[Arab.] The name applied in chemistry to a class of bodies possessing the following common properties: - (I) They have the power of turning vegetable blue colors green, and vegetable yellows brown ; (2) they restore the color to a blue solution which has been reddened by an acid ; (3) they have a strong affinity for acids, combining with them to form salts which pqssess neither acid nor alkaline properties - hence an acid and an alkali are said to neutralize one another ; (4) they are all soluble in water. The alkalies proper are four in number - potash, soda, lithia and ammonia. They exert a powerfully corrosive action on animal and vegetable substances. As bicarbonates they are often used along with carbonic acid to correct acidity of the stomach.