SODA. Natron ; mineral alkali. This important and useful substance is an oxide of sodium. Sodium was discovered by Davy in 1808. It is a metal much re sembling potassium in its general charac ters. It is soft, malleable, fusible at 100°, and burns when heated in contact of air. When thrown upon water it does not burn, but floats about upon the surface, and rapidly disappears, being converted into soda, which is dissolved in the water, and gives it an alkaline reaction. The specific gravity of sodium is 0-97. By the quantity of hydrogen evolved during the action of sodium on water, we learn that soda, or oxide of sodium, consists of 1 equivalent of sodium=24, and 1 of oxy gem=8. The equivalent of soda, there fore, is 32. The commercial demands for soda are chiefly supplied from two sources: the combustion of marine vege tables, such as common sea-weed and the salsola soda, which furnish the impure alkalies called kelp and barilla ; and the decomposition of common salt, or, rather, perhaps, of sulphate of soda, obtained by the decomposition of salt by sulphuric acid. Carbonate of soda forms large rhombo-prismatic crystals, composed of 82 soda+ 22 carbonic acid +90 water. They fuse in their water of crystallization at about 150°, and it may be entirely ex pelled by exposure to heat. They efflo resce when exposed tp air. Sulphate of soda, or Glauber's salt, is the result of the action of sulphuric acid upon com mon salt (see Mualyria Acm.) It con sists of 32 soda+ 40 sulphuric acid; and the crystals are constituted. of 72 dry sul phate and 90 water : they are efflorescent, and soluble in about three parts of cold water. When sodium is introduced into chlorine, it immediately combines with it to form chloride of sodium, or common salt; if heated in the gas, it burns very vividly : 24 parts of sodium combine with 86 of chlorine to form 60 parts of this important and well-known compound (see SALT.) When chlorine gas is passed into a weak solution of caustic soda it is ab sorbed, and a useful bleaching and disin fecting solution is obtained, which has been called Labarracque's disanfectinq soda Caustic Soda—Hydrate of Soda.—Na0,
i I10.—This substance prepared in practice by decomposing a somewhat dilute solution of carbonate of soda by hydrate of lime ; the description of the process employed in the case of hydrate of potash, and the precautions necessary, apply word for word to that of soda.
The solid hydrate is a white, fusible substance, very similar in properties to hydrate Of potash. It is deliquescent, but dries up again after a time ill conse quence of the absorption of carbonic acid. The solution is highly alkaline, and a powerful solvent for animal matter; it is used in large quantity for making soap.
The strength of a solution of caustio soda may be roughly determined from a knowledge of its density, by the aid of the following table, drawn up by Dr. Dalton.
Table of Density.
Per eentago of Density. real &xis.
2-00 1.85 63.6 53 8 466 1.55 , 41.2 1-50 26-8 147 1.44 1-40 1-36 23-0 1-az 23-0 129 19-0 1-23 16.0 1.18 13.0 1.12 1.06 Carbonate of Soda.—NaO, CO2+10I10. Carbonate of soda was once exclu sively obtained from the ashes of sea weeds, and of plants, such as the salsola soda, which grew by the sea-side, or be ing cultivated in suitable localities for the purpose, were afterwards subjected to in cineration. The barilla yet employed in soap-making, is thus produced in several places on the coast of Spain, as Alicant, Carthagena, &c. That made in Brittany is called Dare°.
Carbonate of soda is now manufactured on a stupendous scale from common salt, or rather from sulphate of soda i by a pro cess of which the following s an out line— A charge of 600 lbs. of common salt is placed upon the hearth of a well-heated reverberatory furnace, and an equal weight of sulphuric acid of sp. gr. 11 poured upon it through an opening in the roof, and thoroughly mingled with tho salt ; hydrochloric acid gas is disengaged, which is usually allowed to escape by the chimney, and the salt is converted into , sulphate of soda. This part of the pro . cess takes for completion about tour hours, and requires much care and skill.