The lignin fraction of animal feeding‐stuffs. III—The determination of ‘total lignin’

The method proposed by the authors (see Part II of this series) for the determination of ‘acid‐insoluble lignin’ excludes the humin material which dissolves in 72% (w/w) sulphuric acid but is reprecipitated by dilution. Further work has shown this humin material to possess the properties of lignin. Although it is to be expected that the ‘acid‐insoluble’ lignin will be resistant to the digestive processes and its determination should therefore serve a useful purpose, for the measurement of ‘total’ lignin the method is inadequate. An investigation of the acid‐solubility of lignin has led to the re‐examination of the various separation procedures to obtain a satisfactory method for determining total lignin.