324 



CONSIDERATION OF CARBON COMPOUNDS. 



they become so weak that the acid properties can often scarcely be 

 recognized. As stated above, mono-, di-, and tri-basic organic acids 

 are known, the latter two being capable of forming normal, acid, or 

 double salts. 



Most organic acids are colorless, some of the lower and volatile 

 acids have a characteristic odor, but most of them are odorless ; most 

 organic acids are solids, some liquids, scarcely any gaseous at the ordi- 

 nary temperature. Any salt formed by the union of an organic acid 

 and a non- volatile metal (especially alkali metal) leaves the carbonate 

 of this metal after the salt has suffered combustion. It is for this 

 reason that ashes contain metals largely in the form of carbonates. 



Whilst the hydrogen of the hydroxyl may be replaced by metals 

 or by other residues, the hydrogen of the acid radical may often be 

 replaced by chlorine, and the oxygen of the hydroxyl by sulphur. 

 The acids formed by this last reaction are known as thio acid*, for 

 instance, thio-acetic acid, C 2 H 4 OS. 



When the hydrogen of the hydroxyl is replaced by a second acid 

 radical (of the same kind as the one forming the acid) the so-called 

 anhydrides are produced, which correspond to the inorganic anhy- 

 drides. For instance : 



HN0 3 or tf0 2 .O 



Nitric acid. 



N0 2 \ 



N0 2 / 



Nitric anhydride. 



C 2 H 4 2 or C 2 H 3 O.OH. 



Acetic acid. 



C 2 H 3 0\ 



C 2 H 3 0/ a 



Acetic andydride. 



Amido-adds are compounds obtained from acids by replacement of 

 a hydrogen atom by NH 2 ; these compounds will be spoken of later 

 in connection with amides. 



Patty acids of the general composition, 

 C n H 2n O 2 or 



Occurs in : 



Eed ants and some plants, etc. 

 Vegetable and animal fluids. 

 Sweat, fluids of the stomach, etc. 

 Butter. 



Valerian root. 

 Butter. 

 Castor oil. 



Butter ; cocoanut oil. 

 Leaves of geranium. 

 Butter. 



Cocoanut oil. 



