338 PLANT AND ORGANIC CHEMISTRY 



sidered by him an isomer of grape sugar; but it was shown 

 by Kiliani to possess the formula C 5 H 10 O 5 . Although the 

 natural arabinose turns the plane of polarized light to the right, 

 on account of its relation to /-glucose, it should be considered 

 as a left compound. Artificially, the right-turning arabinose 

 may be made from glucose by a building-down process, as it 

 were, discovered by Wohl. This process consists in passing 

 from a sugar richer in carbon atoms to one containing fewer 

 carbon atoms. 



On boiling bran, wood, jute, straw and like substances, 

 with acids, pentosan compounds are obtained. In some cases 

 they may be isolated, or their presence may be proved by the 

 furfurol reaction. This is a well-known test for their identi- 

 fication. If compounds belonging to the hexose groups be 

 heated with acids, they yield laevulinic acid (CH 3 COCH 2 CH 2 

 CO 2 H). On the contrary, pentose compounds, by distillation 

 with strong acids, yield furfurol compounds, which easily 

 pass over with steam. 



The portions of the coffee berry insoluble in water, when 

 distilled with dilute hydrochloric acid, yield furfurol alde- 

 hyde, which demonstrates the presence in the coffee of a com- 

 pound belonging to the pentosans. 



By warming with phloroglucin and hydrochloric acid, the 

 pentosans, as also all compounds which, by decomposition, 

 yield sugar compounds containing 5 carbon atoms, give a 

 cherry-red color reaction. 



Ribose, a colorless syrup, and xylose, wood sugar, are 

 isomeric with arabinose. 



Rhamnose, formerly erroneously called " isodulcite, " is 

 a methylpentose. It is obtained from datiscin by hydrolytic 

 reaction, and by the same method from different glucosides. 



Fucose, obtained from the sea-tangle or grass wrack, is 

 isomeric with rhamnose, also chinovose, which is derived from 

 chinovite. The alcohols, xylite and adonite, belonging to the 

 sugars xylose and ribose, correspond to arabite, the alcohol of 

 the sugar arabinose, and are inactive. 



The remaining series of compounds, which chemically 

 belong to the same class as the sugars, are designated as 



