATERS,

Experi- ment

Initial B. coli result

Initial

colour

Initial hardness

I

2

+ 0*1 C.C. + 0-001 „

1 2O 114

3'4

273

3

4- o-oi „

110

2*5

(A) Part of experiment

(B) Part of experiment. Final B. coli result

Excess CaO

Final B. coli

result

Final colour

Final hardness

<«>.„.

i in i million

gL

i in 2 millions

i in 4 millions

3'i

— IOO C.C.

40

8-0

— IOO C.C.

— IOO C.C.

+ IO C.C.

2'0

M

60

7-0

+ ,,

+ 10 „

-f- I C.C.

2'2

'>

90

8-26

~~ >»

+ loo „

»

As regards the A part of the experiment, it will be seen that an excess of 2 grains per gallon of CaO was quite effective bacteriologically. The water, however, was considerably harder after than before the treatment, and in the last experiment the reduction of colour was disappointing, looking as if the lime (CaO) had acted on the colouring matter in the water in some way so as to render

95

RURAL WATER SUPPLIES AND THEIR PURIFICATION

it less " coagulable." (See also remarks on p. 25.) In respect of the B part of the experiment, a dose of chlorine of i in i million was sufficient in two out of the three cases.

SERIES VIII. Lime and Sodium Bicarbonate Treatment.

In illustration of this method of treaiment, a hard well-water was chosen (total hardness 23 grains and permanent hardness 6*4 grains per gallon). The well-water in question is sunk in the upper porous chalk and is known to be liable to pollution. In order to increase the B. coli normally present in the water it was inoculated with a little fresh human faeces. Its alkalinity (reduced to CaO) was found to be 10 grains per gallon : that is, 70 c.c. of the water required for its neutralization (see p. 51), 10 c.c. of standard acid (i c.c. = 0*001 gramme CaO). Allowing 3 c.c. for CO2 sterili- zation, &c., the lime (CaO, H2O) required was theoretically 13 x 1*67 = 2171 grains per gallon.

Experiment i. — Forty ounces of well-water re- ceived 5*42 grains of calcium hydrate (CaO, H2O). The initial B. coli determination was + 0*1 c.c. After twelve hours, a little of the clear liquid was drawn off and the excess lime (CaO) was found to be 0*9. After shaking, B. coli cultures were made and no B. coli were found, even in 100 c.c.

96

THE RESULTS OF ACTUAL EXPERIMENTS

Next 0*34 grain of sodium bicarbonate were added to 20 ounces of the mixture, and, after settlement, the hardness was determined and found to be 6*3 grains per gallon.

Experiment 2. — Same as Experiment i, but 7*42 grains of calcium hydrate (CaO, H2O) added. The initial B. coli determination was + croi c.c. After twelve hours, a little of the clear liquid was drawn off and the excess lime was found to be 4*0. After shaking, B. coli cultures were made and no B. coli were found, even in 100 c.c. 1*5 grains of sodium bicarbonate were next added to 20 ounces of the mixture, together with a trace of sodium carbonate to ensure the softening effect. After settlement, the hardness was again determined and found to be 2*5 grains per gallon.

Experiment 3. — Same as Experiment i, but 6*42 grains of calcium hydrate (CaO, H2O) added. The initial B. coli determination was + croi c.c. After twelve hours, a little of the clear liquid was drawn off and the excess lime was found to be 2 '8. After shaking, B. coli cultures were made and no B. coli were found, even in 100 c.c. 1*05 grains of sodium bicarbonate were next added to 20 ounces of the mixture, and after settlement the hardness was determined and found to be 27. The chief results may be tabulated as follows : —

97

RURAL WATER SUPPLIES AND THEIR PURIFICATION

TABLE XIX.— HARD WELL-WATER. LIME AND SODIUM BICARBONATE METHOD. TOTAL HARDNESS 23 (PERMANENT HARDNESS 6-4) GRAINS PER GALLON.

Experi- ment

Initial B. coli result

Excess lime (CaO) in grains per gallon

Final B. eWz re- sult, after twelve hours' contact

Final total hardness, in grains per gallon

I

+ O'l C.C.

0'9

— 100 C.C.

6'3

(nearly 73 per cent.

reduction)

2

+ O'OI C.C.

4'0

) J

2'5

(about 89 per cent.

reduction)

3

»

2-8

tt

27

(about 88 per cent.

reduction)

It will be noted that even so small an excess as 0*9 of lime (CaO) proved effective, although, in practice, it would hardly be safe to rely on so small a dose in the absence of skilled supervision and the application of frequent bacteriological tests. More- over, in cases where there is a fair amount of permanent hardness there is no good reason for running things too fine, because more lime simply means more bicarbonate of soda, greater security and a beautifully soft water as the final product.

SERIES IX. Miscellaneous Experiments.

Experiment i. — An impure river- water in flood (initial colour 208, initial hardness 207, initial B. coli result + 0*1 c.c.) was treated as follows: Three parts were heated and brought barely to the boiling point and then added to one part, which

98

THE RESULTS OF ACTUAL EXPERIMENTS

was not heated. After five minutes, cultures were made and no B. coli were present, even in 100 c.c. of water. Some of the remaining water was treated with aluminium sulphate (in the proportion of 6 grains per gallon) ; after settlement, the colour was 44 (nearly 79 per cent, reduction) and the hardness 21-9.

Experiment 2. — Same as Experiment i, except that clarification by aluminium sulphate was not tried and the sample was collected on a different date. Initial B. ^//result + croi c.c. Final B. coli result negative 100 c.c. These two experiments show that by adding three parts of " boiled " to one part of " unboiled" water, the mixture is rendered perfectly safe to drink. In Experiment i, it is also shown that aluminium sulphate has a powerful clari- fying action.

Experiment 3. — A river-derived water having an average hardness of 19*4 grains per gallon was treated with calcium hydrate. The next day the clear liquid was decanted and the caustic alkalinity estimated. It was found to be 2*2. The hardness was also determined and found to be 77. No bacteriological tests were made, it being clear from the results of the experiments already recorded that this excess would suffice for sterilization pur- poses. Two ounces of the liquid were then placed in a small flask, phenol phthalein solution added, and " carbonic acid water," freshly drawn from a

99

RURAL WATER SUPPLIES AND THEIR PURIFICATION

sparklet syphon, very gradually run in by means of a graduated pipette, until the pink colour dis- appeared. Half the number of cubic centimetres of "carbonic acid water " required were next added for each 2 ounces of the lime-treated water. After the precipitate of carbonate of lime produced (CO2 + CaO == CaCO3) had settled, the hardness was re-determined and found to be 6*5.

Experiment 4. — This experiment was on all fours with Experiment 3. The excess lime (CaO) was 3*8, and the hardness 12*4. After neutraliza- tion with "carbonic acid water" the hardness was reduced to 6*0.

Experiment 5. — Same as Experiments 3 and 4. Excess lime (CaO) 3*6, hardness 117. After neutralization with the "carbonic acid water" the hardness was reduced to 6*2.

Experiment 6. — Same as Experiments 3, 4 and 5. Excess lime (CaO) 4*9, hardness 14*6. After neutralization the hardness was reduced to 7*2.

