212 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



One variety of artificial silk is prepared by dissolving mercerised cotton 

 in Schweitzer's reagent (see p. 616), and running it in a thin stream into dilute 

 sulphuric acid. A thread of cellulose is thus precipitated. 



Reactions. 



(1) Action of Alkali. 



Dilute solutions (1-2 per cent.) of caustic soda even at 100 have no 

 action upon cellulose. More concentrated solutions (10 per cent.) cause the 

 fibres to swell and become cylindrical and destroy the central canal. The 

 appearance becomes glossy. This property was used by Mercer for treating 

 cotton to make it appear like silk. 



Cellulose treated with 15 per cent, alkali reacts with carbon disulphide, 

 forming a thiocarbonate. This substance decomposes in the air giving 

 carbon disulphide and cellulose. The solution, if forced through fine openings 

 and allowed to come into the air, forms continuous threads of artificial silk. 



(2) Action of Acids. 



Dilute sulphuric acid converts cellulose into hydrocellulose. 



Dilute nitric acid (sp. gr. 1-25) at 80 converts cellulose into oxycellulose 

 which reduces Fehling's solution. 



Concentrated sulphuric acid dissolves cellulose. On diluting the solution, 

 a gelatinous compound is precipitated. This substance is called amyloid, as it 

 gives a blue colour with iodine, like starch. Parchment paper is made by 

 treating paper with 2 parts of sulphuric acid and i part of water and then 

 washing the acid away with water. 



(3) Formation of Esters. 



(a) Nitric acid. 



Concentrated nitric acid, or a mixture of this acid with sulphuric acid, con- 

 verts cellulose into nitric acid esters. Collodion is a mixture of the tri- and 

 tetra-nitrates dissolved in a mixture of equal parts of alcohol and ether. 

 Celluloid is a mixture of the tri- and tetra-nitrates with camphor. 



Gun cotton, or pyroxylin, is cellulose hexanitrate and is prepared by treating 

 cotton waste (freed from fats by treating with alkali) with a mixture of i part 

 nitric acid and 3 parts sulphuric acid. The product, which has still the 

 original appearance, is washed with water, moulded and dried. It is con- 

 verted into smokeless powder by dissolving in acetone or ethyl acetate and 

 evaporating the solution. When mixed with nitroglycerine and other sub- 

 stances it forms blasting gelatin, cordite, etc. 



Artificial india-rubber is a product prepared by mixing together tri- and 

 tetra-nitrocellulose with castor-oil. The inflammability of this material is 

 eliminated by treating it with alkali. 



(b) Acetic acid. 



Cellulose acetates are obtained on treating cellulose with glacial acetic 

 acid and acetic anhydride in the presence of concentrated sulphuric acid. 

 These compounds are insoluble in water, but soluble in organic solvents. 

 A solution of tetra-acetyl cellulose in acetone on evaporation yields artificial 

 gutta-percha. 



A white precipitate is formed when a solution of cellulose acetate in 

 glacial acetic acid is poured into alcohol. This solid does not melt, but 

 burns wiihout leaving an ash. It forms " solid spirit ". 



It is also used to make artificial silk. 



(4) Hydrolysis. 



Cellulose is dissolved by concentrated sulphuric acid, which hydrolyses it 

 to glucose 



