GLUCOSE. 213 



(levulose), in honey, sweet fruits, seeds, roots, etc. It occurs in the 

 human and animal intestinal tract during digestion, also in small quan- 

 tities in the blood and lymph, and as traces in other animal fluids and 

 tissues. It occurs only as traces in urine under normal conditions, 

 while in diabetes the quantity is very large. It is formed in the hydro- 

 lytic cleavage of starch, dextrin, and other compound carbohydrates, 

 as also in the splitting of glucosides. The question whether glucose 

 can be formed in the body from proteins or from fats is disputed and will 

 be discussed in a following chapter (VII). 



Properties of Glucose. Glucose crystallizes sometimes with 1 mole- 

 cule of water of crystallization in warty masses consisting of small leaves 

 or plates, and sometimes when free from water in fine needles or prisms. 

 The sugar containing water of crystallization melts even below 100 C. 

 and loses its water of crystallization at 110 C. The anhydrous sugar 

 melts at 146 C., and is converted into glucosan, CeHioOs, at 170 C. 

 with the elimination of water. On strongly heating it is converted into 

 caramel and then decomposes. 



Glucose is readily soluble in water. This solution, which is not as 

 sweet as a cane-sugar solution of the same strength, is dextrogyrate and 

 shows strong birotation. The specific rotation is dependent upon the 

 concentration of the solution, as it increases with an increase in the con- 

 centration. A 10 per cent solution of anhydrous glucose can be taken as 

 -J-52.5 at 20 C. 1 Glucose dissolves sparingly in cold, but more freely 

 in boiling alcohol. One hundred parts alcohol of sp. gr. 0.837 dissolves 

 1.95 parts anhydrous glucose at 17.5 C. and 27.7 parts at the boiling 

 temperature (ANTHON 2 ). Glucose is insoluble in ether. 



If an alcoholic caustic-potash solution is added to an alcoholic solu- 

 tion of glucose, an amorphous precipitate of insoluble sugar-potash 

 compound is formed. On warming this compound it decomposes easily 

 with the formation of a yellow or brownish color, which is the basis of 

 MOORE'S test. Glucose also forms compounds with lime and baryta. 



MOORE'S Test. If a glucose solution is treated with about one 

 quarter of its volume of caustic potash or soda and warmed, the solution 

 becomes first yellow, then orange, yellowish-brown, and lastly dark 

 brown. It has at the same time a faint odor of caramel, and this odor 

 is more pronounced on acidifiying. 3 



Glucose forms several crystallizable combinations with NaCl of 

 which the easiest to obtain is (CeH^Oe^.NaCl+H^O, which forms 



1 For further information see Tollens' Handbuch der Kohlehydrate, 2. Aufl., 44. 



2 Cited from Tollens' Handbuch. 



3 In regard to the products formed in this reaction, see Framm, Pfliiger's Arch., 64; 

 Neff, Annal. d. Chem. u. Pharm., 357; Buchner and Meisenheimer, Ber. d. d. chem. 

 Gesellsch., 39; Meisenheimer, ibid., 41. 



