88 



THE CARBOHYDRATES 



The osazones being, for the most part, insoluble in water, 

 serve as a valuable means of isolating a sugar from a dilute 

 solution ; their identity can then be readily established by 

 means of their crystalline form, melting-point, solubility, and 

 optical activity. 



Other special tests employed for the identification of 

 individual sugars will be given under the various sugars in 

 the following pages. 



The identification of the constituents of a mixture of 

 a number of different sugars may require special methods 

 depending on the use of specific hydrolytic enzymes or of 

 special yeasts which may fermicnt away certain hexoses, or 

 all hexoses, leaving only the non-fermentable pentoses. 



The following list, taken from a paper by Chapman,* shows 

 the behaviour of certain species of Saccharomyces towards 

 several of the more commonly occurring sugars : — 



(The sign -f indicates that the yeast in question is capable, and the 

 sign o that it is incapable, of bringing about fermentation.) 



An individual description of the various naturally occurring 

 sugars will now be given. 



MONOSACCHARIDES. 



A. PENTOSES. 



The pentoses, which are sugars containing five carbon 

 atoms, have the general formula C5H10O5, would not appear 

 to be common in the free state ; their presence has been 



* Chapman : " J. Chem. Soc," 1917, III, 216. 



