CARBOHYDRATES. 4! 



EXPERIMENTS ON LACTOSE. 

 i ii. Repeat these experiments as given under Dextrose, pages 



23-3 I- 



12. Mucic Acid Test. Treat 100 c.c. of the solution containing 



lactose with 20 c.c. of concentrated nitric acid (sp. gr. 1.4) and 

 evaporate the mixture in a broad, shallow, glass vessel on a boiling 

 water-bath, until the volume of the mixture has been reduced to 

 about 20 c.c. At this point the fluid should be clear, and a fine white 

 precipitate of mucic acid should form. If the percentage of lactose 

 present is low it may be necessary to cool the solution and permit 

 it to stand for some time before the precipitate will appear. It is 

 impossible to differentiate between lactose and galactose by this test, 

 but the reaction serves to differentiate these two sugars from all 

 other reducing sugars. 



Differentiate lactose from galactose by means of Barfoed's test, 

 page 31. 



SUCROSE, CjaHaAi. 



Sucrose, also called saccharose or cane sugar, is one of the most 

 important of the sugars and occurs very extensively distributed in 

 plants, particularly in the sugar cane, sugar beet, sugar millet and 

 in certain palms and maples. 



Sucrose is dextro-rotatory and upon hydrolysis, as before men- 

 tioned, the molecule of sucrose takes on a molecule of water and 

 breaks down into two molecules of monosaccharide. The mono- 

 saccharides formed in this instance are dextrose and laevulose. This 

 is the reaction: 



C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 



Sucrose. Dextrose. Laevulose. 



This process is called inversion and may be produced by bacteria, 

 enzymes and certain weak acids. After this inversion the previously 

 strongly dextro-rotatory solution becomes laevo-rotatory. This is 

 due to the fact that the laevulose molecule is more strongly laevo- 

 rotatory than the dextrose molecule is dextro-rotatory. The product 

 of this inversion is called invert sugar. 



Sucrose does not reduce metallic oxides in alkaline solution 

 and forms no osazone with phenylhydrazine. It is not fermentable 

 directly by yeast, but must first be inverted by the enzyme sucrose 

 (invertase or invertin) contained in the yeast. The probable struc- 

 ture of sucrose may be represented by the following formula. 