Experiments 3 to 6 show that if lime is used as a sterilizing agent, the excess CaO can be neutralized by means of "carbonic acid water" derived from a sparklet syphon or gasogene, the carbonate of lime produced being precipitated and the water "softened" in consequence. The volume of "car- bonic acid water" required depends, of course, on the concentration of the carbonic acid gas in it and

100

THE RESULTS OF ACTUA '

the amount of excess lime (CaO). In the above experiments about 2*8 to 5*6 ounces were required per gallon.

It should perhaps be stated that in practically all these experiments comparatively small quantities were dealt with, and a cheap dispensing pair of scales were used for weighing purposes.

In conclusion, the chief points to be noted are as follows : —

Rain-water can be sterilized with very small doses of lime and the excess lime (CaO) neutralized by means of sodium phosphate.

Soft peaty moorland waters may be sterilized with lime (about 2 grains per gallon in excess) and the excess neutralized with aluminium sulphate ; or else sterilized with chlorine (about i in i million).

Hard well-water is conveniently sterilized and softened by means of lime and sodium bicarbonate.

Sterilization can be effected by adding three parts of boiling water to one part of unboiled water.

"Carbonic acid water" can be used for neutraliz- ing the excess lime (CaO) in a lime-sterilized water.

The concluding chapter deals with a description of the apparatus required for the sterilization of water on a domestic scale.

101

' KURAt WATER SUPPLIES AND THEIR PURIFICATION

CHAPTER VIII. DESCRIPTION OF APPARATUS (see Figs. 12 to 18).

Ten gallon a day basis — Description of vessel recommended — Floating arm method of drawing-off the liquid — Rigid outlet method — Notes on filtration — Apparatus described — Cleaning of filter — Disposal of precipi- tate in large vessel — Storage of purified water — " Long time lime" method of treatment— Tanks required — Questions of chlorine— Concluding remarks (p. 113).

The writer has assumed throughout a daily con- sumption for drinking purposes (per household) of ten gallons; where more is needed the tanks or vessels required may be correspondingly increased in size, and where less, provision has been made for more than one day's supply.

The tanks or vessels must be in duplicate so as to allow of their alternate use for purposes of treatment.

The 10 gallon glazed earthenware vessels known technically as " mixing pans" (see Fig. 12) serve admirably for this purpose.

The tubulure is fitted with a perforated rubber bung, but the attachments depend very much on circumstances.

(a) Floating Arm Method (see Fig. 13). — Where it

102

DESCRIPTION OF APPARATUS

is desired to draw off a very clear liquid, a glass tube is inserted in the rubber bung. At the distal (outlet) end is a piece of rubber tubing, a strong pinch-cock or screw clip (see, Fig. 14) and another piece of

^

FIG. 12.

O-^?

FIG. 13. — Floating arm method.

FIG. 14.

glass tubing, which, if thought necessary, may be covered at its free end with one or more folds of fine linen, bound on with a rubber band. Alter- natively, instead of a piece of plain glass tubing, a

103

RURAL WATER SUPPLIES AND THEIR PURIFICATION

" thistle head " tube may be used and the interior packed with absorbent cotton wool or asbestos fibre, kept in place with a piece of linen stretched over the mouth and held in position with a rubber band (see Fig. 15).

-Rubber bung with distal* attachments

X"""^-i

- / \

"*>vH

Screw clip here* (not drawn)

G/ass tube

K

Linen and rubber band

(reduced)

FIG. 15.— Rubber bung with its distal connections.

At the proximal end (inside) is a piece of rubber tubing nearly long enough to extend right across the vessel (see Fig. 13). Its free end is fixed firmly by means of a very long pin (say 2 inches long) to a large cork bung (say 2 to 3 inches in diameter) and it is desirable to stick into the bung two other pins. so as to provide three more or less equidistant legs (see Fig. 16). This allows the cork floater to rest

104

DESCRIPTION OF APPARATUS

securely on the bottom, when the liquid has been drawn down to its lowest level, without disturbing the sediment. Next, the rubber tube is pinched and two or three holes cut out with sharp scissors at different angles close to the cork bung. Obviously,

Rubber tube pinned to cork

Hole in tube

_Tube leading' " to rubber bung

FK;. 16.— Cork floater.

when the vessel is filled with water the cork floats, and when the exit stopcock is opened the liquid escapes from near the surface through these holes, As the liquid falls in level so also does the cork, until finally the pins strike and rest on the bottom of the vessel and all the liquid excepting about the

105

RURAL WATER SUPPLIES AND THEIR PURIFICATION

last gallon (more or less, according to the length of the pins and the position of the holes) is withdrawn without disturbing the sediment.

(b) Rigid Outlet Method. — For all practical pur- poses it is sufficient to have a fixed "draw-off" slightly above the level of the precipitate (say J to i inch). The proximal end of the tube should not project inside the vessel as the precipitate settles on it, and at the very end of the " drawing- off " process, it is liable to be detached and sucked down the tube (see Fig. 17). The distal end of the

V/ece oftinen FIG. 17.— Rigid outlet method.

tube may, as in the " floating arm " method, be covered with linen or a thistle-head tube may be used, the interior being packed, if thought desirable, with absorbent cotton wool or asbestos fibre. Where the precipitate, per se, is absolutely harmless (e.g., a precipitate of carbonate of lime) these straining processes seem unnecessary, unless possibly on aesthetic grounds, and even in the case of alumina their use can hardly be considered at all essential, as practically all the precipitate is left at the bottom of

106

DESCRIPTION OF APPARATUS

the vessel. In all purification processes it is a good thing to ask oneself the question : Is the mixture in the freshly prepared and stirred up condition injurious from the chemical point of view? If not, it is out of the question to regard the final product as a source of danger to health.

(c) Filtration Methods. — This book is concerned chiefly, if not entirely, with non-filtration processes of water purification. This does not necessarily mean that the author has no faith in filters, but the subject of filtration has already been dealt with by numerous writers (e.g., Dr. Sims Woodhead). If, however, it is thought desirable to filter finally the sterilized liquid, the consumer must decide whether it is better to use one of the many patent filters on the market or to construct one himself.

The writer does not propose to enter into a dis- cussion of the respective merits of the different types of patent domestic filters, but only to indicate very briefly how a small filter may conveniently be constructed.

The mixing pans already described may be had in small sizes (one gallon). The tubulure is fitted with a rubber bung, and a bit of glass tubing to which is attached a piece of rubber tubing controlled by means of a screw clip (see Fig. 14). The bottom is filled with gravel varying in size from a bean to a very small pea, the coarse material being under- most. The gravel should extend well above the

107

RURAL WATER SUPPLIES AND THEIR PURIFICATION

level of the outlet tube, as otherwise the sand will be sucked downwards and appear in the filtrate. Next is placed a layer (say \ inch) of coarse sand and then fine sand on the top of this (say 2 to 3 inches). The whole is then well covered with a layer of pea- sized gravel to prevent the onflowing water from disturbing the surface of the sand. It is essential that the gravel and sand should be scrupulously clean, and if any doubt exists as regards its purity,

Screw clip

FIG. 18.— Small filter.

the filter should be filled with boiling water and the outlet tube opened a little and more hot water poured on to take its place, until the temperature of the outgoing water is 70° C. and still rising. When it is certain that the whole of the contents of the filter has been exposed to this temperature, the outlet tube may be closed and in five minutes the filter may be safely assumed to be free from any of the microbes causing epidemic disease, and the

