14 Cellulose 



the solution was considerably retarded by raising its temperature, 

 becoming very slight at 100 F. 



Mercer's favourite method of demonstrating the reaction con- 

 sisted in applying a solution of cupric nitrate to cotton cloth in 

 spots, decomposing the nitrate by plunging the cloth into a weak 

 solution of caustic soda, washing to remove the alkali, partially 

 drying in the air at ordinary temperatures, and exposing the cloth 

 to the vapour of ammonia. In this way the cellulose was fully 

 acted upon in the portions containing the oxide. The demon- 

 stration is an interesting one, and should be repeated by the 

 student. 



Theory of Action of Cellulose Solvents. The causes 

 underlying the processes of dissolution of cellulose above de- 

 scribed will become more apparent as we proceed in the dis- 

 cussion of its special chemistry. For the present it is sufficient 

 to point out that they depend upon the presence in the cellu- 

 lose molecule of OH groups of opposite function, basic and 

 acid, and that the compounds 'formed with the solvents are 

 of the nature of double salts. 



Qualitative Reactions and Identification of Cellu- 

 lose. The properties of cellulose which we have already dis- 

 cussed afford the means of identifying it : that is (i) by reason 

 of its resistance to the action of oxidising agents, to the halo- 

 gens and to alkaline solutions it is obtained as a residue from 

 the treatment of vegetable tissues by these reagents in succes- 

 sion ; (2) it is soluble to gelatinous or viscous solutions in 

 the reagents above described viz. ZnCl 2 .Aq, ZnCl 2 .HCl.Aq, 



/NH 3 NH 4 , 



and Cu< , from which it is obtained by pre- 



^\.N -tig .N .n.4\_/ 



cipitation in the amorphous form or as a gelatinous hydrate. 

 These hydrates react in many cases with iodine, giving a blue 

 colouration ; the reaction is determined upon the original 

 cellulose by simultaneous treatment with iodine and a de- 

 hydrating solution. 



