138 THE CARBOHYDRATES 



consequence, considers that it has no reacting unit such as 

 a crystalline body has, nor has it a fixed molecular constitution 

 such as can be represented by any constitutional formula ; its 

 reacting unit at any moment is a function of the condition 

 under which it is placed. 



INDUSTRIAL USES OF CELLULOSE AND CELLULOSE PRODUCTS. 



One of the industries which consumes the largest amount 

 of cellulose is that of paper manufacture. Formerly the chief 

 sources of cellulose for this purpose were cotton or hemp fibres ; 

 but with the increased consumption of paper other sources had 

 to be found. Although straw contains cellulose which has 

 been only slightly lignified, it is found to be unsuitable for the 

 preparation of pure cellulose, owing to the fact that it contains 

 a considerable quantity of silica. The employment of wood as 

 a source of cellulose became possible with the discovery of 

 chemical methods of destroying the non-cellulose constituent 

 lignin, i.e. the " encrusting substances," without affecting the 

 cellulose proper. 



In the manufacture of paper from linen rags or cotton 

 waste the material is cut up, cleaned, and disintegrated by boil- 

 ing successively with dilute sodium carbonate and caustic soda 

 under pressure ; the fibre is then bleached with chlorine, the 

 excess being subsequently removed ; it is then treated with 

 resin, soap, and alum, and spread in thin layers and dried, 

 whereby the fibres become felted together in a peculiar man- 

 ner, with the formation of paper. When wood is used the 

 " encrusting substances " may be removed by boiling with cal- 

 cium bisulphite, whereby the lignin remains in solution and a 

 fairly pure form of cellulose, known as sulphite cellulose, is 

 produced. In the preparation of inferior quality papers the 

 wood undergoes no chemical treatment for the removal of 

 lignin ; such papers can be recognized by applying to them 

 any of the tests for lignocellulose. Cellulose used for the 

 preparation of filter papers is, after the ordinary methods of 

 purification, treated with hydrofluoric acid to remove silica. 



COMMERCIALLY VALUABLE DERIVATIVES OF CELLULOSE. 



When heated in a concentrated solution of zinc chloride, 

 cellulose is converted into a viscid syrup. This syrup, when 



