398 



work and intricate structure of plants. We are familiar with 

 pure cellulose in the forms of filter paper and cotton. The latter 

 consists of fine, hollow tubes of cellulose (see Fig. 2, p. 2), large 

 tufts of which surround the seed of the cotton plant. Linen is 

 almost pure cellulose, wood is largely cellulose, and paper pulp 

 is practically all cellulose. 



Cellulose interacts with very few chemical substances. It is 

 because it thus remains unchanged, by most substances that come 

 in contact with it, that it can be used as a filter paper. When it 

 does undergo chemical change, it acts as if it contained hydroxyl 

 (OH) groups, and behaves therefore chemically like anjUcohol 

 (see p. 480) forming valuable derivatives (explosives and plastics) 

 which will be discussed later (Chap. XL). 



Paper Manufacture. Paper is composed of cellulose 

 (CeHioOs)^ and is made from a mixture of cotton or linen pulp and 

 wood pulp the cheapest varieties from the latter alone. The 

 wood is cut into chips and heated (" cooked ") with a solution 

 of calcium bisulphite Ca(HS03)2. This dissolves out the lignin, 

 which, together with cellulose, makes up the solid part of its 

 structure. The pulpy material is then washed, beaten with water 

 to reduce it to minute shreds, and bleached with very dilute 

 chlorine-water. The pure cellulose, now paper pulp, suspended in 

 water, is spread on screens, drained, pressed, and dried. During 

 the process other substances are usually added. Thus size (glue 

 or gelatine) prevents the ink from running; pulverized calcium 

 sulphate (gypsum), and other white solids (" loading ") give body 

 to the paper and make possible the subsequent production of a 

 smooth surface by rolling (" calendering "). Ultramarine (blue) 

 and other colored powders are added to the pulp when special 

 tints are required. 



Other Uses of Cellulose. Cellulose dissolves in hot, concen- 

 trated zinc chloride solution. When the liquid is pressed through 





