298 Cellulose 



dyeing process. The combination is of so stable a nature that 

 the base may be diazotised upon the fibre without loss, and 

 then may be further synthesised with chromogenic phenols 

 and bases to form a range of dyes of varying shades. Such 'in- 

 grain' colours constitute an important theoretical and practical 

 advance, and their production by synthetical processes upon the 

 cellulose itself is a further proof that the bond of union of dye- 

 stuff to fibre-substance is ' chemical ' as ordinarily understood. 



Another application of these peculiar relationships of dye- 

 stuff to fibre results from the observation that the diazoprimu- 

 line upon the cellulose is in a highly photo-sensitive condition, 

 a brief exposure to sunlight sufficing to decompose it with 

 evolution of (gaseous) nitrogen. From this observation has 

 resulted the diazotype process of ' positive ' photographic 

 printing (Green, Cross and Bevan, Berl. Ber. 23, 3131). 



The important feature of this process, from the point of 

 view of the present discussion, is the sensitiveness of the diazo 

 derivative when prepared upon the cellulose basis, compared 

 with its relative stability in the free state. The most reasonable 

 explanation of this increased sensitiveness appears to be that 

 the product exists in the cellulose in a condition of solution- 

 dissociation, a solid solution of the product in the colloid cellu- 

 lose having the essential characteristics of solutions in liquid 

 solvents. According to this view, the diazoprimuline, being 

 molecularly disaggregated, is in a more ' responsive ' condition 

 to the decomposing action of the light-energy ; and hence the 

 decomposition. It is no purpose of this discussion, however, 

 to advocate any particular views, but merely to introduce the 

 various aspects from which this in many respects unique dyeing 

 process of the celluloses may be regarded, and to point out 

 that judgment as to the underlying causes must for the present 

 continue to be suspended. 



The lignocelluloses afford a still more characteristic dyeing 



