MONOBASIC FATTY ACIDS. 497 



acid in which one of the hydroxyl groups has been replaced by a 

 hydrocarbon radical, thus: 



Carbonic acid. Acetic acid. f^ 



D \OH 

 Malonic acid. 



This shows that carboxyl, CO 2 H, is made up of hydroxyl, OH, 

 and the bivalent radical, CO, termed carbonyl. By replacement of 

 the hydrogen of the hydroxyl (or of the carboxyl, which is the same) 

 by metals the various salts are formed. 



What is termed the acid radical is the group of the total number 

 of atoms present in the molecule, with the exception of the hydroxyl. 

 In acetic acid, C 2 H 4 O 2 , for instance, the radical is CH 3 CO, or C 2 H 3 O, 

 which group of atoms, known as acetyl, is characteristic of acetic 

 acid, and of all acetates, and may often be transferred from one com- 

 pound into another without decomposition. 



The difference between alcohol radicals and acid radicals may also 

 be stated, by saying that the first contain carbon and hydrogen only, 

 while acid radicals contain carbon, hydrogen, and oxygen. 



In a similar manner, as there are homologous series of alcohols 

 corresponding to the various series of hydrocarbons, there are also 

 homologous series of organic acids running parallel with the corre- 

 sponding series of hydrocarbons or alcohols. 



Occurrence in nature. Organic acids are found and formed both 

 in vegetables and animals, and are present either in the free state, or 

 (and more generally) in combination with bases as salts, or with 

 alcohols as compound ethers. Uncombined or as salts are found, for 

 instance, citric, tartaric, and oxalic acids in plants, formic acid in 

 some insects, uric acid in urine, etc. ; as compound ethers are found 

 many of the fatty acids in the various fats. 



Some organic acids are also found as products of the decomposition 

 of organic matters in nature. 



Formation of acids. Many acids are produced by oxidation of 

 alcohols. As intermediate products are formed aldehydes, which 

 may be looked upon (as stated in the last chapter) as alcohols from 

 which two atoms of hydrogen have been removed. 



The change of a primary alcohol into an aldehyde, and of this 

 into an acid, takes place according to the general formulas : 



32 



