SODA, CARBONATE OF 859 



the coal into carbonic acid, and to present the carbonic acid to tlio particles of caustic 

 soda diffused through the mass, so that it may combine with them. 



"When the blue flames cease, and the saline matters become -white, in the midst of 

 the coaly matter, the batch may be considered as completed. It is raked out, and 

 when cooled, lixiviated in great iron cisterns with false bottoms, covered with mats. 

 The watery solution being drawn off clear by a plug-hole, is evaporated either to 

 dryness, in hemispherical cast-iron pans, as above described, or'only to such a strength 

 that it shows a pellicle upon its surface, when it may be run off into crystallising 

 cisterns of cast-iron or lead-lined wooden cisterns. The above dry carbonate is the 

 best article for the glass manufacture. 



Instead of this last process of roasting with sawdust, Gossage decomposes the 

 sulphide of sodium present in the lye obtained from the ball soda, by means of tho 

 hydrated oxide of some metal, as of lead, thus forming sulphide of lead, and hydrate 

 of soda ; this is then converted into carbonate by passing a stream of carbonic acid 

 through it. The precipitated sulphide of lead is decomposed by hydrochloric acid, 

 thus generating sulphuretted hydrogen, which is burnt and converted into sulphuric 

 acid ; the lead is then converted again into h)'drated oxide by means of lime. This 

 process saves the trouble, time, and fuel used in evaporating to dryness twice as in 

 the ordinary process. 



Various attempts have been made to obtain processes which shall supersede the pro- 

 cess above described, of manufacturing carbonate of soda from common salt. 



Sulphate of iron, being a cheap article, has been heated with common salt, in- 

 stead of using sulphuric acid ; sulphate of soda is formed, and the chloride of iron, 

 being volatile, passes away. By roasting iron or copper pyrites directly with 

 chloride of sodium, sulphate of soda has been obtained, and it has been found possible 

 by this means also to extract the metal from ores of copper or tin with advantage, 

 which are otherwise too poor to work. Mr. Tilghman effects the decomposition of 

 chloride of sodium by steam at a high temperature, in the presence of alumina. 

 Precipitated alumina is made up into balls with chloride of sodium, and exposed to a 

 current of 'steam in a rcverberatory furnace strongly heated. Hydrochloric acid is 

 expelled, and the alumina unites with the soda. When cold, this compound of alumina 

 and soda is decomposed by a current of carbonic acid, .and the carbonate of soda is 

 dissolved, and thus separated from the alumina, which may be again used. Another 

 process is that of MM. Schlcesing andEolland. They dissolve the chloride of sodium 

 in water, and then pass ammonia into it, and afterwards carbonic acid ; bicarbonate of 

 ammonia is first produced, and then double decomposition takes place ; chloride of 

 ammonium is formed, and the more sparingly soluble bicarbonate of soda is precipi- 

 tated in crystalline grains ; it is then separated from the liquid and pressed, to free it 

 "as much as possible from the chloride. This bicarbonate of soda is converted into 

 the monocarbonate by heat, and the carbonic acid thus evolved is used again ; the 

 solution, from which the bicarbonate has separated, is bciled to drive off any ammonia 

 that it may contain, as carbonate of ammonia, which is. collected ; the solution is then 

 boiled with lime, whick liberatcs.tb.e ammonia fcom the chloride of ammonium, and 

 thus little loss is sustained. 



There are three carbonates of soda : 



Monocarbonate. NaO.CO 2 + 10HO (UTa'CO'-f 10H=O). This is the salt which is 

 obtained in the ordinary soda-manufacture. In the crystalline state, it generally con- 

 tains ten equivalents of water of crystallisation, or sixty -three per cent., but has been 

 obtained with only eight, five, and even one equivalent of water. It effloresces in a 

 dry atmosphere, at the same time absorbing carbonic acid. It is very soluble in water, 

 requiring only twice its weight of water at 60 for solution, and even melts in its 

 own water of crystallisation when heated, and eventually by increase of temperature 

 becomes anhydrous. It is generally found in commerce in large crystals, which 

 belong to the oblique prismatic system. It is strongly alkaline, and acts on the skin, 

 dissolving the outside cuticle. It is largely iised in the manufacture of soap, glass, &c. 



Sesquicarbonatc. 2(NaO.C0 2 ),HO.C0 2 (aWa^CO'.H'CO 8 ). This salt is frequently 

 found native. See NATRON. 



Bicarbonate. NaO.C0 2 ,HO.C0 2 (WaHCO 3 ). This salt is found in some mineral 

 waters, as those of Carlsbad and Seltzer ; and is obtained from the waters of Vichy 

 in large quantities. 



It is prepared by saturating the monocarbonate with carbonic acid, for which 

 purpose several methods are employed. 



1. By passing carbonic acid into a solution of the monocarlonate. A cold satu- 

 rated solution of the monocarbonate of soda is made, and carbonic acid obtained 

 by the action of hydrochloric acid on marble or chalk, is passed into it; tho bi- 

 carbonate forms and precipitates to a great extent, and is then collected, and pressed 

 to remove as much of the adhering liquid as possible. A fresh portion of the 



