294 Cellulose 



are due to the highly resistant character of the cuticular 

 tissues and by-products which are associated with these 

 tissues, or formed during the process of breaking them 

 down ; and, in lesser degree, to the wood residues. Both of 

 these have to be entirely eliminated without injury to the 

 cellulose. 



The process is therefore a complete illustration of the gene- 

 ral chemistry of the compound celluloses, and the order of 

 their resistance to hydrolysis and oxidation, i.e. to the chief 

 destructive influences of the natural world. 



It cannot be said that the process has been subjected to 

 exhaustive chemical investigation, such as would reveal the 

 steps by which the various non-cellulose impurities are broken 

 down. From the more theoretical account of these constitu- 

 ents in the earlier sections of this book we may, however, form 

 a tolerably correct estimate of the progress of the breaking- 

 down process. But at the same time a full investigation by 

 chemical and microscopic methods is much more to be desired, 

 and could riot fail to throw considerable light upon the 

 important industrial problems involved. 



DYEING AND PRINTING PROCESSES. It appears, a priori, 

 that these processes of colouring the textile fibres are the result 

 of interaction of colouring matter and fibre-substance as a 

 definitely molecular phenomenon ; and the progress of in- 

 vestigation is confirming this view more and more. At this 

 stage, however, the ' theory of dyeing ' is still the subject of 

 active controversy, and a decisive statement must therefore be 

 avoided. The discussion ranges itself round the two opposed 

 views of dyeing : (i) as a mechanical, and (2) as a chemical 

 process. At the present time, however, these terms have lost 

 much of the significance attached to them in the early days of 

 the controversy. In those days ' solution ' itself was regarded 

 as a ' mechanical ' or * physical,' in contradistinction to a 



