EXAMINATION OF CELLULOSE 27 



The following tests should be performed with the 

 product, and also with ordinary filter paper, which is a 

 fairly pure form of cellulose. 



(i.) The substance in small amount is well shaken 

 in a corked test-tube with Schweizer's reagent (an 

 ammoniacal solution of copper oxide). The cellulose 

 will be found to be gradually disintegrated, and finally 

 completely dissolved. On pouring the blue solution 

 into a large volume of water, the cellulose will be 

 precipitated as a colloidal hydrate. 



(ii.) A similar series of operations is carried out with 

 a concentrated solution of ZnClg containing free HCl. 

 The cellulose will be found to dissolve or swell up, but 

 on pouring the product into water, the milky precipitate 

 of zinc oxychloride produced will mask the cellulose. 



(iii.) Successive portions of the cellulose are well 

 shaken in an open test-tube with \ c.c. concentrated 

 H2SO4. The cellulose will gradually dissolve, being 

 converted into cellulose sulphates. The test-tube is 

 half-filled with water and the solution well boiled for 

 a few minutes, whereby the cellulose sulphates are 

 hydrolysed to glucose. The presence of this latter 

 substance in the solution can be detected by almost 

 neutralising with a concentrated (syrupy) solution of 

 NaOH, and then adding Fehling's solution (alkaline 

 copper tartrate). On boiling, a red precipitate of 

 cuprous oxide is produced, indicative of the presence of 

 glucose (see 16 (^), p. 28). 



Pure cellulose is a colourless, insoluble material, differing in 

 texture according to its source, which can therefore often be decided 

 from a microscopic examination. 



When precipitated from its copper solution (i. above) by dilute 

 acids, it is however, structureless, and dries to a horny, amorphous 

 mass. The digestibility of cellulose in plant products used for 

 food depends largely upon the degree of hydration. In young 

 plants, for example, the cellulose is entirely digestible, but as 



