16 THE CABBOHYDRATES. 



water, and heat it for an hour. Then cool it and examine 

 the precipitate with the microscope. It is phenyl-gluco- 

 sazon : bright-yellow, needle-shaped crystals. They may be 

 single, but are more often in clusters (Plate I, 5). They 

 can be distinguished, if necessary, from similar compounds 

 of the other sugars by their melting-point, which is 204 C. 

 If they separate in the amorphous state, they may be crys- 

 tallized, after filtering, by dissolving in a little hot alcohol, 

 then evaporating the alcohol to a small volume, and letting 

 it stand. Make sketches of these : hand them in. 



32. Crush a piece of condensed yeast as large as a 

 pea in a test-tube of water, and wash it two or three times 

 by decantation to remove any fermentable substances which 

 may be present. Fill the tube completely full of a glu- 

 cose solution. Mix and place it, still full of the liquid, 

 with the mouth downward in a beaker which contains a 

 little water, or, better, some of the grape-sugar solution. 

 Let it stand for twenty-four hours in a warm place. The 

 carbon dioxid, which is formed., is found in the test-tube 

 and the alcohol in the liquid. The gas may be proved to 

 be carbon dioxid by shaking it with lime-water, which it 

 turns white. The presence of the alcohol is shown by 

 warming the liquid after the addition of sodium hydrate 

 and a little iodin. lodoform separates out in yellow scales, 

 or, if the amount of alcohol is very small, the odor alone 

 may be perceived. 



A convenient piece of apparatus for carrying on this 

 fermentation is the saccharimeter. This is essentially a 

 graduated tube with bulb to hold the liquid which is forced 

 out by the gas. From its reading the amount of glucose 

 can be learned. 



