Corbohydrotes 



3 



Living matter is made up of several large classes of compounds. One 

 of these groups includes the substances known as carbohydrates. The 

 compounds thus designated in actual practice are so varied that a suit- 

 able definition really does not exist. Perhaps the simplest statement 

 says that carbohydrates are polyhydroxy aldehydes or ketones or are 

 condensation products involving the carbonyl groups of such aldehydes 

 or ketones. These condensation products are formed by loss of w^ater 

 and give rise to giant molecules in certain cases. Occasionally other 

 groups are present as in the amino sugars. Actually the term carbohy- 

 drate is applied to substances of diverse chemical, physical, and bio- 

 logical properties. But ordinarily all may be hydrolyzed to molecules 

 of relatively similar chemical behavior, the polyhydric aldehydes or 

 ketones. 



OPTICAL ISOMERISM 



Optical Rotation 



As an electromagnetic radiation, light vibrates in directions perpen- 

 dicular to the direction of propagation. When light strikes a flat 

 surface at an angle, the light vibrating in one plane is preferentially 

 reflected and is said to be plane polarized. Light transmitted through 

 most crystals is sorted into two components, each plane polarized. By 

 special cutting and cementing of the crystal, one component can be 

 absorbed, leaving a beam of light with a single plane of polarization. 

 A few materials do this automatically, such as the mineral tourmaline 

 and the industrial product Polaroid. 



49 



