V] CARBOHYDRATES 69 



wash well, dry thoroughly, and dissolve in strong ammonia.) Add strong hydrochloric 

 acid and the cellulose is precipitated out again. Then add water and wash the 

 precipitate until it is colourless. Test the roughly dried precipitate with a little 

 iodine and strong sulphuric acid. A blue coloration is given. 



All the above tests may be repeated with threads from white cotton material, 

 with filter-paper and good white writing paper. 



Try tests {a) and (6) with newspaper, and note that they are not so distinct as 

 with writing paper owing to the presence of ligno-cellulose (see Expt. 73). 



Expt. 72. Hydrolysis of cellulose hy acid. Dissolve as much filter-paper as possible 

 in 5 c.c. of concentrated sulphuric acid and when all is in solution pour into 100 c.c. 

 of distilled water. Boil the solution in a round-bottomed flask fitted with an air 

 condenser (see p. 46) and use a sand-bath for heating. After boiling for an hour, 

 cool and neutralize the solution with solid calcium cai-bonate. Add a little water if 

 necessary and filter. Test the filtrate with the following tests : 



(a) Make the osazone [see Expt. 41 {d)^ Note that crystals of glucosazone are 

 formed. 



(6) Add a little Fehling's solution and boil. Note that reduction takes place. 



Instead of using filter-paper, the above experiment may also be carried out with 

 €otton-wool or threads from white cotton material. 



Ligno-cellulose. As the cells in plants grow older the walls usually 

 become lignified, that is part of the cellulose becomes converted into 

 ligno-cellulose. The extreme amount of change is found in wood. The 

 least amount in such fibres as those from the stem of the Flax (Linum 

 iisitatissimum) which, when freed from such impurities, consist of cellu- 

 lose only and constitute linen. Other fibres, containing more ligno- 

 cellulose, are those of the stem of the Hemp plant {Cannabis sativa) and 

 the Jute plant (Cor chorus) from which string, rope, canvas, sacking and 

 certain carpets are made. The percentages of pure cellulose in these 

 various lignified tissues are as follows : 



Cotton fibre 88-3% 



Flax and Hemp fibre . . . 72-73 % 



Jute 540/0 



Beech and Oak wood . . . 35-38 % 



The ligno-celluloses are generally regarded as consisting of cellulose 

 and two other constituents, of which one contains an aromatic nucleus 

 and the other is of the nature of a pentosan (see xylan, p. 56). Both 

 are sometimes classed together and termed lignin or lignon. The lignin 

 reactions (see below) depend on the presence of an aromatic complex. 

 It has been suggested that coniferin, vanillin and allied compounds 

 which are present in wood are probably the substances responsible for 

 the reaction (Czapek, 8). 



