4 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



generally takes place in a few days. In the meantime distil 

 most of the alcohol off from the main portion, evaporate the 

 residue to a thick syrup, and on cooling stir into this a few 

 crystals of the pure crystallized maltose. After three to five 

 days the syrup will have crystallized to a stiff mass of crystals. 

 These are rubbed to a thin paste with methyl alcohol, 

 drained on paper, and washed once with methyl alcohol, 

 pressed, washed again with methyl alcohol, and purified by 

 further crystallization. For this purpose dissolve 500 grms. 

 of the dried, pressed maltose in 15 c.c. water on the water- 

 bath, add 130 c.c. 90$ alcohol, boil, filter, and allow to cool. 

 No syrup should separate out. Add a few crystals of pure 

 maltose, and shake often, until the entire liquid after a few 

 hours crystallizes into a thick mass of crystals. After draining 

 the crystals they may be recrystallized from methyl alcohol, 

 which is done by heating 50 grms. of the crystals with 12 c.c. 

 water until all has dissolved, and adding 300 c.c. methyl alco- 

 hol; boil, filter, and allow to cool. Shaking facilitates crystal- 

 lization considerably. (Soxlilet.) 



Properties. Maltose crystallizes generally in microscopic 

 needles containing 5$ (1 mol.) water of crystallization. The 

 dried crystals are hygroscopic, specific rotatory power being 

 () J}= -J- 137. Maltose reduces alkaline solutions of copper, 

 bismuth, and other metallic salts, but its reducing power as 

 measured by Fehling's solution is -| less than that of dextrose. 

 With phenyl-hydrazine acetate it gives after heating for 1-J 

 hours clusters of yellow crystals, C 24 H 32 N 4 9 , melting at 206 0. 

 Maltose is easily and completely fermented by yeast. When 

 heated with very dilute sulphuric acid, maltose yields dex- 

 trose. The diastatic enzymes act in the same way. 



Dextrose, C 6 H 12 O fi . 



Preparation. Warm a mixture of 1.5 litres 90^ alcohol 

 and 60 c.c. strong HC1 on the water-bath to 45 C., and 



