-------+---------------------------------+-------------------------------- | HYPOCHLORITE ALONE. | HYPOCHLORITE AND AMMONIA. +---------------+-------+---------+--------------+-------+--------- | Bacteria | |Available| Bacteria | |Available | per cubic | _B. |chlorine | per cubic | _B. |Chlorine | centimeter. | coli_ | parts | centimeter. | coli_ | Parts +------+--------+ Index | per +------+-------+ Index | per | Agar | Agar |per 100|million. | Agar | Agar |per 100|Million. |1 Day | 3 Days | cubic | |1 Day |3 Days | cubic | | at | at |centi- | | at | at |centi- | |37° C.| 20° C. |meters.| |37° C.| 20° C.|meters.| -------+------+--------+-------+---------+------+-------+-------+--------- Mar. | 90.9 | 95.8 | 99.9+ | 0.90 | 90.0 | 95.0 | 99.7| 0.22 15-31| | | | | | | | April | 98.9 | 99.6 | 99.7 | 1.10 | 98.3 | 98.9 | 99.6| 0.25 1-19 | | | | | | | | -------+------+--------+-------+---------+------+-------+-------+--------- TABLE XXVIII _Cost Per Million Imperial Gallons_[A] -----------+--------------+-------------- | Hypochlorite | Hypochlorite | alone. | and ammonia. -----------+--------------+-------------- Mar. 15-31 | $1.12 | $0.46 April | 1.26 | 0.54 -----------+--------------+-------------- [A] Calculated as Bleach at $3.80 per 100 pounds and aqua ammonia (26° Bé.) at 5-1/2 cents per pound. The results were so satisfactory that the author recommended the adoption of the process on the main chlorinating plant but owing to conditions imposed by the Provincial Board of Health the process was not operated until February, 1917. In place of ammonia fort, aqua ammonia (26° Bé.), containing approximately 29 per cent of anhydrous ammonia, was used. The material was first examined by the presence of such noxious substance as cyanides and found to be very satisfactory. [Illustration: FIG. 12.--Sketch of Ottawa Chloramine Plant.] The general design of the plant is shown in Fig. 12. The bleach is mixed in tank _A_ as a solution containing 0.3 to 0.6 per cent of available chlorine and delivered to tanks _B_ and _D_, each of which has a twenty-four-hour storage capacity. The ammonia solution is mixed and stored in tank _B_ and contains 0.3-0.5 per cent of anhydrous ammonia. The two solutions are run off into boxes _E_ and _F_ which maintain a constant head on valves _V_ and _V'_ controlling the head on the orifices. Both orifices discharge into a common feed box _G_ from which the mixture is carried by the water injector _J_ through one of duplicate feed pipes and discharged into the suction well through a perforated pipe.