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at one time. When the correct quantity is applied the water is usually cleared within three to four days. Table 7 is made up from data furnished by Moore and Kellerman, Whipple, various other sources and New York City's experience.

Chlorine in dosage of 0.3 p.p.m. has attacked microscopic organisms in several instances, setting free the distasteful oil so that about onehalf the usual troublesome amount of organisms caused complaints. This has occurred with tabellaria, dictyosphaerium, synura and uroglena. Likewise additional chlorine will destroy the taste thus produced. A dosage of 0.3 p.p.m. has destroyed and rendered odorless and tasteless approximately 50 units of synura. A dosage of 0.5 to 0.7 p.p.m. has acted similarly upon 100 units and a dosage of over 0.7 p.p.m. is necessary for 200 units. A growth of uroglena to the number of 2000 units has been killed and the resulting taste destroyed by a dosage of 0.5 p.p.m. chlorine and 6000 units have been killed by the same dosage, but the taste not destroyed. The taste was not noticeable, however, after a flow of from 10 to 15 miles in an aqueduct. A growth of 500 units of dinobryon has been destroyed and deodorized by 0.5 p.p.m. chlorine. A dosage of 0.5 p.p.m. chlorine has so affected the organisms entering a reservoir of a few days storage capacity that the amount in the effluent water was reduced by 25 per cent against previous experience of considerable increase. This reduction has occurred with such organisms as asterionella, anabaena, aphanizomenon, coelosphaerium, tabellaria, melosira, etc. A dosage of 0.85 p.p.m. has reduced aphanizomenon, 1500 units, by 50 per cent. Melosira in sufficient numbers to interfere with filtration has been controlled by dosage of 2 p.p.m. chlorine (Davenport, Iowa). Chlorine and also chloramine have been used to control crenotrhix in dosage of 0.51 p.p.m., and chlorine has destroyed cyclotella in dosage of 1 p.p.m., and in dosage of 3 p.p.m. has destroyed the gnats of the blood worm, Chlorine is also used to prevent clogging of condensers by prevention of formation of jelly masses or fungus slime, in dosage of 0.33 p.p.m.

If necessary, considerable excess chlorine, 1 to 2 p.p.m., may be employed and the excess destroyed by thiosulphate or by sulphur dioxide. The thiosulphate would be handled in solution, the sulphur dioxide as a gas from cylinders of the compressed liquid similarly to chlorine.

It has been reported that excess hydrate alkalinity has a restraining influence upon microscopic organisms. Attempt has also been made with varying success to decrease the number of organisms in a distribution reservoir by draining it and whitewashing the walls or treating them with a heavy wash of copper sulphate.

CHAPTER VII

CHLORINATION

Historical

As early as 1902 Dr. Duyk of Belgium had perfected a process combining coagulation and chlorination which was successfully applied at Middlekerke. Solutions of ferric-chloride and bleach were mixed just prior to application to the raw-water.

Credit for the first systematic use of chlorine for treatment of a large water supply is due to Sir Alexander Houston, with whom Dr. McGowan was associated, when in 1904–1905 a dosage of 1 part per million of chlorine was applied, in the form of sodium hypochlorite, to the raw-water supplying the Lincoln filters. The bacteriological results were entirely satisfactory, but many complaints of the "mawkish" taste imparted to the water were received. A similar process was used, as a temporary expedient, at Maidstone, England, during the 1897 typhoid epidemic, by Sims Woodhead.

Electrolytic solutions of sea-water or salt have been used in a number of instances, as at Worthing, England; Nice, France, and at Poplar, England, for general disinfecting purposes, including street watering; for application to sewage effluent at Maidenhead, England; by Rideal, for application to sewage effluent at Guilford, England, and by Woolf for the disinfection of sewage effluent at Brewsters, N. Y., the disinfection of Jerome Park Reservoir of the New York City water supply, and for general disinfection purposes at Havana and Vera Cruz.

Solutions of bleach have been used for the disinfection of sewage or sewage effluents on the river Brent in England; at Hertford, England; on the Hooghly River, India; at the Tittagurh installation near Calcutta, India, and at Guilford, England; by Schultz of Hamburg in connection with the effluents of hospital sewage works; by Phelps at Baltimore, Md., and Red Bank, N. J.; by Pratt and Kimberly at Camp Perry and other points in Ohio, and by others at numerous places, with generally successful results. In North America hypochlorite of soda and chlorine were tried by Geo. W. Fuller in 1896 at the Louisville Experimental Station. The first commercially successful attempt at chlorination was made by Geo. A. Johnson in 1908, with the application of bleach solution (hypochlorite of lime) to the raw water of the Bubbly Creek (Chicago) filter plant. The results were very satisfactory.

