-------------+--------+-------+--------+---------+----------+--------- | | | Oxygen | Chlorine| | Source of | Alkali-|Colour.|Absorbed| Required| Bacteria | Per Cent Supply. | nity. | | (30 | p.p.m. | per c.cm.| Removed. | | | mins.) | | | -------------+--------+-------+--------+---------+----------+-------- Ottawa river | 15-20 | 50-70 | 14.0 | 1.50 | 3,000 | over 98 St. Lawrence | | | | | | river | 90-100 | Nil. | 0.30 | 0.30 | 500 | over 99 -------------+--------+-------+--------+---------+----------+--------- Ellms[7] obtained similar results and reported "that the rate at which sterilisation proceeds varies, in a general way, directly with the concentration of the applied available chlorine and the temperature, and inversely as the amount of easily oxidisable matter present." Experience with filter plants shows the same facts, the amount of chlorine required for the sterilisation of a filter effluent being invariably less than that necessary to purify the raw water to the same extent. The effect of coloured organic matter upon the absorption of chlorine, in the form of hypochlorite, is shown on Diagram I. [Illustration: DIAGRAM I EFFECT OF COLOUR ON ABSORPTION OF CHLORINE BY WATER +-------------------------------+----------------------------+ | | Value of K calculated from | | | | | Absorption of Chlorine | Log(N_{1}/N_{2}) | | by water at 63° F. | K = ----------------- | | | _t__{2} - _t__{1} | | | | +-------+ +-------+ When _t__{1} = 0 | |Time of+-----------------------+Time of+--------------------+ |Contact| Colour of Water |Contact| Colour | | in +-------+-------+-------+ in +------+------+------+ |Minutes| 3 | 25 | 40 |Minutes| 3 | 25 | 40 | +-------+-------+-------+-------+-------+------+------+------+ | Nil | 10.00 | 10.00 | 10.00 | | | | | | 5 | 9.62 | 7.70 | 6.50 | 5 |0.0033|0.0227|0.0374| | 10 | 9.41 | 7.03 | 5.91 | 10 |0.0026|0.0153|0.0228| | 20 | 9.17 | 6.40 | 5.18 | 20 |0.0018|0.0096|0.0190| | 40 | 8.95 | 5.82 | 4.47 | 40 |0.0012|0.0057|0.0087| | 60 | 8.85 | 5.63 | 3.90 | 60 |0.0008|0.0041|0.0068| | 80 | 8.80 | 5.58 | 3.65 | 80 |0.0007|0.0032|0.0056| +-------+-------+-------+-------+-------+------+------+------+]