AbstractThe purpose of this study was to determine the nature and composition of the organic colloids extracted from Brookston clay with neutral sodium pyrophosphate solution. The number of electrically homogeneous organic colloids present on the clay was determined electrophoretically. Some of the amino acids and monosaccharides in the hydrolysate of the colloids were identified by paper chromatography.It was found that the colloidal extract consisted of one main component, a brownish‐black material, with a second present in small concentration. The electrophoretic mobility of the second component corresponded closely to that of nucleoproteins.Eight amino acids: aspartic acid, glutamic acid, glycine, serine, threonine, alanine, valine and leucine, were identified. Two sugars, galacturonic acid and xylose, were also present together with an unidentified spot which was probably a mixture of mannose, arabinose, glucose, and galactose. Traces of ribose and glucurone were detected.