108

DESCRIPTION OF APPARATUS

water finally run off. It is a good plan to place a small piece of flat slate on the surface of the filter as the onflowing liquid impinging on it is spread over a larger area. It is desirable as well to alter from time to time the position of the slate and the delivery tube. As regards the latter, a piece of copper wire may be tied firmly on to the glass tube and the rubber tube fastened loosely to it as well. Then by bending the wire slightly the direction of the flow of water may be altered at will. When filtering, the outlet tube should be completely open and the rate of filtration controlled by the screw clip on the delivery tube. The speed of filtration may be made as slow as circumstances permit, but must never be so fast as to cause "ponding" on the surface of the filter with a consequent risk of an overflow. The first few ounces of filtrate should be rejected or poured back on to the surface of the filter. Once a week (or more frequently, if thought desirable), the bits of gravel should be removed from the surface of the gravel and also about half an inch of the top layers of sand. This is readily done by means of a little scoop — a bit of bent tin does well for this pur- pose. The sand and gravel should be washed separately, first in cold, and then in very hot water and replaced and any loss made good. About once a month it may be desirable to remove the whole of the material from the filter and replace it with fresh gravel and sand, or the same material after it has been thoroughly cleaned. It will be noted that this

109

RURAL WATER SUPPLIES AND THEIR PURIFICATION

is the " percolation " as opposed to the " submerged " method of filtration and it has the advantage of encouraging aeration. At the same time, such a filter may actually not achieve as good results as a dirty " mature" filter, the reason being that in the former case practically all the non-sporing bacteria have been banished, whereas in the latter case microbes are present in enormous numbers and some species exercise a purifying action on the water. In the present case, however, the water is supposed to be sterile to start with, and the filter is only required in order to remove the suspended matters from the water. Of course, any ingenious person can make a filter out of almost anything, e.g., a flower pot can be readily adapted for this purpose.

A few words must be said about the disposal of the precipitate left in the 10 gallon vessel. One way is to run the whole of it to waste. If this method is decided upon, a couple of wedge-shaped pieces of wood should be inserted laterally towards the side of the vessel farthest from the outlet. Next, a pail should be placed underneath the out- let, the precipitate well stirred up and the bung removed, so as to allow the contents to escape from the tilted vessel with a rush. Some more water may be used to flush out the residue, but this is hardly necessary in actual practice.

Another way is to leave the precipitate and supernatant water in situ, and make an allowance for its presence by adding fresh chemicals in reduced

110

DESCRIPTION OF APPARATUS

amount to the next lot of water. This entails knowledge of its volume ; and this information is readily obtained either by measuring the amount drawn off and deducting it from the total, or ascer- taining beforehand what volume of water the vessel holds up to the ''draw-off'' level. Within limits, the old precipitate rather helps in the production of a further deposit, but, of course, the time comes (say in a week) when the whole of the sludge must be swept out to waste. Generally speaking, the first method should be adopted in cases where an accumulation of the deposit is for some reason undesirable. On the other hand, where the pre- cipitate is per se innocuous (e.g., carbonate of lime) the final flushing operation may be delayed for some considerable time.

The writer has not dealt so far with the vessel or vessels in which the purified liquid is to be collected, This obviously depends upon circumstances ; for example, if the whole of the water is required daily, it may be collected in one large vessel and the whole of the plant duplicated for use each alternate day. On the other hand, if only a small proportion is needed daily it may be convenient to fill a series of Winchester quart bottles (carefully dated) and delay the preparation of a fresh lot of purified water until their contents have been nearly exhausted. No one of intelligence can fail to find out by experi- ence the method best adapted for his (or her) particular requirements. Needless to say the

111

RURAL WATER SUPPLIES AND THEIR PURIFICATION

vessels should be scrupulously clean, and if more than one day elapses between collection and con- sumption they should be glass stoppered.

When what may be described as the " long time lime" method of treatment (see Chapter II.) is adopted, duplicate tanks capable of holding, say seven days' supply, are provided. Here the dose of lime required is so small as not to need neutrali- zation and the tanks may be drawn on, on alternate weeks, just when the water is actually needed. Galvanized iron tanks may be used for this purpose, the outlet pipe being placed laterally a few inches from the bottom, Another outlet pipe may be pro- vided for periodical flushing out of the accumulated deposit, and this should preferably be placed on the actual bottom (i.e., facing upwards). In adding the lime, enough should be employed for the volume of water down to the level of the lateral outlet pipe, not for the total contents, which include, of course, the bottom water which is not drawn off, except occasionally. It is quite unnecessary to enter into any details as regards supports, height from the ground, &c., these being matters which the con- sumer is in the best position to deal with. When the foregoing method is adopted, it is assumed that the water is so reasonably clear to start with as not to require any filtration process. At the same time, there is no reason why the liquid drawn off from the large tank should not be filtered, if this is thought desirable.

112

DESCRIPTION OF APPARATUS

There is not much, if any real, objection to the use of chlorine as a sterilizing agent in connection with galvanized iron tanks. The zinc may be gradually dissolved, but, in the writer's opinion, the danger of zinc poisoning has been greatly exaggerated. The tanks could, of course, first be painted with " bituminous " or other suitable paint, but the water would be apt at first to have an appreciable taste. On the whole, however, the writer prefers lime to chlorine in those cases where it is proposed to reduce the dose of chemical to the lowest possible limit by greatly extending the period of contact, for the reason that the lime never ceases to act bactericidally until it is all carbonated, whereas the chlorine loses its effectiveness much more speedily.

In conclusion, the chief points to be noted are as follows : —

The vessels or tanks and their connections required for the domestic purification of water may be of the simplest kind.

The method of working them presents no real difficulties.

If filtration is considered desirable, and a sand filter is preferred to a patent domestic filter, a home- made one is easily prepared, and readily kept sweet and clean.

8 113

RURAL WATER SUPPLIES AND THEIR PURIFICATION

For the "long time lime" method of sterilization, galvanized iron tanks, holding, say seven days' supply, may be used.

MISCELLANEOUS INFORMATION. The following notes are meant for the non- expert reader.

The word lime is used by some persons to describe quicklime or calcium oxide (CaO = 56, sol. about i in Qoo)1 ; others apply it only to slaked lime, caustic lime, calcium hydroxide, or calcium hydrate (CaO, H2O = 74) ; yet others use it in con- nection with calcium carbonate or carbonate of lime (CaCO3 = 100). Chalk, whiting, marble, limestone, &c., are composed chiefly of carbonate of lime (sol. about i in 50,000).

Calcium bicarbonate or bicarbonate of lime (CaCO3, H2CO3 = 162). The chief cause of the temporary hardness of waters. Precipitated on boiling, or on addition of calcium hydrate.

Carbonic acid gas (CO2 = 44). Occurs in water free as dissolved carbonic acid gas, or fully-bound (as, e.g., in carbonate of lime, CaCO3), or half- bound (as, e.g., in bicarbonate of lime, CaCO3, H2CO3). Can be used to precipitate calcium hydrate as calcium carbonate. If in excess it re-dissolves the carbonate to form the soluble bicarbonate of lime.

1 See Table XX, p. 117. 114

MISCELLANEOUS INFORMATION

Aluminium Sulphate or sulphate of alumina (A12 (SOJ8, 1 8 H2O = 666). Very soluble, forms a flocculent precipitate with alkalies, much used in the purification and clarification of waters.

