Compound Celluloses 191 



progressive increase of methoxyl with age ; (2) there is a highei 

 proportion of methoxyl in the wood of the branches as com- 

 pared with the main stem ; (3) the proportion of methoxyl is 

 unaffected by ' extracting ' the wood, i.e. it is a characteristic 

 constituent of the wood-substance (lignocellulose) itself. 



THE ACETIC RESIDUE. Acetic acid is produced in a 

 number of the decompositions of the lignocelluloses (ante^ 

 p. 1 60). It is obtained more readily, and in larger proportion, 

 from the (dicotyledonous) woods than from jute (et simili&). 

 The following reactions producing acetic acid may be cited : 



(1) Alkaline hydrolysis. The solutions obtained by treating 

 beech wood with dilute aqueous alkalis contain acetic acid 

 (acetate of soda), which is separated by distillation after acidi- 

 fication. The proportion is large, amounting to 7-8 p.ct. on 

 the wood. 



(2) Acid hydrolysis.- Acetic acid is formed on digesting the 

 woods with dilute sulphuric acid at 60-100. Larger yields 

 are obtained by dissolving the wood-substance in concentrated 

 sulphuric acid in the cold, diluting and distilling. 



(3) Oxidising processes. (a) Acid. The wood, in fine 

 shavings, is covered with normal sulphuric acid, and oxidised 

 at ordinary temperatures, with its own weight of chromic acid 

 (CrO 3 ) added in successive quantities. The solution on distil- 

 lation yields acetic acid, equal to 5-6 p.ct. of the weight of 

 the wood (dicotyledonous). The following are the results of 

 actual determinations : 



Beech Sycamore Birch 



5 -o p. ct. 5 -2 p. ct 6 -o p. ct. 



Oxidised with dilute nitric acid (10 p ct. HNO 3 ) at 

 60-100 (ante, p. 146), very much larger quantities of acetic acid 

 are obtained, viz. from 10-15 p.ct. of the weight of the wood. 



(&) Alkaline. The maximum yields are obtained in the 

 drastic decomposition, determined by heating with the alkaline. 



