The term is derived from an Arabic word kali, the name of a plant containing an alkali. The alkalies possess these general properties in their pure state. They are caustic and acrid to the taste. They dissolve animal matter, and form a saponaceous compound with oils or fat. They combine with acids in definite proportions; the respective properties of each are destroyed, and a neutral salt is the result. On this account, they precipitate most metals from their acid solutions. They change most of the vegetable blues to green, and restore the colour of a vegetable blue reddened by an acid. They combine with water in any proportion. The most important of the alkalies in commerce and in the arts, are potash, soda, and ammonia. The two former of these are generally called the fixed alkalies, and the latter, the volatile. Some of the earths possess powerful alkaline properties, and have, therefore, by some writers in chemistry, been classed with the alkalies: these are lime, magnesia, barytes, and strontites.

Many vegetables also contain matter decidedly alkaline; such as morphia, hyosciama, strychnia, etc.

The properties and uses of these bodies, will be found under their respective heads.