2IO THE CARBOHYDRATES 



potassium hydroxides, cellulose undergoes complete decom- 

 position with the formation of oxalic and acetic acids. 



The so-called alkaU cellulose obtained by treating cellulose 

 with 17-5 per cent caustic soda reacts with carbon disulphide 

 to form xanthogenates ; * these compounds are used in the 

 manufacture of viscose (see below). 



2. Acids. — Nitric acid (sp. gr. 1-25) at 180° converts cellu- 

 lose into oxycellulose, a substance of a weak acidic character, 

 which reduces Fehling's solution (see below). Concentrated 

 nitric acid, or a mixture of this acid with concentrated sul- 

 phuric acid, converts cellulose into nitrates, the composition 

 of which varies with the conditions of the experiment ; di-, 

 tri-, tetra-, penta-, and hexa-nitrates, which are of considerable 

 technical importance, are known. 



If dilute sulphuric acid is allowed to act for some hours at 

 100° C. on cotton, it does not alter the structure of the fibre, 

 but makes it friable. This was at one time thought to be 

 due to the formation of a definite substance, hydrocellulose. 

 That this material is not a simple substance may be shown 

 by the fact that it has acquired reducing properties, the sub- 

 stance responsible for which may be extracted with alkali 

 leaving behind unchanged cellulose. The fact that the alkaline 

 extract is yellow in colour suggests the presence of an alde- 

 hyde, possibly glucose. For these reasons it is considered that 

 the term hydrocellulose implies a stage in the hydrolysis of 

 cellulose rather than a definite chemical substance ; it may be 

 a mixture of cellulose, cellulose dextrins, and glucose. 



Cellulose, when treated with concentrated sulphuric acid, 

 undergoes considerable swelling, and goes into solution with 

 the ultimate formation of dextrose. This is made use of in 

 the preparation of vegetable parchment for which purpose 

 paper is rapidly drawn through a mixture of 4 parts of 

 sulphuric acid with I of water ; the paper is then thoroughly 

 washed with water until free from acid. If, on the other hand, 

 cellulose is left in contact with concentrated sulphuric acid for 

 a time sufficient to dissolve it, and the solution is immediately 



* Cross, Bevan, and Beadle : " Ber. deut. chem. Gesells.," 1893, 26, 

 1090 ; and Cross and Bevan : id., 1901, 34, 1513. 



