116 § 84. BASES AND ACIDS WITH EKAOENTS. 



Saccharose is converted into glucose and levulose when 

 heated with very dilute sulphuric acid, by treatment with 

 yeast, or even by long boiling of its aqueous solution alone. 



Quantitatiye estimation. — This may be effected by first 

 converting the saccharose into glucose and levulose, and 

 then determining the amount of these with the standard 

 cupric solution. 



The solution, containing about 2.5 grms. of saccharose, 

 is diluted to about 250 c.c, 12 drops of concentrated sul- 

 phuric acid are added, and the mixture is heated 3 hours 

 on the water-bath, with renewal of the water as it is 

 evaporated (§ 36). If, after this operation, the solution 

 has a dark color, as may often be the case, add 20 c.c. of 

 the solution of plumbic acetate (§ 24, a), shake the mix- 

 ture well, dilute to exactly 500 c.c, let it stand awhile, 

 and use the clear supernatant liquid for the determination 

 of glucose (§ 81). 



If it does not need clarifying with plumbic acetate, neu- 

 tralize the free acid with sodic carbonate, dilute to exactly 

 500 c.c, and determine glucose as above. 



10 c.c. of the standard cupric solution correspond to 

 0.0475 grm. of saccharose. 



In case a solution contains both glucose and saccharose, 

 and it is desired to determine the amount of each, esti- 

 mate the glucose at once by titration with the cupric so- 

 lution ; then convert the saccharose into glucose, as above, 

 and titrate the solution again ; the last determination 

 gives the sum of the glucose originally in the solution 

 and that which was derived from the saccharose. 



LACTOSE. MILK SUGAR. C12H24O12. 



84. This sugar is soluble in water, but not in cold 

 alcohol. 



It reduces an alkaline solution of cupric oxide like glu- 

 cose, but in a different proportion. It is converted into 

 glucose by dilute acids. 



