12 Cellulose 



several celluloses under treatment with the cuprammonium reagent 

 The evaporation of the cuprammonium solutions of cellulose upon 

 glass surfaces gives a film of the mixed cellulose-cupric hydrate, 

 but of little tenacity. It will appear as we proceed that high tensile 

 strength of a film obtained from solutions of cellulose compounds 

 indicates a relatively high molecular weight, and conversely, a 

 brittle product is evidence that in forming the compound the mole- 

 cular weight or aggregation of the cellulose has been lowered. 



According to recent investigations of E. Gilson (Chem. 

 Centr. 1893, ii. 530) cellulose maybe crystallised from its solu- 

 tion in cuprammonium. If such solution is left to stand in a 

 loosely closed vessel the ammonia escapes, cellulose being pre- 

 cipitated together with hydrated copper oxide. On removing 

 the latter by treatment with hydrochloric acid, the cellulose is 

 stated to remain in the form of nodular crystals. It is also 

 stated that when sections of cellulosic tissues are allowed to 

 remain for some time in contact with the reagent, then gradu- 

 ally washed with ammonia and water, the interior of the cells 

 are found to contain the cellulose in crystalline form. This 

 requires confirmation. 



These cuprammonium solutions are, of course, deprived of 

 their copper by digestion upon zinc, the latter metal replacing 

 the copper in solution and, under carefully regulated conditions, 

 without precipitating the cellulose, so that a colourless solu- 

 tion of the latter in zinc-ammonium-hydroxide results. Some 

 of these solutions have been observed to be laevogyrate. 

 Cotton cellulose in i p.ct. cuprammonium solution was found 

 by Levallois to show a rotation of 20 ; the rotation, however, 

 is not constant, but varies with the concentration and the ratio 

 of cupric oxide to cellulose in the solution. These observations 

 have been called in question by Bechamp, but reaffirmed by 

 the former observer, and apparently on sufficient evidence. 



On adding a solution of lead acetate to these solutions of 

 cellulose a precipitate is obtained of a compound of cellulose 



