54 CELL-CONTENTS AND CELL-WALLS. 



(3) Sucrose (cane sugar) occurs in crystals ; it is only 

 slightly soluble in alcohol ; on being heated with caustic 

 soda it does not become yellow, though it slowly darkens ; 

 it does not reduce alkaline solutions of metallic oxides ; it 

 gives no osazone. After hydrolysis by acids or by the 

 enzyme invertase, sucrose is converted into " in vert sugar" 

 which gives the same reactions as glucose with caustic soda, 

 alkaline metallic solutions, and phenylhydrazine. 



63. Reactions of Glucose. Dissolve some glucose in 

 water, and to portions of the solution in test-tubes apply 

 the following tests. 



(a) Add caustic potash or caustic soda, and boil. The 

 solution turns yellow, then dark brown, and smells of 

 caramel; the smell becomes more distinct on acidifying 

 with dilute sulphuric acid. 



(ft) Tromnier's Test. Add some caustic potash or 

 soda ; then add copper sulphate solution, drop by drop, 

 shaking after each addition until the solution becomes 

 deep blue. (Excess of copper sulphate causes the precipi- 

 tation of copper hydrate, i.e. it is 110 longer d'ssolved by 

 the sugar solution ; a few drops of Rochelle salt cause this 

 to redissolve see Fehling's test). Heat nearly to boiling 

 a yellowish red precipitate of cuprous oxide is formed. 



(c) Fehling's Test. Add equal quantities of Fehling 

 A and Fehling B (see Appendix). No precipitate is 

 formed with the excess of copper sulphate present (compare 

 Tromnier's test). Heat to boiling cuprous oxide is pre- 

 cipitated. 



(d) Barfoed's Test. Add Barfoed's solution (see 

 Appendix), and boil. Red cuprous oxide is precipitated. 

 This test is not given with maltose or sucrose. 



(e) Reduction of Silver. Prepare some ammoniacal silver 

 nitrate in a test-tube, by adding dilute ammonia to silver nitrate 

 until the precipitate first formed is just redissolved. Add some of 

 this solution to the sugar solution, and warm in the water bath. A 

 mirror of metallic silver is formed on the inside of the tube. 



(/) Phenylhydrazine Test. To some sugar solution add 

 equal quantities of phenylhydrazine and glacial acetic acid (about 

 10 drops of each). Place in a water bath at 100 for half an hour, 



