The organisms where odors are expressed have been in sufficient quantity in water supply at one time or another to cause the characteristic odor. * Dosage successful in New York City's supplies.

†These organisms have been affected by chlorine and in some cases controlled by dosage ranging from 0.5 to 2 p.p.m. depending largely on amount of organism.

These organisms have caused trouble other than odor.

if they have a storage capacity of five to six days, the influent half of the reservoir may be treated. The treated water will displace the untreated water within a week and sufficient time will elapse for disappearance of taste and odor from the treated water so that complaint will not result.

Copper sulphate may be fed to an aqueduct by continuous dryfeed to destroy organisms feeding from one reservoir to another. A reservoir should interpose between the point of feed and the distribution system to allow time for removal of odor caused by the treatment. The chemical should feed through a hopper to a moving shutter actuated by a motor and adjustable in stroke or to a revolving disc with adjustable arm for scraping off the chemical. The apparatus should be of copper where subject to corrosion. Feed to the water may be through a wooden chute to a wooden crib bored full of holes, the latter floating in the water. Continuous dry-feed of copper sulphate to the water has been eminently successful. The dosage of chemical is definitely known and the application and admixture with the water are thoroughly under control. The effective dosage by continuous dry-feed is apparently the same as that in launch treatments of reservoirs.

The effect of treatment of microscopic organisms by copper sulphate is shown by an immediate production of distinctive odors, usually disagreeable, by reduction of the number of organisms in the water through sedimentation, by the appearance of the organisms under the microscope the coloring matter being knocked to pieces, so to speak. Sometimes there is an increase in the water bacteria which feed upon the decayed organisms. The cyanophyceae usually produce scum after treatment, of varied colors, pale blue, yellow, red or brown.

Sometimes fish are killed by the treatment by swimming into the concentrated streaks of copper sulphate, but this is more apt to occur a day or more later from smothering due to clogging of the gills with dead organisms or to reduction of oxygen by the dead organisms.

Experience differs with waters of different composition, with temperature, and with amount of organisms present as to the right dosage to apply for each organism. About twice as much chemical is required in winter as in summer. It is believed that it is a waste of copper sulphate to apply an insufficient quantity at one dosage. If a smaller dosage fails, the entire larger dosage must be applied

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 0.54 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