JEWELL FILTER. 0.64 | 0.60 | | 97.16 | 96.60 | 0.88 | 0.91 | | 97.90 | 98.16 | 1.11 | 1.13 | | 97.25 | 98.30 | 1.37 | 1.43 | 1.42 | 97.53 | 98.70 | 98.58 2.17 | 1.59 | 1.74 | 99.57 | 99.38 | 98.43 | 2.00 | 2.81 | | 99.33 | 98.68 ----------+----------+---------+-----------+------------------------- It appears from this table that waters of various degrees of turbidity give substantially equal bacterial efficiencies with equal quantities of sulphate of alumina, the results varying as often in one direction as the other. Within certain limits it may thus be said that turbidity is without influence upon the bacterial efficiency obtained in mechanical filtration. It must be borne in mind, however, that the quantities of sulphate of alumina, with very few exceptions, were sufficient to produce full coagulation. Mr. Fuller has shown in his Louisville report that considerable quantities of sulphate of alumina may be added to turbid waters without producing appreciable coagulation; and therefore if a quantity of sulphate of alumina sufficient to produce a certain bacterial efficiency in a clear water should be added to a water so turbid that it was unable to coagulate it, scarcely any effect would be produced. The above statement therefore only applies in those cases where sufficient sulphate of alumina is used to adequately coagulate the water. As the numbers of bacteria often vary with the turbidity, the variation in the numbers of bacteria in the different classes is much less than in the first tables; but to further investigate the question of whether the numbers of bacteria in the raw water have an important influence upon the bacterial efficiencies, each of the two largest classes in the foregoing tables was divided into two parts, according to the bacterial numbers in the raw water, namely, the results from the Jewell filter with turbid waters and with sulphate of alumina quantities ranging from 0.75 to 1.00 grain per gallon, and the results from the Warren filter with turbid waters and with sulphate of alumina quantities of 1.25 grains per gallon and upward. The results are as follows: