204 THE CARBOHYDRATES. 



The r-arabinose is crystalline, has a sweetish taste, and melts at 

 163-164 C. Its diphenylhydrazone, which, according to NEUBERG 

 and WoHLGEMUTH, 1 can be used in its quantitative estimation, melts 

 at 206 C., is insoluble in cold water and alcohol, but readily soluble 

 in pyridine. The osazone melts at 166-168 C. 



The dextrorotatory Z-arabinose is obtained by boiling gum arable or 

 cherry gum with dilute sulphuric acid. The d-arabinose has been pre- 

 pared synthetically. The phenylozasone of Z-arabinose melts at 160. 

 The Z-arabinose which crystallizes in plates or prisms melts at about 

 164. The specific rotation is (a) D = + 104.5. 



Xyloses. The first pentose to be isolated from organs was Z-xylose 

 by NEUBERG from the pancreas neucleoproteins. NEUBERG and BRAHN 

 claim to have isolated Z-xylose from inosinic acid, but the investigations 

 of LEVENE and JACOBS 2 show that the pentose in this case is not Z-xylose, 

 but rather d-ribose. Z-Xylose occurs very extensively in the plant king- 

 dom, and is obtained from wood-gums by boiling with dilute acids. 

 Xylose is crystalline, melts at 150-153 C., dissolves very readily in water 

 but with difficulty in alcohol, is faintly dextrorotatory, (a) D = -f 18.1, 

 and gives a phenylosazone which melts at 155-158 C., and according 

 to TOLLENS and MUTHER a diphenylhydrazone which melts at 107-108. 

 According to BERTRAND 3 xylose can be transformed into xylonic acid, 

 CH 2 (OH)[CH(OH)] 3 COOH, by bromine-water and the- brom-cadmium 

 compound or the brucine salt (NEUBERG) of this acid is well suited for 

 the detection and isolation of Z-xylose. 



Hexoses (C 6 H 12 6 ). 



The most important and best-known simple sugars belong to this 

 group, and most of the other bodies which have been considered as car- 

 bohydrates in the past are anhydrides of this group. Certain hexoses, 

 such as dextrose and levulose, either occur in nature already formed 

 or are produced by the hydrolytic splitting of other more complicated 

 carbohydrates or glucosides. Others, such as mannose or galactose, 

 are formed by the hydrolytic cleavage of other natural products, while 

 some, on the contrary, such as gulose, talose, and others, are obtained 

 only by artificial means. 



and Arch. f. exp. Path. u. Pharm., 1908, Schmiedeberg-Festschr. ; Barszczewski, 

 Maly's Jahrb., 27, p 733. 



1 Zeitschr. f . physiol. Chem., 35. 



2 Neuberg, Ber. d. d. chem. Gesellsch., 35; Neuberg and Brahn, Biochem. Zeitschr., 

 5, and Ber. d. d. chem. Gesellsch., 41, p. 3376; Levene and Jacobs, Ber. d. d. chem. 

 Gesellsch., 41 and 42. 



3 Tollens and Miither, Ber. d. d. chem. Gesellsch., 37; Bertrand, Bull. soc. chim. 

 (3), 5. 



