302 



SODA. 



salicornia, in particular, furnish the pure barilla (q. 

 v.). These products contain much foreign matter: 

 the soda is combined with the carbonic acid, and 

 with that are associated muriate and sulphate of 

 soda, a small portion of hydriodate of potash or 

 soda, charcoal, lime, magnesia, silica and alumina. 

 The origin of the soda in these cases is undoubtedly 

 from the muriate of soda, with which such plants 

 are supplied from their situation ; since it has been 

 UMvrtained concerning some of them, that, when 

 transplanted to inland situations, they cease to 

 yield soda, and only afford potash. It is usually 

 from barilla, that soda is procured. The barilla, in 

 powder, being lixiviated with boiling water, the 

 solution, on evaporation, affords crystals of carbo- 

 nate of soda. To remove the acid, the same pro- 

 cess is employed as in procuring potash. The salt 

 is dissolved in twice its weight of water, and filtered 

 through slacked lime. The lime abstracts its car- 

 bonic acid, principally : to obtain the soda perfectly 

 pure, however, it must be submitted to the action 

 of alcohol. Soda thus obtained is in the state of a 

 solid white mass. In its driest state, it contains,' 

 like potash, a portion of combined water, or is a 

 hydrate, consisting of soda 32, and of water 9. 

 Soda is possessed of all the alkaline properties in 

 common with potash. It is acrid, and caustic, and 

 abundantly soluble in water. It changes the vege- 

 table colours to green, is powerful in neutralizing 

 the acids, and in rendering saponaceous the animal 

 and vegetable oils. It is acted on by sulphur and 

 phosphorus, but does not itself act so powerfully 

 on the metals, or the earths, as potash. It com- 

 bines with the latter, however, by fusion, and 

 forms, with silica, in particular, a very perfect glass. 

 The basis of soda is a peculiar metal, called sodium, 

 discovered by Sir H. Davy, in 1807, a few days af- 

 ter his discovery of potassium. It may be procured 

 in exactly the same manner as potassium, by elec- 

 trical or chemical decomposition of the pure hydrate. 

 It requires, however, a somewhat higher degree of 

 heat, and a greater voltaic power, to decompose 

 soda than potash. Sodium is a white metal, having 

 a colour intermediate between those of silver and 

 lead. At the common temperature of the air, it is 

 solid, and very malleable, and so soft that pieces of 

 it may be welded together by strong pressure. It 

 retains its softness and malleability at the tempera- 

 ture of 32. It is an excellent conductor of elec- 

 tricity ; specific gravity 0-972. It melts when 

 heated to the temperature of 194, and requires a 

 much higher temperature to be volatilized than 

 potassium. Its affinity for oxygen is similar to that 

 of potassium. When exposed to the air, it speedily 

 absorbs oxygen, and becomes converted into soda. 

 When thrown into water, that liquid is rapidly de- 

 composed ; its hydrogen escapes in the state of gas, 

 while its oxygen converts the sodium into soda. 

 When projected on hot water, it burns with a yel- 

 lowish flame, whereas that of potassium is reddish. 

 Soda is composed of sodium 100 and oxygen 33-3. 

 Another compound of sodium and oxygen is the 

 peroxide of sodium. It is formed by heating sodium 

 in oxygen gas. It is of a deep orange colour, very 

 fusible, and a non-conductor of electricity. When 

 acted on by water, it gives off oxygen, and the wa- 

 ter becomes a solution of soda. Only one combi- 

 nation of sodium and chlorine is known. This is 

 formed when sodium is introduced into chlorine gas; 

 the sodium takes fire, and is converted into a 

 chloride of sodium. It may be formed, likewise, by 

 [lassing a current of chlorine gas over soda, previ- 



ously heated to redness. The soda gives out its 

 oxygen in the state of gas, and is converted into u 

 chloride. It is composed of chlorine 4-5 and sodium 

 3. It is the important substance known under the 

 name of common salt, or muriate of soda. Vast bed? 

 of it exist in the bowels of the earth, whence it is 

 quarried under the name of rock suit; and sea- water 

 contains about 3-5 per cent, of it, from which it is 

 easily procured by evaporation. In the latter case 

 it is less pure than in the former, requiring some 

 care in the evaporation, in order to separate it from 

 the salts with which it is contaminated. In warm 

 climates, it is obtained by spontaneous evaporation ; 

 the sea-water is admitted into shallow trenches by 

 the sea-side, and spread over an extensive surface ; 

 as it becomes concentrated by evaporation, the 

 liquor is removed, by sluices, from one trench to 

 another, until at length the salt crystallizes spon- 

 taneously, and nearly pure. In colder climates, the 

 sea-water is evaporated in large boilers by the ap- 

 plication of heat, and the evaporation is carried so 

 far, that the salt concretes on the surface of the 

 boiling liquor in small crystals. As obtained by 

 this mode, small portions of muriate of magnesia 

 and sulphate of magnesia adhere to it, which some- 

 what impair its antiseptic properties, and, at the 

 same time, render it slightly deliquescent. _ Rock 

 salt, as it comes from the mine, sometimes requires 

 to be dissolved and evaporated, in order to free it 

 from the oxide of iron and clay with which it is 

 often blended. On account of these impurities, it 

 presents, occasionally, a variety of colours, such as 

 yellow, flesh-red, and blue. Its depositories are 

 transition rocks which are in connexion with gypsum 

 and sandstone. Mines of salt are found in Poland, 

 England, Russia, Spain, and the East Indies. The 

 most remarkable deposits, however, are those of 

 Poland and Hungary. That at Wiliczka, near Cra- 

 cow, in Poland, is supposed to contain salt enough 

 to supply the whole world for many centuries, al- 

 though it has been wrought for six or seven hun- 

 dred years. It has been explored to an astonishing 

 depth ; and its subterranean regions are excavated 

 into houses, chapels, and other ornamental forms, 

 the roof being supported by decorated pillars of 

 salt. When illuminated by lamps and torches, they 

 are described as objects of great splendour. The 

 purity of rock salt may be seen from the following 

 analysis by doctor Henry : 



Chloride of sodium, 

 Sulphate of lime, . 

 Chloride of magnesium, 

 Chloride of calcium, 

 Undissolved matter, 



983-35 



6-50 



19 



06 



lO'OO 



Common salt, when artificially prepared, or in its- 

 state of greatest purity, has the following proper- 

 ties : It is white ; crystallizes in cubes (rarely in 



octahedrons) ; has a specific gravity of 2-12 to 2-25. 



100 parts of water 



at 57 dissolved 36 of salt. 

 at 140 " 37 do. 

 at 229J " 40-38 do. 



When heated, it decrepitates, and at a red heat 

 melts into a liquid without undergoing decomposi- 

 tion. In a high temperature it may be sublimed. 

 It contains no water of crystallization. 



Sodium combines readily with sulphur and phos- 

 phorus, presenting similar phenomena to those pre- 

 sented by potassium. The sulphurets and phosphu- 

 rets of sodium are less inflammable than those of 

 potassium. Potassium and sodium combine with 

 great facility, and form peculiar compounds, which 

 differ in their properties according to the propor- 



