6 A - Q [ 
 
 OF THE 
 
 UNtVE.'fiSITY of ILLINOIS. 
 
 rfmqtf storage 
 
 POTABLE WATER 
 
 BY 
 
 PROFESSOR FLOYD DAVIS, M. Sc., Ph. D., 
 
 ...^GJrEMtST OF IOWA STATE BOARD OF HEALTH. 
 
 “ lie who learns the rules of wisdom without conforming to them in his life y 
 is like a man who labored in his fields but did not sow — Saadi. 
 


 L! cn Aii.i 
 
 OF THE 
 
 UNIVERSITY of ILLINOIS. 
 
 POTABLE WATER. 
 
 « 
 
 I. PURE WATER. 
 
 Water is a chemical compound of hydrogen and oxygen, which 
 is widely diffused in nature. As a solid, it exists as snow and ice; 
 as a liquid, it constitutes streams, lakes and seas, and in a state of 
 minute subdivision, mist and clouds; while as a colorless gas, it is 
 always a constituent of the air. Natural waters are always impreg- 
 nated with certain foreign constituents which give to them their 
 varying properties; and in the examination of water for sanitary 
 purposes, it is not the water which is analyzed, but its impurities. 
 
 The palatability of water depends upon its occluded gases, which 
 are principally oxygen, nitrogen, carbonic anhydride and hydrogen 
 sulphide. These gases are readily absorbed, and they give to the 
 water an agreeable taste, and a sparkling brilliancy. The high 
 degree of palatability of spring-water is mainly due to its carbonic 
 anhydride. Distilled water, or water deprived of its gases by boil- 
 ing, is insipid or u flat ; ” but by aeration and acidification it regains 
 its palatability. Water must be more or less impregnated with 
 gases before it is even suitable to the dietetic needs of man; for 
 when water deprived of its gases, is used for purposes of experi- 
 ment, it is found to be prejudicial to health, as the stomach cannot 
 gratefully receive and advantageously appropriate it. (*) 
 
 Researches in etiology have shown that the health of an individ- 
 ual, or of a community, depends largely upon the purity of the 
 water supply. It is not chemically pure water, however, that is 
 needed for the maintenance of perfect health, for such water does 
 not exist in nature. As chemically pure water contains nothing 
 injurious to the system, it likewise contains nothing beneficial, and 
 for healthy persons, such water is not the most wholesome. The 
 
 (!) Van Nostrand’s Engineering Magazine, December, 1872, p. 593. 
 
 
— 4 — 
 
 healthy human system ordinarily requires mild cathartics and other 
 mineral salts for the continuity of health. These, in part, can be best 
 furnished to the system as the mineral constituents of potable water. 
 The wholesomeness of water is therefore increased by the presence of 
 small quantities of certain mineral salts, in solution, which act as laxa- 
 tives, and which are essential to the development of animal tissue; 
 but drinking water should be free from organic impurities. As a 
 rule, chemists condemn all waters which are contaminated with sew- 
 age, such contamination being shown by chemical and micro- 
 scopical analyses, and by an examination of the sources of supply. 
 From a sanitary standpoint, pure water may be defined as water 
 which is unobjectionable for general domestic use, and especially that 
 which may be used with perfect safety for drinking purposes. 
 
 Some waters are so unpotable that the appetite does not demand 
 the amount required for the normal functions of the body. Such 
 waters not only lessen bodily vigor and frequently produce disease, 
 but an insufficient supply of any water is manifested by great pain, re- 
 laxation of muscular strength and of mental vigor, and diminution in 
 the elimination of pulmonary carbonic anhydride and bodily excre- 
 tions. So, when we consider that about seventy ( 2 ) per cent of the 
 human body is composed of water, which is being constantly 
 eliminated, the need of maintaining a copious supply of pure water 
 becomes apparent; but an abundance of water is no more necessary 
 to the support of life than its purity is to the continuity of health. 
 People may habitually drink impure water and still live, but its 
 use unquestionably affects the human system and tends to the degen- 
 eration of a race. Experience shows that even slightly impure 
 water may be productive of a host of ailments for which the sufferer 
 finds no apparent cause; for the results are often so slow and grad- 
 ual as to evade ordinary observation, and the evil is borne with 
 the indifference and apathy of custom. It is only when striking 
 and violent effects are produced that public attention is arrested. 
 
 A water which is constantly used for domestic purposes should 
 have the following qualities: 
 
 (2) Human Physiology, Dalton, Seventh Edition, p. 36. 
 
— 5 — 
 
 1. It should be free from odor and taste. 
 
 2. It should be free from dead vegetable and animal organ- 
 isms, and should contain only such living forms as are purifying 
 agents. 
 
 3. It should at all seasons of the year be well aerated, uniform 
 in temperature, and free from suspended matter. 
 
 4. It should contain only a small quantity of mineral matter 
 in solution, and be free from all the poisonous salts. 
 
 For persons afflicted with renal diseases, distilled water in its 
 crystalline purity is probably the most healthy beverage, for it acts 
 upon the kidneys as a powerful therapeutic agent in the solution 
 and removal of the waste products of the body. Upon this point 
 Professor Charles Mayr( 3 ) says : 4 ‘ Those who have never drunk pure 
 
 water do not realize what an effect such water has upon the kidneys; 
 its effect is better than that of acetates, nitrates, opiates or alcohol, 
 and for people with tendency to kidney diseases or Dropsy there is 
 no better drug than pure water. Of the thousands of chemical 
 compounds and waste products found in the human system, many 
 require pure water for their solution and elimination; and water so 
 overloaded with salts as average well-water will not work satis- 
 factorily.” 
 
 II. INORGANIC IMPUEITIES. 
 
 Water is the most nearly universal solvent in nature, and as it 
 passes into the earth, charged with atmospheric gases, it dissolves 
 many salts. When it reappears again on the surface in springs, 
 and flows away in streams, it is often heavy laden with mineral con- 
 stituents; but the streams and lakes in granite regions are very 
 nearly pure. The oceans and inland seas are the final reservoirs of 
 flowing water, and they become saline from the concentration of 
 their mineral matter, through evaporation. Sea water contains 
 about two thousand grains of total solids per gallon, while the 
 waters of the Great Salt Lake and the Dead Sea each contain about 
 twelve thousand grains. ( 4 ) 
 
 ( 3 ) Report of New Jersey State Board of Health, 1887, p. 338. 
 < 4 ) Manual of Mineralogy and Petrography, Dana, p. 252. 
 
— 6 — 
 
 From an examination of the water supplies of sixty-five Eng- 
 lish and Scotch cities and towns, Dr. H. Letherby,( 5 ) an emi- 
 nent English chemist and sanitarian, concluded that the rate of 
 mortality was inversely as the amount of mineral salts in the water 
 supplies. 
 
 Only certain constituents, however, are beneficial to health; others 
 are deleterious; and a water which contains too large an amount of 
 mineral salts should be avoided, as it is liable to produce derange- 
 ments in the alimentary canal. 
 
 When the amount of mineral constituents in water becomes so 
 excessive as to give it decided medicinal properties, the water is 
 styled mineral or abnormal. Many salts have a characteristic taste, 
 and the nature of mineral waters can, therefore, often be determined 
 by the sense of taste alone. Mineral waters are classified according 
 to the principal substance in solution. Thus a chalybeate water 
 has in solution an excess of an iron salt, usually carbonate or sul- 
 phate, and which, upon standing exposed to the air, generally 
 deposits a yellow precipitate of carbonate of iron; a saline water 
 has in solution an excess of some salt, like sodium chloride, or 
 sodium and magnesium sulphate; a carbonated, effervescent or 
 acidulous water has carbonic anhydride in excess; while a sulphur 
 or hepatic water contains an excess of hydrogen sulphide. Upon 
 standing, hepatic waters become somewhat turbid and deposit sul- 
 phur. 
 
 Saline waters, when used occasionally and moderately, are bene- 
 ficial to health, owing, in part, to the cathartic action of the 
 sulphates and phosphates of the alkalies and alkaline-earths, which 
 are usually found in such waters; but their excessive use, or the 
 prolonged use of waters containing too much salts in solution, 
 should be avoided. Saline waters often afford relief to persons 
 afflicted with Inflammatory Rheumatism, when they are frequently 
 used for bathing purposes. Carbonated waters are not only highly 
 palatable, but they are very beneficial to persons suffering from 
 Dyspepsia. But waters containing much hydrogen sulphide are 
 
 ( 6 ) Report of Michigan State Board of Health, 1876, p. 78. 
 
— 7 — 
 
 not really wholesome, as they will produce Diarrhea, ( 6 ) especially 
 if organic matter be present; but in small quantity hydrogen 
 suphide is not in any way injurious to health. 
 
 Some salts are productive of Indigestion, and in many cases Con- 
 stipation and visceral obstruction are induced by the use of mineral 
 waters. Chalybeate waters not unfrequently induce in the 
 drinker, Headache, Indigestion and Dyspepsia. A drinking water 
 should not contain more than one fifth( 7 ) of a grain of iron per 
 gallon. Calcium and magnesium chlorides and sulphates will pro- 
 duce Chronic Diarrhea, and if the water also contains ammonium 
 and calcium nitrates and sodium chloride in excess, and is used 
 freely, it is sometimes the cause of Dysentery. Dyspepsia is also 
 frequently produced by water containing calcium and magnesium 
 salts. Goitre, so frequently found among the inhabitants of some 
 of the valleys of Switzerland, is caused by the excessive permanent 
 hardening constituents of the water. A water containing not more 
 than seven( 8 ) grains of salts per gallon is said to be injurious to 
 many persons. u With regard to the total quantity of impurities 
 admissible in good drinking water, the Sanitary Congress which 
 met at Brussels decided that water containing more than thirty-five 
 grains of impurity in one gallon is not wholesome, and that there 
 should not be much more than one grain of organic matter.”( 9 ) 
 
 The normal carbonates of the alkaline-earths, magnesium and 
 iron, are practically insoluble in pure water. ( 10 ) But the bicarbon- 
 ates of these metals, which are readily soluble, are formed by the 
 union of carbonic anhydride and water, with the normal carbonates, 
 and there is scarcely a natural water which does not contain a small 
 amount of them. It is claimed by some eminent authorities that 
 small quantities of these bicarbonates in drinking water are bene- 
 ficial to health; but experience has also shown that large quantities 
 
 (6) Practical Hygiene, Parkes, Seventh Edition, p. 58. 
 
