190 CELLULOSE 



obtained. Its composition corresponds to the empiric formula C 6 H 10 O 5 . 

 Ordinary air-dried specimens always contain 7 to 9 per cent of hygro- 

 scopic moisture. It is insoluble in most solvents, but can be obtained 

 in solution by means of zinc chloride or ammoniacal copper oxide. 

 The solubility of cellulose in these solutions is taken advantage of in 

 the arts, the former being used in the preparation of the " carbon fila- 

 ment " of incandescent electric lamps, and the latter in the manufac- 

 ture of " Willesden " waterproof paper. Cellulose appears to have at 

 the same time faint acid and basic properties ; it will absorb and retain 

 either bases or acids. 



By the action of caustic soda solutions (exceeding 10 per cent 

 Ka 2 O) ordinary cotton fibre (practically cellulose) is converted into a 

 compound which, on treatment with water, is decomposed, a molecule 

 of water apparently taking the place of Na 9 0. The properties of the 

 fibre are changed considerably, it swells laterally or thickens with a 

 corresponding shrinkage in length, its tensile strength is increased, and 

 it possesses greater affinities for dyes. These facts were discovered by 

 Mercer many years ago, and cotton fabrics so treated have lately been 

 extensively made. They are sold as " mercerised cotton ". If cotton 

 be treated with a solution containing 15 per cent of caustic soda, 

 squeezed, and placed in a bottle with about 40 per cent of its weight 

 of carbon disulphide, CS 2 , a substance is produced after three or four 

 hours which will dissolve in water on standing. This cellulose thio- 



C^(C* TT O \ 

 carbonate, CScWr 6 10 ' spontaneously decomposes, especially in 



contact with a large amount of water, giving a jelly or coagulum. 

 Heating also effects the coagulation. This product lends itself to 

 many useful applications and is employed commercially under the 

 name of "Viscose". 



By the action of nitric acid, or better, a mixture of nitric and sul- 

 phuric acids, cellulose is converted into various nitro-derivatives or 

 nitrates, some of which are of great value in the arts. 



Gun-cotton is chiefly cellulose hexa-nitrate, C 12 H 14 (N0 3 '> 6 O 4 , and is 

 valued for its explosive properties. Pyroxylin or collodion is mainly 

 tetra-nitrate, C 12 H lf) (N0 3 ) 4 O 6 , and penta-nitrate, C 12 H 15 (N0 3 ) 5 O 5 . These 

 substances are soluble in ether and alcohol and are then known as 

 collodion. This is employed in surgery and photography, also in the 

 manufacture of celluloid, which is a mixture of nitrocellulose and 

 camphor. 



Parchment paper is obtained by immersing ordinary unsized paper 

 in sulphuric acid and then washing it with water. It closely resembles 

 true parchment in strength and apparently has the outer part of its 

 cellulose altered into a substance known as amyloid. A similar change 

 is produced by zinc chloride solution, and since amyloid is, like starch, 

 coloured blue by iodine, a solution of iodine in concentrated zinc 

 chloride forms a useful reagent for the identification of cellulose. 



By the action of sulphuric acid cellulose is eventually converted into 

 dextrin and dextrose. 



Gums, (G 6 H 10 6 )n, are very widely distributed in plants. They are 

 amorphous and either dissolve in water or absorb it and swell up when 



