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consistent retention of trichloroacetic acid by dried precipitates of proteins, although some of the series (TableI, columns 7 and 8; Table II, No. 3) show mean minimum weights approximately 4 to 8% in excess of the amounts of protein determined by direct drying or by spectrophotometric methods.Gravimetric determination of proteins dried without other treatment at temperatures between 80°and 110°C. has been reported (3, 5-7, 18-20, 24)', such weights have been stated to represent anhydrous weights of proteins (3, 5, 6). It is possible that residual water may lead to errors in the estimation of dry weights of proteins. The weights obtained in these studies after precipitation of proteins with trichloroacetic acid are consistent and reproducible and may represent anhydrous weights; however, no attempt has been made to investigate the dried residues for content of water.

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