In 1908 Geo. A. Johnson and Professor Leal commenced the treatment of the Boonton supply of Jersey City, N. J. This was an epoch-making venture in view of the great quantity treated (40,000,000 gallons per day).

During the next few years the use of hypochlorite in water purification became popular and by 1911 over 800,000,000 gallons per day were being treated in America. The results obtained in the reduction of water-borne diseases caused a rapid increase in the adoption of chlorination, until in 1918 over 3,000,000,000 gallons per day were being treated in more than 1000 cities and towns in North America.

In 1910 Major C. R. Darnall of the United States Army, through experiments on a small plant scale at Fort Meyer, Va., proved that liquid chlorine could be successfully applied at water treatment plants on a practical basis to replace bleach. The first installation of liquid chlorine on a commercial basis was at the new Niagara Falls filter plant of the Western New York Water Company about July, 1912. The installation was by Dr. Ornstein, representing the Electro Bleaching Gas Company, who with the aid of Mr. H. F. Huy, now General Manager of the Water Company, perfected the first commercial chlorinator.

By 1913 apparatus for applying liquid chlorine from cylinders had been perfected and placed on the market. In the same year, at Wilmington, Delaware, the second successful chlorinator for applying liquid chlorine was installed. Since this time bleach has been largely replaced by liquid chlorine.

In 1924 over 3,750,000,000 gallons per day were being treated in more than 3000 cities and towns in the United States.

Chemical-biological effects

Chlorinated lime (commonly called “bleach" or chloride of lime), used almost universally as the chlorinating agent prior to the advent of liquid chlorine, shows upon analysis the hypothetical combination:

4CaOC12.2Ca(OH)2:51,0

2,

The "available" chlorine content usually varies between 35 and 37 per cent. Its stability depends largely upon the excess of hydrated lime, Ca(OH)2, in the presence of the oxychloride (CaOCl,) which is formed during the passage of dry chlorine gas over hydrated lime. The above formula indicates that ordinary bleaching powder contains 68 per cent calcium hypochlorite, 20 per cent calcium hydroxide and 12 per cent water.

The first action upon dissolving chlorinated lime in water is the decomposition of the oxychloride into calcium hypochlorite and calcium chloride. Upon further dilution, as when applied to the water treated, hydrolysis occurs and in the presence of an acid-ion, usually supplied by the carbon dioxide naturally present, hypochlorous acid and calcium bicarbonate are formed. Further decomposition of the hypochlorous acid in water reasonably free of organic matters results in the liberation of nascent oxygen and hydrochloric acid. The hydrochloric acid combines with the natural carbonate or bicarbonate alkalinity of the water to form calcium chloride, carbon dioxide and water. The presence of 5 to 10 p.p.m. of caustic alkalinity will materially retard the velocity of the germicidal action of hypochlorites. Even the presence of normal carbonates tends to reduce the velocity. Acids in small quantities will produce marked acceleration and even such a weak acid as carbonic is a satisfactory accelerator.

In the bleaching industry it was assumed that the nascent oxygen produced by aqueous solution of "bleach” was the active principle in decolorizing materials and oxidization of organic matters. The oldest authorities also applied the same reasoning to the action of "bleach" solutions in water treatment. The explanation in the famous Boonton, N. J., suit exists as a court record to wit: “The process (chlorination) is wholly an oxidizing one, the work being done entirely by the oxygen set free from the hypochlorous acids.

During the investigations and court hearings Earle Phelps suggested that hypochlorous acid in itself was toxic to micro-organisms, but due to lack of support by evidence, his view was not accepted and the nascent oxygen hypothesis met with almost universal acceptance. Race in Ottawa (1916–1917) and Wolman and Enslow in Maryland (1917–1918) produced data which cannot be explained by the nascent oxygen hypothesis.

The strongest bit of evidence against the nascent oxygen hypothesis was produced by Race in 1916 when he destroyed the bleaching property of "bleach” by addition of ammonia to it. When this ammoniated” bleach liquor was compared with plain bleach liquor as a germicide, it was found to be superior and at the same time the available chlorine failed to disappear as rapidly as that from the plain bleach. Dakin also concludes the toxic action of hypochlorites during wound disinfection by Carrel's method is due to the chlorine and its derivatives rather than to nascent oxygen. Rideal was the first to note the strong germicidal power of chloramine. When compared to their oxygen equivalents, other active oxidizing agents fail to produce the germicidal efficiency of chlorine.

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