The treatment was commenced by gradually increasing the quantity of ammonia, until a dosage of 0.12 p.p.m. was reached, and constantly increasing the dosage of bleach, which was formerly 0.93 p.p.m. of available chlorine. Owing to the restrictions imposed by the Provincial authorities it has not been possible to maintain a dosage as low as that indicated as sufficient by the experimental plants results, but some interesting data have been obtained. [Table XXIX] shows the results obtained from February to October, 1917, from the chloramine treatment at Ottawa and also those obtained with liquid chlorine at Hull where the same raw water is treated with 0.7-0.8 p.p.m. of chlorine.
TABLE XXIX.—CHLORAMINE RESULTS AT OTTAWA
| 1917 | B. coli Per 100 c.cms. | Tur- bidity. | Colour. | Dosage p.p.m. | Hull B. coli Per 100 c.cms. | ||
| Raw Water. | Tap Water. | Chlo- rine. | Ammo- nia. | ||||
| Feb. | 268 | 0.88 | 3 | 40 | 0.57 | 0.05 | .... |
| Mar. 1-18 | 250 | 0.96 | 4 | 40 | 0.32 | 0.11 | .... |
| Mar. 1-31 | 643 | 0.43 | 4 | 40 | 0.47 | 0.14 | .... |
| April | 5228 | 0.34 | 31 | 32 | 0.56 | 0.10 | .... |
| May | 162 | <0.08 | 3 | 39 | 0.52 | 0.08 | .... |
| June | 114 | <0.08 | 3 | 41 | 0.51 | 0.08 | .... |
| July | 237 | 0.08 | 5 | 41 | 0.51 | 0.08 | 44.4 |
| Aug. | 165 | 0.08 | 4 | 42 | 0.51 | 0.10 | 28.0 |
| Sept. | 55 | <0.08 | 6 | 42 | 0.50 | 0.09 | 15.2 |
| Oct. | 31 | 0.15 | 5 | 42 | 0.42 | 0.08 | 1.1 |
| Average | 211 | 0.22 | 7 | 40 | 0.51 | 0.09 | |
At the height of the spring floods the raw water contained 80 p.p.m. of turbidity and over 500 B. coli per c.cm. but 0.6 p.p.m. of chlorine and 0.13 p.p.m. of ammonia reduced the B. coli index in the tap samples to 2.5 per 100 c.cms.; samples taken in Hull on the same day (treated with 0.7-0.8 p.p.m. of liquid chlorine) gave a B. coli index of 26.7. Previous experiences in Ottawa has shown that a dosage of approximately 1.5 p.p.m. of available chlorine is required to reduce the B. coli index to 2.0 per 100 c.cms. under similar physical and bacteriological conditions.
During the period of nine months covered by the results in [Table XXIX], only five cases of typhoid fever were reported in which the evidence did not clearly indicate that the infection had occurred outside the city. The reduction in the bleach consumed during the same period effected a saving of $3,200.
During one period of operation the hypochlorite dosage was gradually reduced to ascertain what factor of safety was maintained with a dosage of 0.5 p.p.m. of available chlorine and 0.06-0.08 p.p.m. of ammonia. The results are shown in [Diagram VIII]. The percentage of samples of treated water showing B. coli in 50 c.cms. was calculated from the results of the examination of 4-7 samples daily.
The results showed that it was possible to reduce the chlorine dosage to 0.25 p.p.m. with 0.06 p.p.m. of ammonia without adversely affecting the bacteriological purity of the tap supply and fully confirmed the experimental results previously obtained.
The lowest ratio of available chlorine to ammonia used during this test was approximately 4 : 1. This is the ratio indicated by a consideration of the theory of the reaction, and not 2 : 1 as was formerly stated (Race[4]). If bleach is represented as Ca(OCl)2, the equation
Ca(OCl)2 + 2NH3 = 2NH2Cl + Ca(OH)2
would indicate a ratio of 2 : 1; but only one molecule of Ca(OCl)2 is produced from two molecules of bleach and the theoretical ratio is therefore 4 : 1 (142 : 34),