2 HANDBOOK FOE BIO-CHEMICAL LABORATORY. 



potassio-mercuric iodide and then return to filter. This 

 treatment must be repeated at least four times. The 

 several filtrates are united and, while stirring, treated with 2 

 vols. 96$ alcohol, which precipitates the glycogen, and allow 

 it to stand in a cool place overnight. Filter off the precipitate 

 and wash first with 62$ and then with 98$ alcohol. This 

 glycogen generally contains but a trace of albumins, but if re- 

 quired more pure, dissolve it while still moist in a little warm 

 water, add some HC1 and potassio-mercuric iodide after al- 

 lowing to cool, and proceed as above. Lastly, wash the glyco- 

 gen, which has been previously treated with absolute alcohol, 

 a couple times with ether, and allow it to dry in the air or 

 over sulphuric acid. (It. Eulz.} 



2. Briiclce's method consists in precipitating the albumin- 

 ous bodies from the watery extracts by HC1 and potassio- 

 mercuric iodide without previously extracting with caustic 

 potash, and then proceeding as above directed. 



Properties. Glycogen is a white amorphous powder, easily 

 soluble in hot water, yielding an opalescent solution, which 

 when allowed to evaporate on the water-bath forms a pellicle 

 over the surface which disappears again on cooling. The 

 solution is dextro-rotatory, (a) D = -j- 211 (Kulz). On boil- 

 ing with dilute mineral acids, or by the action of diastatic 

 enzymes (ptyalin, diastase), it is readily converted into malt- 

 ose, isomaltose, and dextrose. Its solution does not reduce 

 Fehling's solution on boiling, but holds copper oxyhydrate in 

 solution in alkaline liquids. With a solution of iodine glyco- 

 gen solutions are colored wine-red which disappears on heat- 

 ing. Glycogendoes not ferment with yeast. 



Lactose, C 12 H 22 O n +H 2 0. 



(MILK-SUGAR.) 



Preparation. The sweet whey obtained after the precipi- 

 tation of casein from milk (see page 13) is heated to boiling, 



