+----------------------------+----------------------------------+ | | Value of K calculated from | | | absorption at 63° F. | | Absorption of Chlorine by | | | water containing 40 p.p.m. | Log(N_{1}/N_{2}) | | of colour | K = ----------------- | | | _t__{2} - _t__{1} | +-------+--------------------+ | |Time of|Temperature of Water+-------+--------+--------+--------+ |Contact+--------------------+_t__{2}|_t__{1} |_t__{1} |_t__{1} | |Minutes|32° F.|46° F.|63° F.|minutes| = 0 | = 5 | = 10 | +-------+------+------+------+-------+--------+--------+--------+ | Nil |10.00 |10.00 |10.00 | | | | | | 5 | 8.00 | 7.45 | 6.50 | 5 | 0.0374 | ---- | ---- | | 10 | 7.23 | 7.09 | 5.91 | 10 | 0.0228 | 0.0082 | ---- | | 20 | 7.00 | 6.60 | 5.18 | 20 | 0.0190 | 0.0066 | 0.0057 | | 40 | 6.42 | 6.05 | 4.47 | 40 | 0.0087 | 0.0043 | 0.0040 | | 60 | 6.22 | 5.60 | 3.90 | 60 | 0.0068 | 0.0040 | 0.0036 | | 80 | 6.13 | 5.40 | 3.65 | 80 | 0.0056 | 0.0033 | 0.0029 | +-------+------+------+------+-------+--------+--------+--------+] Tables VIII and IX, however, show that the temperature coefficient of the germicidal action has a greater effect than the reduction in the amount of chlorine absorbed and removed from the reaction. The results obtained on the works scale with these waters are very different to the laboratory ones and show that more chlorine is required during the summer season than in winter. The results with bleach and liquid chlorine are in the same direction (_vide_ Diagrams III and IV). The bleach was regulated so as to maintain a constant purity, whilst in the other case the dosage was constant with a varying _B. coli_ content. In Diagram IV the _B. coli_ is plotted; this does not represent all the factors involved as the _B. coli_ content of the treated water is also a function of that of the raw water, but in the example given this factor is of no moment because it was comparatively constant during the period plotted (extreme variation 80 per cent). The discrepancies between the laboratory and works results cannot be easily explained. The only difference in the conditions is the nature of the containing vessel. Glass is practically inert at all temperatures but the iron pipes, through which the water passed before the samples were taken, may exert an absorptive influence on the chlorine at the higher temperatures experienced during the summer months.