 (7) Water Analysis, Wanklyn and Chapman, Sixth Edition, p. 61. 
 
 (8) Practical Hygiene, Parkes, Seventh Edition, p. 56. 
 
 ( 9 ) Report of American Public Health Association, Vol. I, p. 538. 
 
 ( 10 ) “ About one grain of calcium carbonate to the gallon is usually stated to be the 
 proportion dissolved, but it has been pointed out lately by Allen, that this is an under- 
 statement, since solutions have been obtained containing twice this amount.”— 
 [Examination of Water for Sanitary and Technical Purposes, Leffmann and Beam, p. 
 
— 8 — 
 
 of these salts are sometimes injurious. If in excess, they are 
 decomposed in passing through the system, and give rise to renal 
 and bladder difficulties, which often culminate in Gravel. The 
 bicarbonates are not generally found in well-waters in excessive or 
 dangerous quantities; but the continued use of spring-water which 
 flows from limestone rock will eventually give rise to disease, for 
 communities which use only limestone water are generally afflicted 
 with diseases which arise from overworked kidneys. These bicar- 
 bonates are the constituents of temporary hardness in water, and 
 they can be removed by boiling, as by this operation bicarbonates 
 are decomposed into normal carbonates, which precipitate, and 
 carbonic anhydride and water which escape. Water is usually 
 rendered permanently “hard” by the solution of the sulphates of 
 calcium, magnesium and iron. 
 
 The salts of some elements, like arsenic, antimony, barium, 
 chromium, zinc, copper and lead, are dangerous poisons, and 
 water containing even traces of them should always be avoided. 
 Lead poisoning is not unfrequent in some cities where the water 
 for domestic use passes through lead pipes. Aerated water tends 
 to dissolve lead, forming a hydrate, which in presence of carbonic 
 anhydride in excess, forms a slightly soluble bicarbonate of lead. 
 Chlorides and nitrates in water also tend to form insoluble com- 
 pounds on the inner surface of the pipes, which prevent further 
 action of the oxygen upon the lead. Lead pipes should, therefore, 
 only be used in conveying drinking water, which contains an excess 
 of sulphates or normal carbonates in solution. Indeed, it is 
 doubtful whether lead pipes should be used at all for a water sup- 
 ply, as a water which contains a sufficient quantity of the necessary 
 salts to prevent the solution of lead, is liable to produce derange- 
 ments in the alimentary canal. 
 
 Potable water often contains suspended mineral matter, such as 
 sand and clay, and it is believed that an excessive turbidity caused 
 by these, is productive of intestinal difficulties, Indigestion, 
 Dyspepsia and Diarrhea. The character of the suspended matter 
 can only be fully determined by means of the microscope. 
 
— 9 — 
 
 III. VEGETABLE IMPURITIES. 
 
 r 
 
 The turbidity of water is sometimes produced by decomposing 
 organic matter, which is, with the exception of pathogenic germs, 
 the most deleterious of all impurities. 
 
 Although the products of vegetable decay indirectly produce 
 malarious diseases, they are not in themselves especially injurious 
 to the human system ; they merely furnish a pabulum in which cer- 
 tain disease germs flourish, for the malarious influence is attributed 
 by medical science to micro-organisms. These living germs are 
 most frequently conveyed to the system in the air, but the most 
 dangerous types of malaria are caused by polluted water, which 
 seems to be a more concentrated and dangerous poison than malari- 
 ous air. And in the production of remittent fever ( u ) by malarious 
 surface-water, it is noticeable that the disease is always of a more 
 aggravated type than when caused by exhalations from miasmatic 
 soil. So, water which shows by analysis that it contains decom- 
 posing vegetable matter, should always be avoided. 
 
 By the drainage of swamps and the cultivation of the soil, com- 
 munities have often freed themselves of much sickness of a dangerous, 
 malarious character. Decaying wood, like pump-stocks and storage- 
 tanks, often produce harmful results, through the water, and the 
 decomposition of sawdust ( 12 ) in water is a fruitful source of all 
 forms of malarious fever. 
 
 Many cases are on record from the American Civil War, in which 
 the use of surface-water, impregnated with the debris of plants, 
 like cellular tissue and chlorophyl, also produced Diarrhea ; but 
 when such water was filtered the disease abated. ( 13 ) The water 
 supplies of some of the eastern cities have at times a decidedly fish- 
 like odor, which Professor Lattimore has shown to be due to the 
 presence of Algos , , perhaps in a state of decomposition. The little 
 filaments of decomposing Algos, when seen under the microscope, 
 are usually changed in color and broken down in structure. It is 
 
 (U) Water Supply of U. S. Capitol, 49th Congress, 1st Session, Ex. Doc. No. 154, pp. 8-9. 
 ( 12 J Report of Michigan State Board of Health, 1882, p. 155. 
 
 ( 13 ) Practical Hygiene, Parkes, Seventh Edition, p. 57. 
 
10 — 
 
 the opinion of the most competent judges that waters containing 
 such filaments, if used for a considerable length of time, are very 
 injurious to health ; and certain Algoe in a water supply are some- 
 times accompanied by an alarming mortality of fish.( 14 ) Pond 
 water, in which there is a copious growth of aquatic plants, is said 
 to produce intestinal worms. 
 
 Recent investigations^ 5 ) have shown that many varieties of Algae 
 are probably capable of producing an objectionable taste and odor 
 in water, which, in case of the grass-green varieties, are especially 
 rancid ; but power to produce these changes is entirely independent 
 of color. Nostoc , a greenish, gelatinous, translucent variety of 
 Algae , which develops rapidly in wet places after a rain, is a fre- 
 quent source of contamination of water ; and it is of especial inter- 
 est in this connection as being the chief source of the unpleasant 
 u pig-pen” odor of water. The* intensity of the physical exponents, 
 taste and odor, may be taken as a measure of the rapidity of decom- 
 position of the Algae present in water at any given time, and they 
 are consequently a measure of its cryptogamic pollution. 
 
 But there are certain living Algae that may be taken as a measure 
 of the organic pollution of water. Thus, the Flagillata are gener- 
 ally found in water containing decaying infusions of vegetable and 
 animal matter, and they have been detected in the dejections from 
 Cholera and Typhoid Fever patients. The Beggiatoa alba , a species, 
 of Algae closely resembling some forms of Bacteria , is also only 
 found in stagnant waters, and it is, therefore, indicative of harmful 
 pollution. 
 
 Some waters which come from clay soil have so strong an odor of 
 hydrogen sulphide and sulphuretted hydro-carbons as to be undrink- 
 able, and yet the organic matter in them will not often warrant their 
 condemnation. These gases are probably produced in the decom- 
 position and reduction of sulphates, by decomposing organic matter, 
 and by living Bacteria and low forms of Algae. According to 
 Professor Nichols, ( 16 ) decaying organic matter, in water, under 
 
 (i±) On the Micro-Organisms in Hemlock Water, Rafter, p. 16. 
 
 ( 15 ) On the Fresh Water Algae, and Their Relation to the Parity of Public Water Sup- 
 plies, Rafter, p. 2. 
 
 (16) On the Fresh Water Algae, and Their Relation to the Purity of Public Water Sup- 
 plies, Rafter, p. 10. 
 
— 11 — 
 
 favorable conditions of temperature, reduces sulphates to sul- 
 phides, and from these, hydrogen sulphide is liberated by the acid 
 products of decay. 
 
 The genus Beggicttoa only exist in water containing some form of 
 sulphur, when free from iron. ( 17 ) These organisms probably possess 
 the power of extracting sulphur from decomposing organic matter 
 containing it, with the liberation of hydrogen sulphide. They also 
 possess the power of extracting sulphur from sulphates in water, 
 appropriating the sulphur in an amorphous state into the proto- 
 plasmic mass of their cell structure, with the liberation of the balance 
 of the sulphur as hydrogen sulphide. The presence of hydrogen 
 sulphide in a water supply is, therefore, no reliable indication of 
 organic pollution. 
 
 Pure water in thin layers is almost colorless, but in considerable 
 volume it has a decidedly bluish tint, which comes from its power 
 to absorb, reflect, and transmit white light. Rain-water is some 
 times highly colored with vegetable matter from the roofs of build- 
 ings, but it is often the healthiest of drinking water, on account of 
 the stability of its organic matter. The chlorophyl of unicellular 
 Algae , growing in water, often colors the water green. Peat gives 
 to water a brownish color, but analyses and long continued use 
 demonstrate that such water is usually wholesome. It is true that 
 such water has sometimes a laxative effect upon the system, but its 
 action is only temporary, and so can in no sense be injurious. Peat 
 water is often used for drinking purposes on long ocean voyages, 
 on account of its power of retaining freshness. 
 
 IV. ANIMAL IMPURITIES. 
 
 The products of decomposition of animal matter are always more 
 dangerous to the human system than those from vegetation, as some 
 of them are highly nitrogenous; and water which is contaminated 
 with the animal accumulations of sewers, cess-pools, and privies, is 
 a most loathsome and dangerous poison. A microscopic examina- 
 tion of polluted water often reveals the presence of hair, excreta, 
 intestinal epithelial cells, and living organisms. Such water should 
 
 ( 17 ) Water Analysis, McDonald, p. 25. 
 
