CHAPTER IV 



I 

 CARBOHYDRATES 



THESE substances comprise an exceedingly important group of 

 compounds, the members of which constitute the major proportion 

 of the dry matter of plants. The name " carbohydrate " indi- 

 cates the fact that these compounds contain only carbon, hydro- 

 gen, and oxygen, the last two elements usually being present in 

 the same proportions as in water. As a rule, natural carbo- 

 hydrates contain six, or some multiple of six, carbon atoms and 

 the same number of oxygen atoms less one for each additional 

 group of six carbons above the first one; e.g., CeH^Oe, Ci2H220n, 

 CisH32Oi6, etc. 



Carbohydrates are classed as open-chain compounds, that is, 

 they may be regarded as derivatives of the aliphatic hydrocarbons. 

 From the standpoint of the characteristic groups which they 

 contain, they are aldehyde-alcohols. In common with many other 

 poly-atomic open-chain alcohols, they generally possess a charac- 

 teristic sweet, or mildly sweetish, taste. In the case of the more 

 complex and less soluble forms, this sweetish taste is scarcely 

 noticeable and these compounds are commonly called the 

 " starches," as contrasted with the more soluble and sweeter forms, 

 known as " sugars." 



The characteristic ending ose is added to the names of the 

 members of this group. As systematic names, the Latin numeral 

 indicating the number of carbon atoms in the molecule is com- 

 bined with this ending; e.g., CsHioOs, pentose, CeH^Oe, hexose, 

 etc. 



In recent years, as a matter of scientific interest, many sugar- 

 like substances which contain from two to nine carbon atoms com- 

 bined with the proper number of hydrogen and oxygen atoms to 

 be equivalent to the same number of molecules of water in each 

 case, have been artificially prepared in the laboratory and desig- 

 nated as dioses, trioses, tetroses, pentoses, hexoses, heptoses, 



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