CHEMISTRY OF COMMON THINGS 



Vinegar, which is made mostly from apple juice, is a 

 dilute solution of acetic acid. Hydrochloric acid 1 (HC1) 

 is formed by the gastric glands of the human stomach 

 to aid in digestion. The air contains small amounts of 

 carbonic acid gas, and where much coal is burned the 

 air contains some sulphur dioxide. Some spring waters 

 contain carbonic acid, while soil waters contain various 

 acids from the decay of plants and animals. The acids 

 taken from plants are made up of molecules which are 

 very complex. Those that are called common acids 

 have molecules that are more simple. 



The chemical symbols for acids, as well as for other 

 compounds, show the number of the atoms in the mol- 

 ecules. Some common* acids are hydrochloric 

 acid (HC1), sulphuric acid (H 2 S0 4 ), nitric acid 

 (HNO 3 ), and acetic acid H(C 2 H 3 O 2 ). 



Tests for acids. Litmus is a substance 

 taken from the group of plants called lichens. 

 A solution is made of the litmus coloring 

 matter, then paper that has been prepared 

 for the purpose is dipped into the litmus 

 solution and allowed to dry; this colored 

 paper is called litmus paper. The common 

 acids and nearly all other acids will turn 

 litmus paper from blue to red. 



Very dilute solutions of the common acids 

 taste sour. Fruit acids are all sour. Sul- 



LlCHENS 



These forms 

 grow on rocks, 



phuric acid and nitric acid, when strong, bark, and 

 will make a brown spot on wood, paper, or 

 clothing, and will also injure any part of the body which 

 they touch. For this reason it is very important to 

 learn the nature and properties of another group of 



1 See Glossary, under heading "Chemical Symbols." 



