130 THE CARBOHYDRATES 



which may be removed by redissolving the crude glycogen in 

 water and saturating with ammonium sulphate. The pre- 

 cipitated glycogen, after being washed with saturated am- 

 monium sulphate, is dissolved in water, and the solution again 

 saturated with ammonium sulphate, the process being repeated 

 three times. The final precipitate is again dissolved, the 

 solution dialysed until free from ammonium sulphate, and the 

 glycogen precipitated with alcohol. For details of the further 

 purification of the glycogen the original paper should be 

 consulted. 



Properties. 



Pure glycogen is a snow-white amorphous solid. It is 

 readily soluble in hot water, forming an opalescent solution, 

 from which it may be precipitated again by alcohol, provided 

 small quantities of dissolved salts are present; 100 c.c. of a 

 I per cent solution when mixed with 200 c.c. of absolute 

 alcohol remain clear, but on adding O'O3-O'O5 gram of sodium 

 chloride, an immediate precipitate is formed. Glycogen is 

 strongly dextro-rotatory, a D = + 1 89'9, and is coloured red 

 to brown by iodine ; it does not reduce Fehling's solution, but 

 is broken up by diastase into dextrin and maltose, and by 

 acids into glucose. 



Identification. 



1. The opalescent appearance of its aqueous solution is 

 characteristic, arid is strongly dextro-rotatory. 



2. A brown coloration is given with iodine solution (cf. 

 inulin, p. 136). 



3. A white precipitate is given with basic lead acetate. 



4. It does not reduce Fehling's solution. 



5. On boiling with mineral acids, it is converted into 

 dextrose. 



Estimation. 



This is best effected by heating the aqueous solution for 

 three hours in a boiling water bath with about 2 '2 per cent 

 HC1, and then neutralizing and estimating the resulting glu- 

 cose by means of Fehling's'solution ; the amount multiplied by 

 0*9 gives the weight of glycogen. 



