In the science of chemistry, alkalis are basic ionic salts, deriving their name from the arabic word for “ashes of the saltwort” or “potash”. The general definition of an alkali is any base that can be dissolved in water, and any solution with a pH greater than 7.0. They were the earliest known bases known to obey the traditional definition of a base, and they are still the most common bases in chemistry. Alkalis and acids have the same common properties, such as the fact that concentrated solutions of both are caustic, slippery to the touch, and generally water soluble. The term base and alkali are generally used interchangeably, but the two are not identical. Alkalis are always a basic salt of an alkali metal or alkaline earth metal, and any base that is both soluble in water and forms hydroxide ions is considered an alkali.