210 THE CARBOHYDRATES. 



colored solutions with special absorption-bands which can be made use of in 

 identifying the various sugars. FR. SACHS has tested BIAL'S test and has given 

 special precautions to prevent confusion with glucuronic acid. JOLLES l pre- 

 cipitates (from urine) the pentoses as osazones, distills the precipitate with 

 hydrochloric acid, and tests the distillate with BIAL'S reagent. 



In performing the above two tests for pentose it must be borne in mind that 

 glucuronic acid gives the same reactions and also that the colors alone are not 

 sufficient. The spectroscopic examination must therefore never be omitted. 

 Both tests are to be considered as tests of detection rather than definite pentose 

 reactions, and therefore for a positive detection of pentoses we must prepare also 

 the osazones or other compounds. 



Arabinoses. The pentose isolated by NEUBERG from human urine 

 is r-arabinose. It can be isolated from the urine as the diphenylhydra- 

 zone, from which the arabinose can be separated by splitting with for- 

 maldehyde. The inactive r-arabinose seems to be the pentose regularly 

 occurring in pentosuria and thus far, in only one case, has Z-arabinose 

 been found. /-Arabinose is said to pass into the urine after partaking of 

 certain fruits, such as plums, in large amounts (C. BARSZCZEWSKI 2 ) . 



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

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

 and WoHLGEMUTH, 3 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 arabic or 

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

 pared synthetically. The phenylosazone 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 Z-xylose occurs extensively in the plant kingdom and 

 is prepared from wood-gum by the action of dilute acid. Xylose is 

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

 with difficulty in alcohol, is faintly dextrorotatory, (a) D = +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 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. On oxidation with nitric acid 

 the optically inactive trioxyglutaric acid, with a melting-point of 152 C. 

 is obtained. 



1 Fr. Sachs, Biochem. Zeitschr., 1 and 2; Jolles, ibid., 2, Centralbl. f. inn. Med., 

 1907, and Zeitschr. f. anal. Chem., 46. 



2 Neuberg, Ber. d. d. chem. Gesellsch., 33; Barszczewski, Maly's Jahrsb., 27, 733. 



3 Zeitschr. f. physiol. Chen?., 35. 