— 12 — 
 
 be absolutely condemned for all sanitary purposes, as the impuri- 
 ties could only come from sewers and privy-vaults, and the living 
 organisms feast upon the products of decay. 
 
 Animal matter is highly putrescible, and water containing it is 
 liable to produce putrefactive changes in persons drinking it. The 
 nitrogenous matter decomposes by oxidation and disintegration, 
 through the agency of micro-organisms, producing in its earlier 
 stages, Ptomaines , bodies which are closely allied to the vegetable 
 alkaloids, but more susceptible of decomposition. Although the 
 Ptomaines are present in very small quantity in polluted water, 
 yet they are very active in their physiological effects, and produce 
 harmful results when taken into the system. Other products of 
 decomposition furnish a suitable pabulum for the accumulation and 
 multiplication of germs of disease. Many contagious and infec- 
 tious zymotic diseases are produced by water polluted with decom- 
 posing animal matter, and indeed, it is highly probable that certain 
 diseases are seldom produced in any other way. ( 18 ) Polluted waters 
 are often deceptive, since they generally have an agreeable taste 
 and are highly palatable. 
 
 In the Fall of 1887, Typhoid Fever became epidemic in Ottawa, 
 Minneapolis, Pittsburgh, and many other cities, and it was found 
 on examination that in every case known to the writer, the disease 
 was communicated through potable water. In Pittsburgh the cir- 
 cumstances were especially interesting. The south side of the city 
 was supplied by the Monongahela Water Co.’s works, and the fever 
 was located in districts supplied by that company. Upon chemical 
 and microscopical examination of the water, the pollution was 
 traced many miles above the city to a ravine into which drained the 
 privies of houses where four Typhoid Fever patients had been loca- 
 ted several weeks before. ( 19 ) 
 
 From 1856 to 1866 there were twenty-one thousand deaths from 
 
 ( 18 ) “ There is abundant proof that drinking water has been instrumental in the 
 spread of the following diseases: Cholera, Typhoid Fever, Dysentery, Diarrhea 
 Diphtheria, Malaria, Cholera Infantum, and Cerebro-spinal Meningitis; and in addition 
 to these, certain low forms of fever to which no other name than Continued Fever can 
 be given.”— [Report of Brooklyn Commissioner of Health, March 10, 1884, p. 19,] 
 
 (19; Report of Special Committee on South Side Water Supply, Pittsburgh, Decem- 
 ber 23d, 1887. • 
 
LIBRARY 
 
 OF THE 
 
 UNIVERSITY of ILLINOIS. 
 
 -13- 
 
 Cholera, and one hundred and fifty thousand deaths from Typhoid 
 Fever, in England and Wales ;( so ) while now in all of Great Britain 
 twenty thousand persons die and two hundred thousand suffer annu- 
 ally from Typhoid Fever, and the majority of cases are produced by 
 polluted water. ( 21 ) 
 
 In Michigan the annual mortality from Typhoid Fever is about 
 one thousand, while ten thousand persons are annually afflicted 
 with this disease. ( 22 ) 
 
 In the United States thirty thousand people die annually from 
 this fever alone. The mortality from Typhoid Fever in many of 
 the eastern cities is proportional to the quantity of sewage which 
 enters the water supplies. ( 23 ) The annual death rate from this 
 disease per one hundred thousand inhabitants in Brooklyn is 
 about fifteen, in Hew York city twenty-five, and in Boston forty ; 
 while in the city of Vienna, from 1851 to 1874, while impure 
 well-water and a supply from the Danube were used, the annual 
 death-rate was from one hundred to three hundred and forty per 
 one hundred thousand inhabitants. By the use of spring-water in 
 place of the former supplies, the mortality from Typhoid Fever,, 
 in Vienna, has been greatly reduced. During the last three years 
 the annual death-rate in that city has only reached eleven per one 
 hundred thousand inhabitants. 
 
 Some of the lowly-organized animal scavengers, which assimilate 
 the decomposition products of organic matter, are injurious to the 
 human system, but the majority of them are harmless, and nearly 
 all of them are purifying agents. 
 
 Polluted water is generally infested with Infusoria. ( 24 ) This is 
 especially true of stagnant surface-water, and the water from many 
 surface wells. Recent investigations in biology demonstrate that 
 nitrogenous food is necessary for the development of such life in 
 water ; but there are certain conditions not yet clearly understood, 
 
 (20) Report of Brooklyn Commissioner of Health, March 10, 1884, p. 78. 
 
 (21) Report of Michigan State Board of Health, 1884, p. 116. 
 
 (22) Report of Michigan Sanitary Convention, December 6 and 7, 1887, p. 24. 
 
 ( 23 ) Report of Committee on the Pollution of Water Supplies, American Public 
 Health Association, 1888, p. 5. 
 
 (24) “The Animal World of Well-waters,” Popular Science Monthly, June, 1889, pp. 
 251-257. 
 
— 14 — 
 
 favoring the transformation of harmless organic matter, in presence 
 of nitrogen salts and phosphates, into a favorable pabulum for the 
 growth of micro-organisms. ( 25 ) Phosphates are not usually found 
 in potable water, and the presence of infusorial life in water free 
 from phosphates, is, therefore, very reliable evidence of its pollu- 
 tion. 
 
 The ciliated embryos of certain Entozoa are sometimes found in 
 potable water. They are generally very active in early life, but 
 finally lose their ciliated covering and perish, unless they find their 
 way into the body of some animal drinking the water. 
 
 Cyclops , or water flea, is one of the most common genera of 
 Entomonstraca found in potable water. Dr. H. C. Sorby( 26 ) has 
 shown that the number of certain of the Entomostraca in water 
 may be taken as a measure of its organic pollution, for an increase 
 in sewage is indicated by an increase in their total number, or by 
 an alteration in the relative number of each species, or by both. 
 It is not known whether Infusoria , Entomostraca , and certain forms 
 of microscopical animal life are the agents or the companions of 
 disease, but serious outbreaks of Fever, Diarrhea, and Dysentery 
 have been produced by water swarming with these forms of life. ( 27 ) 
 
 Leeches are sometimes accidentally swallowed in potable water. 
 They are liable to attach themselves on the pharynx, and when 
 once fixed they seldom fall off spontaneously. Coughing, nausea, 
 and spitting of blood are produced by them, and repeated bleeding 
 from the larynx produces anaemia. ( 28 ) 
 
 Y. BACTERIA IN WATER. 
 
 Living germs are even more dangerous in drinking water than 
 animal organisms and dead organic matter. Some diseases, such 
 as Cholera, Typhoid Fever and Diphtheria, are generally believed 
 to be produced by micro-organisms, which, like the spores of some 
 plants, are thrown off with the excretions of persons suffering with 
 
 ( 25 ) On The Micro-Organisms in Hemlock Water, Rafter, p. 4. 
 
 ( 26 ) On the Micro-Organisms in Hemlock Water, Rafter, p. 25. 
 
 ( 27 ) On the Use of the Microscope in Determining the Sanitary Value of Potable 
 Water, Rafter, p. 11. 
 
 ( 28 ) Practical Hygiene, Parkes, Seventh Edition, p. 78. 
 
— 15 — 
 
 the disease, and they find their way mainly through the water sup- 
 ply, to those who, from predisposing causes, are in a suitable con- 
 dition for the reception and multiplication of the germs and the 
 production of the specific form of disease. These pathogenic micro- 
 organisms are known as Bacteria , and the diseases which they pro- 
 duce, zymotic, in consequence of their course resembling a process 
 of fermentation; but only few Bacteria are pathogenic. The most 
 common forms of these organisms are not more than one fifteen 
 thousandth or one twenty thousandth of an inch in length, and it 
 has been estimated that it would require four hundred million of 
 them of average size, to cover one square inch of surface. In their 
 multiplication, a single germ becomes the causative parent of thirty 
 or forty million descendents in a day. 
 
 In an interesting investigation ( 29 ) at the city of Paris it was 
 found that in a cubic metre of air above ground there were ten 
 thousand germs; in the sewers, thirty-six thousand; in old houses, 
 forty thousand; and in the hospital of Petie, seventy thousand. 
 And these organisms are absorbed by water exposed to the air. 
 
 Dr. Percy F. Frankland( 30 ) has found that average river-water, 
 like the Thames, contains about twenty thousand germs per cubic 
 centimetre, and that this number is greatly reduced when the water 
 is submitted to storage and filtration; but there is no reliable artifi- 
 cial method for their entire removal, except by the agency of heat. 
 
 Bacteria are almost universal in all kinds of matter. They in- 
 habit the air we breathe and the food we eat, and even the purest 
 water is never free from them. The harmless forms of Bacteria 
 have their uses in the economy of nature. It is to them that we 
 owe the phenomena of fermentation and decay, as they effect a 
 transmutation in organic substances, and finally elaborate them 
 nto organic products. By the united efforts of Bacteria , sugar 
 is converted into alcohol, and the cork of the champagne bottle is 
 discharged with explosive violence. While one class of Bacteria is 
 thus engaged in making alcohol, another class is fermenting it into 
 
 (29) Water, Moore, p. 7. 
 
 (39) Report of Maine State Board of Health, 1887, p. 316. 
 
—16 
 
 acetic acid; and other classes still are servants to the baker in rais- 
 ing his bread. 
 
 Each group of pathogenic Bacteria has its specific organ for at- 
 tack. Thus the Bacillus Tuberculosis generally has its seat in the 
 lungs; the Typhoid Bacillus penetrates the mucus membranes of the 
 intestines and accumulates in the spleen; and the Bacillus of Diph- 
 theria produces extensive layers of false membranes in the fauces. 
 Each group has its own distinctive character; some seem to evolve 
 higher types of life; some prey upon and seem to devour others; 
 and they are quite probably the cause or the result of every zymotic 
 disease. 
 
