SODA, CARBONATE OF 



855 



furnace and condensing towers, by connecting the first ifcwcr with the second, as re- 

 presented at ff, and the second tower with the main chimney, K, of the works. In 

 tlio first bed of the furnace, about half of the common salt is decomposed, leaving a 



1855 



mixture of bisulphate of soda and common salt, which requires a greater heat for the 

 expulsion of this latter portion of hydrochloric acid ; for this purpose it is pushed 

 through a door into the roaster, or second division, B, of the furnace. 

 The reaction in the first bed of the furnace is represented as follows : 



2XTaCl 



2HO.S0 3 = NaO.SO 3 . HO.SO 3 + 



Sulphuric acid. Bisnlphate of 



soda. 



H- SO 1 :-= WaHSO 1 



HC1 



Hydrochloric 

 acid. 



BC1 



NaCl. 



Common salt. 



Nad 



By the higher temperature obtained in the second part of the furnace, the bisul- 

 phate of potash reacts on the undecomposed chloride of sodium, yielding neutral 

 sulphate of soda and a fresh quantity of hydrochloric acid. 



NaO.SO 3 . HO.SO 3 + 

 Bisnlphate of soda. 



NaHSO 4 + 



NaCl 

 Common salt. 



2(NaO.S0 3 ) 



Na SO 1 



HC1. 



Hydrochloric 

 acid. 



HC1 



The hydrochloric acid gas, as it is liberated from B, passes off through the flue, d, 

 and is carried on to the condensing towers. Heat is applied to the outside of the 

 roaster, B; the smoke, c, circulating in separate flues around the chamber, in the direc- 

 tion indicated by the arrows, but never coming into contact with the salt-cake in B. 



The process used at present in the Tyne district differs but little from that above 

 described, with the exception that in the decomposition of the mixture of bisulphate 

 of soda and common salt, in the second portion of the furnace, the smoke and pro- 

 ducts of combustion from the fire, are allowed to come in contact with the materials, 

 and the hydrochloric acid which is then given off is carried into condensing towers 

 filled with bricks over which water is continually slowly running, and the dilute 

 hydrochloric acid, thus obtained, is used for the liberation of carbonic acid in the 

 manufacture of bicarbonate of soda. The first part of the furnace is a circular metal 

 pan, and the hydrochloric acid from this, being unmixed with smoke, &c., is condensed 

 apart from the other. 



The next step in the manufacture is the decomposition of the sulphate of soda into 

 sulphide of sodium, and its subsequent conversion into carbonate of soda. This is 

 effected in the following manner: The dry sulphate of soda, obtained by the process 

 above described, is mixed with small coal and chalk, or limestone, in about the fol- 

 lowing proportions : sulphate of soda 3 parts, chalk 3J parts, and coal 2 parts. It 

 is necessary that these materials should bo first separately ground, and sifted into a 

 tolerably fine powder, and then carefully mixed, as a great deal depends on the atten- 

 tion to these points. The mixture is then subjected to heat in a reverberatory furnace, 

 Jigs. 1856, 1857, 1858. 



In the section/^. 1857, there are two hearths in one furnace, the one elevated above 

 the level of the other by the thickness of a brick, or about three inches. A is the 



