696 



SODA AND SODA COMPOUNDS. 



may exist or result, is that of heating the dry 

 impure soda with sawdust, or with ground coal 

 or charcoal, in a reverberatory furnace, but not 

 to a heat exceeding 700 F., frequently turning 

 and stirring the mixture, until the burning jets 

 of carbonic oxide from it cease ; after which the 

 mass is to be again leached, and the lixivium 

 evaporated. In the more expeditious process 

 of Gossage, the sulphide of sodium is decom- 

 posed by a hyd rated oxide, as of lead, giving 

 caustic soda, which is carbonated by parsing 

 carbonic acid into the solution, and sulphide 

 of lead, which is precipitated. The precipitate 

 removed, its decomposition is effected by chlor- 

 hydric acid, giving sulphydric acid, which is 

 burned for sulphuric acid, and chloride of lead, 

 which by means of lime is restored to the hy- 

 drated oxide for re-use. 



Other methods of obtaining a comparatively 

 pure monocarbonato of soda' (NaO.CO,) are 

 also in use. For removing ordinary impurities, 

 of course, the lixiviation of the alkali may be 

 once or more repeated. The conversion of the 

 monocarbonate into the bicarbonate (NaO. 

 C0 2 , HO.00. 2 ) is effected either by passing 

 into a solution of the former a stream of 

 carbonic acid, or by exposing the crystallized 

 monocarbonate to the action of carbonic acid 

 gas. In the method of Schlosing and Rol- 

 land, common salt being at the outset dis- 

 solved in water, ammonia and carbonic acid 

 are successively added, with production at first 

 of bicarbonate of ammonia, and then (by re- 

 action) of bicarbonate of soda and chloride of 

 ammonium. The former can, if desired, be 

 reduced to the monocarbonate by heating. 

 The chloride of ammonium being boiled with 

 lime, the ammonia is re-formed for use again. 

 Finally, when the hydrated or caustic soda is 

 the article desired, this is readily obtained by 

 treating a solution of the monocarbonate with 

 milk of lime, the resulting carbonate of lime 

 separating by precipitation. 



Theory of Leila-no's Process. This pro- 

 cess has of late been discussed from a theoret- 

 ical point of view by different writers, among 

 them especially by M. J. Kolb and by M. 

 Pelouze. M. Kolb considers that, in a heated 

 mixture of one equivalent of sulphate of soda, 

 one equivalent of chalk, and three equivalents 

 of carbon, in an atmosphere of carbonic acid, 

 the following reactions take place, and in a 

 manner simultaneously: 



Oa0.00 3 + G = 20O (burnt in furnace) + 

 CaO; 



NaS + CaO + OOa (in excess) = NaO.CO,+ 

 CaS. 



The proportibns here given correspond to sul- 

 phate of soda 100 parts, carbonate of lime 70.4, 

 and carbon 25.5 parts, by weight ; and theoreti- 

 cally the mixture should yield 74.0 parts of mono- 

 carbonate of soda. In reality, however, it will 

 commonly yield only about 62 parts, in carbonate 

 and hydrate of soda, the causes being such as 

 that of imperfect mixing, loss of some carbon 



by burning, failure to maintain the proper tem- 

 perature, etc. The author judges that the best 

 practicable yield of soda is obtained when the 

 proportions of sulphate, chalk, and carbon are 

 100, 94, and 44, the yield then being of carbo- 

 nate of soda 64.20, and of caustic soda 4.72 

 parts, the whole equivalent (when the latter 

 has been carbonated) to 72.2 parts of carbonate 

 of soda. He thinks, however, the excess of, 

 chalk and charcoal a difficult matter to state 

 generally that it must be left to the discretion 

 of the manufacturer, and will depend in a 

 measure on the form of his furnace, the method 

 of stirring, and other points. Ohem. News, 

 March 23, 1866, from Ann. de Chim., etc., Feb- 

 ruary, 1866. 



In another paper, M. Kolb argues also, 

 consistently with his view of the reactions 

 above given, and at variance with the theory 

 of the change previously presented from Ure, 

 that the carbonic acid of the chalk does not 

 contribute to the formation of the carbonate of 

 soda, but that it is especially from the gases of 

 the furnace [referring doubtless in part at 

 least to the carbonic acid generated by burn- 

 ing of the oxide of carbon] that the final re- 9 

 action results: N"aS, OaO, and CO 2 then re- 

 sulting in NaO.CO 2 and CaS. The author 

 considers the action, respectively, of dry air, of 

 moist air, and of water, on the rough or crude 

 soda. He finds that from to 100 0., per- 

 fectly dry air exerts no sensible action on crude 

 soda, not even by its carbonic acid ; but that 

 somewhat below and at a red heat, dry air oxid- 

 izes some sulphide of calcium into sulphate of 

 lime, which then lowers in a degree the alka- 

 limetric richness of the lixivium. Moist air 

 acts very energetically, some lime present being 

 hydrated and then carbonated, while part of the 

 still remaining sulphide of sodium is transformed 

 into sulphate of soda, either directly or through 

 intervention of the oxide of iron present here 

 [it would appear, referring to soda obtained by 

 Kopp's process], and which keeps up the trans- 

 formation by being indefinitely regenerated. 

 The action of water on crude soda is to give 

 a lixivium of varying composition, depending 

 on these conditions the concentration of the 

 liquid, the duration of the digestion, and the 

 elevation of the temperature. The last two of 

 these favor the caustifying of part of the car- 

 bonate of soda by lime, and a slow, and of 

 course wasteful, reaction between the carbonate 

 of soda and sulphide of calcium. The first- 

 named condition, and the presence of caustic 

 soda, as also of lime, oppose this last formation.' 

 A little fresh lime would then seem desirable in 

 rough sodas, as having the effect of producing 

 small quantities of caustic soda, and thus op j 

 posing an obstacle to the sulphuration of the 

 lixivium. (Ohem. News, April 6, 1866, from 

 Oompt. Bend., Ixii., 638.) A more full discus- 

 sion of the topics here considered, and with 

 tabular statements, is commenced in the Chem. 

 News, July 13, 1866, vol. xiv., p. 16, an abstract 

 from Ann. de Chim., etc., June, 1866. 



