v] HYDROLYZING ENZYMES 67 



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 by 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. 45) and use a sand-bath for heating. After boiling for an hour, 

 cool and neutralize the solution with solid calcium carbonate. Add a little water if 

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



(a) Make the osazone [see Expt. 41 (c?)]. 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 

 cotton-wool or threads from white cotton material. 



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

 become lignined, 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 

 mitatissimum) 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 (Cannalris sativa) 

 and the Jute plant (Corchorus) 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 54% 



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. 53). 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, 6). 



Although the best paper is made from cellulose, cheaper forms of 

 paper are manufactured from ligno-cellulose, and, as a result, they give 

 reactions for lignin and are also turned yellow by exposure to light. 



Expt. 73. Reactions of lignin. 



One of the most striking reactions of lignin (due as it is supposed to a furfural 



52 



