CARBOHYDRATES AND RELATED BODIES. 2 5 



CH 2 OH.(CHOH) 3 CHO + HCN = CH 2 OH.(CHOH) 3 .CHOHCN, 

 and this by the usual reaction gives arabinose carboxylic acid : 



CH 2 OH.(CHOH) 3 CHOHCN + 2H 2 O = 



CH 2 OH.(CHOH) 3 .CHOH.COOH -f NH 3 . 



By loss of water from this acid the corresponding lactone is 

 formed : 



CH 2 OH. (CHOH) 4 COOH H 2 O = 



CH.OH.CHOH.CH.CHOH.CHOH.CO = CH 10 O 6 . 



s~\ 



By reduction with sodium amalgam this lactone becomes a 

 sugar, identical with that obtained by the other condensation : 



CH.OH.CHOH.CH.CHOH.CHOH.CO + H 2 = 



-o 



CH 2 OH.(CHOH) 4 .CHO = C 6 H 12 O 6 . 



By an extension of the principle, sugars with 7, 8 and 9 carbon 

 atoms have been obtained. In what is to follow a brief dis- 

 cussion of the more important natural substances will be given. 



THE MONOSES OR MONOSACCHARIDES. 



A number of pentose and hexose bodies must be considered 

 here. 



Pentoses. Small amounts of these sugar-like compounds 

 exist in nature, but they are mostly derived from simple ante- 

 cedent substances called pentosans. The pentoses bear the 

 same relation to the pentosans that dextrose bears to starch; 

 by hydration the latter 'compounds are converted into the 



former, thus : 



CsHsCX + H 2 O = C 5 H 10 O 5 . 

 C 6 H 10 5 + H 2 = C 6 H 12 Oe. 



Among the pentoses two, known as /-arabinose and /-xylose, 

 are the most important. 



ARABIXOSE, or pectin sugar, is made by warming cherry 

 gum, wheat bran, gum arabic, quince or gedda mucilage, ex- 

 hausted brewers' grains and various other substances with 

 dilute acids. It has a specific rotation [a]^ = -f- 104.5. 



