Membrane filter procedures previously used for concentration of virus from tapwater were modified to concentrate humic acid. These procedures were capable of recovering approximately 50% of added humic acid from tapwater. Thirty milligrams of naturally occurring humic acid was detected in 1000-1. samples of tapwater.
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Acknowledqemems This study was supported in part by a grant from the Carborundum Company, Niagara Falls, N.Y. 14302, U.S.A. The technical assistance of Clarence Johnson is gratefully acknowledged.