530 CONSIDERATION OF CARBON COMPOUNDS. 



Monosaccharides. 



The monosaocharides are white, odorless, sweet, crystallizable, neu- 

 tral substances, readily soluble in water, sparingly soluble in alcohol, 

 insoluble in ether. Like all aldehydes and ketones they are easily 

 oxidized, acting as strong reducing agents. Trommer's, Fehling's, 

 and Boettger's " reduction tests " depend on this property. Solutions 

 of monosaccharides, acidified with acetic acid, give with phenyl-hy- 

 drazine crystalline precipitates of substances called osazones. The tri- 

 oses, hexoses, and nonoses are capable of alcoholic fermentation, the 

 others are not. Most of the monosaccharides are optically active. 



According to the number of carbon atoms present, the monosaccharides are 

 again subdivided into classes called trioses, tetroses, pentoses, hexoses, heptoses, 

 octoses, and nonoses, having the composition C 3 H 6 O 3 , C 4 H 8 O 4 , C 5 H 10 O 5 , C 6 H 12 CX., 

 C 7 H U O 7 , C 8 H 16 8 , and C 9 H 18 O 9 , respectively. The hexoses are the best-known 

 group, which is again subdivided into two groups, viz., the aldoses, containing 

 the alcohol group, CH. 2 OH, and the aldehyde group, COH ; and the ketoses, 

 containing the alcohol group and the ketone group, CO. The constitution of 

 these compounds is shown thus : 



Aldoses 



Ketoses 



Glucose is an aldose-hexose, while fructose is a ketose-hexose. 



Dextrose, Glucose, Grape-sugar, C 6 H 12 O 6 . This substance is 

 very abundantly diffused throughout the vegetable kingdom, and is 

 generally accompanied by fruit-sugar. It is contained in large quan- 

 tities in the juice of many fruits; the percentage of grape-sugar in 

 the dried fig is about 65, in grape 10-20, in cherry 11, in mulberry 9, 

 in strawberry 6, etc. 



Dextrose is found also in honey and in minute quantities in the 

 normal blood (0.1 per cent, or less), and traces occur, perhaps, in 

 normal urine, the quantity in both liquids rising, however, during 

 certain diseases, as high as 5 per cent, or higher. 



Grape-sugar is produced in the plant from starch by the action of 

 the vegetable acids present; it may be obtained artificially from 

 starch (and from many other carbohydrates) by heating with dilute 

 mineral (sulphuric) acids, which convert starch first into dextrin and 