 In some instances, Bacteria are capable of being conveyed to 
 great distances in water, without losing the vitality necessary to 
 produce disease. Indeed, it is a very difficult matter to deprive 
 some forms of Bacteria of their vitality; they may be frozen or 
 even heated to the boiling point of water and yet many of them 
 are not destroyed. They may be kept dried for years, and when 
 placed in a favorable medium are yet capable of producing disease. 
 
 The noted outbreak of Typhoid Fever at Lausen, Switzerland, 
 and at Plymouth, Pennsylvania, has shown that the dejections from 
 a single Typhoid Fever patient are sufficient to poison the water 
 supply of a whole town, and give rise to an extended outbreak of 
 fever. It is, therefore, apparent that human faecal matter is very 
 dangerous, as it may contain germs capable of setting up a specific 
 form of disease. As sewage is largely made up of this kind of 
 matter, it is a very dangerous form of pollution. Sewer gases 
 are also productive of disease, ( 31 ) especially when the atmosphere 
 is heavy, as it then favors the accumulation of the products of 
 decomposition and the production of germs. Wherever Bacteria 
 are found abundantly, decomposing nitrogenous organic matter is 
 always present; and Pasteur has shown that Bacteria do not multiply 
 without a putrefactive environment, but remain infertile until they 
 perish. These germs only flourish in a neutral or alkaline mens- 
 trum, such as is produced by decomposing sewage matter, when 
 
 (31) Report of Michigan State Board of Health, 1885, pp. 64-65. 
 
— 17 — 
 
 aided by heat, and all standard authorities agree that these alkaline 
 waters are dangerous for drinking purposes. Water which contains 
 an excessive quantity of the alkaline carbonates tends to make the 
 system alkaline, and physicians often find it necessary to put 
 patients suffering with digestive, intestinal, and renal diseases, upon 
 distilled water as a beverage, and with happy effects. 
 
 In the healthy human system germs do not thrive, as the reaction 
 therein is acid. But in persons afflicted with digestive disorders, in 
 which the gastric juice is restrained, pathogenic germs find a fertile 
 soil and muliply with inconceivable rapidity. A free supply of 
 gastric juice will kill and digest them. ( 32 )* A good corrective for 
 alkaline polluted waters is sulphuric acid. This arrests putrefaction 
 and destroys the germs. Workmen, whose employment, location 
 and habits, favor an attack of zymotic disease, sometimes prevent 
 an epidemic by drinking water acidified with one or two drops of 
 sulphuric acid per pint of water. ( 33 ) Sulphuric acid is also often 
 used with great advantage in treating cases of Cholera and Typhoid 
 Fever, by giving ten to thirty drops of acid in water three times 
 a day. Hydronaphthol is aiso recommended as a corrective for 
 polluted water; it is a powerful germicide and is harmless to the 
 human system. Pyridine, a constituent of tobacco smoke, is 
 also a powerful destroyer of Bacteria. It is a fact worthy of notice 
 that men who use tobacco are less susceptible to zymotic infection 
 that those who do not use it, and that women are more frequently 
 attacked with Diphtheria and Typhoid Fever than men. 
 
 In the production of contagious and infectious diseases, it appears 
 that the organic matter throws the Bacteria into a state of excite- 
 ment in which they seize upon the membranes of the body and de- 
 velop the functional disturbance known as disease, and this disturb- 
 ance is in proportion to the degree of pollution of the water; while 
 in pure water the Bacteria remain in a latent condition. ( 34 ) Slightly 
 
 (32) The Sanitary Era, October 1, 1888, p. 76. 
 
 (33) Report of Examination of Water from the River Schuylkill, Cresson, pp. 13-14. 
 
 (34) Report of Connecticut State Board of Health, 1886, pp. 294-298; Reports of Kansas 
 State Board of Health, 1886, pp. 228-235; and 1887, p. 303. 
 
 2 
 
- 18 - 
 
 contaminated water often produces zymotic diseases in weakly per- 
 sons, while persons of robust health may withstand its action. But 
 it is impossible to banish disease from a town whose water supply 
 has been even slightly contaminated with the dejections from fever 
 patients, as the weakly inhabitants will contract the disease first, 
 from the almost inappreciable amount of infection contained in the 
 water, and from them the disease will spread to those who have 
 resisted its action in a diluted condition. 
 
 VI. WATER SUPPLIES. 
 
 Rain-water . — There is a popular idea that rain-water, as it falls, 
 is perfectly free from impurities; but in fact, the first fall of rain 
 after a drouth is swarming with living organisms, which multiply 
 and perish, polluting the water with the products of their decom- 
 position. Even the purest air contains myriads of motes which can 
 be seen in the sunbeam with the naked eye, and they are washed 
 from the air by the descending rain. The exhalations which rise 
 from decomposing organic matter, and float in the atmosphere, are 
 also carried down in the rain or even humid air, so the first rain 
 that falls during a storm is always more or less impure, and unfit 
 for drinking purposes; but the air becomes purified in a short time, 
 and the rain that falls thereafter is approximately pure water. 
 v The British Bivers Pollution Commissioners concluded that 4 4 half 
 a pint of rain-water often condenses out of about three thousand 
 three hundred and seventy-three cubic feet of air, and thus in drink- 
 ing a tumbler of such water, impurities, which would only gain 
 access to the lungs in about eight days, are swallowed at once.”( 35 ) 
 These impurities consist of ammoniacal salts, nitrous and nitric acids, 
 sodium chloride, calcium compounds, and organic matter; and the 
 solid impurities usually amount to two or three grains per gallon. 
 And when the water has drained from the roofs of buildings, after 
 a dry season, the . additional impurities consist of dust, dead insects, 
 excreta of birds, and probably dried disease germs. As the rain 
 falls, it becomes thoroughly aerated; but rain-water has usually a 
 
 (35) Potable Water, Ekin. p. 9. 
 
— 19 — 
 
 Eat, smoky taste, caused by the absence of carbonic anhydride and 
 alkaline salts. 
 
 In some of the southern cities, ( 36 ) near the Gulf of Mexico, where 
 it is impossible to secure a supply of pure well or spring-water, 
 rain-water is used extensively for domestic purposes. It is very 
 important in the construction of cisterns for storage of drinking 
 water that great care should be exercised in preparing the walls 
 against any leakage from cess-pools and privies. Rain-water, when 
 collected toward the end of storms and properly filtered through 
 sand and charcoal, is perfectly wholesome, provided there is no 
 drainage into the cistern. 
 
 Well-water . — The purity of well-water depends mainly upon the 
 depth and situation of the well, and the nature of the surrounding 
 soil. Deep wells, when properly made, are generally free from 
 organic impurities, but their waters are impregnated with harden- 
 ing salts. Artesian well-water is also free from organic impurities, 
 but it is usually highly mineralized. Deep well-waters are not 
 best suited to the digestive powers of man; and every intelligent 
 groom and herdsman knows that such waters are also more preju- 
 dicial to horses and cattle than even the water of a muddy stream. 
 
 The abundance of filth in densely populated cities renders the 
 soil unfit for the filtration and storage of water, and surface wells 
 in such soil furnish only a polluted and dangerous supply, as the 
 water is not sufficiently aerated for the oxidation of its organic 
 matter. These wells are frequently situated in too close proximity 
 to dwellings, stables, cess-pools, privy-vaults, and other sources of 
 pollution, and they are thus frequently important factors in dissem- 
 ' mating disease. 
 
 Rain-water, as it passes into the earth, extracts from the surface 
 soil great quantities of impurities, like decaying vegetation and the 
 filth and excrement of animals, which it carries down into the cir- 
 culating currents, and it often happens that the drainage of cess- 
 pools and privies finds a direct channel into the well. The germs 
 from diseased patients thus find their way to the water supply, and 
 
 (3®) Report of Connecticut State Board of Health, 1885, pp. 254-255. 
 
— 20 — 
 
 many surface wells are nothing more than receptacles for diluted 
 excrementitious matter. 
 
 It is said that the circulation of water is so thorough in the earth 
 that if a barrel of kerosene oil be placed ten feet under ground, every 
 well within a quarter of a mile will be contaminated, and the oil 
 will be apparent to the taste. ( 37 ) It has been demonstrated that in 
 compact soils, the level of the ground water is influenced by pump- 
 ing, for a distance of two hundred feet in all directions around a 
 well, while in loose, gravelly soils, the circle of influence may have 
 a radius of more than two thousand feet. ( 38 ) This produces a cir- 
 culation of water toward the center, and consequently a washing of 
 the filth of the soil into the well. No stable, cess-pool, privy-vault, 
 or other source of contamination should be within this radius. 
 
 Many severe outbreaks of epidemic diseases have been traced to 
 the use of surface well-water in cities, and there is strong reason 
 to believe that sporadic attacks oi Typhoid Fever often occur in 
 isolated country homes from the same cause. When scientific views 
 concerning the pollution of well-waters are disseminated, surface 
 wells will be rapidly abandoned by the intelligent classes. 
 
 In the ordinary method of bricking or walling a well, no protec- 
 tion is offered against surface drainage, and a deep well thus con- 
 structed is no better than a surface well. Open wells should always 
 be walled with hydraulic cement above the water line, to prevent 
 the admission of filth. Surface contamination is also prevented by 
 the use of deep “ drive-wells with these the only pollution comes 
 from the downward circulating currents. Wooden curbing for 
 wells is a serious source of danger, as the wood soon becomes 
 rotten, contaminates the water, and promotes the growth of fungi. 
 
 Spring- water . — Springs are fountains of water which flow from 
 subterranean channels. This term is sometimes incorrectly applied 
 to mere shallow pits, filled with water oozing from marshy sur- 
 roundings, and with little or no visible outflow. The water which 
 gathers into the subterranean channels descends from the earth’s 
 surface; and if the surface water is polluted, the springs which 
 
 ( 37 ) Water, Moore, p. 31. 
 
