206 THE CARBOHYDRATES. 



BOKORNY l has shown, by special experiments on alga? Spirogyra, that formalde- 

 hyde sodium sulphite was split by the living algae cells. The formaldehyde set 

 free is immediately condensed to carbohydrate and precipitated as starch. 



Among the hexoses known at the present time only dextrose, levulose 

 and galactose are really of physiological-chemical interest; therefore of 

 the other hexoses only mannose will be incidentally mentioned. 



Dextrose (d-glucose) GLUCOSE, GRAPE-SUGAR, and DIABETIC SUGAR 

 occurs abundantly in the grape, and also, often accompanied with 

 levulose (^-fructose), in honey, sweet fruits, seeds, roots, etc. It occurs 

 in the human and animal intestinal tract during digestion, also in small 

 quantities 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 dextrose 

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

 be discussed in a following chapter (VIII). 



Properties of Dextrose. Dextrose 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, CeHioOg, at 170 C. 

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

 caramel and then decomposes. 



Dextrose 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 

 +52.5 at 20 C. 2 Dextrose dissolves sparingly in cold, but more freely 

 in boiling alcohol. 100 parts alcohol of sp. gr. O.S37 dissolves 1.95 parts 

 anhydrous dextrose at 17.5 C. and 27.7 parts at the boiling temperature 

 (ANTHON 3 ) . Dextrose is insoluble in ether. 



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

 tion of dextrose, an amphorous precipitate of insoluble sugar-potasn 

 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. Dextrose also forms compounds with lime and baryta. 



1 Biolog. CentralbL, 12, pp. 321 and 481. 



2 For further information see Tollens, Handbuch der Kohlehydrate, 2. AufL, 44. 



3 Cited from Tollens' Handbuch. 



