472 SODIUM. 



distant from the fire; the chimney is provided with a damper p y 

 by which the draught is regulated. 



(1) The sulphate of soda is prepared by throwing 600 pounds 

 of common salt into the chamber of the furnace, already well 

 heated^ and running down upon it from an opening in the roof, 

 an equal weight of sulphuric acid of density 1.600, in a moderate 

 stream. Hydrochloric acid is disengaged and carried up the 

 chimney, and the conversion of the salt into sulphate of soda is 

 completed in four hours. (2) The sulphate thus prepared is 

 reduced to powder and mixed with an equal weight of ground 

 chalk, and half its weight of small coal ground and sifted. This 

 mixture is introduced into a very hot reverberatory furnace, 

 about two hundred weight at a time. It is frequently stirred 

 until it is uniformly heated. In about an hour it fuses, is then 

 well stirred for about five minutes, and drawn out with a rake 

 into a cast iron trough, in which it is allowed to cool and solidify. 

 This is called ball soda or British barilla, and contains about 22 

 per cent of alkali. (3) To separate the salts from insoluble 

 matter, the cake of ball soda, when cold, is broken up, put into 

 vats, and covered by warm water. In six hours the solution is 

 drawn off from below, and the washing repeated about eight 

 times, to extract all the soluble matter. These liquors being 

 mixed together are boiled down to dryness, and afford a salt 

 which is principally carbonate of soda, with a little caustic soda 

 and sulphuret of sodium. (4) For the purpose of getting rid 

 of the sulphur, the salt is mixed with one-fourth of its bulk of 

 sawdust, and exposed to a low red heat in a reverberatory 

 furnace for about 4 hours, which converts the caustic soda into 

 carbonate, while the sulphur also is carried off. This product 

 contains about 50 per cent of alkali, and forms the soda-salt of 

 best quality. (5) If the crystallized carbonate is required, the 

 last salt is dissolved in water, allowed to settle, and the clear 

 liquid boiled down until a pellicle appears on its surface. The 

 solution is then run into shallow boxes of cast iron to crystal- 

 lize, in a cool place ; and after standing for a week the mother 

 liquor is drawn off, the crystals drained, and broken up for the 

 market. (6) The mother liquor, which contains the foreign 

 salts, is evaporated to dryness for a soda salt, which serves for 

 soap or glass making, and contains about 30 per cent, of alkali. 



The most essential part of this process is the fusion of sul- 

 phate of soda with coal and carbonate of lime ; by the first, the 

 sulphate is converted into sulphuret of sodium (page 448), and 



