46 ON THE PREPARATION OF SODA AND CHLORINE. 



contrary becomes and remains hard aDd compact, and can only 

 with, difficulty, be taken out of the furnace. These blocks of 

 smelted material, which contain sulphur, sodium and iron, are im- 

 mediately broken up, and introduced in a boiler exactly similar to 

 that used for evaporating alkaline solutions in the ordinary me- 

 thod of manufacturing soda, in which the furnace is placed at one 

 end, and the flame and products of combustion pass over the sur- 

 face of the solution. On the introduction of the smelted material 

 into the water, it is partially dissolved, and the solution assumes a 

 deep greenish color, from dissolved sulphuret of iron. When 

 however heat is applied, and the carbonic acid from the furnace 

 produced in the combustion of the fuel, is passed over the 

 surface of the solution, it is gradually decolorized, carbonic acid 

 and oxygen being absorbed, and becomes a solution of carbonate 

 of soda with caustic soda. In the event of the solution being too 

 much evaporated before the decolorization is effected, water is ad- 

 ded, and the heatiDg and exposure to the carbonic acid and air 

 continued. During the whole of this operation the insoluble sul- 

 phuret of iron remains at the bottom of the boiler. "When the 

 supernatant solution has become colorless, the heat is discontinu- 

 ed, and the contents of the boiler allowed to settle. The clear 

 liquid is then drawn off by means of a syphon or stop-cock, and 

 water is added to residue. If this solution also becomes green, 

 it is decolorized in the same manner as the first. This second so- 

 lution is then drawn off in the same manner, and the oper- 

 ation repeated with fresh water, until the latter dissolves no more 

 soda from the residue. The first and more concentrated solutions 

 thus obtained are evaporated to dryness, the product is heated in 

 a carbonating furnace, and crystallized carbonate of soda and soda- 

 ash obtained from it in the usual manner. The weaker solutions 

 are used for treating fresh quantities of smelted material from the 

 furnace. The sulphuret of iron which remains after having been 

 thus repeatedy washed with fresh water-is run off from the bottom 

 of the boiler into a large wooden box, having a perforated false 

 bottom over which a linen cloth is spread. The greater part of 

 the water here drains off and the sulphuret of iron is then fit to 

 be treated in the manner next to be described. This production 

 of carbonate of soda and of soda, ash may be termed the second 

 part of the process. 



The insoluble sulphuret of iron obtained as above described, 

 while still in a moist state, is exposed, with as much surface as . 



