CARBOIIYDRA TES. 537 



vents, its resistance to either alkaline or acid liquids, and its tough 

 and flexible nature. Some parts of vegetables (cotton, hemp, and 

 flax, for instance) are nearly pure cellulose. 



Pure cellulose is a white, translucent mass, insoluble in all the 

 common solvents. It is not colored blue by iodine. 



The best solvent for cellulose is an ammoniacal solution of copper hydrox- 

 ide, known as Schweizer's reagent, a very efficient preparation of which is 

 obtained as follows : 2 grammes of pure crystallized copper sulphate are dis- 

 solved in 100 c.c. of water to which a few drops of a concentrated solution of 

 ammonium chloride have been added. 1 gramme of potassium hydroxide is 

 dissolved in 100 c.c. of water and a little of a solution of barium hydroxide 

 added to precipitate any carbonate in the alkali. The two solutions are mixed 

 and the precipitate thoroughly washed by decantation and on the filter-paper. 

 The moist copper hydroxide is finally covered in a beaker with just enough 

 concentrated ammonia water to dissolve it. The clear solution is decanted or 

 filtered through glass wool. It must be preserved in a dark place. 



Cellulose is precipitated from its solution in Schweizer's reagent by acids as 

 a gelatinous mass which forms a grayish powder when dried. 



Treated with concentrated sulphuric acid it swells up and gradu- 

 ally dissolves ; water precipitates from such solutions a substance 

 known as amyloid, which is an altered cellulose giving a blue color 

 with iodine. Upon diluting the sulphuric acid solution with water 

 and boiling it, the cellulose is gradually converted into dextrin and 

 dextrose. 



Unsized paper (which is chiefly cellulose), dipped into a mixture 

 of two volumes of sulphuric acid and one volume of water, forms, 

 after being washed and dried, the so-called " parchment paper," 

 which possesses all the valuable properties of parchment. 



Official purified cotton, known commercially as absorbent cotton, is prepared 

 from raw cotton by boiling it in a weak solution of alkali to remove fatty 

 matter, then treating it with a weak solution of chlorinated lime to bleach it, 

 It is then washed and dried. 



Medicated cotton is usually prepared by impregnating absorbent cotton with 

 a solution of the medicinal agent in alcohol and glycerin, and drying. The 

 glycerin is not volatilized and serves as an adhesive agent for retaining the 

 active ingredient on the fiber of the cotton. Benzoated, borated, carbolated, 

 iodized, salicylated, and other medicated cotton is prepared in this or a simi- 

 lar manner. The percentage of medicinal agent present must be calculated on 

 the basis of finished product ; thus, 25 grammes of 10 per cent, borated cotton 

 should contain 2.5 grammes of boric acid, or 10 grammes of 5 per cent, carbo- 

 lated cotton should contain 0.5 gramme of pure carbolic acid. 



Pyroxylin, Pyroxylinum, chiefly cellulose tetm-nitrate, C 12 H 16 O 6 - 

 (NO 3 ) 4 . (Soluble gun-cotton, Nitro-cellulose.) Cellulose has the 



