322 CONSIDERATION OF CARBON COMPOUNDS. 



43. MONOBASIC FATTY ACIDS. 



General constitution of organic acids. When hydroxyl, OH, 

 replaces hydrogen in hydrocarbons, alcohols are formed ; when the 

 univalent group, CO 2 H, known as carboxyl, replaces hydrogen in 

 hydrocarbons, acids are formed. Monatomic, diatomic, and triatomic 

 alcohols are formed by introducing hydroxyl once, twice, or three 

 times respectively into hydrocarbon molecules; monobasic, dibasic, 

 and tribasic acids are formed by substituting one, two, or three 

 hydrogen atoms by carboxyl. For instance : 



Hydrocarbons. Monobasic acids. Dibasic acids. 



/TTT r^TT C*C\ TT C*T /t/OjjJti 



^-LL^ ^Aig. l-AJj-f- '^'**1\ C*f\ TT* 



Methane. Acetic acid. Malonic acid. 



/C0 2 H 



C 2 H 6 C 2 H 5 CO 2 H 



Ethane. Propionic acid. Succinic acid. 



The constitution of carboxyl is represented by O=C O H, 

 which shows that of the four affinities of the carbon atom, two are 

 saturated by an atom of oxygen, one by hydroxyl, whilst one is 

 unprovided for; any univalent hydrocarbon residue may attach itself 

 to this unprovided affinity, when an acid is formed. Acids may be 

 looked upon, therefore, as being composed of hydrocarbon residues 

 and hydroxyl, united by 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. 



of chloral and chloral hydrate. 415. What decomposition takes place when 

 alkalies act upon chloral? 416. Describe the process of preparing and purify- 

 ing chloroform. 417. What is the composition of chloroform and what are 

 its properties? 418. How is chloroform tested for impurities? 419. By what 

 tests may chloroform be recognized? 420. How is iodoform made, and what 

 are its properties ? 



