498 CONSIDERATION OF CARBON COMPOUNDS. 



R.CH 2 OH + O == O=C^ + H 2 0. 

 Alcohol. Aldehyde. 



=<H + O = =<OH- 

 Aldehyde. Acid. 



Acids are obtained from compound ethers by boiling them with 

 alkalies, Avhen salts are formed, which may be decomposed by sul- 

 phuric or other acids. For instance : 



+ KOH = 



Acids are formed also by destructive distillation (acetic acid) ; by 

 fermentation (lactic acid) ; by putrefaction (butyric acid) ; by oxida- 

 tion of many organic substances (oxalic acid by oxidation of 

 starch), etc. 



Properties. Organic acids show the characteristics mentioned of 

 inorganic acids, viz., when soluble, have an acid or sour taste, redden 

 litmus, and contain hydrogen replaceable by metals, with the forma- 

 tion of salts. 



Most organic acids, and especially the higher members, show these 

 acid properties in a less marked degree than inorganic acids ; in fact, 

 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. 



While 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 acids, for 

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



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



