An Investigation of the Carbonising of Wool*

Wool of crossbred quality, in the form of cloth, was carbonised with sulphuric acid (5% by weight). Part of the baked cloth was rinsed with water at the mill, part was stored in the laboratory in a desiccator over silica gel, and a third part was stored for up to 29 weeks in the conditioning room at 65% R.H. After storage for five weeks and seven weeks respectively, part of the dry and part of the humidified cloth was neutralised. Subsequently the wool was examined for modification by the following methods—alkali solubility, pH of aqueous extract, pyridine extraction, total sulphate, Van Slyke amino nitrogen, and end‐group analysis using 1 ‐fluoro‐2,4‐dinitrobenzene. The findings led to the following conclusions—(1) The alkali solubility of carbonised wool, if tested soon after preparation and corrected for the sulphuric acid content, is not increased. (2) When wool which has been carbonised but not neutralised is stored under humid conditions a progressive increase in alkali solubility is observed. During dry storage the alkali solubility does not change significantly. (3) Carbonised wool contains about double the number of serine and threonine amino end‐groups, whereas the other end‐groups of wool are not affected. (4) Dry storage leads to further increase in the number of serine and threonine end‐groups and has some effect on the glycine and valine end‐groups. (5) Humid storage results in a much faster increase in end‐groups. (6) Neutralised wool contains fewer serine and threonine end‐groups, whereas the end‐groups of the other amino acids remain unchanged or increase slightly. The results are best explained by assuming a partly reversible N‐O‐peptidyl shift on the serine and threonine amino residues during carbonising and neutralisation. Storage of carbonised wool under humid conditions induces irreversible hydrolysis of peptide links involving aspartic and glutamic acids, glycine, alanine, and valine. The practical implications are discussed.