CARBON. 11 



elements just described. Among these compounds the follow- 

 ing are important : 



1. Carbohydrates, e.g., starch and cellulose, C (i H 10 O 5 , grape 



sugar, C H 12 O,,, cane sugar, C^H.^On, &c. 



2. Organic acids, e.g., acetic acid, CH..COOH, oxalic acid, 



C,HA, &c. 



3. Fats, essentially salts of glycery], C S H 5 , combined with a 



fatty acid, e.g., stearic acid, HC 18 H ; O. 2 , oleic acid, 

 HC^H^Oa, &c. These glyceryl salts, or glycerides as 

 they are sometimes called, are possessed of a constitu- 

 tion similar to the following, which represents glyceryl 

 stearate (glyceride of stearic acid, or " stearine"). 



C 8 H 5 (C 1S H,A).3 



H 



I II 



H-C 0-C C 17 H,, 

 



H C O C C 17 H... 

 O 



H C C C 17 H ; ,, 

 H 



4. Hydrocarbons, e.g., turpentine, C 10 H 10 . 



5. Albuminoids, containing all four of the elements in ques- 



tion associated with small quantities of sulphur and 

 phosphorus. The constitution of these substances is 

 riot understood. They always contain about 16% of 

 nitrogen. 



6. Amides. These also are compounds of carbon, hydrogen, 



oxygen, and nitrogen, but their structure is much less 

 complex than that of the albuminoids. A large number 

 have been prepared, the characteristic feature being 

 that they contain the group NH. 2 united with an oxygen - 

 containing compound of carbon; e.g., urea is an amide, 

 CO(NH. 2 ),. 