 ( 38 ) Water Supply, Nichols, pp. 109-114. 
 
— 21 — 
 
 receive their supplies from it are liable to be impure. The organic 
 constituents, in filtering through the earth, oxidize to harmless in- 
 organic products, if the filtering bed is sufficiently deep; but disease 
 germs are not thus destroyed. 
 
 Spring-water which flows from hill or mountain sides is generally 
 cold, and has a uniform temperature the year around. Springs are 
 also superior to wells on account of their freedom from the accumu- 
 lated matter which is always found on the surface of well-waters. 
 
 Average porous soil contains about two hundred and fifty times 
 as much carbonic anhydride as does air, and this is taken into the 
 percolating water as it filters into the subterranean channels, and it 
 renders the water especially palatable. It is this carbonic anhydride 
 in water which dissolves limestone, converting it into soluble bicar- 
 bonates. 
 
 It is, therefore, evident that springs furnish us the best water, as 
 they are generally free from organic pollution, and their waters are 
 very palatable from the gases held in solution. “A perfectly pure 
 spring-water is certainly the most healthy beverage in the world. 
 Such waters are abundant, and can now be easily obtained. It will 
 be a happy day for us all when their use shall have become general 
 or universal for drinking purposes. ”( 39 ) 
 
 River cmd Lake-water . — Rivers are the natural drains of the ter- 
 ritory through which they flow, being fed by smaller streams, 
 springs, rains and surface drainage. “They are the receptacles of 
 all the waste products of the inhabitants of the district; they receive 
 the contents of sewers, cess-pools and privies; the offal of distiller- 
 ies, slaughter-houses and tanneries, and the refuse of factories. 
 Into them are thrown carcasses of dead animals, as the most expe- 
 ditious method of burial. From swamps they receive the matter 
 of vegetable decomposition, and are discolored by flowing over 
 beds of peat.”( 40 ) The factories that are especially objectionable 
 are dye works, sugar refineries, starch works, and glucose works. 
 Rivers are also sometimes polluted by the filth from stock yards. 
 
 The Prussian government protects its public water supplies by 
 
 ( 39 ) Hand-book for Water Drinkers, Austin, p. 13. 
 
 (40) Water Supply, Dickinson, p. 5. 
 
- 22 - 
 
 forbidding the discharge of sewage into its rivers. Many of the 
 organic substances which are washed into rivers from cities situ- 
 ated on their banks, undergo decomposition, and give rise to pro- 
 ducts, some of which have the power to produce disturbances in 
 the human system, and others to propagate the germs of disease. 
 
 River-water, below the discharge of city sewage, is a filthy and 
 dangerous beverage, and notwithstanding its natural purification 
 by sunlight, by oxidation and by living organisms, it may never 
 become free from disease germs. A stream which has received much 
 filth in its course, should be considered objectionable for domestic 
 use, unless the volume-ratio of the filth to the water is inapprecia- 
 bly small. The pollution of streams in rural districts, from the 
 decay of vegetation, is always greatest in the Fall, and that from 
 suspended matter, is always greatest in the Spring. 
 
 River-water originating in mountainous districts is unquestionably 
 the best for city supplies, as under ordinary conditions it is softer 
 than well or spring-water, and it is freer from organic and living 
 matter than surface wells and stagnant lakes and ponds. The 
 objections that are offered against the use of river-water are on 
 account of its high temperature, frequent turbidity, and its liability 
 to contamination; and it is true that some rivers furnish water only 
 fit for hydrant and manufacturing purposes. But by the use of ice, 
 efficient systems of purification, and proper precautions against 
 pollution, river-waters are generally excellent supplies for cities 
 and towns, where an abundance of pure water is needed. In the 
 deep-well system for the purification of water, the wells receive 
 only a part of their water from the river, on whose bank they are 
 situated, as the ground-water is constantly flowing toward the river 
 channel. 
 
 Lakes are the reservoirs into which rivers and other streams 
 empty, and their waters are not widely different from their sources 
 of supply. These great bodies of water remain cold during Sum- 
 mer, and they become somewhat purer by the sedimentation of 
 their suspended matter. Pond-water often becomes unfit for 
 domestic use, from the growth of Algce and fresh water Sponges . 
 
— 23 — 
 
 VII. NATURAL PURIFICATION. 
 
 Streams are partially purified by the sedimentation of their sus- 
 pended matter ( 41 ) which takes place as the velocity of the current 
 diminishes. A stream which is very turbid after a heavy rain may 
 soon become clear, owing to its diminishing velocity, and the- 
 insoluble matter either sinks to the bottom or is precipitated along 
 the banks. The retarding influence of tidal waves also assists in 
 the precipitation of suspended matter; and Barus( 42 ) has shown 
 that the sedimentation of fine particles is promoted by the action 
 of salt water, so there is a rapid precipitation of silt where rivers 
 enter the sea. As the mineral matter subsides, it generally carries 
 down with it much of the flocculent, organic matter that would 
 otherwise remain in suspension for many days. 
 
 An apparent purification of polluted water is effected by 
 dilution, and the self-purification of many streams is largely due to 
 this cause. Some of the chemical waste products of factories, 
 when poured into rivers in large quantities, are sufficient to render 
 the water wholly unfit for domestic use, but in the course of a few 
 miles the pollution becomes so much diluted that the water is 
 rendered harmless. In some cases, however, these products fur- 
 nish a rank growth of Algos , and the water is thereby rendered so 
 objectionable that even fish cannot survive in it. This is the case 
 with the Iowa River pollution. ( 43 ) 
 
 The mineral impurities of streams are sometimes removed by 
 mingling their waters with other streams of a different nature, or 
 by flowing over rocks which act chemically upon them. This is 
 beautifully illustrated in the purification of the Schuylkill River 
 before it reaches Philadelphia. ( 44 ) This river receives the drain- 
 age from many mines, and is in its upper course highly charged 
 
 ( 41 ) “ The water of the Mississippi contains forty grains of mud per gallon; and it is 
 estimated that this river carries four hundred million tons of sediment per annum 
 into the Gulf of Mexico. The Ganges is said to carry down six billion, three hundred 
 and sixty-eight million cubic feet annually.” — [Report of American Public Health 
 Association, Vol. I, p. 536.] 
 
 ( 42 ) Bulletin, No. 36, United States Geological Survey. 
 
 ( 43 ) Monthly Bulletin, Iowa State Board of Health, July. 1889. 
 
 ( 44 ) Examination of Water for Sanitary and Technical Purposes, Leffmann and 
 
 Beam, pp. 10-11. 
 
— 24r~ 
 
 with iron salts and free mineral acids, and its water is unfit for 
 domestic and manufacturing purposes. In its course, the river 
 passes through an extensive limestone district, and into it are 
 emptied several large streams, highly charged with calcium bicar- 
 bonate. The free acids are thus completely neutralized, and the 
 iron and much of the calcium are precipitated. At Philadelphia 
 the water is soft and superior to the water at the source of the river 
 or at the middle Schuylkill region, as it contains only traces of 
 iron and a small amount of calcium sulphate. 
 
 Running water, especially when it flows over cataracts or is thor- 
 oughly agitated in the air, absorbs oxygen to such an extent that 
 its organic matter becomes rapidly oxidized; and the purification of 
 water is also greatly promoted by the agency of sunlight. This is 
 one of nature’s most efficient methods of self -purification, and 1 c the 
 pure water of mountain streams and swiftly-running brooks and 
 rivers owe their freedom from organic impurities largely to their 
 continued and violent contact and admixture with atmospheric 
 air.”( 45 ) Some organic substances easily oxidize into ammonia, 
 nitrites, nitrates, and carbonic anhydride, while others, like muscu-. 
 lar fibre, may remain for months in water, and still be recognizable 
 under the microscope. These chemical changes take place most 
 rapidly in Summer, owing to the favorable conditions of heat, light 
 and motion; but in Winter the oxidation is retarded by the low tem- 
 perature and the ice formations which shut out the light and air and 
 impede the motion of the water. 
 
 The pollution of English streams is carried to such an enormous 
 extent that the waters of many, where city sewage enters them, are 
 actually offensive. In their course, the water and banks become 
 blackened from the formation of sulphide of iron, and with this 
 formation the Sewage Fungus appears. Further on in their course, 
 the black color of the water and the Fungus decrease and disappear, 
 and in their place vegetation is luxuriant, fish abound, and the 
 water becomes clear and apparently pure, from its dilution and oxi- 
 dation, and from the agency of vegetable and animal life. The 
 
 (*5) Water Supply of U. S. Capitol, 49th Congress, 1st Session, Ex. Doc. No. 154. p. 20. 
 
- 25 - 
 
 distance which running water requires for its apparent purification, 
 depends mainly upon the extent and nature of its pollution, the 
 inflowing streams, and the agitation of the water in its course, and 
 it is safe to say that it generally requires from five to twenty 
 miles. ( 46 ) 
 
 But self-purification is no guarantee that running water is per- 
 fectly wholesome at any distance below a point where it was cer- 
 tainly polluted with the contents of sewers and privy-vaults, or the 
 products of decomposition of vegetable and animal matter. The 
 question, to what extent must impure water be diluted or oxidized 
 to render it safe for domestic purposes, cannot be answered. Mere 
 dilution of polluted water does not render inoperative the action of 
 living Bacteria , owing to the marvelous rapidity of their reproduc- 
 tion ; and under favorable conditions, it requires only a few days 
 for pathogenic Bacteria to render water exceedingly dangerous, even 
 though in other respects it is comparatively pure. 
 
