378 ORGANIC CHEMISTRY. 



casks, is one of its most important salts. Another has 

 been mentioned under the head of antimony. Oxalic 

 acid is found in wood sorrel and in certain lichens. It 

 is also prepared by the action of nitric acid on wood, 

 sugar, and starch. When these substances are burned 

 in the air, their carbon is converted into carbonic acid. 

 Oxalic acid contains half the proportional quantity of 

 oxygen, and may be regarded as the product of a less 

 perfect combustion by the oxygen of nitric acid. It is 

 a white crystalline solid and a most dangerous poison. 

 The effect of heat on oxalic acid, with its precise com- 

 position, is given in the section on carbonic oxide. 

 Citric acid is the acid of lemons, malic acid, that of 

 the apple, and formic acid that of the red ant. The 

 latter may also be formed from wood spirit, by oxida- 

 tion, through the agency of platinum black, as acetic 

 acid is formed from ordinary spirit or alcohol. Lactic 

 acid will be again mentioned under the head of animal 

 chemistry. 



949. THEIR COMPOSITION. All of these 



What is the 



composition of acids differ in taste and in various chem- 

 *acids? Ve * ca ^ P r P ert i es ? as do those of inorganic 

 chemistry. Yet all of them contain the 

 same three elements which are also contained in wood, 

 gum, and starch. They contain these elements in 

 various proportion, but their peculiarities are not to be 

 ascribed to this cause alone. They may be regarded 

 as in part, at least, the consequence of a difference of 

 arrangement of the atoms, as has already been ex- 

 plained 



