296 Cellulose 



species of double-salt formation. On the more general view 

 of dyeing, this is in fact a well-grounded hypothesis, viz. that 

 as the colouring matters available for dyeing show invariably 

 a * saline' constitution, and the formation of * lakes' with 

 inorganic bodies is due to reaction with salt-forming groups 

 as also the fibre-substances in reaction show a similar differen- 

 tiation into acid and basic groups the interaction of the two 

 groups of compounds in the dyeing process is, on the more 

 general view, a special case of double-salt formation. But even 

 should this hypothesis be found to afford a consistent general- 

 isation of the whole range of dyeing phenomena, it carries us 

 only a certain length as a theory of dyeing. We have next 

 to deal with the selective relationships of the two groups of 

 carbon compounds, i.e. the particular ' colouring affinities ' of 

 the soluble colouring matters or dye-stuffs. Speaking gene- 

 rally, for instance, the celluloses are resistant to such solutions ; 

 the number of dye-stuffs giving a direct dye on cotton is ex- 

 tremely limited. In striking contrast to the celluloses, on the 

 other hand, the lignocelluloses are distinguished by ' cosmopo- 

 litan ' relationships, resembling the animal fibres wool and silk, 

 in being dyed directly with a wide and varied range of colouring 

 matters. This at once suggests that the essential factors 

 of the dyeing process are molecular and constitutional, i.e. 

 chemical, in the narrow sense of the term, rather than structural ; 

 and this conclusion is strongly emphasised by everything which 

 has preceded this discussion in regard to the constitution of 

 these typical groups of fibre-constituents. Further, by chemical 

 modification of the celluloses, their dyeing capabilities are con- 

 siderably modified ; thus the oxycelluloses were shown by Witz 

 to exhibit not merely an increased attraction for colouring 

 matters of the 'basic' class, but a diminished attraction for 

 those of the class more acid in character and generally requir- 

 ing to be dyed with mordants. Of these two groups the fol- 



