132 THE CARBOHYDRATES 



2. Acids. — Nitric acid (sp. gr. 1-25) at 180° converts cellu- 

 lose into oxycellulose, a substance of a weak acidic character, 

 which reduces Eehling's solution (see below under oxidizing 

 agents). Concentrated nitric acid, or a mixture of this acid 

 with concentrated sulphuric acid, converts cellulose into nitrates, 

 the composition of which varies with the conditions of the 

 experiment ; di-, tri-, tetra-, penta- and hexa-nitrates,* which 

 are of considerable technical importance, are known. Dilute 

 sulphuric acid on prolonged action converts cellulose into 

 hydro-cellulose, a substance of the formula Cj^H^^O^^ ; this sub- 

 stance retains the structure of the cotton fibre from which it 

 is produced, but on rubbing it breaks up into a fine powder. 

 The same substance may also be obtained by the action of 

 aluminium or magnesium chlorides at a temperature of 300° F. 



Concentrated sulphuric acid dissolves cellulose, gradually 

 converting it into dextrin and ultimately into dextrose. If 

 the solution as soon as made is diluted with water, a gelatinous 

 hydrate is precipitated ;f this substance is known as amyloid,+ 

 since it resembles starch in giving a blue colour with iodine. 

 The same substance is formed by the action of chlorzinc iodide, 

 the reaction being used as a test for cellulose. 



The combined action of glacial acetic acid and acetic an- 

 hydride in the presence of concentrated sulphuric acid or zinc 

 chloride converts cellulose in acetyl cellulose, which is insoluble 

 in water but soluble in several organic solvents. Acetyl cellu- 

 lose is also used in the manufacture of artificial silk. 



Cellobiose,§ C^2^2-2^ii' ^^ ^ disaccharide obtained in the 

 form of its acetate by acting on cellulose with acetic anhy- 

 dride and concentrated sulphuric acid. It stands in the same 

 relation to cellulose as does maltose to starch ; since cellulose 

 and starch yield different disaccharides on hydrolysis, it would 

 appear that these two substances are fundamentally different 

 and that cellulose is not a higher polymer of starch. 



* See footnote, p. 137. 



t This reaction is made use of in the preparation of parchment paper. For 

 this purpose paper is rapidly drawn through a mixture of four parts of concen- 

 trated sulphuric acid with one part of water; the paper is then thoroughly 

 washed with water until it is free from acid. 



JThis substance must not be confused with a compound of the same name 

 which occurs naturally in several plants (cf p. 120). 



§ Skraup and Konig : " Ber. deut. chem. Gesells.," 1901,34,1115; Schlie- 

 mann ; " Annalen," 1911, 378, 366. 



