07 
CONCLUSIONS. 
(1.) A1 unite is unaffected by dry heat at temperatures lip to 
300° C. 
(2.) The decomposition of the mineral in alum roasting’ is in 
two stages. At 400° C. the mineral loses four and a half molecules 
of water with the formation of a basic sulphate of aluminium and 
potash, and on further heating to a temperature of 500° 0., the re- 
maining water is removed, forming an anhydrous basic sulphate. 
On the addition of water the basic sulphates dissociate, producing a 
true alum and precipitating aluminium hydrate. 
(3.) Alunite heated to a temperature of 800° 0. dissociates 
completely into potassium sulphate, alumina, sulphur trioxide and 
water. Part of the sulphur trioxide dissociates further into a mix- 
ture of sulphur dioxide and oxygen. 
(4.) On heating alunite to a temperature of 960° C., the potas- 
sium sulphate formed is dissociated and interacts with the alumina 
to form soluble potassium aluminate, or, in the presence of silica, 
insoluble potassium alumino-silicates. 
(5.) Alunite is readily soluble in warm dilute solutions of 
caustic alkali, hydrofluoric acid, and hot strong sulphuric acid. 
(().) Alunite is slowly soluble in cold solutions of sodium car- 
bonate, but readily soluble in warm solutions of that reagent. 
(7.) Alunite is moderately soluble in hydrochloric acid and 
warm dilute sulphuric acid. 
(8.) Alunite is sparingly soluble in water. 
(9.) Alunite is attacked fairly readily by a solution of caustic 
lime, the whole of the potash passing into solution. 
(TO.) Alunite is appreciably attacked by calcium carbonate 
solutions. 
I wish to express my deep appreciation to my Chief, Dr. E. 8. 
Simpson, who has given me every encouragement to pursue these 
investigations, for the great interest lie has taken in this work, and 
the way in which he has at all times been ready to assist me with 
suggestions and give advice when it was most urgently needed. L 
wish to thank Mr. E. M. .Toll for his careful work and interest shown 
in carrying out the digestion experiments with caustic lime and cal- 
cium carbonate, 1 also wish to acknowledge the courtesy of the 
Hon,, the Minister for Mines in giving permission to publish the 
figures shown in Tables I., 11., and ITT. 
