366 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



yielded by the different pentose sugars and pentosans under the 

 conditions of the work have been determined by experiments. 



Stoklosa found considerable quantities of water-soluble pen- 

 tosans in sugar beet seed, and DeChalmot found small quantities 

 in the leaves and bark of a number of plants. But pentose sugars 

 have not been separated as such from plants, but are prepared by 

 the hydrolysis of certain pentosans. The pentoses do not fer- 

 ment with yeast. 



Arabinose, C 5 H 10 O 5 = CH 2 OH(CHO) 3 CHO, has been pre- 

 pared from the pentosans found in lupines, soja beans, rye bran, 

 wheat bran, plums, and cherry gum. It is easily prepared by boil- 

 ing cherry gum with 2 per cent, sulphuric acid. It crystallizes 

 beautifully, and has a sweet taste, but not as sweet as sucrose. 



Xylose, C 5 H 10 O I5 , has been prepared from beech wood, jute, fir 

 wood, cherry wood, laurel wood, wheat straw, corn cobs, oat 

 straw, rye straw, corn bran, apples, etc. It crystallizes in prisms. 



Rhamnose, C 6 H, B O 3 = CH 3 (CHOH) 4 CHO, is methyl pen- 

 tose, which yields methyl furfural by distillation with hydro- 

 chloric acid. It is obtained from certain glucosides, and 

 crystallizes in beautiful, sweet crystals. 



Hexose Sugars, C 6 H 12 O 6 . The two hexose sugars of common 

 occurrence are fructose and glucose. They occur, in equal 

 quantity, in sweet fruits, flowers, certain vegetables. The other 

 hexoses are formed by the hydrolysis of certain carbohydrates. 

 All the hexoses are fermented by yeast. 



d-Glucose, C 6 H 10 O 5 , or grape sugar, occurs in grapes, sweet 

 fruits, tomatoes, seeds, roots, leaves, flowers, honey, etc. To- 

 gether with fructose, it is formed by the hydrolysis of cane sugar. 

 It is also formed by the hydrolysis of starch, and is the chief 

 ingredient of many syrups. Nitric acid oxidizes it to saccharic 

 acid, and glucose may be detected by means of this reaction. It 

 is also detected through its optical properties. Glucose is a white 

 crystalline substance, which is not so sweet as cane sugar. It is 

 easily soluble in water and alcohol. It undergoes fermentation of 

 various kinds readily. Glucose is produced commercially by the 



