These tests were made by the author of a set of Jewell filters at Lorain, Ohio. The filters were six in number, each 17 feet in diameter, having an effective filtering area of 226 square feet each, or 1356 square feet in all. The construction of the filters was in all respects similar to the Jewell filter used at Louisville. The raw water was from Lake Erie, and during the examination was always comparatively clear, but contained considerable numbers of bacteria. The problem was thus entirely one of bacterial efficiency. The question of clarification hardly presented itself. Although the water became turbid at times it did not approach in muddiness the condition of the Ohio River water, and an amount of coagulant sufficient for a tolerable bacterial efficiency in all cases was more than sufficient for clarification. A summary of the results obtained is as follows: -----------+--------------+-----------+--------+---------+---------- | Average Rate |Sulphate of| | |Bacterial Week Ending|of Filtration,| Alumina, |Bacteria|Bacteria |Efficiency 6:00 P.M. | Gallons per |Grains per | in Lake| in |per cent. | Sq. Ft. Min. |Gallon. | Water. |Effluent.| -----------+--------------+-----------+--------+---------+---------- June 19 | 1.06 | 2.58 | 1441 | 16 | 98.9 26 | 1.10 | 2.50 | 385 | 6 | 98.4 July 3 | 1.11 | 2.27 | 367 | 9 | 97.5 10 | 1.28 | 1.07 | 154 | 14 | 90.9 17 | 1.14 | 0.94 | 189 | 26 | 86.3 +--------------+-----------+--------+---------+---------- Average | 1.14 | 1.83 | 507 | 14 | 96.4 -----------+--------------+-----------+--------+---------+---------- The average bacterial efficiency was 96.4 per cent with 1.83 grains of sulphate of alumina per gallon. PITTSBURG EXPERIMENTS.[42] The Pittsburg experiments were inaugurated by the Pittsburg Filtration Commission. The operation of the filters extended from January to August, 1898. A Jewell and a Warren filter were used similar in design to those used at Louisville. The raw water contained large numbers of bacteria, and was also often very turbid, although less turbid than at Louisville. At times more coagulant was necessary for clarification than was required for bacterial efficiency; while as a rule more was required for satisfactory bacterial purification than was necessary for clarification. The opportunities were therefore favorable for the study of both of these conditions. The amount of coagulant necessary for clarification has been mentioned in connection with coagulation. The results secured upon the relation of the quantity of coagulant to the number of bacteria in the effluent were more complete than any other experiments available, and are therefore here reproduced from the Pittsburg report nearly in full.