THE CARBOHYDRATES 195 



C. GALACTOSE. 



Galactose gives the same reactions as glucose. It differs from glucose in 

 the following particulars : 



(3) Reduction. Galactose on reduction with sodium amalgam gives the 

 hexahydric alcohol, dulcitol. 



(4) Oxidation. Galactose on oxidation gives galactonic acid. On further 

 oxidation with nitric acid it yields mucic acid. 



(9) Formation of Osazones. Galactose gives a different phenylosazone. 



(10) Fermentation. Galactose is fermented by yeast, but much less 

 rapidly than glucose. 



(12) Rotation. Galactose has a higher dextrorotatory power than glucose. 



D. MANNOSE. 



Mannose differs in the following particulars from glucose : 



(3) Reduction. Mannitol is formed by reduction with sodium amalgam. 



(4) Oxidation. It yields mannonic acid and saccharic acid on 

 oxidation. 



(9) Formation of Hydrazone and Osazone. Mannose forms a 

 phenylhydrazone which is soluble with difficulty in water. It forms the same 

 phenylosazone as glucose. 



(12) Rotation. Mannose is dextrorotatory, but has a different rotatory 

 power. 



E. PENTOSES. 



The pentoses give most of the reactions given by glucose but with 

 the following differences : 



(3) Reduction. They give pentahydric alcohols. 



(4) Oxidation They give acids containing five carbon atoms. 



(6) Action of Concentrated Hydrochloric Acid. The pentoses 

 on boiling with hydrochloric acid yield furfural, which is volatile with 

 steam and may be detected with aniline acetate. 



If a solution containing pentose, 1 or pentosan, e.g. gum arabic 

 solution, be boiled with about half its volume of hydrochloric acid and 

 if a piece of filter paper moistened with aniline acetate solution (pre- 

 pared from equal parts of aniline, glacial acetic acid and water) be held 

 in the vapour escaping from the vessel after most of the hydrochloric 

 acid has been evolved, a bright crimson colour will be formed. 



(7) Reduction of Metallic Oxides in Alkaline Solution. Pen- 

 toses reduce Fehling's solution on warming for some time. 



(9) Formation of Osazones. The pentoses form phenylosazones 

 with phenylhydrazine in acetic acid solution. They differ from 

 phenylglucosazone in melting-point, analysis, etc. 



(10) Fermentation. Pentoses are not fermented by yeast. 

 (12) Rotation. Pentoses are dextrorotatory, or inactive. 



1 A solution containing arabinose may be readily prepared by boiling 5 gm. of gum 

 arabic in 100 c.c. water with 10 c.c. of concentrated hydrochloric acid for 5 minutes and 

 then neutralising with alkali. 