 In freezing, water is partially purified, ( 47 ) as this operation elimin- 
 ates a large portion of its suspended matter, but the inorganic salts, 
 and the organic constituents, are only partially removed. The 
 experiments of Dr. C. P. Pengra( 48 ) show that water in freezing is 
 only freed of about fifty per cent of its organic crystalloids, twenty 
 per cent of its colloids, forty per cent of its mineral salts, and 
 ninety per cent of its Bacteria. It is, therefore, evident that ice 
 may be a prolific source of disease, and many dangerous epidem- 
 ics( 49 ) have been caused by it. The impurities excluded in freezing 
 remain in the unfrozen water, in a concentrated and more danger- 
 ous form, and this may in part explain why Typhoid Fever so often 
 prevails, and is of such a severe type, during cold Winter weather. 
 
 (46) Report of Massachusetts State Board of Health, Vol. VII, p. 146. * * 
 
 *The Royal Commissioners concluded, however, that running water is so slowly 
 purified that there is not a river in England sufficiently long to dispose of a moderate 
 amount of sewage, through natural agencies. 
 
 (47) On Bacteria in Ice and Their Relations to Disease, Prudden; Our Ice Supply and 
 its Dangers, Prudden. 
 
 (48) Reports of Michigan State Board of Health, 1882, pp. 48-50; and 1884, pp. 79-81. 
 
 (49) Report of Massachusetts State Board of Health, Vol. VII, p. 465; Report of Con- 
 necticut State Board of Health, Vol. II, p. 90. 
 
—26— 
 
 The soil may act as a mechanical purifier of water, by the re- 
 moval of suspended matter as the water filters through it, and as a 
 chemical purifier, by its oxidizing and other chemical action upon 
 the organic impurities, whether they are held in suspension or solu- 
 tion. The filtering power of soil is found to vary greatly. ( 50 ) Sand 
 and gravel act mainly as mechanical filters, while ferric oxide is the 
 oxygen carrier of the soil. In general, a coarse soil is not so- 
 efficient in its mechanical and chemical action as a similar finer one; 
 and every soil which has been charged with organic inpurities is 
 unquestionably inefficient. Even a good filtering soil which receives 
 an excess of impurities, becomes, at last, ineffective. 
 
 Too much confidence, however, is often ignorantly placed in the 
 purifying power of the soil. From experiments instituted by the 
 National Board of Health, ( 51 ) it appears that sand and gravel inter- 
 pose absolutely no barrier between wells and the Bacteria of cess- 
 pools, privy-vaults, and cemeteries, lying even at great distances 
 from them. In further support of this view, one celebrated case 
 will suffice: In August, 1872, an outbreak of Typhoid Fever 
 occurred at Lausen, near Basil, in Switzerland. ( 52 ) The village 
 water supply was from a spring at the foot of the Stockhalden. 
 Suspicion was attached to this water, for it was found that the six 
 houses using well-water were free from the disease, but scarcely 
 one of the others escaped. Upon investigation it was found that 
 Typhoid Fever had occurred at a farm-house on the opposite side 
 of the Stockhalden, and the drainage from this house went into a 
 brook, a part of which was lost in the mountain, about a mile dis- 
 tant from Lausen. Large quantities of salt were thrown into the 
 stream and the salt was soon detected in the Lausen supply, thus 
 proving the connection between the two. Several hundred pounds 
 of flour were then thrown into the stream, but not a trace of it was 
 detected in the water supply, showing the thorough filtration of the 
 water in passing through the mountain. The case was elaborately 
 investigated by Dr. A. Hagler, of Basil, and it is of the greatest 
 
 ( 50 ) Report of Michigan State Board of Health, 1876, pp. 110-111. 
 
 ( 51 ) Report of National Board of Health, 1882, p. 582. 
 
 ( 52 ) Nature, Vol. XIII, p. 447. 
 
- 27 - 
 
 interest in showing that the most thorough filtration through soil is 
 insufficient to remove Typhoid Fever germs from polluted water. 
 
 Finally, we are indebted to low forms of life for much of the self- 
 purification of water. The decomposition of organic matter is the 
 joint work of a number of independent organisms, the results of 
 one class following those of another until organization is entirely 
 destroyed. 
 
 The Entomostraca and other low forms of animal life, owing to 
 their fecundity, are very important factors in removing organic 
 impurities from water. Some of them seem to act mostly as cata- 
 lytic ^agents, producing chemical changes by which the noxious 
 organic constituents are converted into harmless products. 
 
 Notwithstanding what has been said concerning ^ decomposing 
 Algae, the living forms of Algae should not be considered an unmiti- 
 gated evil, as most of them are really purifying agents, since they 
 assimilate the dissolved organic matter in water. They also assim- 
 ilate the carbonic anhydride, ammonia, and nitrogen acids produced 
 by lower forms of cryptogamic life. The main function of Fungi 
 in the purification of water is apparently the oxidation of organic 
 carbon. ( 53 ) Next of importance is the great army of Bacteria y 
 which embraces many families of similar physical structure, but 
 the families are endowed with very different chemical powers. 
 They sweeten water by a chemical process necessary for their own 
 nutrition; and our water supplies would become magazines of 
 deadly poisons, were it not for the myriads of these micro-organisms 
 which attack dead organic matter, and cause its elements to enter 
 into new and useful combinations. One class of Bacteria converts 
 the nitrogen in nitrogenous organic matter into ammonia; another 
 class elaborates this ammonia into nitrous and nitric acids; while 
 another class is engaged in converting organic carbon into carbonic 
 anhydride. Experiments ( 54 ) show that sterilization of polluted 
 water arrests the decomposition of its organic matter, for ozone and 
 hydrogen peroxide fail to oxidize it; but when such water is sub- 
 jected to biological agencies, it is. purified as usual. Indeed, it 
 
 (53) Report on the Waters of the Hudson River, Chandler, January, 1885, pp. 7-14. 
 (5*) Report of Kansas State Board of Health, 1887, pp. 328-329. 
 
— 28 — 
 
 appears that the removal of organic impurities is more of a biolog- 
 ical than of a chemical question, and in considering the natural 
 purification of water, the action of micro-organisms should have 
 the first rank, even though some of them are pathogenic. 
 
 It is well known that these chemical changes are more rapidly ef- 
 fected when the water filters through the pores of the soil, than 
 when it is stagnant, or even when it is flowing in the current of a 
 stream. This is explained by the fact that the purifying Bacteria 
 mainly have their abode in the three or four feet ( &5 ) of surface soil 
 of the earth, and that they so modify the organic matter of water 
 us it passes through this layer of soil, that the roots of living plants 
 can absorb and assimilate it. 
 
 VIII. ARTIFICIAL PURIFICATION. 
 
 Processes . — Water may be artificially purified by any of the fol- 
 lowing processes: Boiling, distillation, aeration, sedimentation, 
 precipitation and filtration. 
 
 Boiling . — By boiling polluted water for some time, the living 
 organisms in it are always partially, and generally entirely de- 
 stroyed. Algce and Fungi are easily killed in this way. Professor 
 Tyndall ( 56 ) has shown that there are periods in the life of Bacteria 
 when they can resist the action of boiling water; but as they soften 
 before propagation, water containing them, can be completely 
 sterilized by repeated boiling, for at the proper time, this not only 
 destroys the Bacteria but it destroys their spores as well. In order, 
 then, to guard ourselves against these organisms, polluted water 
 should never be used for drinking purposes, without first being 
 boiled for some time (two or three hours), as this prolonged opera- 
 tion thoroughly sterilizes it. Indeed, it is perhaps true that the 
 two most effective measures which can be taken in avoiding zymotic 
 diseases, consist in boiling all k the water and milk that we use for 
 drinking purposes. 
 
 (55) Report of Committee on the Pollution of Water Supplies, American Public Health 
 Association, 1888, p. 11. 
 
 ( 56 ) Practical Hygiene, Parkes. Seventh Edition, p. 79. 
 
—29— 
 
 Distillation . — Water may be freed from its solid impurities by a 
 process of distillation. In this way, inland bodies of water and 
 the seas, become saline from the concentration of their mineral con- 
 stituents, while water in its crystalline purity evaporates from the 
 surface. In the first part of distillation, the occluded gases are 
 liberated, and they pass over with the distillate. It has also been 
 claimed that Bacteria and their spores are carried over with the dis- 
 tillate, but the evidence is very unreliable. The flatness of distilled 
 water, which is always objectionable at first, is said to be preferred 
 by some people who have accustomed themselves to it; but this ob- 
 jection can be partially overcome by aeration. Distilled water is. 
 not generally used for drinking purposes, except by persons afflicted 
 with renal and bladder difficulties. But it is said to be used reg- 
 ularly on the coast of Chili, ( 57 ) where it is made from sea water, 
 and it is used oftentimes on long ocean voyages and expeditions, 
 where fresh water cannot be obtained. As coal will distill about 
 eight times its weight of water, there is an advantage in conveying 
 coal instead of fresh water on board of ships. 
 
 Aeration . — Artificial aeration is a process by which we imitate 
 nature in the purification of water. This oxidizes organic matter to. 
 harmless products, and renders the water highly palatable. As a 
 process, aeration was introduced by Lind more than a century ago,, 
 for the purification of water on the western coast of Africa. This 
 process has since been used on a large scale in Russia, by allowing 
 the water to flow down a series of steps, passing through wire- 
 gauze as it descends, and it has also been used on a small scale in 
 Paris. But artificial aeration has only recently been introduced in 
 this country for city water supplies. In 1883, ( 5S ) Professor Albert 
 R. Leeds demonstrated by laboratory experiments, that the tem- 
 porary offensive contamination of the Schuylkill water at Phila- 
 delphia, could be removed by oxidation, and at his suggestion the 
 Philadelphia Water Company removed the objection by pumping 
 air under great pressure into its supply. At a subsequent date, 
 the water supply of Hoboken, Hew Jersey, became extraordinarily 
 
 (57) Water Analysis, Wanklyn and Chapman, Sixth Edition, p. 107. 
 
