ALUM, NATIVE 



123 



various degrees of impurity, sometimes with a smaller amount of water. Knapp has 

 collected the list of analyses shown in the Table : 



Analyses of Natural Sulphate of Alumina or Feather Alum. 



MTATIVE. This term includes several compounds of sulphato of 

 alumina with the sulphate of some other base, as magnesia, potash, soda, the pro- 

 toxides of iron, manganese, &c. They occur generally as efflorescences, or in fibrous 

 masses ; when crystallised they assume octahedral forms ; they are soluble in water, 

 and have an astringent taste. The following species are the chief native alums, but it 

 should be understood that the proportion of water of crystallisation is not the same in 

 all, and hence in some cases they cannot be brought within the general formula given 

 under the aifcicle ALUM. 



Kalinite, or Potash Alum, found as an efflorescence on alum-slate at Whitby, Hurlet 

 and Campsie. 



Mendozite t or Soda-alum, fbund in South America. The following analyses may 

 be cited : 



Soda-alum from Peru, by T. Thomson. 

 Sulphate of soda . . . 6-50 



Alumina. .... 22*55 

 Sulphuric acid . . . 32-95 

 Water . ... 39-20 



101-20 



Soda-alum from the Andes. 



Sulphuric acid . . .36-199 



Alumina .... ITSll 



Soda 7-259 



Water . ... . . 43-819 



Silica 0-180 



Lime . . . . . 0-255 



Peroxide of iron . . . 0-199 



Protoxide of iron . . . 0-760 



100-162 



TscKermigite, or Ammonia-alum, found at Tschermig in Bohemia. Analyses have 

 been made of specimens from Tschermig, by Stromeyer : 



Alumina . . . 



Ammonia . . . 



Magnesia . . . 



Sulphuric acid . . 



Water. . . . 



Pickeringite, or Magnesia-alum, found near Iquique in Peru, and in Nova Scotia, 

 Ayjohnite, or Manganege-alum, from Lagos Bay in South Africa. 



