322 PLANT AND ORGANIC CHEMISTRY 



the sugar-cane or beet-root, and milk sugar. Starches and 

 gums, though conveying little idea of sugar, are chemically 

 to be considered as sugars. 



The characteristics of these different compounds are very 

 unlike. They vary from very soluble to insoluble compounds, 

 and from crystalline to non- crystalline bodies. But the in- 

 soluble compounds, like starch and cellulose, may be con- 

 verted into the soluble sugars by the action of heat and dilute 

 acids, and by certain ferments, as diastase. The reaction 

 which accompanies this conversion involves the taking up of 

 water, and at the same time the complicated molecule splits 

 into several simpler ones. This reaction is called hydrolosis: 

 x(C 6 H 10 O 5 ) + xH 2 O = xC 6 H 12 O 6 . 



As will be observed, the sugar group collectively desig- 

 nated as "carbohydrates" comprehends a vast widening- 

 out vista of compounds, from a simple compound derived 

 directly from the elements, to complex bodies with numerous 

 isomers. 



The sugars of physiological consequence are widely spread 

 in animals and plants, and, as carbohydrates, constitute one 

 of the three great classes of natural organic compounds, the 

 fats and albuminoids constituting the other two classes. La- 

 voisier discovered that the materials of which carbohydrates 

 are composed were carbon, hydrogen, and oxygen; but the 

 objection to the use of the term carbohydrate, which is denned 

 as a compound containing carbon and hydrogen and oxygen 

 in the proportion of 2 to i, is its non- universality. The sugar 

 called rhamnose, C 6 H 12 O5, may be mentioned as an excep- 

 tion to the definition, but for purposes of classification the 

 name carbohydrate has been retained by writers. 



The carbohydrates have been divided for convenience into 

 three groups: 



(1) Simple sugars, or monosaccharides, as grape or fruit 

 sugars. 



(2) Decomposable sugars, or polysaccharides, as cane or 

 milk sugar and raffinose. 



(3) Polysaccharides unlike sugar, as starch, cellulose, and 

 dextrine. 



CQIJ 



