2 ALUNTTE AS A SOURCE OF POTASH. 



The pyrometer A was introduced into the tube B (preferably made 

 of quartz) containing the sample of alunite and heated by the burn- 

 ers or furnace C. A solution of sodium carbonate was contained in 

 the dropping funnel D. The flask E containing water colored with a 

 few drops of methyl orange was connected with an aspirator. 



The burners were lighted and a gentle stream of air drawn through 

 the apparatus, while the temperature, shown by the pyrometer, and 

 the color of the methyl orange in the flask E were carefully watched. 



At 520 C. the oxides of sulphur began to come over and the color 

 of the methyl orange changed to red. The acidity was neutralized 

 by dropping in a little sodium carbonate from the funnel D. At 

 530 C. the evolution of gas became quite copious and the methyl 

 orange again changed color. A drop or two of sodium carbonate was 

 added and the temperature was kept at this point for 20 or 30 

 minutes. It was then increased to 670 C., where the methyl orange 

 again became red. Another drop of sodium carbonate was added 

 and the temperature slowly increased to 750 C. Apparently no 

 more gas was evolved above a temperature of 700 G. 



The residue in the tube was then removed and washed repeatedly 

 with hot water. It was found very difficult to wash the residue en- 

 tirely free from soluble sulphates. At first sight this might be ex- 

 plained by hydrolysis of the aluminum sulphate and selective absorp- 

 tion of the alumina. The washings, however, gave no precipitate 

 with ammonia or lime water, thus showing the absence of soluble 

 aluminum compounds and indicating that the decomposition was 

 practically complete. 



In order to see how much sulphur trioxide could be actually recov- 

 ered by heating alunite and collecting the evolved gases, a sample of 

 10 grams was ignited in a combustion tube drawn out and attached 

 to an absorption train as shown in figure 2. Both the flask B and the 

 absorption bulbs C, C', G" contained a solution of caustic potash. 

 The furnace was started and a gentle stream of air drawn through 

 the apparatus. Great care had to be exercised to prevent the gases 

 evolved from the alunite from passing through the entire train and 

 escaping. 



After heating the charge for a part of two days (eventually carry- 

 ing the temperature to 700 C.) the contents of the absorption train 

 were emptied into a beaker, the bulbs and flask were carefully rinsed 

 into the same beaker, the solution rendered slightly acid with hydro- 

 chloric acid, and made up to definite volume. Aliquots of this were 

 then taken for analysis. 



The temperature at which the final decomposition of the alunite 

 takes place (viz, 700 C.) is far above that at which sulphur trioxide 

 is decomposed. Much of the gas evolved, therefore, was sulphur 



[Cir. 70] 



