DETERMINATION OF SUGARS AND DEXTRINS 155 



Barfoed's solution is made by taking 200 cc. of a solution of 

 neutral acetate of copper, containing one part of the salt to 1 5 of 

 water and adding to it 5 cc. of a 38 per-cent. solution of acetic 

 acid. 



3. Cobaltous nitrate (five per-cent. solution). Add 5 cc. of 

 cobaltous nitrate solution to about 1 5 cc. of the solution to be 

 tested. After the solutions have been well mixed add 2 cc. of a 

 50 per-cent. solution of sodium hydrate. With this reagent cane- 

 sugar will give a permanent amethyst violet color. Dextrose 

 gives a turquoise blue color but in a mixture of the two sugars 

 the cane-sugar color reaction is predominant, and can be detected 

 though the cane-sugar may not form more than one tenth of the 

 mixture. The cane-sugar coloration on boiling turns slightly 

 bluish, but is restored to its original condition on cooling. In a 

 few hours the color given by dextrose will change to pale green. 

 Maltose gives about the same color as dextrose, though not so 

 fine a green color at last. 



4. Phenyl-hydrazine hydrochloride. To about 10 cc. of the 

 sugar solution in a test-tube add two parts of phenyl-hydrazine 

 hydrochloride and three parts of sodium acetate. Keep in boil- 

 ing water in the water-bath for an hour and a half and then place 

 the tube in cold water. Examine the crystals under a micro- 

 scope. Dextrose, levulose, maltose and galactose form osazones 

 with phenyl-hydrazine, but cane-sugar does not. Galactose is 

 very rare in plants and the osazone of levulose has the same prop- 

 erties as that of dextrose. To separate roughly these two osa- 

 zones allow the tube containing the mixture to stand in the cold 

 several hours, and finally filter. 



Maltosazone is quite soluble in cold water and will appear in the 

 filtrate upon evaporation to a small volume, while the dextrosazone 

 will remain in the solid state. The maltosazone should be purified 

 by dissolving it again in water and reprecipitating it by alcohol. 

 The sugars from which the osazones come can be better identified 

 by the melting points of their phenyl-hydrazine compounds. 

 Maltosazone melts at 206 C., Dextrosazone at 2O4-2O5 C. 