 (58) Water, Moore, pp. 72-74. 
 
30- 
 
 offensive in odor and taste, and an examination by Dr. Leeds 
 showed this water also to be deficient in oxygen. In September, 
 1886, the evil was removed . by artificial aeration, and the impuri- 
 ties were diminished and vegetable growth ceased, n 
 
 The water of the Greenwood Cemetery Water Works, Brooklyn, 
 ~Ne w York, some time since became nauseous from the accumula- 
 tion of a greenish, vegetable slime. Examination revealed the fact 
 that the water was deficient in dissolved oxygen, and that it con- 
 tained an unusual number of Diatoms. The problem was, there- 
 fore, to devise a process which would remove the pabulum neces- 
 sary for their growth. An amount of air equal to one tenth of the 
 water, under a pressure of eighty pounds per square inch, was 
 found sufficient to oxidize the pabulum, and the water was rendered 
 clear and sparkling by this artificial aeration. 
 
 Under great pressure, air oxidizes nitrogenous substances to inor- 
 organic products, and it therefore deprives the minute forms of life 
 of the pabulum on which they thrive, and they are rendered latent. 
 But it must not be understood that mere aeration effects these trans- 
 formations, for experiments ( 59 ) have clearly demonstrated that 
 without the aid of biological agencies, there is no oxidation, and 
 no purification from the aeration of water. Oxidation is, indeed, 
 but a finishing process, and, therefore, after coagulating and filter- 
 ing out the bulk of impurities, a vigorous aeration, under high 
 pressure, in such a manner as to cause the oxygen to reach every 
 portion of the water should be effected, and the oxidation there 
 completed so far as possible. The excessive air should then pass 
 to the filtering beds, and in its slow passage through them assist in 
 the separation and removal of the organic impurities. From such 
 a system water would emerge from the pipes highly charged with 
 air, clear, sparkling, and as wholesome as the best standard of na- 
 ture’s purified springs. 
 
 Sedimentation . — In this country, the water for city supplies is 
 often only partially purified by a process of sedimentation. This 
 process is frequently used for the waters of the Mississippi and 
 
 ( 59 ) Report of Kansas State Board of Health, 1887, pp. 328-329. 
 
Missouri Rivers. The water is allowed to remain at rest for some 
 hours, in large, shallow settling basins, in which much of the sus- 
 pended inorganic matter subsides, and thus mechanically removes 
 much of its organic matter; but owing to the expense of construct- 
 ing, maintaining and operating settling basins, their use is not 
 more extended. Other systems of greater sanitary merit do the 
 work of purification more beautifully and to the satisfaction and 
 delight of the water consumers. After subsidence of the impuri- 
 ties, the water is drawn off, and at regular intervals the sediment is 
 removed from the basins. If the water contains finely divided 
 particles of clay, then the subsidence is so slow that for purifying pur- 
 poses this process is a failure, and the softer the water the more 
 slowly the sedimentation. It is said that the fine argillaceous mat- 
 ter in the River Rhone requires four months of undisturbed repose 
 for its subsidence. Time is, therefore, an important element in the 
 purification of water by this process. 
 
 If the water is contaminated with sewage, or with the decompo- 
 sition products of vegetable and animal matter, the sooner it is 
 used the less harm it will generally do. u To detain it in a settling 
 basin, especially in Summer, long enough for even its suspended 
 mineral matter to go to the bottom, is to brew a sort of devil’s 
 broth out of the putrescent ingredients, that will grow more poison- 
 ous every day it is kept.”( 60 ) As the growth of micro-organisms 
 is prevented or at least retarded by the absence of sunlight, it has 
 been found advantageous to store water, after sedimentation and 
 filtration, in covered reservoirs. Dr. Percy F. Frankland( 61 ) has 
 found that the twenty thousand germs per cubic centimetre in the 
 Thames River water are reduced to about four hundred by subject- 
 ing the water to sedimentation and filtration; but from ninety-five 
 .and five tenths to ninety-eight and nine tenths per cent of the micro- 
 organisms in the London water supply are claimed to be removed 
 by filtration alone. ( 62 ) 
 
 (*0) Water, Moore, p. 72. 
 
 ( 61 ) Report of Maine State Board of Health, 1887, p. 316. 
 
 («2, Report on Water Supply of East Saginaw, Michigan, p. 4. 
 
— 32 — 
 
 Precipitation . — Many substances have been found useful in pre- 
 cipitating the impurities from water. Among those that have been 
 mentioned are carbon, borax, ferric chloride, potassium perman- 
 ganate, alum, calcium hydrate, and sodium carbonate. The choice 
 of a substance depends upon the nature of the impurities, the use 
 of the water, and the magnitude and expense of the purifying sys- 
 tem. A few points concerning some of these substances will suf- 
 fice. 
 
 Ferric chloride( 63 ) to the amount of two and one half or three 
 grains per gallon of water has been used successfully in Holland 
 in removing argillaceous and finely divided organic matter from 
 water. It is a powerful oxidizing agent, and when followed by a 
 solution of sodium carbonate, it gives excellent results, as the car- 
 bonate precipitates the iron, which entangles and removes the or- 
 ganic matter. 
 
 Potassium permanganate (in solution as Condy’s red fluid) is an 
 excellent purifying agent, as it partially destroys organic substances 
 by oxidation, and its manganese is generally precipitated as the 
 binoxide, carrying with it much of the suspended matter present. 
 A yellowish tint is sometimes produced in the water by the finely 
 divided particles of oxide of manganese, and although this may be 
 objectionable to the sense of sight, it has perhaps no ill-effects upon 
 the human system. This reagent readily removes any offensive 
 odor from water, but the degree of oxidation of the organic matter 
 depends somewhat upon the structure of the organic matter and 
 the temperature of the water. Potassium permanganate is not a 
 complete purifier of water, but it does work which alum cannot do. 
 
 Alum has been used for centuries in China and India to purify 
 water. It is especially efficient with waters containing calcium 
 bicarbonate, and it clarifies them by precipitating the calcareous 
 and argillaceous impurities, and in their removal it is itself precip- 
 itated as calcium sulphate and aluminium hydrate, which coagulate 
 and remove the albuminous matter. So perfect is its self-precipita- 
 tion that rarely can we find a trace of alum in the filtered water. 
 
 ( 63 ) Water, Moore, p. 76. 
 
- 33 - 
 
 
 Professor Leeds has shown that alum has also the remarkable prop- 
 erty of removing Bacteria from water. This is the coagulent used 
 in the Hyatt system of purification. The amount of alum used is 
 from one half to six grains per gallon of water. Alum can be 
 obtained for one and one half to two cents per pound; so its use 
 under the most unfavorable circumstances is very inexpensive. 
 
 Clark’s process for softening water by precipitating its lime as a 
 normal carbonate, has been successfully used in several European 
 water supplies, and also for private consumers. This is accom- 
 plished by adding to the water in settling basins a sufficient quantity 
 of calcium hydrate, in solution, to completely neutralize the carbonic 
 acid, and thus precipitate all the lime as a normal carbonate. This 
 carbonate mechanically precipitates the clayey substances, and 
 effects a nearly complete removal of the coagulated, gelatinous and 
 albuminous matter, as well as a complete removal of the coloring 
 matter. Professor Edward Frankland has shown that Clark’s pro- 
 cess is very efficient in removing living organisms from water. 
 The completion of the removal of lime is determined by means 
 of a solution of silver nitrate. So long as the bicarbonates remain 
 in solution the silver nitrate gives a white precipitate with the 
 water; but as soon as the bicarbonates are removed, then a brown- 
 ish or yellowish precipitate is formed. The objections offered against 
 this system are that if organic matter is present in large quantity 
 the chalk will not readily precipitate; the expense of constructing 
 settling basins is very great; and the accumulated chalk needs fre- 
 quent removal from the basins, and consequently entails much 
 expense. A modern improvement in this process, known as the 
 Porter-Clark process, consists in a remarkably rapid separation of 
 the precipitate by means of a filter-press, which obviates the diffi- 
 culty of sedimentation, and dispenses with the expensive settling 
 basins. 
 
 Sodium carbonate, or salsoda, is frequently used in softening- 
 water for laundry purposes, as it precipitates the hardening salts as 
 normal carbonates. 
 
 Filtration . — The purification of water by filtration for city sup- 
 plies has become quite general in Europe and most parts of the 
 3 
 
— 31— 
 
 United States. The essential object attained in this method, when 
 the water is to be used for domestic purposes, is the removal of the 
 pabulum or infectious matter, on which disease germs multiply and 
 develop. Experience shows that this is best effected by first 
 coagulating and filtering out the organic matter, in part, and then 
 complete its removal by rapid oxidation under high pressure. A 
 large per cent of the Bacteria are thus removed in filtering, and the 
 remaining few are rendered latent, and the water becomes harmless 
 and palatable. 
 
 A filter should not only be capable of arresting suspended matter, 
 but also all substances in solution which are physically or chemically 
 dangerous, and it should so retain them that the water cannot wash 
 them out again. It should also be so constructed that it can be used 
 for some time without deteriorating the quality of the water. 
 
 Filtration effects purification in three distinct ways: 
 
 1. By straining, in which the efficiency and rapidity of the 
 operation depends upon the size of the pores. 
 
 2. By adhesion of the impurities to the filtering substances, in 
 which the efficiency depends upon the nature of the filters, and the 
 relative surface of the filter pores to the water filtered. 
 
 3. By sedimentation within the pores of the filter, and the 
 efficiency here depends upon the size of the porous cavities and the 
 rate of filtration. 
 
 Professor Edward Frankland, of the Royal Commission, has 
 thoroughly investigated the efficiency of the various methods of 
 purifying water, and the following are the results of his observa- 
 tions upon filtration :( 64 ) 
 
 1. A proper filtration may entirely deprive water of its living 
 organisms. 
 
 2. By storing water in receptacles which are biologically unclean, 
 living organisms may be introduced and rapidly multiplied. 
 
