192 COMPOUNDS RESEMBLING CARBOHYDRATES 

 0=C H 



H C OH O-C H 



HO C H G / \CH + 3H 2 



HO C-H CH CH 



2 OH 



Arabinose. Furfural. 



By collecting the distillate and causing the furfural to combine 

 with .phloroglucinol, a solid body which can be weighed is obtained. 

 The red colouration formed when a pentose is heated with a solution 

 of phloroglucinol in strong hydrochloric acid is often used as a test for 

 the presence of a pentose. 



The Carbohydrate Alcohols. 



Erythritol, C 4 H (; (OH) 4 , occurs in algae and mosses. It has a 

 sweet taste, melts at 126 and is optically inactive. 



Adonitol, C 5 H 7 (OH) 5 , occurs in certain plant saps, e.g., in Adonis 

 vernalis and can be obtained by the reduction of ribose. Similar 

 sweet substances, arabitol and xylitol, can be obtained by the re- 

 duction of arabinose and xylose respectively, but do not occur natur- 

 ally. 



Mannitol, C t} H 8 (OH) (5 , occurs in many plants, flotably in the 

 manna ash, Fraxinus ornus, and in fungi. It melts at 168 and is 

 dextro-rotatory. It can be prepared by reducing mannose with 

 sodium amalgam. 



Dulcitol, an isomeric substance, also occurring in plants, is opti- 

 cally inactive and melts at 188. It can be prepared by the reduction 

 of galactose. 



Sorbitol, a third isomer, occurs in the berries of the mountain 

 ash, Sorbus aucuparia, and in the sap of many trees. It melts at 

 110 and, on oxidation, yields sorbose. 



Perseitol, C 7 H 9 (OH) 7 , occurs in the Avocado pear, Persea gratis- 

 sima, is laevorotatory and melts at 180. It corresponds to the sugar, 

 manno-heptose, C 7 H 14 O 7 . 



Yolemitol, an isomeride of perseitol, melting at 154 and dextro- 

 rotatory, occurs in Lactarius volemus and in the rhizomes of certain 

 primulce. 



The Furfuroids. By this name Cross and Bevan 1 refer to the 

 substances present in cereal straw, jute fibre and other vegetable 

 products, which, when subjected to acid hydrolysis, give furfuralde- 

 hyde. The term includes the pentoses and pentosans proper, but also 

 another group of bodies pentose derivatives to which the authors 

 just quoted ascribe the constitution 



1 Jour. Chem. Soc., 1896, Trans., 804, 1604 ; 1897, Trans., 1001. 



