Alkalies feel slippery. Alkalies change the color of litmus from red to blue. Alkalies become less alkaline when they are combined with acids. In essence, Boyle defined alkalies as substances that consume, or neutralize, acids. Acids lose their characteristic sour taste and ability to dissolve metals when they are mixed with alkalies.
Alkalies even reverse the change in color that occurs when litmus comes in contact with an acid.
In 1884 Svante Arrhenius suggested that salts such as NaCl dissociate when they dissolve in water to give particles he called ions . An Arrhenius base is any substance that gives the OH - , or hydroxide, ion when it dissolves in water. It also explains why acids neutralize bases and vice versa. The Arrhenius theory has several disadvantages. It can be applied only to reactions that occur in water because it defines acids and bases in terms of what happens when compounds dissolve in water.