150 



THE CARBOHYDRATES 



Such cellulose, however, in its native condition is not in a 

 pure state, being in more or less intimate chemical union with 

 other substances, such as pectic- bodies, * lignocellulose and 

 colouring matters from which it has to be freed by a series of 

 successive chemical treatments before the pure cellulose can 

 be isolated. 



The chemical treatments referred to are as follows : 



1. Alkaline hydrolysis, which consists in boiling the fibres 

 with 1-2 per cent caustic potash, and washing to remove the 

 pectic bodies. 



2. Exposure of the washed fibres to bromine or chlorine 

 at the ordinary temperature ; by this process the lignone 

 complex of the lignocellulose is destroyed. 



3. A second alkaline hydrolysis with sodium sulphite, 

 carbonate or hydrate. 



The cellulose is thus isolated in a very pure state. 



CHARACTERISTICS AND PROPERTIES OF NORMAL 

 CELLULOSE. 



In describing the chemical properties of cellulose, the 

 cellulose isolated as above described from the fibre substance 

 of cotton is chosen as typical. 



Pure cellulose is a white hygroscopic substance, which 

 absorbs about 6-12 per cent of water, which it loses again when 

 heated to 1 00; it is insoluble in water at ordinary pressure, 

 but when heated with water in sealed vessels at 500 F., it 

 is dissolved completely with decomposition. 



SOLUBILITY OF CELLULOSE. 



Cellulose is insoluble in all ordinary solvents, but when 

 treated with zinc chloride in the presence of water, it is con- 



