246 Cellulose 



Cellulose Solvents. Prepare solutions of cotton and other 

 celluloses by treatment with zinc chloride. To dissolve I part 

 cellulose take 4-5 parts Zn.Cl 2 , dissolve in 5-7 parts water, add 

 the cellulose, heating in a porcelain dish over a water-bath. Stir 

 from time to time, and add water to replace that which evapo- 

 rates. 



Precipitate the solution (i) by pouring into water. Wash till 

 free from Zn salt, dry, and weigh. Burn off the cellulose, and 

 estimate the residue of Zn.O. 



(2) Pour into dilute hydrochloric acid. The precipitate will be 

 cellulose hydrate free from ZnO. Wash thoroughly, dry, and weigh. 



Calculate to original cellulose, and show that the molecule is 

 hydrated. Control by examining the solution in which the cellulose 

 was precipitated for dissolved products of hydrolysis. 



(3) Precipitate by pouring the solution into alcohol in a fine 

 stream, or by spreading the viscous solution as a thin film on glass. 

 Submerge the whole in alcohol, and detach the coherent film of the 

 cellulose compound. Digest with HCl.Aq to remove Zn.O. Wash, 

 and dehydrate by lengthened exposure to alcohol. 



The progress of the action of the zinc chloride solution should 

 be followed up microscopically. Cotton fibres are mounted in the 

 strong solution, covered with cover glasses, and the glass slips 

 ranged on a hot surface, so that they may acquire a temperature of 

 80-90. Examine from time to time under low and high power, 

 noting the progress of the disintegration, swelling-up, and rupture 

 of the cell wall. The structural points may be further differentiated 

 by staining with iodine. To apply the iodine without precipitating 

 the dissolved cellulose it is necessary, after dissolving the iodine in 

 a little potassium iodide in the usual way, to dilute with 40 p.ct. 

 zinc chloride solution. A drop of this solution may be added to the 

 solution on the slide without otherwise affecting the cellulose than 

 staining the fibrous residues. 



Dilute ammoniacal solutions of cuprous oxide are without action 

 upon cellulose. An interesting demonstration of the difference 

 between the cuprous and cupric oxides in this respect may be carried 

 out as follows : Cuprous chloride is prepared by the action of hydro- 

 chloric acid upon copper, with addition of potassium chlorate in suc- 

 cessive small quantities. The chloride is washed with water free 

 from oxygen, and, after settling, portions of the magma of crystals 