Sodium Carbonate or carbonate of soda (Na2CO anhydrous = 106 ; Na2C03, 10 H2O crystalline = 286). Very soluble, sometimes called "washing soda," frequently used for removing the permanent hardness of water due to sulphates, sodium sulphate being formed and the carbonates precipitated.

Sodium Bicarbonate or bicarbonate of soda (NaHCO3 = 84). Very soluble, sometimes called " baking soda," can be used to precipitate calcium hydrate as calcium carbonate, sodium carbonate remaining in solution.

Sodium Hydrogen Phosphate (Na2HPO4, 12 H2O = 358)- Very soluble, can be used to precipitate calcium hydrate as calcium phosphate.

Phenol Phthalein Solution. — A solution prepared by dissolving 0*2 gramme of phenol phthalein in 60 c.c. of alcohol (90 per cent.) and making up to 100 c.c. with distilled water. Used as an indicator ; colourless in acid and bright pink in solutions of hydrates and carbonates.

Methyl Orange Solution. — A solution prepared by dissolving 0*2 gramme of methyl orange in dis- tilled water, adding 25 c.c. of alcohol (90 per cent.), and making up to 100 c.c. with distilled water.

115

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Used as an indicator ; yellow colour with alkalies and pinkish with acids.

Potassium Iodide and Starch Solution. — Rub 2 grammes of potato starch with enough distilled water to form a paste. Add 100 c.c. of distilled water and bring mixture gently to boiling point. Allow to settle, decant relatively clear liquid and add two or three crystals of potassium iodide. Used to detect the presence of active chlorine, &c. Citric Acid (H3C6H5O7, H2O - 208-5), Tar- taric acid (H2C4H4O6 — 149) and diluted Phos- phoric acid (B.P.) can be used to neutralize calcium hydrate.

These, together with the standard lime (i c.c. == O'ooi gramme CaO), sulphuric acid (i c.c. = o'ooi gramme CaO), and soap (i c.c. = i degree of hardness), solutions may' be obtained from any first class firm of chemical dealers employing well-trained chemists.

Calcium Hypochlorite, in the form of bleaching powder or chloride of lime. Should contain about 33 per cent, of available chlorine. A most powerful germicide.

" Chloros" a solution of sodium hypochlorite, containing aboift 12 to 15 per cent, of available chlorine. Used, like bleaching powder, for steriliz- ing impure water.

Sodium sulphite (Na2SO3, 7H2O = 250), can be used as an " anti-chlor." (i.e., to remove any excess of active chlorine).

116

MISCELLANEOUS INFORMATION

TABLE XX.— SYMBOLS AND

ATOMIC WEIGHTS.

Symbols and Atomic Weights of the

Chief Elements mentioned

in this Treatise.

Symbol Atomic weight

Aluminium

Al ... 27

Calcium...

Ca ... 40

Carbon ...

C ... 12

Chlorine

Cl ... 35

Hydrogen

H ... i

Iodine ...

I ... 126

Magnesium

Mg ... 24

Manganese

Mn ... 55

Nitrogen

N ... 14

Oxygen ...

O ... 16

Phosphorus

P ... 31

Potassium

K ... 39

Sodium ...

Na ... 23

Sulphur ...

S ... 32

TABLE XXL— WEIGHTS AND MEASURES.

17 minims — i cubic centimetre About 15 grains = i gramme

gallon = 10 Ib. = 70,000 grains = 160 ounces = 4546 cubic centimetres

FLUID MEASURES.

i fluid drachm = 60 minims = 54*68 grains (3*552 c.c.) 8 fluid drachms = i fluid ounce 20 fluid ounces = i pint 2 pints = i quart

4 quarts = i gallon (160 ounces)

SOLID WEIGHTS. i cwt. = 112 Ib. i ton = 2240 Ib.

About 109 grains = \ ounce About 219 grains = \ ounce About 328 grains = £ ounce About 437 grains = i ounce i 750 grains --£lb. = 4 ounces 3500 grains = % Ib. = 8 ounces 5250 grains = f Ib. = 12 ounces 7000 grains = i Ib. = 16 ounces

117

RURAL WATER SUPPLIES AND THEIR PURIFICATION

The above notes relate to the avoirdupois or imperial standard weights and measures and they must not be confused with apothecaries' weight.

In the apothecaries' weight : —

TABLE XXII.— APOTHECARIES' WEIGHTS.

20 grains = i scruple 3 scruples (60 grains) — I drachm 8 drachms (480 grains) = I apoth. ounce (Note that the Imperial ounce = 437*5 grains.)

When working with liquids in small amounts, use measures divided into fluid drachms (8 to the fluid ounce) and minims (60 to the fluid drachm). For larger amounts work with the pint (20 ounces), quart (2 pints = 40 ounces), or gallon (4 quarts = 160 ounces.)

It is to be hoped that the day is not far distant when we shall finally adopt the simple and scientific way of measuring liquids in terms of litres and cubic centimetres. In all scientific laboratories the International system (both for weights and measures) has been in vogue for many years.

When dealing with weights in small amount, the weights (apothecaries') will be in grains, scruples (20 grains), and drachms (60 grains), and the ordinary apothecaries' scales may be used.

For heavier weights, use the imperial ounce (437*5 grains) or its fraction (letter-weight balance), and pound (16 ounces, 7,000 grains), or its fractions (kitchen balance). Of course, the different balances and their weights encroach, so to speak, on each

118

MISCELLANEOUS INFORMATION

other, but, generally speaking, the kitchen balance should not be used below J Ib. and the letter-weight balance below ounce.

CONVERSIONS.

Grammes (or cubic centimetres) into grains, ounces or pounds, multiply by 15*432, 0*03528 and 0*0022046 respectively.

Grains, ounces or pounds into grammes (or cubic centimetres), multiply by 0*0648, 28-35 an<^ 453'6 respectively.

Degrees Centigrade into degrees Fahrenheit, multiply by 9, divide by 5, and add 32.

Degrees Fahrenheit into degrees Centigrade, sub- tract 32, multiply by 5 and divide by 9.

Parts per 100,000 into grains per gallon, multiply by 7 and divide by 10.

Grains per gallon into parts per 100,000, multiply by 10 and divide by 7.

"Hardness" parts per 100,000 (CaCO3) into degrees of hardness = Clark's scale = grains per gallon, multiply by 7 and divide by 10.

Grains into scruples (apothecaries'), drachms (apothecaries'), ounces (imperial), and pounds (imperial), divide by 20, 60, 437*5, and 7,000 respectively.

Scruples (apothecaries') into drachms (apothe- caries'), ounces (imperial), and pounds (imperial), divide by 3, 21-875 (say, 21-9), and 350 respectively.

119

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Drachms (apothecaries') into ounces (imperial) and pounds (imperial), divide by 7*29167 (say, 7*3), and 1 16*667 (sav» 1167) respectively.

Ounces (imperial) into pounds (imperial), divide by 1 6.

All these little difficulties may be overcome by the purchase of a set of weights from 10,000 grains down to i/io grain. Their use renders it un- necessary to consider the " grain value " of scruples, drachms and ounces (apothecaries' weights), and ounces and pounds (imperial weights). The weights are arranged in the simple and scientific manner pertaining to the gramme weight (and its multiples and fractions), which apparently only our insular prejudice prevents us from finally adopting.

