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The basic principles and never developments in the reactions of reactive dyes with cellulosic fibres are discussed and reviewed. It is shown that the proposed reactive systems may be classified in a straight‐forward manner according to their reaction mechanisms. They can be divided into two classes, nucleophilic substitution reactions and nucleophilic addition reactions, respectively. The most important systems belonging to the first class are based on halogen‐containing nitrogen heterocycles, whereas dyes with activated double bonds, either free or masked, are of importance in the second. Apart from their intrinsic reactivity, reactive groups may also influence the substantivity of the chromophoric system. Application of bifunctional reactive compounds leads to cross‐linking of the fibres and this links dyeing with the field of chemical finishing.

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It is shown that only Schiff's method is suitable for the determination of formaldehyde in methylated cellulose formals. These are intermediates in the elucidation of the structure of cotton cross-linked with formaldehyde. Some modifications of the usual procedure are recommended to obtain an accuracy of 3% relative to the amount of formaldehyde present. The modified Schiff's method was standardized with cellulose formals containing C 14 -formaldehyde whose activity was determined by ionization chamber assay after combustion to CO 2 . A routine determination of C 14 -formaldehyde in cellulose formals by the liquid scintillation method is also described..