THE CARBOHYDRATES 21 r 



CELLULOSE. 



The cell walls of plants, which are elaborated by the protoplasm, are sup- 

 posed to consist primarily of the substance termed cellulose, but during growth 

 the plant forms other substances which are encrusted in the cellulose, so that 

 the material of the cell wall consists of a mixture (or compound) of cellulose 

 and other substances. The materials which are encrusted in the cellulose are 

 lignin 1 or lignone forming lignocellulose in wood, straw, etc., pectins and 

 gummy substances forming pectocellulose, fatty substances forming adipo- 

 cellulose. The material which contains most cellulose is the fibre of the 

 cotton plant, hemp and flax. Pure cellulose is generally made from these 

 products. Wood contains 50-60 per cent, of cellulose; straw contains a 

 similar amount, but silica is also present. 



Cellulose is also found in the animal kingdom ; the tunicin in the cell 

 walls of tunicates is said to be identical with cellulose. 



Preparation of Cellulose from Cotton. 



Since cellulose is very resistant to most chemicals pure cellulose is pre- 

 pared from cotton fibre by the following treatment : 



The fibre is boiled with 1-2 per cent, caustic potash and washed with 

 water. Pectins are thus removed. The fibre is treated with bromine or 

 chlorine at the ordinary temperature. The lignin or lignone is destroyed and 

 dissolves. The fibre is then treated with sodium sulphate, carbonate or 

 hydrate. The residue is washed with water and dried. 



Preparation of Paper Cellulose* 



Linen rags or cotton waste are cleaned, cut up and boiled under pressure, 

 firstly with dilute sodium carbonate and secondly dilute caustic soda so as to 

 disintegrate them. The material is bleached with chlorine, washed free from 

 the halogen, treated with resin, soap and alum, and spread out in thin layers 

 to dry. The fibres thus become felted together. Wood is disintegrated 

 and the lignin dissolved out by treatment with calcium bisulphite. The 

 residue is treated as above with soap, etc. 



Paper of an inferior quality is made from wood which has not been 

 treated ; it gives the reactions for pentose if a solution of aniline acetate be 

 poured upon it or if it be treated with a 1-2 per cent, solution of phloro- 

 glucinol in alcohol and dilute hydrochloric acid. On exposure to light such 

 paper becomes yellow. 



Properties. 



Pure cellulose is a white substance which is hygroscopic and absorbs 

 about 10 per cent, of water. The water is removed by heating it to 100. 



Solubility. 



It is insoluble in water and all ordinary solvents, but it is decomposed by 

 heating with water under pressure. 



It becomes gelatinous in a solution of zinc chloride and finally dissolves. 

 On stirring i part of cellulose with 6 parts of zinc chloride in 10 parts of 

 water at 60, it gelatinises after some time ; on raising the temperature by 

 placing it in a boiling water-bath the cellulose gradually dissolves. 



Cellulose dissolves rapidly in a cold solution of zinc chloride in twice its 

 weight of hydrochloric acid. 



Cellulose dissolves in a solution of ammoniacal cupric oxide (Schweitzer's 

 eagent). On adding acid, it is precipitated. 



1 Lignin appears to contain aromatic substances and pentosans. 



