The Typical Cellulose and the Cellulose Group 53 



(a) NON-OXIDISING ACIDS. (i) Sulphuric arid, si i'5-i'6 

 sp.gr. (H 2 SO 4 .3H 2 O), produces the effects previously de- 

 scribed, but in such a way as to be controlled within the 

 earlier stages of molecular resolution. Unsized paper plunged 

 into the cold acid, diluted to the above formula, is rapidly 

 attacked, the paper becoming transparent owing to the swell- 

 ing and gelatinisation of the fibres. The reaction quickly 

 becomes one of solution ; but if the paper be transferred, 

 after short exposure, to water, the acid compound is at once 

 decomposed and the resulting gelatinous hydrate of cellulose 

 precipitated in situ. The product, after exhaustive washing 

 and drying, is obtained zs parchment paper. This modification 

 of cellulose gives a tough translucent sheet, necessarily very 

 much less absorbent than the original. 1 



The compound itself, from its resemblance to starch, 

 has been termed amyloid. It is represented by the formula 

 ^(C^HasOn), the semi -hydrate of 7z(C 6 H 10 O 5 ). Like 

 starch, the compound is coloured blue by iodine, and the joint 

 action of iodine and sulphuric acid is frequently used in dia- 

 gnosing cellulose. As a further result of the reaction, the 

 product differs from cellulose, in containing active CO groups \ 

 it reacts with phenyl hydrazine salts, and is oxidised by CuO in 

 alkaline solution. 



Effects of a similar character are produced by treating 

 cellulose with concentrated solutions of phosphoric acid and 

 zinc chloride. 



(2) Nitric acid, of 1*4 sp.gr., also produces (without oxi- 

 dation) an effect of a similar character. A short immersion 

 of unsized paper e.g. filter paper in the acid, followed by 

 copious washing, has a considerable toughening action, due to 

 superficial conversion of the fibres into a gelatinous hydrate. 



1 See Guignet on Soluble and Insoluble Colloidal Cellulose, and Com- 

 position of Parchment Paper,' Compt. Rend. 108, 1258. 



