The second example deals with a water containing 40-45 p.p.m. of colour. This supply was taken from the river by low-lift pumps and discharged into a header which was connected with the high-lift pumps by two intake pipes about 5,000 feet in length. During 1914 a baffled storage basin of two hours capacity was constructed and in June the hypochlorite was added at the inlet to this basin by means of a perforated pipe. The object was to increase the contact period prior to the delivery of the water into the header. The results for this month were as follows: AVAILABLE CHLORINE 1.88 PARTS PER MILLION ------------------------+-------------------------+---------- | BACTERIA PER C.CM. AGAR.| +------------+------------+ B. Coli. | 3 Days at | 1 day at | Index | 20 C. | 37 C. | Per c.cm. ------------------------+------------+------------+---------- Raw water | 410 | 104 | 0.280 Treated water | 49 | 26 | 0.036 Percentage purification | 88.2 | 75.0 | 87.5 ------------------------+------------+------------+---------- During August the point of application of the hypochlorite was changed from the inlet of the basin to the suctions of the pumps and the solution proportioned to the amount of water pumped by the starch and iodide test. The average of the daily tests for this month were: AVAILABLE CHLORINE 1.55 PARTS PER MILLION ------------------------+-------------------------+------------ | BACTERIA PER C.CM. AGAR.| +------------+------------+ B. Coli. | 3 Days at | 1 day at | Index | 20 C. | 37 C. | Per c.cm. ------------------------+------------+------------+---------- Raw water | 448 | 100 | 0.600 Treated water | 26 | 12 | 0.005 Percentage purification | 91.9 | 88.0 | 99.2 ------------------------+------------+------------+---------- Here again thorough admixture produced better results than inefficient admixture plus a longer contact period. Langer[10] has also noted the effect of local concentration and found that the disinfecting action is increased by adding the bleach solution in fractions, a cumulative effect replacing that of concentration. The importance of the admixture factor was not thoroughly appreciated during the earlier periods of chlorination but later installations, and particularly the liquid chlorine ones, have been designed to take full advantage of it.