CARBOHYDRATES 31 



Remembering that KOH has the power to absorb CO 2 how do you explain the 

 result? 1 Filter some of the mixture. To 5 c.c. of the filtrate add several drops 

 of a solution of iodine in potassium iodide (enough to give a yellow color to the 

 whole mixture). Warm gently. Note iodoform odor and examine under 

 microscope for crystals of iodoform (see Fig. 4). What does a positive test 

 here indicate? 



9. Formation of Caramel. Gently heat a small amount of pulverized glu- 

 cose in a test-tube. After the sugar has melted and turned brown, allow the 

 tube to cool, add water and warm. The coloring matter produced is known as 

 caramel. 



10. Demonstration of Optical Activity. A demonstration of the use of the 

 polariscope, by the instructor, each student being required to take readings and 

 compute the "specific rotation." 



USE OF THE POLARISCOPE 



For a detailed description of the different forms of polariscopes, the 

 method of manipulation and the principles involved, the student is 

 referred to any standard text-book of physics. A brief description fol- 



FIG. 6. ONE FORM or LAURENT POLARISCOPE. 



B t Microscope for reading the scale; C, a vernier; E, position of the analyzing^Nicol prism; 

 H, polarizing Nicol prism in the tube below this point. 



lows. An ordinary ray of light vibrates in every direction. If such a 

 ray is caused to pass through a "polarizing" Nicol prism it is resolved 

 into two rays, one of which vibrates in every direction as before and a 

 second ray which vibrates in one plane only. This latter ray is said to 

 be polarized. Many organic substances (sugar, proteins, etc.) have the 

 power of twisting or rotating this plane of polarized light, the extent to 

 which the plane is rotated depending upon the number of molecules 



1 The findings of Neuberg and associates 2 indicate that the liberation of carbon di- 

 oxide by yeast is not necessarily a criterion of the presence of sugar. The presence of 

 an enzyme, called carboxylase, has been demonstrated in yeast which has the power of 

 splitting off CO* from the carboxyl group of amino- and other aliphatic acids. 



J Neuberg and Associates: Biochem. Zeitsch., 31, 170; 32, 323; 36, (60, 68, 76), 1911. 



