THE CARBOHYDRATES. 5 



(/) Silver Nitrate. To 5 c.c. of AgN0 3 solution -in a clean 

 test-tube add dilute NH 4 OH, drop by drop, until the precipi- 

 tate, which is at first formed, dissolves. Then add a few 

 drops of the dextrose solution and warm on the water-bath. 

 Note the formation of a metallic mirror on the side of the 

 test-tube. Explain the chemical changes. 



(g) Phenylhydrazin. In a test-tube prepare a mixture 

 of 5 drops of phenylhydrazin, 10 drops of glacial acetic acid, 

 and 1 c.c. of a saturated solution of NaCl; then add 5 c.c. of 

 the dextrose solution and boil for a few minutes. Yellow 

 phenylglucosazone crystals will appear on cooling. 



Under the microscope these appear as fine yellow needles, 

 usually arranged in sheath-shaped bundles. If determina- 

 tions are made of the composition and melting-point of these 

 crystals, this test furnishes most characteristic and conclusive 

 evidence for dextrose. Write the equations for the forma- 

 tion of the osazones. 



(h) Fermentation. In a test-tube shake 20 c.c. of the 

 dextrose solution with a small piece of compressed yeast. 

 Place the mixture in a saccharometer and allow it to stand 

 in a thermostat at 40 C. A gas collects at the top of the 

 tube and its volume is in a direct ratio to the amount of dex- 

 trose in the solution. What is the character of the chemical 

 changes which have taken place? 



(i) Polarization. See demonstration and make a read- 

 ing on the instrument of the degree of right-handed rotation. 



HEXABIOSES OR DISACCHARIDES, C 12 H 22 O n . 

 SACCHAROSE. LACTOSE. MALTOSE. 



The disaccharides possess, with the exception of saccha- 

 rose, the same general properties as the simple sugars. As 

 their name implies, upon hydrolysis they take up a molecule 



