144 THE CARBOHYDRATES 



acetic acid into alcohol ; a white solid is produced which does 

 not melt, and burns when ignited without leaving any ash. 



Finally, mention may be made of a few substances which 

 are made from cellulose as a starting point, but which are 

 produced only by the profound decomposition of the molecule. 

 Thus by heating cellulose with a strong solution of caustic 

 potash and soda, oxalic acid is produced, and by the de- 

 structive distillation of wood, acetic acid, acetone and methyl 

 alcohol are obtained. 



MICROCHEMICAL REACTIONS. 

 A. Normal Cellulose. 



1. With a dilute solution of iodine a yellow coloration 

 results. 



2. After staining well with iodine, the addition of strong 

 sulphuric acid causes the cellulose walls to swell considerably 

 and to turn blue. 



3. Chlorzinc iodide causes swelling, accompanied by the 

 assumption of a blue colour. 



4. Calcium chloride iodine solution turns pure cellulose 

 rose-red, and finally violet. 



Zimmermann gives the following directions for making 

 this reagent. A concentrated solution of calcium chloride is 

 made, and for each 10 c.c. of this solution there is added 

 •5 gram of potassium iodide and "i gram of iodine. The 

 mixture is then gently heated and filtered through glass-wool. 



5. Pure cellulose is easily soluble in cuprammonia. 



6. The hemi-celluloses give different reactions ; some turn 

 blue with dilute iodine, and either do not dissolve in cupram- 

 monia, or only after prolonged treatment. 



B. Compowid Celluloses, 

 (a) Lignin. 



1. A brownish-yellow colour is given with iodine. 



2. The addition of strong sulphuric acid, alter previous 

 treatment with iodine, turns lignified walls brown. 



3. The same colour is obtained with the use of chlorzinc 

 iodide. 



