CARBOHYDRATES. 43 



solution. Heat gently and note the formation of iodoform crystals. 

 Examine these crystals under the microscope and compare them 

 with those in Fig. 6, p. 42. 



(b) Aldehyde Test. Place 5 c.c. of the distillate in a test-tube, 

 add a few drops of potassium dichromate solution, K 2 Cr 2 O 7 , and 

 render it acid with dilute sulphuric acid. Boil the acid solution and 

 note the odor of aldehyde. 



TRISACCHARIDES, C 18 H 32 16 . 



RAFFINOSE. 



This trisaccharide, also called melitose or melitriose, occurs in 

 cotton seed, Australian manna and in the molasses from the prepara- 

 tion of beet sugar. It is dextro-rotatory, does not reduce Fehling's 

 solution and is only partially fermentable by yeast. 



Raffinose may be hydrolyzed by weak acids the same as the poly- 

 saccharides are hydrolyzed, the products being laevulose and meli- 

 biose; further hydrolysis of the melibiose yields dextrose and 

 galactose. 



POLYSACCHARIDES, (C 6 H 10 5 ) X . 



In general the polysaccharides are amorphous bodies, a few, how- 

 ever, are crystallizable. Through the action of certain enzymes 

 or weak acids the polysaccharides may be hydrolyzed with the for- 

 matiori of monosaccharides. As a class the polysaccharides are 

 quite insoluble and are non- fermentable until inverted. By inversion 

 is meant the hydrolysis of disaccharide or polysaccharide sugars 

 to form monosaccharides, as indicated in the following equations : 



(a) C 12 H 22 O n + H 2 = 2(CH 12 O fl ). 



(b) C 6 H 10 B + H 2 = C fl H 12 6 . 



STARCH, (C 6 H 10 5 ) X . 



Starch is widely distributed throughout the vegetable kingdom, 

 occurring in grains, fruits and tubers. It occurs in granular form, 

 the microscopical appearance being typical for each individual 

 starch. The granules, which differ in size according to the source, 

 are composed of alternating concentric rings of granulose and cel- 

 lulose. Ordinary starch is insoluble in cold water, but if boiled 

 with water the cell walls are ruptured and starch paste results. In 

 general starch gives a blue color with iodine. 



