Abstract
1) Some characteristic colour reactions were found when the reduced wool was immersed in acidic nitrite solution. Nitrosofication which brings yellow colouration was preceded by red colour reaction due to the reaction between nitrite and sulfhydryl groups of free reducing reagents or cysteine residues in the reduced wool. On strong acid side, the reduced wool turned into orange with the progress of nitrosofication. In acetic acid solution, therefore, this nitrite treatment is applicable for a convenient method of the qualitative detection of sulfhydryl graups in wool.
2) Although bisulfite never coloured up with nitrite, wool reduced by this reducing reagent showed slight red colouration. owing to the appearance of sulfhydryl group in the acetic nitrite treatment. When wool was reduced in sulfite solution, however, no red colouration was recognized.
3) Colouration was affected by acidity of the reduced wool. Nitrite reacted more easily for the wool reduced on acidic side than on the basic. On the other hand, actions of hydrogen peroxide for them were in contrast.
4) On acidic side, the nitrite treatment for the reduced wool brought the decreases of its phenol-shrinkability and alkali-solubility. Although it seems that they owe to the increase of covalent bonds or hydrogen bonds in it by nitrosofication, deamination, diazotation and rebuilding of cystine bridges, the increase of stability arose from the masking its sulfhydryl groups by this treatment cannot also be ignored.
