6 • BULLETIN 415, U. S. DEPAETMENT OF AGKICULTTJEE. 



three hours. The ignited mass is then treated with the proper quan- 

 tity of sulphuric acid (30° B.) to convert the alumina present into 

 sulphate. After standing for some time an amount of potassium sul- 

 phate is added sufGicient to convert the aluminum sulphate into the 

 double salt. The clear liquid is then decanted off and evaporated 

 until the potash alum crystallizes out. The reactions on heating to 

 800° C. may be represented thus: 



Alunite. 



K20.3Al203.4S03.6H20= 



Potassium Alumina. Sulphur Water, 



sulphate. trioxide. 



K2SO4 + 3AI2O3 + 3SO3 + 6H2O 



2. 



3. 



Alumina. Sulphuric acid. Aluminum sidphate. Water. 

 3AI2O3 + 9H2SO4 = 3Al2(S04)3 + 9H2O 



Aluminum Potassium Water, 



sulphate. sulphate. 



3Al2(S04)3 + 3K2SO4 + 144H20= 



Potash alum. 

 6 KAl (804)2 24H2O 



In the production of alum from the alunite occurring at Bullah 

 Delah, Austraha/ a process similar to that just described is practiced, 

 but no particular temperature of ignition is specified and the excess 

 of alumina is not converted into alum by the addition of potassium 

 sulphate, since it is considered more profitable to manufacture 

 aluminum sulphate as a by-product and to produce alum equivalent 

 only to the potash present in the alunite. This practice is no doubt 

 the best in localities far removed from other sources of potash. 



While it was not the purpose of the present investigation to study 

 details of alum manufacture, it would seem that in regions where 

 another source of potash is readUy and cheaply available a combina- 

 tion of the two processes outlined above promises greater possibihties 

 than either of the methods employed at present. 



In brief, it is thought that the ignition of alunite at a moderate 

 temperature (500° to 550° C.) and subsequent treatment with sul- 

 phuric acid and potassium sulphate would mean a saving both in 

 fuel and in the quantity of acid required to convert all the alumina 

 of the mineral into alimi. 



THE PRODUCTION OF POTASH FROM ALUNITE. 



Besides the processes just outhned for the production of alum six 

 general schemes have been proposed for the utilization of the potash 

 in alunite for other purposes. 



1 Pittmaaij E. P. Alunite in New South Wales. Report Geol. Survey New South Wales (1901). 



