114 THE CARBOHYDRATES 



brown substance known as caramel, which is used for colouring 

 beer and wine. 



Reactions. 



1. Solutions of cane sugar heated with concentrated 

 hydrochloric acid turn reddish-pink. 



2. If warmed with concentrated hydrochloric acid and a 

 few crystals of resorcin a deep red colour is produced owing 

 to the liberation of levulose. 



3. Cane sugar does not react with phenylhydrazine. 



4. Cane sugar does not reduce Nylander's reagent. 



5. Solutions of cane sugar do not reduce Fehling's solution 

 until they have been inverted by boiling for a short time with 

 a few drops of dilute sulphuric acid ; if then made alkaline and 

 boiled with Fehling's solution reduction ensues. 



If a solution in water is boiled with a few drops of mineral 

 acid, the sign of the optical activity of the solution changes 

 from -f to — . This change, which is known as inversion, is 

 due to the fact that the mineral acid hydrolyses the cane sugar, 

 converting it into equal molecular proportions of the two 

 sugars dextrose and levulose, 



and since the optical activity of levulose is greater than that 

 of dextrose the resulting invert sugar is laevo-rotatory. 



Aqueous solutions of cane sugar, if kept for some time, 

 gradually become inverted, the change being somewhat 

 accelerated by prolonged boiling. 



Extremely small quantities of acid suffice to effect the 

 change in a boiling solution; thus 80 parts of cane sugar 

 dissolved in 20 parts of water are completely hydrolysed by 

 heating in boiling water for one hour with an amount of 

 hydrochloric acid corresponding to 0-005 per cent of the weight 

 of the sugar ; within certain limits, however, the action is 

 accelerated by increasing the concentration of the acid. If, 

 however, the acid is too strong and the heating be continued 

 too long, the solution is liable to darken and decompose. 

 Moreover, prolonged action, even at temperatures of 10-15°, of 