Capacity in gallons of rectangular vessels : Multiply length by breadth, by depth in inches, and divide by 277*5.

Capacity in gallons of cylindrical vessels : Square of half the diameter in inches multipled by 3*1416 ; multiply product by depth in inches ; divide answer by 277*5.

EXCESS LIME (CaO) METHOD.

Each grain per gallon of excess lime (CaO) requires for its neutralization —

Sodium hydrogen phosphate 4*26 grains (2 grains of sodium bicarbonate subsequently added to 'form sodium carbonate), or—

120

MISCELLANEOUS INFORMATION

Aluminium sulphate crystals 3*96 grains (5*11 grains of sodium carbonate crystals subse- quently added (see, however, p. 25) to precipitate the sulphates + an extra 2*86 grains for every degree of permanent hardness in the water before treatment), or —

Sodium bicarbonate, 3 grains, or —

4 'Carbonic acid water." Half the amount required to remove the pink colour from a known amount of the lime-treated water to which phenol phthalein has been added, or —

Citric acid, 1*24 grains, or— Tartaric acid, 2*66 grains.

All these substances are very soluble (sodium bicarbonate much less soluble) and may be added, if preferred, as solutions. One fluid ounce would be the correct dose for 10 gallons, if the foregoing figures are in each case multiplied by 800 and that amount dissolved in 80 ounces (i Winchester quart or J gallon) of water. Hot water may be used to accelerate solution, except in the case of sodium bicarbonate, which unfortunately is the least soluble of those specified.

Dose of excess lime (CaO) for sterilization pur- poses. About 3 grains (excess CaO) per gallon with about twelve hours' contact, but a good deal

121

RURAL WATER SUPPLIES AND THEIR PURIFICATION

depends upon the quality of water being dealt with.

Generally speaking, this is considerably in excess of the dose actually required, but in these matters it is well to err on the side of safety. Given several days' contact the dose may be reduced to a fraction of i grain, and even with only twelve hours' contact i to 2 grains may suffice, but in these cases skilled estimations of the actual excess of lime (CaO) and frequent bacteriological tests are desirable. Only an expert can be trusted to sterilize a water with the absolute minimum dose.1

Dose of Chlorine for sterilization purposes, in terms of available chlorine. About 0*07 and 0*0234 grain per gallon according to the quality of the water to be treated, with about twelve hours' con- tact. In terms of actual materials (bleaching powder and chloros), multiply by 3 and 8 respectively.

COST OF CHEMICALS, APPARATUS, &c.

The pre-war retail prices of the chief chemicals, apparatus, &c., mentioned are taken from well- known dealers' price lists. (See Table XXI 1 1. )

Of course, the price of these reagents varies greatly according to their degree of purity, and all of them, if bought in larger quantities, would cost far less.

1 For amount of lime, as slaked lime, see pp. 19, 30, 33, 34.

122

MISCELLANEOUS INFORMATION

The price of the standard sulphuric acid, lime water, and soap solution would be about is., is. and 2s. 3d. a Ib. respectively.

The phenol phthalein and methyl orange solu- tions would each cost about 5d. an ounce.

The potassium iodide and starch solution would cost about 2S. 6d. a Ib.

TABLE XXIII.— TABLE OF COSTS.

Per Ib. (7,000 grains

Sodium phosphate (crystals) .. ... 8d.

„ carbonate ,,

„ bicarbonate (powder)

Citric acid (crystals)

Tartaric acid „

Bleaching powder (in tins) ...

Calcium hydrate ...

Aluminium sulphate (crystals)

Wood charcoal1 (powder) ...

6d.

6d.

is. gd. is. 6d.

5d.

44. 2s. 3d.

5d.

Dispensing hand scales (with weights, 2 drachms to i grain) cost about 55. to 73. 6d.

A better and more delicate dispensing balance (nominally sensitive to ^ grain) costs about i6s. 6d. to 255.

Letter-weight and kitchen balances are (at all events the latter) household necessities. Their price varies greatly, according to quality, but is comparatively small.

_r —

1 Wood charcoal can be prepared quite easily at home. Fill an empty tobacco tin (or any other convenient tin) with bits of ordinary firewood. If the lid fits very tightly, bore one or two small holes through the tin. Place on a red fire, The escaping gases will catch fire and burn, but after a time this action ceases, and the tin becomes red hot. Leave for a little longer and then remove tin and set it aside to cool.

123

RURAL WATER SUPPLIES AND THEIR PURIFICATION

A cheap burette stand (to hold two burettes) costs about 2s. gd.

50 c.c. burettes cost 35. 6d. to 55. each.

The necessary small flasks, bottles, &c., cost only a few pence each.

The lo-gallon and i -gallon mixing pans cost about 22s. and 35. respectively.

Galvanized iron tanks holding 10, 25, 50, 75 and 100 gallons cost about 125., 125. 6d., 175., 2os., and 255. respectively.

The following useful practical notes (with plan) on the Utilization of Rain-water for Domestic Purposes, taken from pp. 22 to 25 of Kershaw's Book on " Sewage Purification and Disposal," are of interest from many points of view : —

"It may not be out of place at this point to refer briefly to rain-water collected from the roofs of cottages and out-buildings as a drinking water supply for places where water is scarce. It seems strange that this source of water supply is not more frequently utilized in England. In Bermuda (pop. in 1907, 21,000; rainfall about 48 in. p.a.) the only water supply is obtained from the rainfall falling on roofs and specially constructed "catches," from which it flows into large tanks cut out of the limestone and rendered with Portland cement. All roofs of dwelling-houses have an inclined fillet of cement running round them to collect the rain falling on them at one point. Unfortunately, the water is seldom filtered. Fig. 19 shows a plan and

124

MISCELLANEOUS INFORMATION

125

RURAL WATER SUPPLIES AND THEIR PURIFICATION

section of a rain-water tank constructed by excava- tion in rock, the walls and floors being rendered." * * * * *

"The following table (taken from Quantity Surveyors Diary and Tables (Metchim and Sons, Princes Street, London, S.W.) gives the run-off of rain from a roof having an area of 100 square feet with varying degrees of rainfall : —

TABLE XXIV.— SHOWING DAILY YIELD OF WATER FROM 100 SQUARE FEET OF ROOF WITH VARYING RAINFALL.

Mean rainfall

Loss from evaporation

Requisite capacity of tank

Mean daily yield of water

Mean daily yield wettest year

Mean daily yield driest year

Inches

Per cent.

Cubic feet

Gallons

Gallons

Gallons

20

25

52

2*1

3'3

1-6

25

2O

67

2-8

37

1-9

30

20

72

3*4

47

2'2

35

2O

77

3'9

5-5

2 '5

40

15

83

6-1

3*6

45

15

85

5'5

7-1

4'3

"Thus, with a roof area of 1,000 square feet, the mean daily yield in a district having an annual rainfall of 25 inches would be equivalent to 2*8 x 10 = 28 gallons.

" Rain-water Separators. — As the first washings from roofs generally contain soot, dust, bird drop- pings, decayed leaves, &c., it is advisable to turn to waste the first washings off the roof, before running the rain-water to the storage tank. To effect this, automatic contrivances termed Rain- water Separators have been devised : that form

126

MISCELLANEOUS INFORMATION

known as the ' Roberts ' separator, made by Rogers, of Haslemere, being perhaps as well known as any.

