EXPERIMENTAL CONDITIONS CONCERNING POTENTIOMETRIC TITRATION OF HUMIC ACID

Abstract

Summary The humic acids of four soils from Denmark have been extracted by EDTA. The humic acids were separated from EDTA by precipitation with Ba 2+ . The ash content was lowered by treatment with HF and HC1. The ash content in the four humic acids was less than 0.6 per cent. Chemical analysis of the humic acids supply some evidence for the suggestion that EDTA extracted organic matter is a more definite fraction than humic acid extracted by NaOH. It was shown that an alkaline humate solution stored in sterile, sealed ampoules under N 2 does not change its initial pH, indicating that the protolytic equilibrium is established instantly. It is therefore proposed that the titration of humic acid should be carried out as quickly as a normal acid‐base titration.