98 On the Decomposition of Substances by Steam, 



phosphate of soda and the sulphate of alumina, and adding to the 

 solution a slight excess of ammonia. I mix the alumina, in the state 

 of powder, with an equal weight of the sulphate of potash or of soda, 

 also powdered, and spi-ead the mixture upon the hearth of a rever- 

 berating furnace, such as I have before described for the decompo- 

 sition of the sulphate of bai-yta. The mixture is then heated, ex- 

 posed to steam, stirred, and the operation conducted in all respects 

 in the manner described for the treatment of the sidphate of baryta. 

 When it is desired to collect the sulphuric and sulphurous acids pro- 

 duced by the decomposition of the sulphates of potash and soda, I 

 prefer to moisten the mixture of alumina and the sulphate with 

 water, and form it into balls about half an inch in diameter, which 

 I heat and expose to steam in a close cylinder, in the manner for- 

 merly described for the sulphate of lime. When a specimen of the 

 charge shews by the usual tests that it contains no notable proportion 

 of sulphate undecomposed, the operation is completed. I then with- 

 draw the charge, lixiviate it with hot water, and when the clear solu- 

 tion of aluminate of potash or soda thus obtained has become cold, I 

 pass through it an excess of carbonic acid, until no more precipitate 

 of alumina is formed. The clear solution of carbonate of potash or 

 soda is then drawn off, and evaporated. The alumina thus recovered 

 is again used as the combining substance. When I wish to obtain 

 the aluminate of potash or of soda, I merely evaporate the solution 

 above described, without introducing the carbonic acid. 



The muriate of potash or of soda, I merely evaporate the solution 

 above described, without introducing the carbonic acid. 



The muriate of potash or of soda may also be decomposed when 

 in a fused state by the action of steam ; alumina or the subphos- 

 phate of alumina being present, the operation is to be conducted in 

 all respects in the same manner as that just described for the sul- 

 phates of potash and soda. But owing to the great volatility of the 

 muriates of potash and soda, when exposed at a high temperature to 

 a current of air or steam, a large quantity of the muriate will escape 

 with the steam and gases of the fire in the state of vapour undecom- 

 posed, and will be lost or will be difficult to condense. I prefer 

 therefore to effect the decomposition of the muriates of potash and 

 soda by causing their vapours, intimately mixed with highly-heated 

 steam, to pass slowly through a mass of small pieces of alumina kept 

 at a high red heat. I use for this purpose a vertical fire-clay 

 cylinder lined with a coating of native carbonate of magnesia to dimi- 

 nish the corrosion of its sides by the alkali, and made with conve- 

 nient openings at top and bottom, for charging and discharging, 

 which openings should be capable of being closed air-tight. I ar- 

 range a cast-iron retort, so that its tube enters directly the cylinder 

 near its bottom. The retort should have a charging door at the top, 

 capable of being made air-tight, through which is introduced the 

 muriate of potash or soda to be decomposed. 



