SODA, in mineralogy and chemistry, is a species of fossil salts, divided by mine ralogists into common and radiated na tron. Common natron is of a yellowish Frey colour : it occurs in fine hakes, or in dusty particles; it has a sharp alkaline taste ; effervesces with nitric acid ; is easily soluble in water, and its solution changes blue vegetable tinctures to a green; it is fusible before the blow-pipe. It is found either as an efflorescence on the surface of the soil; or on decompos ing certain rocks; or on the sides and bottoms of lakes, that become dry by the heat and drought of summer. It is ob tained in great abundance in many parts of Germany, and also in Egypt. That from Egypt has, according to Klaproth, yielded to analysis the following substan ces: Carbonate of soda . 32.6 Sulphate of soda . . 20.8 Muriate of soda . . 15.0 Water . . . 31.6 100.0 am The radiated natron is of a yellowish grey colour : it occurs in crusts, and in capillary or acicular crystals, which are aggregated on one another ; it is glisten ing and translucent. This is found na tive about two days journey from Fezzan, at the bottom of a rocky mountain, forming crusts, usually the thickness of a knife, and sometimes even aninch thick, on the stir lase of the earth. it is always crystalline.
Besides the great quantity carried to Egypt and other parts, there are said to be fifty tons annually sent to Tripoli. It is not adulterated with salt. Though there is abundance of salt in this part of Africa, it must be observed, that the salt mines are situated on the sea coast ; whereas the radiated natron, called tro na, occurs at the distance of twenty eight days journey up the country. It is principally employed in the manu facture of glass and soap, and also for the washing of linen. This species has been analyzed by Klaproth, and found to consist of Sulphate of soda . . 2.5 Pure soda . . . 37.0 Carbonic acid . . 31.0 Water of crystallization 22.5 100.0 Soda was long regarded as a simple body ; it has, however, at length been de composed by Mr. Davy. See the article POTASH, where a brief account is given of the discovery.