SODA. 



303 



fions of the constituents. By a small quantity of 

 sodium, potassium is rendered fluid at common tem- 

 peratures. A little potassium, on the other hand, 

 destroys the ductility of sodium, and renders it very 

 brittle. 



Salts of Soda. In general, the salts of soda are 

 much more soluble in water than those of potash. 

 Many of the salts of the latter alkali contain no 

 water of crystallization ; but most of the salts of 

 soda contain a great deal. One of the easiest me- 

 thods of ascertaining whether the base of a given 

 salt be soda, is to determine the shape of the cry- 

 stals which it forms. If it does not shoot into re- 

 gular crystals, separate the acid by means of sul- 

 phuric or nitric acid, and let the newformed salt 

 crystallize. Sulphate and nitrate of soda are easily 



recognised by the figure of their crystals Sulphate 



of soda. This salt was discovered by a German 

 chemist, named Glauber, and for that reason is 

 commonly known under the name of Glauber's salt. 

 It may be procured by saturating soda with sul- 

 phuric acid, but is more usually obtained by decom- 

 posing common salt with sulphuric acid in order to 

 procure muriatic acid. It crystallizes with great 

 readiness in the form of an oblique rhombic prism ; 

 specific gravity, 2-2 to 2-3. Its taste at first re- 

 sembles that of common salt, but soon becomes dis- 

 agreeably bitter : 100 parts of water, at 60 Fahr., 

 dissolve 48-6 parts of crystallized salt. When ex- 

 posed to the air, it loses great part of its water, and 

 falls into a white powder, but is not otherwise al- 

 tered. In this alteration, it loses about 56 per 

 cent, of its weight. When exposed to heat, it first 

 .undergoes the watery fusion, then its water is evap- 

 orated, it is reduced to a white powder, and in a 

 red heat it melts. (For the solubility of Glauber's 

 salt, see the article Salt.") As a purgative, the use 

 of this salt is very general ; and it has been em- 

 ployed to furnish soda. It has been employed also 

 in the art of glass-making : equal parts of carbonate 

 of lime, sand, and dried sulphate of soda, produce a 

 clear, solid, pale-yellow glass. Bisulphate of soda 

 may be obtained by dissolving sulphate of soda in 

 dilute sulphuric acid, and, after concentrating it 

 sufficiently, setting it aside. The crystals are 

 oblique, four-sided prisms, resembling pretty nearly, 

 in dimensions, those of the sulphate. They do not 

 deliquesce in the air. Its taste is very acid. It 

 may be exposed to a red heat without losing its 

 excess of acid. It is more than twice as soluble as 

 Glauber's salt. 



Nitrate of soda is obtained by adding dilute 

 nitric acid to soda, or by mixing nitrate of lime 

 and sulphate of soda together, filtering the solution 

 and evaporating. The crystals are transparent, 

 arrd have the form of the rhombic prism. Specific 

 gravity, 2-0. It has a cool, sharp taste, and is 

 more bitter than nitre. One hundred parts of 

 water, at 32 Fahr., dissolve 80 parts of this salt, 

 whereas at 50, only 22 - 7 parts are dissolved. As 

 it attracts moisture when exposed to the air, it does 

 not answer for the manufacture of gunpowder. It 

 is sometimes used in fire-works, on account of its 

 communicating a fine orange colour to combustibles 

 while burning. It contains no water of crystalliza- 

 tion, but usually about three per cent, of water, 

 mechanically lodged between the plates of the 

 crystals. Its constituents are, nitric acid 6-75 and 

 soda 4-0. An immense deposit of it, extending for 

 many leagues, is said to exist in the desert of Ata- 

 cama, in Peru. Attempts were made, some years 

 ago, to introduce it into commerce; but they did 



not succeed. It might be used with advantage for 

 the nianufacture of nitric acid, and probably, also, 

 in that of sulphuric acid. 



Carbonate of soda. This salt has been also long 

 known, as well as common salt, above described. 

 It is obtained from the lixiviation of marine plants, 

 which do not afford it in purity, but associated 

 with other salts: to separate it from these, the 

 solution requires to be evaporated at a low heat, 

 skimming off the crystals of common salt as they 

 form on its surface. Of late years, large quantities 

 of carbonate of soda have been manufactured from 

 common salt ; the consequence of which is, that it 

 may now be obtained at one third of its former 

 cost; and it is taking the place of potash in those 

 manufactories that require an alkali. The process 

 followed in Great Britain is to convert common 

 salt into sulphate of soda by means of sulphuric 

 acid. The sulphate of soda is heated with sawdust, 

 or small dross of pit-coal, by which it is converted 

 into sulphuret of sodium. Sometimes the sulphur 

 is got rid of by means of lime, but more commonly 

 by roasting the sulphuret, so that air from a coal 

 fire passes through it. The sulphur is gradually 

 dissipated, and the sodium converted into carbonate 

 of soda. The matter thus treated is dissolved in 

 water, and subjected to two successive crystalliza- 

 tions in open iron coolers. By this process beauti- 

 ful crystals of carbonate of soda are obtained. 

 They in general contain about one half per cent, 

 of sulphate of soda. The crystals are large, fre- 

 quently eight or nine inches long, and are rhombic 

 prisms with dihedral summits. Its taste is similar 

 to that of the carbonate of potash, but less caustic. 

 Its specific gravity is 1-62. It dissolves in rather 

 less than its weight of boiling water, so that, when 

 dissolved in such water, it crystallizes as the solu- 

 tion cools. When exposed to the air, it very soon 

 effloresces, and falls to powder. When heated, it 

 undergoes the watery fusion; indeed, the soda of 

 commerce sometimes contains so much water of 

 crystallization, that, when once melted, it remains 

 permanently liquid. If the heat be continued, the 

 water gradually evaporates, and the salt becomes 

 dry. In a red heat, it melts into a transparent 

 liquid. A very violent heat drives off a part of 

 the acid. It melts rather more easily than carbo- 

 nate of potash, and for that reason it is preferred 

 by glass manufacturers. Its constituents are, 



Carbonate acid, 



Soda, 



Water. 



2-75 

 4-00 



n-25 



The trona, found in the province of Sukena, near 

 Fezzan, in Africa, and which occurs in hard, 

 striated masses, of such firmness that the walls of 

 Cassar, a fort now in ruins, are said to have been 

 constructed of it, differs from the carbonate of 

 soda in the proportion of its constituents. It is 

 called by doctor Thomson a sesquicarbonate of soda. 

 It consists of 



Carbonic acid, 



Soda, 



Water, 



4-125 

 4'00 

 2-25 



10-375 



It may be formed artificially by exposing the com- 

 mon carbonate of soda to an atmosphere of carbonic 

 acid gas, and is largely manufactured for the soda- 

 water makers, being sold in the condition of a white 

 powder. Its taste is alkaline, but much milder 

 than the common carbonate : specific gravity, 1 -98. 



