228 THE CARBOHYDRATES 



to the nature of the material ; hard woods require less than 

 soft woods since they contain as a rule rather less lignin. 



E. Schmidt and Graumann * suggested the use of an 

 aqueous solution of chlorine dioxide f in place of gaseous 

 chlorine ; the original procedure was to employ a solution 

 of approximately 0-3 per cent strength, but Heuser and 

 Merlau $ recommend a 1-5 per cent solution. For the esti- 

 mation 0-5 gram of wood, which has been extracted with 

 alcohol and benzene to remove resins, etc., is placed in a 

 glass-stoppered flask with 100 c.c. of 1-5 per cent solution of 

 chlorine dioxide ; after forty-eight hours the residue is washed 

 free from chlorine dioxide and then with 2 per cent sodium 

 sulphite until the filtrate is no longer coloured ; a second 

 similar treatment is generally sufficient to remove all the 

 lignin ; the residue is washed and dried and may be weighed 

 as cellulose. According to Schmidt and Graumann, chlorine 

 dioxide solution has no action on the carbohydrate con- 

 stituents of the cell wall, whereas small quantities of incrustive 

 substance are readily attacked ; it is thus possible to estimate 

 quantitatively the percentage of incrustive and tissue sub- 

 stance in portions of plants ; thus in Piniis sylvestris they 

 found 63-28 per cent of tissue substance and 3672 per cent 

 of lignin, whereas Willstatter and Zechmeister found only 

 27-25 per cent of the latter. 



The Nature of the Union Between Lignin and Cellulose. 



Opinions are divided as to the nature of the association 

 between lignin and cellulose ; the view formerly held by 

 Cross and Bevan § was in favour of some form of chemical 

 union, but later they admit the possibility of there being only 

 a physical association, while Klason, who formerly beheved 

 in physical union, now favours combination. j| According to 

 Konig and Rump ^ the fact that wood when treated with 



* Schmidt and Graumann : " Ber. deut. chem. Gesells.," 1921, 54, 

 B., i860. 



t Prepared from potassium chlorate and oxalic acid. 



X Heuser and Merlau : " Cellulosechemie," 1923, 4, loi. 



§ Cross and Bevan : " Ber. deut. chem. Gesells.," 1893, 26, 2520. 



II Klason : id., 1923, 56, 300. ^ Konig and Rump : loc. cit. 



