210 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



sulphate, again dissolved and again precipitated. Finally it is dissolved in 

 water, the ammonium sulphate removed by dialysis, and the glycogen pre- 

 cipitated by alcohol. It is washed with alcohol and ether and dried. 



Properties. 



Pure glycogen is a white amorphous powder, soluble in cold 

 water forming an opalescent solution, which is very characteristic. 

 Reactions. 



(1) Action of Alcohol. 



Glycogen is precipitated from solution by adding an equal volume 

 of alcohol. The precipitation does not occur if the solution does not 

 contain some salts ; a small quantity, '05 gm. of sodium chloride, is 

 required to precipitate a I per cent, solution of glycogen with two 

 volumes of absolute alcohol. 



(2) Action of Iodine. 



Solutions of glycogen give a reddish-brown colour on treatment 

 with I to 2 drops of iodine solution. The coloration disappears on 

 heating and reappears on cooling. 



(3) Basic Lead Acetate. 



Solutions of glycogen are precipitated by basic lead acetate. 



(4) Ammonium Sulphate. 



Solutions of glycogen are not precipitated by half saturation with 

 ammonium sulphate, but the glycogen is precipitated by complete 

 saturation of the solution with ammonium sulphate crystals. 



(5) Fehlings Solution. 



Glycogen does not reduce Fehling's solution. 



(6) Hydrolysis. 



Glycogen is converted into glucose by hydrolysis. Solutions of 

 glycogen, boiled with dilute acid and neutralised, reduce Fehling's 

 solution. 



(7) Action of Alkali. 



Glycogen is not acted upon by alkali. 



(8) Fermentation. 



Glycogen is not fermented by yeast. 



(9) Rotation. 



Glycogen has a high dextrorotatory power. 