" These separators are guaranteed to take a rain- fall at the rate of 2 inches per hour, and to work with a rainfall of J inch per twenty-four hours on the areas given in the table below. In tropical countries where the rainfall sometimes exceeds 2 inches per hour, and in smoky cities, large separators are needed.

"It should be remembered that the separator must correspond to the size of the roof if it is to work properly.

TABLE XXV. — GIVING PARTICULARS OF RAIN-WATER SEPARATORS.

Area of roof in square feet

Distance between the levels of inlet and outlet pipes

Free to any railway station in Great Britain

£ s. d. 300 4 10 0 600

7 10 o

900 10 10 0

No. I

3 5 7 9 ii

In the country

600 to 1,000 1,000 „ 3,000 3,000 ,, 5,000 5,000 „ 7,000 7,000 ,, 9,000 9,000 ,,11,000

In the city or tropics

700 to 2,000 ... 2,000 ,, 4,000 ... 4,OOO ,, 6,OOO

... 6,000 ,, 8,000 ... 8,000 ,, 10,000

Pure outlet Inches

::: f ::.

'.'.'. 8 '.'.'. ... 9 ...

... 10

Foul outlet Inches II 13 - 13* -

:55i ::

16 ...

" Each further increase of 2,000 square feet in area of roof adds 305. to the cost. The makers observe that the separators need no attention except washing out at intervals of about three months in the country and one month in town.

" With regard to the construction, size, and posi- tion of the storage tank, this should be constructed of cement concrete, or brickwork in cement with

127

RURAL WATER SUPPLIES AND THEIR PURIFICATION

excess manholes, and placed underground for reasons of temperature. According to the makers of the separators, it should be capable- of holding a rainfall of about 4 inches, or, say, i cubic foot for each three superficial feet of roof, so that for a roof having an area of about 2,000 square feet the storage tank should hold 666 cubic feet or about 4, 1 50 gallons ; a larger capacity is desirable, how- ever, if it can be obtained, but much depends upon what purposes the water is used for. In the case of most houses a tank holding 100 days' supply would be * drought-proof.' The water before being used for drinking purposes should be passed through an efficient filter.

" There is no question that many rural districts might make far more use of rain-water for domestic purposes than is now the case."

In this brief account of Rural Water Supplies and their Purification the Author has doubtless failed in many particulars, but if the reader cares to write and explain his (or her) difficulties, or to offer any suggestions or criticisms, the Author will endeavour to answer any such communications to the best of his ability.

A. C. HOUSTON,

19, Fairhazel Gardens, London, N W.

128

INDEX

INDEX.

Acids :

For estimating alkalinity, etc., 51, 55,

Il6, 122

For neutralizing lime (CaO) : Citric, 34, 116, 121, 123 Phosphoric, 33, 116 Tartaric, 34, 116, 121, 123 Actual experiments:

Results of (Chaps. VI.andVII.),69-iol Algal (and other) growths :

See Growths (in water) Alkalinity :

Determination of, 51, 55 Aluminium sulphate:

For clarification, 36, 41, 46, 47, 78,

93,99

For neutralizing CaO, 24, 28, 31 Analysts :

Should be consulted, 52, 62 Animals :

Contrast between pollutions of human

and " lower animal" origin, 61 " Anti-chlor. " :

See Sodium sulphite Apparatus :

Description of, 102-114

Filtration methods, 107

Floating-arm method of draw-off, 102

Mixing pan, 102

Rigid outlet method, 106 Atmospheric pollution:

Committee's investigations, I

Composition of, 2

Gas and electric heating v. coal fires, 4 Atomic weights, 117 Awakening :

Great awakening in progress, vii.

B

Bacillus coli :

Why its destruction is evidence of

safety, 70 Presumptive and confirmatory tests

(see these headings) Reasons for applying the test, 70 Bacteria (microbes, bacilli) : See Bacillus coli

See Typhoid fever (typhoid bacillus) Baird and Tatlock :

Reference to, xv.

Bale, Messrs. John, Sons and Daniels- son, Ltd.:

Publishers of this book and " Rivers as Sources of Water Supply," i., ii., v. Bermuda : , Population of, 2, 124

Rain-water, supply of, 2, 124 Birds (also rats, mice, insects, etc.) : In relation to pollution of rain-water,

8, n, 38, 126

Bleaching powder (chloride of lime) : See Chlorine

Strength in available chlorine, 39 Braisted (Surgeon-General) :

U.S. Navy and distilled water, 36 Brooks (burns):

See Rivers Buildings :

Destructive action (on) of sulphur and ammonia, 4

C

Call

Of the country, viii. Cambridge University Press:

Publishers of "Sewage Purification and Disposal," 124

9

129

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Capacity :

In gallons of rectangular and cylin- drical vessels, 120 Carbon :

In air, 3 Carbon-dioxide :

In air, 2

In water, 14, 49 Carbonic acid:

Amount of lime needed to combine with CO2 in water, 29

" Carbonic acid water," 26

In air, 2

In water, 14, 49 Changes :

Impending, vii. Chapter I. :

Rain-water, 1-12

Summary, i

Concluding remarks, 12 Chapter II. :

Rain-water (continued), 13-34

Summary, 13

Concluding remarks, 34 Chapter III. :

Rain-water (continued), 35-47

Summary, 35

Concluding remarks, 46 Chapter IY.:

Well-water and spring-water, 48-57

Summary, 48

Concluding remarks, 57 Chapter Y. :

Rivers and lakes (taste of water),58-68

Summary, 58

Concluding remarks, 67 Chapter YI.:

Actual experiments, 69-89

Summary, 69

Concluding remarks, 88 Chapter YIL:

Actual experiments (contd.)t 90-101

Summary, 90

Concluding remarks, 101 Chapter YIII. :

Description of apparatus, 102-114

Summary, 102

Concluding remarks, 113

Charcoal :

As an " anti-chlor.," 43 For removing taste, 64 How to prepare it, 123

Chemicals :

Atomic weights, &c., of, 117 Description of, 114

Chloride of lime (bleaching powder) :

See Chlorine Chlorine (for sterilization purposes) :

As bleach solution, 37 As chloros, 37

As electrolytic compounds, 38 As liquid chlorine, 44 Chlorine sterilization and clarification by means of aluminium sulphate, 41 Ditto plus charcoal, 43 Combined with lime sterilization, 43 Dose for sterilization purposes, 39, 122 Potassium iodide and starch test for

active chlorine, 40, 116 Prejudice against its use, 38 Preparation of bleach solution, 39 Results of actual experiments with bleach solution and rain-water, 69 Results of actual experiments with

lime and rain-water, 76 Sodium sulphite as an "anti-chlor.,"

4i> H6

Strength of bleaching powder (or chloride of lime) and of chloros in terms of available chlorine, 37 "Chloros":

For sterilization purposes, 37 Strength in available chlorine, 37 See also Chlorine Coagulants :

See Aluminium sulphate Coal:

Fires wasteful and polluting, 5 Products of combustion, 4 Coastguard stations: Water supply of, 2 Colon bacillus:

See Bacillus colt

Combined lime and chlorine methods of sterilization, 43

130

INDEX

Committee on atmospheric pollution :

Expression of results, 6

Standard gauge, 6 Comparison

Between drinking and breathing im- purities, 5 Concluding remarks:

(See end of each chapter) Conclusions

At end of each chapter

See concluding remarks Confirmatory B. coli test :

See Chap. VI., Series L, II., III. and

IV. (I., II., III.), 69-83 Contamination :

Of atmosphere, 3

Of water, i, 5, 8, 10, 12, 38, 48, 59,

61, 70-101 Contents :

Arrangement of, xiii. Conversions :

English weights and measures into Continental weights and measures, &c., 119 Cost of

Chemicals, apparatus, &c., 122 Country :

Rural yearnings foreshadowed, viii.