 3. Filters lose their efficiency by constant use, and instead of 
 removing Bacteria , they finally increase the number of these 
 organisms. 
 
 (64) Journal of the Society of Chemical Industry, December, 1885. 
 
35— 
 
 4. Some substances which manifest no chemical action on water, 
 are very successful agents in removing living organisms from it. 
 Such are charcoal and coke. 
 
 5. The best results are attained when the filtering substances are 
 frequently removed. 
 
 6. What is gained in the rapidity of filtration is lost in its 
 efficiency. 
 
 Sand is the material most frequently used in filtering-beds, 
 although, compressed sponge, animal and wood charcoal, coke, 
 brick, porous tiles, unglazed earthenware, sandstone, ( C5 ) carbide of 
 iron, and spongy iron have been suggested. 
 
 Animal and wood charcoal, coke and spongy iron are the only 
 substances which can be relied upon for the removal and destruc- 
 tion of organic matter. Charcoal condenses oxygen in its pores, 
 and as water passes through it the organic matter is rapidly and 
 powerfully oxidized, the charcoal acting as a catalytic agent. But it 
 is necessary that charcoal filters be frequently removed and exposed 
 to the air, or sometimes reburnt, that they may become purified 
 and absorb a fresh supply oxygen, for a filter that is kept constantly 
 in use soon become worthless. 
 
 Dr. Percy F. Frankland has found that powdered coke as a filter- 
 ing material completely removes micro-organisms from water; and 
 Salamon and Matthews ( 66 ) have further shown that the action of 
 the coke is due mainly, if not entirely, to the presence of iron. 
 
 In constructing filters for cisterns, care should be taken to so 
 arrange the parts of the filter that all organic matter possible may 
 be removed, and that no color may appear in the water. For this 
 purpose the conducting pipe from the roof should lead directly to 
 the filtering box, in which there should be layers of charcoal, 
 gravel, and sand of such a thickness as to effect this purification. 
 The water should only flow into cisterns during the Winter and 
 Spring months, when the atmosphere is clear and the rain pure. 
 
 (65) “ The Japanese use porous sandstone hollowed into the form of an eg g, and set in a 
 frame over a vessel, into which the water drops as it percolates through the stone. The 
 Egyptians adopt the same method for clarifying the water of the Nile.”— [American 
 Cyclopaedia, Second Edition, Revised, p. 189.] 
 
 (66) Journal of the Society of Chemical Industry, 1885, p. 261. 
 
— 36 — 
 
 The filters should be cleansed at least once a year. Under proper 
 management a supply of pure, cold, cistern water may always be 
 at hand. Cisterns are sometimes constructed in two vertical com- 
 partments, separated from each other by a porous brick partition, 
 laid in hydraulic mortar. The water is allowed to flow directly into 
 one of the compartments, and filter through the brick wall into the 
 other, from which it is drawn for use. At first, this is a very suc- 
 cessful means of Alteration, but the partition soon becomes charged 
 with impurities, and finally does more for contamination than for 
 purification. 
 
 Any filtering medium, like sand, and uncompressed charcoal and 
 coke, which has pores larger than one twenty-five thousandth of 
 an inch in diameter, cannot successfully mechanically remove 
 Bacteria from water. But Pasteur has devised a sanitary filter 
 which eminent authorities claim is germ-proof. The filtering 
 material in this is a fine porcelain imported from France. These 
 filters, which are only suitable for domestic purposes, consist of 
 two concentric tubes, the outer one being connected with the water 
 pipe, and the inner tube is the porcelain filter. The water is 
 admitted to the anular space between the two tubes, and it filters 
 through into the central space, from which the clear, sparkling 
 water is drawn. These filters are so constructed that they can be 
 easily and daily cleansed. Other forms of sterilizing filters are in 
 use, but the writer is not prepared to attest to their efficiency. 
 
 Systems for central filtration . — One of the simplest and cheapest 
 methods ( 67 ) of securing filtered water for city supplies is to sink 
 wells or pits to a depth of ten to forty feet into the soil, near the 
 bed of a river or lake, and from them pump the water for general 
 distribution. These wells are inclosed with iron or masonry walls, 
 which prevent an influx of surface soil-water. The river or lake 
 water only enters them at the bottom, and it is thus subjected to 
 filtration through natural soil. These wells generally receive a 
 portion of their supply from the ground-water, and if this flows 
 from underneath a densely-populated city it is liable to be impure. 
 But this system gives satisfactory results wdien the wells are sunk 
 
 (67) Water Supply, Dickinson, pp. 10-11. 
 
below an impervious stratum, for this separates the surface water 
 •of the city from the influx to the well. 
 
 In the Filter-bed system( 68 ) the basins, as usually constructed, are 
 from ten to sixteen feet in depth. Their size varies from twenty 
 thousand to one hundred and fifty thousand square feet, and is 
 determined by estimating that ninety gallons of water can be filtered 
 per day through each square foot of surface. These basins are 
 made water-tight by masonry, concrete or puddled clay walls. In 
 the bottom are radiating drains, upon which is a layer of broken 
 stone some two feet in thickness; then layers of coarse gravel, fine 
 gravel, and finally the true filter, which is a layer of fine sand, 
 from one to four feet in thickness. The water is kept from one to 
 four feet in depth abof e the filters, and it is purified in its down- 
 ward passage through the sand, and flows through the drains to a 
 clear-water basin. When the filters become clogged the water is 
 drawn below the surface of the sand, and a layer of sand from one 
 half to three fourths of an inch in thickness is removed, together 
 with the debris which has accumulated on its surface. This prac- 
 tice is continued until the sand becomes too thin for efficient filtra- 
 tion, and then a new filtering-bed is prepared. This system is espec- 
 ially applicable to the purification of river-water, but the sand only 
 acts as a mechanical strainer. 
 
 In the Bishof system the sand of the filtering bed is mixed with 
 a prepared spongy iron, which is said to successfully remove organic 
 matter from the water, and thus render it wholesome. If the water 
 contains a large amount of fine sand, a preparatory filtration is 
 necessary, and if there is also a large amount of salts in solution, 
 then the water is liable to be impregnated with salts of iron derived 
 from the filtering-bed. 
 
 The Anderson system, so successfully used in purifying the 
 Antwerp water supply, consists in passing the water slowly through 
 revolving iron cylinders, having inside projecting shelves. These 
 cylinders are about two thirds filled with iron borings, and are 
 slowly revolved, so that some of the iron passs into solution as 
 
 (68) Water Supply of U. S. Capitol, 49th Congress, Ex. Doc. No. 154, pp. 13-15. 
 
— 38 — 
 
 ferrous hydroxide. Every particle of the water passing through 
 the cylinder is thus brought into direct contact with the iron, and 
 the ferrous hydroxide successfully removes the odor from the water 
 and precipitates the organic matter, which is removed by filtering 
 through sand, and in filtering, the ferrous salt is oxidized and re- 
 moved. Professor Edward Frankland has shown that prolonged 
 agitation with solid particles in the water completely destroys the 
 living organisms; but the Anderson process, at Antwerp, only par- 
 tially sterilizes the water. The quantity of nitrogen is reduced to 
 one half or one third the amount which the water originally fur- 
 nished. At Antwerp, the time required for the water to pass 
 through the cylinder is about three and one half minutes, and for 
 the completion of the purification, about six hours. 
 
 The Tweeddale system, ( 69 ) devised by Col. William Tweeddale, 
 of Topeka, Kansas, has proved very efficient on a small scale, and 
 gives promise of great satisfaction for the purification of city water 
 supplies. The lime is precipitated as in the Clark process; then a 
 sufficient quantity of carbonate of iron is added to render insoluble 
 the organic matter. If the water is hard and clear, a small quantity 
 of clay is then added. The water is then violently agitated by 
 means of an air injector, after which the water is allowed to stand 
 for ten minutes to complete the reaction. The water is again 
 violently agitated from fifteen to twenty-five minutes, after which 
 the impurities are allowed to settle, and the water is removed by 
 decantation. The impurities must be frequently removed from the 
 tanks. The time required for the clarification by this process, is 
 from three to four hours. In this system the water is softened, the 
 organic matter is largely precipitated and the balance oxidized to 
 inorganic salts, while the living organisms are mostly destro} T ed. 
 
 In the Hyatt system of purification, the inconvenience and dif- 
 ficulty attending the frequent removal of sediment and sand in the 
 previous methods, are obviated. In this system the filters can be 
 easily, cheaply and thoroughly cleansed. The impurities are coag- 
 ulated by means of alum, and the water then passes to the steel fil- 
 tering chamber where they are removed. This is a vertical cylinder, 
 
 ( 69 ) Report of Kansas State Board of Health, 1887, pp. 330-331. 
 
- 39 - 
 
 having a diameter nearly twice its height. Through the middle is 
 a horizontal diaphragm capable of withstanding the hydrostatic 
 pressure necessary for rapid filtration. The lower section of the 
 cylinder is filled with the filtering material, which consists of two 
 parts of coke and three parts of sand. The upper part of the cyl- 
 inder is used for washing the filtering material, which is transferred 
 to it at regular intervals in a state of violent agitation by hydraulic 
 currents, and the impurities flow away through pipes situated near 
 the surface. The water is admitted through pipes to the upper 
 part of the lower section of the cylinder, and it is drawn out 
 through perforated cups which admit the water but exclude the 
 sand. The efficiency of this system depends more upon the suc- 
 cessful precipitation and entanglement of germ life by the coagu- 
 lent than upon the merits of the filter. Aerating systems are also 
 attached to large plants, and are said to give excellent results. The 
 Hyatt system is not only one of the most perfect for central puri- 
 fication, but it is also successfully used for private supplies. 
 
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