§ 81. GLUCOSE. 113 



It is colored dark brown when heated with a strong so- 

 lution of sodic hydrate. 



If triturated with cold concentrated sulphuric acid, it 

 is dissolved without being blackened. 



If a concentrated solution of glucose is mixed with co- 

 baltic nitrate and a small quantity of fused caustic soda, 

 the solution remains clear on being boiled. 



If baric hydrate is added to an alcoholic solution of 

 sugar, a white precipitate is formed. 



If a little caustic soda is added to a solution of glucose, 

 and then, drop by drop, a dilute solution of cupric sul- 

 phate, a deep blue liquid is formed ; but after a few mo- 

 ments a yellowish or red precipitate of hydrated cuprous 

 oxide is separated. A solution containing 0.00001 of glu- 

 cose will give a notable red precipitate on the addition of 

 soda and a few drops of cupric sulphate ; 0.000001 of glu- 

 cose in the solution gives a red tint to it with the above 

 reagents. 



QuantitatiTe estimation. — This may be eifected by 

 making use of the delicate reaction just described. One 

 equivalent of glucose will reduce ten equivalents of cupric 

 oxide to cuprous oxide ; if, then, we know the quantity 

 of cupric oxide that has been reduced, we can calculate 

 the corresponding amount of sugar. For this determina- 

 tion, a standard solution of cupric oxide containing an 

 excess of alkali is commonly used, or Fehling's solution, 

 as it is often called. 



Dissolve 34.639 grms. of pure, crystallized cupric sul- 

 phate in about 200 c.c. of water ; make another solution 

 of 173 grms. of |)ure, crystallized potassic sodic tartrate 

 in 480 c.c. of a solution of sodic hydrate (Sp. Gr. = 1.14). 

 Add the first solution gradually to the second, and dilute 

 the mixture to 1000 c.c. Each 10 c.c. of this solution 

 corresponds to 0.05 grm. of glucose. Keep the solution 

 in small, well-stoppered bottles, in a dark place ; the bot- 