D

Dakin

On sterilization, 46 Dedication

(To Sir William Osier), iii. Deposit

From rain, nature of, 7 Dose

Of chlorine for sterilization, 39, 43,

69, 81, 122

Of lime for sterilization, 17, 19, 29, 3i, 33. 43. 76, 82, 83, 86, 88, 90, 93, 96, 101, 121 Dunham

On sterilization, 46

E Elements :

Symbols and atomic weights of, 117

Estimations of

Amount CO2 required to neutralize

CaO, 26 Amount of lime (CaO) rendered inert

by certain substances in water, 14, 49 Bicarbonates, carbonates and

hydrates, 55

Excess lime (CaO), 14, 55 Permanent hardness, 18 Sulphates, 17 Total hardness, 50 Excess lime method

As applied to rain-water, 13, 76, 82 As applied to river-water, 61, 78, 83,

88,99

As applied to well-water, 49, 96

Dose required (see Dose)

How added to water, 19

How estimated, 14, 55

Lime, time and sterilization, 32, 84

Neutralization of excess, 22-31, 120

Simple " blind " methods, 29 Excremental pollution :

Human, I, 10, 12, 61

Lower animals, 8, n, 38, 126 Experiments :

The result of actual experiments, 69, 101

F

Factors for

Amount to neutralize active chlorine of

Sodium sulphite, 41 Amount to neutralize aluminium sul- phate of

Sodium carbonate, 24 Amount to neutralize CaO of Aluminium sulphate, 24, 12 1 Sodium bicarbonate, 25, 121 Sodium phosphate, 22, 120 Available chlorine in bleaching pow- der, 39

Available chlorine in chloros, 39 Figures :

Description of, xv. Filtration methods : Home-made filter, 107 Patent filters, 107 Future

Possibilities r; rural water supplies.vii.

131

RURAL WATER SUPPLIES AND THEIR PURIFICATION

G

Oases

In air from coal combustion, 4 Gibraltar:

Water supply of, 2 Growths (in water) :

Algal and other growths, 66

Anabsena, 66-67

Chara, 66-67

Eudorina, 66-67

Glenodinium, 66-67

Pandcrina, 66-67

Sponges, 66-67

Stephanodiscus, 66-67

Synura, 66-67

H

Halazone

For sterilization purposes, 46, 47 Hardness :

Estimation of, 18, 50

Hard waters, 49

Permanent, 18

Removal of, 96

Soft waters, 13, 93

Temporary, 50

Total, 50 Heat

As a sterilizing agent, 35, 98 Help

Offer of, 128 Hypoehlorites from salt solution :

Hypochlorites (calcium), see Bleaching powder

Hypochlorites (sodium), see Chloros

Illustrations :

Description of, xv. Indebtedness to, xv.

Indicators :

Methyl orange, 16, 55, 115 Phenol phthalein, 14, 55, 115 Potassium iodide and starch solution, 40, 116

Information (lack of)

In relation to purification of rural water supplies, vi.

Iron (in waters), 66

K

Kershaw, G. B. :

Author of 'Sewage Purification and

Disposal," 124 Views on rain-water supplies, xv., 124

Lakes (reservoirs) :

See Rivers "Lancet":

Reference to, 2 Lime:

See also Excess lime

Word used to describe substances of

different composition, 1 14 Lime water:

Its preparation, 21

Macmillan and Co.:

Publishers of "Studies in Water

Supplies," ii., v., 66 Malvern :

Type of rain-water, 8 Mason (Dr. W. P.) :

Reference to, 2, 36 Measures :

Burette, 16

Measuring cylinder, 15 Measures and weights, 117 Medical Officers of Health

should be consulted, 49 Methyl orange (see Indicators) Metropolitan Water Board:

Tribute to the. xi. Micro-photographs :

Description of, xv. Milk of lime :

Its preparation, 21 Miscellaneous :

Miscellaneous experiments, 98

Sterilization by means of heat, 98 Sterilization by means of lime, 99

Miscellaneous information, 114 Mode of life :

Contemplated changes in, viii.

132

INDEX

Moorland (soft peaty) water :

Sterilization by means of lime and chlorine, 93

N Neutralization of excess lime :

Amount required of

Aluminium sulphate crystals, 24,

121

" Carbonic acid water," 26, 121 Citric acid, 34, 121 Sodium bicarbonate, 25, 121 Sodium hydrogen phosphate, 22,

120

Tartaric acid, 34, 12 1 Nitrogen : In air, 2

Osier (Sir William)

Dedication to, iii. Oxygen

In air, 2 Ozone for sterilization purposes, 45

P

Photographs :

Description of, xv. Pollutions :

Of air (gaseous), 4

Of air (solid), 3

Of water (see Contamination) Potassium iodide and starch test for

active chlorine, 40, 116 Precipitants :

See Aluminium sulphate Preface :

Anticipated changes, vii.

Future possibilities, vii.

Lord Sydenham's views, xi.

Metropolitan Water Board, xi.

Potential readers, ix.

Questions of scope and principle, x.

Rural needs, v.

Tribute to staff, xi.

War (effect of), vii. Presumptive B. coli test:

See Chap. VI., Series I., II., III., and IV. (I., II., III.), 69-83

Principles of treatment:

Much the same for rural as for public supplies, x.

Qualifying considerations :

Re safety of rain-water, 10 Quality of water:

See Contamination of water Questions of safety:

Analysts, medical officers of health, &c., should be consulted, 49, 52, 62

Topographical surroundings, &c., of wells, &c., should be studied, 48, 49, 57. 60, 67

Rain-water:

Bermuda water supply, 2, 124 Chemical analyses of, 8, IO Collection of, 8, II, 124 Gibraltar water supply, 2 Impurities from roofs and gutters, 8,

126 In relation to : —

Ammoniacal nitrogen, 10

Chemical composition, 7, 8, 10

Colour, 10

Excess lime method, 13, 76, 82

Excreta of lower animals, 8, 11, 38, 126

External sources of pollution, 10

Human excremental pollution, 10

Inter-communicable diseases, 1 1

Its use for drinking purposes, 12, 124

Oxidizable matter, 10

Physical appearances, 8, 9, 12

Potability, 12, 63

Qualities of, compared with raw Thames and Thames - derived filtered waters, 10

Questions of safety, I, IO, 12

"Separators," 8, 126

Softening, 17

Sterilization (see that heading)

Storage in bulk, n, 124

Straining through wire gauze (also muslin or linen), 19

133

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Rain-water— continued : Taste, n, 12, 63

Kershaw's views re utilization of, 128

Pollution from air, 5

Separation of first " washings," 8, 126

Soluble and insoluble matter in, 7

Yield per 100 square feet of roof, 126 Readers :

Writer hopes to reach, ix. Reason

Why B. coli test a criterion of safety,

70 Rivers as Sources of Water Supply :

Reference to, ii., v. Rivers (brooks and lakes) :

