272 Cellulose 



for the examination of fibrous mixtures, with a view of determining 

 their composition. In textile fabrics this matter seldom arises, 

 unless in the broader distinction of the vegetable from the animal 

 fibres. The subject is exhaustively treated by H. Schlichter 

 (J. Soc. Chem. Ind. 1890, 9, 241). The vegetable fibres are 

 separated as a group by the process of boiling with the alkaline 

 hydrates (5-10 p.ct. solution), which dissolves the nitrogenous 

 animal fibres, leaving the vegetable fibres not, of course, un- 

 acted upon, but sufficiently so to enable the method to be re- 

 garded as a quantitative separation. The distinguishing of the 

 various vegetable fibres, thus separated, from one another is only 

 possible by microscopic observation with the additional aid of reac- 

 tions. No general directions can be given for investigations of this 

 character. They involve experience of histological methods, and 

 acquaintance with the characteristics of minute structure, and of the 

 special features which render their quantitative estimation possible 

 within a sufficient approximation for all practical purposes. The 

 examination of papers involves the identification of the vegetable 

 fibres only. The composition of a paper is first generally indicated 

 by its appearance. It is only in the mixed class of white papers 

 that investigation has to be carried out in minute detail. The fol- 

 lowing are briefly the methods adopted, so far as these are chemical : 



(1) The paper is treated with aniline sulphate solution in the 

 cold. The presence of mechanical wood pulp is indicated by the 

 yellow stain produced, and the proportion approximately by the 

 depth of colour. Many of the ground woods, it may be remarked, 

 yield a pulp of sufficient whiteness to be used in what may be called 

 white paper, and is frequently present in ' white ' and ' toned ' 

 printing papers. 



(2) The paper is boiled with the solution of aniline sulphate. 

 The presence of esparto and straw ' celluloses ' is indicated by the 

 characteristic rose-red reaction. Papers giving no colour reaction 

 with aniline sulphate are probably composed of rag fibres (cotton 

 linen), with or without bleached wood cellulose. It is evident that 

 the approximate composition of a paper is thus very quickly deter- 

 mined by its chemical reactions ; but it is often necessary (3) to 

 make quantitative estimations within narrower limits, and for these 

 a microscopic investigation is at present the only method to be re- 

 commended. The examination is, of course, facilitated by taking 



