I 



and Mamifacture of Sulphate and Muriate of Potash. 99 



The muriates of potash and soda will not vaporise freely when 

 fused and highly heated, unless the atmosphere ahove them is con- 

 tinually changed. This may be effected by a current of steam, and 

 I find that I can sufficiently regulate the quantity of the salt vola- 

 tilised from the retort, by the amount of steam which I blow over 

 its melted surface. I therefore insert a small steam pipe into the 

 top of the retort, so as to throw a jet of heated steam upon the sur- 

 face of the melted salt, and thus force its vapour to enter the cylinder. 

 The quantity of steam thus introduced to aid the volatilisation, is not 

 sufficient to decompose all the salt volatilised. The rest of the steam 

 necessary for this purpose is passed directly into the cylinder by a fire- 

 clay pipe entering it near the bottom, and connected through a series 

 of fire-clay tubes kept red hot with a steam boiler. Both steam 

 pipes are provided with cocks ; an escape tube is inserted into the top 

 of the cylinder, to convey the acid vapour and the vapour of any un- 

 decomposed muriate into suitable condensers. I have an opening in 

 this tube, by which I can withdraw at times a portion of the vapours 

 in it, to examine their saline and acid characters. 



Tlie cylinder and retort are to be so constructed and arranged, as 

 to allow their contents to be heated to high redness and upwards, by 

 any of the well-known means. The mode of operating is as follows : 

 The discharging door being closed air-tight, I fill the cylinder with 

 alumina in pieces of about a quarter of an inch in diameter, and fill 

 the retort with the muriate of potash or soda, and then close both 

 the charging door of the cylinder and that of the retort air-tight. I 

 now bring the cylinder to a high red or white heat, and the retort to 

 a cherry-red heat, so that the salt in it is melted and ready to vola- 

 tilise freely at the admission of steam upon its surface. Steam is 

 now passed from the boiler through the red-hot tubes into the cy- 

 linder by the pipe entering near its bottom, so that it is filled with 

 highly-heated steam passing upward in a slow current through the 

 interstices of the pieces of alumina. I now admit, by degrees, a jet 

 of heated steam into the salt retort, by the pipe entering its top, and 

 thus drive a quantity of salt vapour into the cylinder, where it mixes 

 thoroughly with the current of steam which has entered by the other 

 pipe, and ascends with it through the column of highly-heated alu- 

 mina. In its passage, the alkaline base of the muriate combines with 

 the alumina, forming an aluminate of potash or soda, and the muri- 

 atic acid, together with any salt vapour which may have escaped de- 

 composition, passes off with the steam through the escape tube at 

 the top of the cylinder into the condensers provided. The progress 

 of the operation can be ascertained by examining the nature of the 

 vapours which are passing through the escape tube. 



When these vapours contain a large quantity of salt, and are strongly 

 acid at the time, I admit more steam through the pipe leading di- 

 rectly into the cylinder, and if this does not have the efl:ect of dimi- 

 nishing the quantity of salt in the vapours, I lessen the quantity of 



