248 Cellulose 



calculated to produce a solution of any desired percentage strength 

 (cellulose). 



The progress of the reaction should be followed by microscopic 

 examination of the fibre at intervals. The rupture of the cell walls 

 is preceded by an exaggeration of the structural details of the fibre, 

 which will be found useful in differentiating cotton from celluloses 

 of other types. 



From the solution of the crude thiocarbonate the solid product 

 is precipitated, in the form of a gelatinous hydrate, by various 

 'neutral' dehydrating liquids or solutions: of these the most 

 convenient are alcohol and a solution of common salt, and the 

 modus operandi may be instructively varied in the following 

 ways : 



(1) Alcohol. The solution maybe poured into a photographer's 

 developing dish to a depth of, say, inch, strong alcohol may then 

 be poured upon the solution, the dish covered with a glass plate, 

 and set aside. Coagulation of the cellulose product proceeds gradu- 

 ally, and after some time a coherent slab is obtained of a greenish 

 colour, the yellow by-products of the reaction having been dis- 

 solved by the alcohol. 



Or the solution may be caused to flow in a fine stream into the 

 alcohol, when the cellulose xanthate (hydrated) will be precipitated 

 as a continuous gelatinous thread. In the latter case it is advisable 

 to add a certain quantity of alcohol to the crude solution, which can 

 be done without causing precipitation, the xanthate being soluble 

 in dilute alcohol. Such a solution will obviously be more sensitive 

 to the further action of the alcohol, and precipitation in slender and 

 uniform threads is facilitated. 



(2) Brine. If prepared from the commercial salt, the solution 

 should be freed from magnesia by previous treatment with sodium 

 carbonate and filtering. The precipitation may be carried out as 

 described under (i), or any surface may be coated with the 

 crude solution, and the xanthate precipitated upon the surface by 

 immersion in the brine. The xanthate, purified by any of these 

 treatments, may be redissolved in water, and again precipitated by 

 a repetition of the treatment. With each precipitation the ratio of 

 both alkali and sulphur to cellulose in the product is considerably 

 diminished. 



The precipitated xanthate may be treated with solutions of 