Comparison purified and non-purified supplies, 59

Concluding notes as regards treat- ment, 61-67

Danger of contamination from "car- riers," 60, 62

Danger of surface supplies, 59, 60, 67

Flood water, 60-6 1

General guiding considerations, 61

Importance of topographical survey, 67

Questions of lead poisoning, 60

Questions of taste, 65

Suggestions as regards treatment, 60

Variations in quality, 59 " Roberts " Separator, 127

" Sewage Purification and Disposal " :

Quotations from, re rain-water, 124 Simple

Methods of sterilization, 29 Smoke Abatement Exhibition (1912), i Sodium bicarbonate

For neutralizing CaO, 25, 28, 121 Sodium carbonate

For neutralizing aluminium sulphate, 24, 28, 31

For removing permanent hardness, 18 Sodium phosphate

For neutralizing CaO, 22, 120 Sodium sulphite

As an " anti-chlor.," 41

Sooty matters :

As affecting taste (see Rain-water) Produced by imperfect combustion of coal, 3

Springs :

Concluding notes as regards, 56 If impure, how best treated, 56 Purity of, 56 Questions of potability and palata-

bility, 56, 65

Topographical surroundings, 57 Staff:

Tribute to, xi.

Standard solutions :

Lime water, 116

Soap, 116

Sulphuric acid, 116 Starch :

See Potassium iodide Sterilization:

Actual experiments on the steriliza- tion of rain and other waters by means of lime, chlorine, heat, &c., 69 et seq.

Amount of lime used up by COa. bicarbonates, &c., in rain-water must be allowed for, 14, 49, 55

Available chlorine in bleaching powder and "chloros," 39

B. coli test taken as criterion of safety, 70

Chlorine compounds in relation to sterilization (bleaching powder, "chloros," liquid chlorine, elec- trolytic compounds), 37 et seq.

Combined lime and chlorine methods for sterilizing rain-water, 43

Dose of available chlorine for sterili- zation of rain-water, 39

Dose of lime and chlorine for general sterilization purposes, 121-122

Excess lime method of sterilizing well-waters, 49, 96

Halazone as a sterilizing agent, 46

Heat, chlorine and electrolytic com- pounds, ozone and ultra-violet rays and combined lime and chlorine methods of sterilizing well-waters ,54

134

INDEX

Sterilization— continued :

Heating water in order to sterilize

it, 35

How to determine amount of lime used up by CO2, &c., in rain- water, 14 Lime (excess) method (see Excess

lime method)

Lime needed for sterilization of rain- water, 17, 30, 33, 76, 82, 83, 88 Liquid chlorine as a means of steriliz- ing water, 44 Ozone, hypochlorites and ultra-violet

rays in relation to sterilization, 45 Preparation of bleach solution for

sterilization purposes, 39 Rivers and lakes in relation to sterili- zation, 60

Spring-water in relation to sterili- zation, 56 Sterilization by means of chlorine (see

Chlorine) Sterilization by means of distillation,

36 Storage tanks

For holding rain-water in bulk, 1 1, 124 Studies in Water Supply:

Reference to, ii., v. Sulphate cf aluminium: Ste Aluminium sulphate Sulphates :

In relation to destructive effect on

buildings, 4

In relation to hardness, 17 Sulphite of soda:

See Sodium sulphite Sulphur :

In air, 4 Sulphuretted hydrogen:

In well-water, 66 Summary :

(See beginning of each chapter) Suspended matters:

Photographed (see figs. I and 9) In rain-water, 9 In river-water, 6l Sydenham (Lord):

Views on Home Settlement, xi. Symbols, 117

Tables (in I. II.

III. IV.

V. VI. VII. VIII.

IX.

X.

XI.

XII.

XIII.

XIV.

XV.

XVI.

XVII.

XVIII.

XIX.

XX.

XXI.

XXII.

XXIII.

XXIV.

XXV,

T

sequence) :

Composition of normal air, 2

Analysis of solid matter from

ventilator filters, 3 Analysis of sooty matters, 4 Deposit per acre per month

(rain-water), 7 Analysis of relatively pure

rain-water, 8 Analysis of town rain-water,

10 Analyses of raw Thames and

Thames//^ra? waters, 10 Lime, time and tank capacity

in relation to sterilization,

33

Estimation of bicarbonates, carbonates and hydrates (based on A.P.H. A. table),

55

Sterilization of rain-water with bleach solution, 75

Sterilization of rain-water with lime, 77

Purification, clarification, softening of impure river- water by means of lime, 80

Compare with Table X., 81

Compare with Table XI. , 82

Compare with Table XII. ,83

Lime, time and sterilization, 86

Rain-water, lime and sodium phosphate treatment, 92

Sterilization and clarification of moorland waters, 95

Hard well-water, lime and sodium bicarbonate treat- ment, 98

Symbols and atomic weights, 117

Weights and measures, 117

Apothecaries1 weights, 118

Table of costs, 123

Daily yield of water from 100 square feet of roof, 126

Particulars of rain-water 11 separators," 127

135

RURAL WATER SUPPLIES AND THEIR PURIFICATION

Tarry matter:

In air, 3 Taste :

Chlorine (due to), 43, 44, 64

Of brooks, 65

Of deep wells, 66

Of lakes, 66

Of rain-water, II, 12, 63

Of rivers, 65

Of wells and springs, 65

Potassium permanganate, filtration, charcoal, chlorine, &c., in relation to taste, 63

Some causes of taste (algal growths, chara, sponges, &c.). 66

Sooty matters (causing), 63 Time (duration of contact) :

In relation to sterilization, 32, 84 Typhoid fever (typhoid bacillus) :

Death of B. colt taken as index of destruction of typhoid bacillus, 70

Heating water, 36 Topographical notes:

As regards springs, 56

As regards surface supplies, 60, 61, 67

As regards wells, 48

U

Ultra-Yiolet rays :

For sterilization purposes, 45

W

Water supplies :

Distilled water, 36

Rain-water, Chapters I., II., III.,

i, 13, 35 Rivers, brooks and lake - water,

Chapter V., 58 Rural, importance of, v. Various waters in relation to actual

experiments, 69-101 Well - water and spring - water,

Chapter IV., 48

Water Supply

Rivers as sources of,

Studies in,

References to, ii, v. War:

Post-war conditions, viii. Weights and measures, 117 Well-water :

Amount of lime needed to combine with CO:., bicarbonates, &c., 49

Combined lime and chlorine method, 54

Concluding notes, as regards treat- ment, 56

Estimation of alkalinity, 51

Estimation of total hardness, 50

Excess lime treatment of, 53, 96

How to estimate bicarbonates, carbonates and hydrates, 55

Lime and sodium bicarbonate treat- ment as judged by actual experi- ments, 96

Lime required for sterilization pur- poses, 55

Points to be remembered in lime treatment, 54

Questions of purity, 48

Substances used for neutralizing excess lime (sodium bicarbonate, " carbonic acid water," citric and tartaric acids), 53

Topographical surroundings, 48, 57, 167

Treatment by means of heat, chlorine, electrolytic compounds, ozone and ultra-violet rays, 54

Usually hard, 49, 57 Where to find things:

See Contents

See Summary at beginning of each

chapter Wiley (Messrs. John, and Sons) :

Reference to, 2, 36 Woodhead (Sims) :

Authority on filters, 107

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