CA RBOH YDEA TES. 529 



and other carbohydrates having the composition C 6 PTi O 5 or C 12 H 22 O n can he 

 readily shown by the equations : 



*(C 6 H 12 6 - H 2 0) (C 6 H 10 5 )z 



2(C 6 H 12 6 )- H 2 : C 12 H 22 O n , 



which show that abstraction of water leads to the formation of compounds 

 having the composition of starch, C 6 H 10 O 5 , and cane-sugar, C 12 H 22 O n , respec- 

 tively. While this abstraction of water is difficult, it is an easy matter to 

 cause starch or cane-sugar to take up water, with the result that sugars of the 

 composition C 6 H 12 O 6 are formed. 



Properties. Carbohydrates are either fermentable, or can, in most 

 cases, be converted into substances which are capable of fermentation. 

 They are not volatile, but suffer decomposition when sufficiently 

 heated ; they have neither acid nor basic properties, but are of a neu- 

 tral reaction. Oxidizing agents convert them into saccharic and 

 mucic acids and finally into oxalic acid. (Soluble carbohydrates 

 have generally the property of turning the plane of polarized light.) 



Most carbohydrates are white, solid substances, and, with the ex- 

 ception of a few, soluble in water. Those carbohydrates belonging 

 to the sugars have a more or less sweet taste. Many of them, 

 especially glucose, are good reducing agents, as is shown by the 

 fact that they deoxidize in alkaline solution salts (or oxides) of 

 copper, bismuth, mercury, gold, etc., either to a lower state of 

 oxidation or to the metallic state. 



Occurrence in nature. No other organic substances are found in 

 such immense quantities in the vegetable kingdom as the members 

 of this group, cellulose being a chief constituent of all, starch and 

 various kinds of sugar of most plants. Carbohydrates are also found 

 as products of animal life, as, for instance, the sugar in milk, in bees' 

 honey, etc. 



Classification. The carbohydrates are conveniently divided into 

 the following three groups : 



1. Monosaccharides, or simple sugars. To this group belong the 

 sugars which cannot be broken down into two or more simple sugars. 

 They contain from 3 to 9 atoms of carbon, in most cases the same 

 number of oxygen atoms, and double the number of hydrogen atoms. 

 (Dextrose, levulose, galactose, etc.) 



2. Disaccharides, or complex sugars. These are sugars which, on 

 taking up 1 molecule of water, split up into two simple sugars. 

 (Cane-sugar, maltose, lactose, etc.) 



3. Polysaccharides. These do not resemble sugars, have no sweet 

 taste, and form simple sugars only after repeated cleavages. (Starches, 

 gums, cellulose, etc.) 



34 



