68 . PHYSIOLOGY 



to lower oxides. On this behaviour is founded the commonest of all 

 the tests for the presence of reducing sugar Trommer's test. 



(b) On oxydising a monosaccharide the COH group becomes con- 

 verted to COOH. Thus, glucose on oxidation gives gluconic acid : 



COH(CHOH) 4 CH 2 OH + = COOH(CHOH) 4 CH 2 OH. 



On further oxidation the end group CH 2 OH also is affected, and we 

 obtain a dibasic acid. Thus glucose gives saccharic acid. 



(c) By means of nascent hydrogen the monosaccharides can be 

 reduced to the corresponding polyatomic alcohol. Thus the three 

 hexoses, glucose, fructose, and galactose, give the corresponding three 

 alcohols, sorbite, mannite, and dulcite C 6 H 14 6 . 



(d) Another important general reaction of the monosaccharides 

 depending on the COH or the CO group is the reaction with phenyl 

 hydrazine. On warming a solution of sugar with a solution of phenyl 

 hydrazine in acetic acid, the following reactions take place. The first 

 reaction results in the production of a hydrazone : 



CH 2 OH(CHOH) 3 CHOHCHO + H 2 N.NH.C 6 H 5 == 

 CH 2 OH(CHOH) 3 CHOH.CH : N : NH.C 6 H 5 + H 2 0. 



The hydrazone then reacts with another molecule of phenyl hydrazine 

 with the production of an osazone : 



CH 2 (OH)(CHOH) 3 CHOH.CH : N.NH.C 6 H 5 -f H 2 N.NHC 6 H 5 = 

 CH 2 OH(CHOH) 3 C . CHN . NH . C 6 H 5 



II 



N.NH.C 6 H 5 + H 2 + H 2 . 



The hydrogen formed in this reaction acts upon a second molecule of 

 phenyl hydrazine, splitting it into aniline and ammonia. On this 

 account it is always necessary to have an excess of phenyl hydrazine in 

 the operation. 



The osazones form well-defined crystalline products which are 

 generally yellowish in colour and differ in their melting-point and in 

 their crystalline form. They are therefore of extreme value in the 

 separation and identification of different carbohydrates. They can 

 be also used for the artificial preparation of certain sugars. Under 

 the influence of acetic acid and zinc dust they form osamines, which on 

 treatment with nitrous acid are reconverted into the corresponding 

 sugar, generally a ketose. 



GLUCOSE, DEXTROSE or GRAPE SUGAR, is the chief con- 

 stituent of the sugar of fruits, especially of grapes. It occurs in the 

 body as the end-product of the digestion of starch. When pure it 

 forms white crystals which melt at 100 C., and lose the one molecule 

 of water of crystallisation at 110 C. It is easily soluble in water, and 



