Alkali, in chemistry; from the Arabian kali, the name of a plant from the ashes of which one species of alkali can be extracted. The true alkalies have been arranged by a modern chemist in three classes: - I, those which consist of a metallic basis, combined with oxygen; these are three in number - potash, soda and lithia; 2, that which contains no oxygen, viz., ammonia; 3, those containing oxygen, hydrogen and carbon; in this class are placed aconita, atropia, hrucia, cicuta, datura, delphia, hyoscyamia, morphia, strychnia. And it is supposed that the vegetable alkalies may be found to be as numerous as the vegetable acids. The original distribution of alkaline substances was into volatile and fixed,the volatile alkali being known under the name of ammonia; while, of the two fixed kinds, one was called potash or vegetable, because procured from the ashes of vegetables generally; the other, soda or mineral, on account of its having been principally obtained from the incineration of marine plants." - Encyc. Am. The sulphate of ammonia has been used with success as a stimulant to vegetable growth - and is now prepared and sold by chemists for that purpose.