At Cincinnati, on the other hand, where the amount of suspended matters was five times as great as at Pittsburg, the effluents which could be obtained by sand filtration without recourse to the use of alum, even under most favorable conditions, were very much more turbid than those obtained at Pittsburg, and were, in fact, so turbid as to be seriously objectionable for the purpose of public water-supply. With rivers no more turbid than the Allegheny River at Pittsburg, and rivers having floods of such short duration that the use of flood-flows can be avoided by the use of reservoirs, sand filters are adequate for clarification. For waters which are much muddier than the Allegheny, as, for instance, the Ohio at Cincinnati and at Louisville, sand filtration alone is inadequate. Mr. Fuller,[31] as a result of his Cincinnati experiments, has stated the case as follows: “For the sake of explicitness it is desired to show, with the data of the fairly normal year of 1898, the proportion of the time when English filters (that is, sand filters) would be inapplicable in the purification of the unsubsided Ohio River water at Cincinnati. This necessitates fixing an average limit of permissible suspended matter in this river water, and is a difficult matter from present evidence. “In part this is due to variations in the character and in the relative amounts of the suspended silt, clay, and organic matter; and in part it is due to different amounts of clay stored in the sand layer, which affects materially the capacity of the filter to retain the clay of the applied water. During these investigations the unsubsided river-water was not regularly applied to filters; and, with the exception of the results of tests for a few days only, it is necessary to depend upon general information obtained with reference to this point. So far as the information goes, it appears that an average of 125 parts per million is a conservative estimate of the amount of suspended matters in the unsubsided river-water, which could be regularly and satisfactorily handled by English filters. But at times this estimated average would be too low, and at other times too high.... “While English filters are able to remove satisfactorily on an average about 125 parts of silt and clay of the unsubsided water, actual experience shows that they can regularly handle suspended clay in subsided water in amounts ranging only as high as from 30 to 70 parts (depending upon the amount of the clay stored in the sand layer), and averaging about 50 parts per million. But it is true that for two or three days on short rises in the river, or at the beginning of long freshets, the retentive capacity of the sand layer allows of satisfactory results with the clay in the applied water considerably in excess of 70 parts. If this capacity is greatly overtaxed, however, the advantage is merely temporary, as the stored clay is washed out later, producing markedly turbid effluents.”