PHYSIOGRAPHY. 



Alum Alum-stotie. 



1. Alum is very soluble in water, melts before the blow-pipe iu its 

 water of crystallization, and is converted into a spongiform mass. 



2. Analysis. 



Potash 9-94 



Alumina 10-82 



Sulphuric acid .... 33-77 

 Water 45-47 



3. It occurs in a state of efflorescence upon minerals and rocks which 

 contain alumina, potash and sulphuret of iron ; as upon alum-stone, alum- 

 slate and mica-slate : it is also found accompanying brown-coal, and is 

 contained in the waters of certain mineral springs. 



4. Alum occurs on the alum-slate rocks near Christiania in Norway, 

 and under the same circumstances as near Moffat in Dumfries-shire, and 

 Ferry-town of Cree in Galloway ; on bituminous shale and slate-clay at 

 Hurlet near Paisley in Scotland : in coal mines in Bohemia, Bavaria and 

 Italy ; and in various places, too numerous to be mentioned, in New- 

 England, upon mica-slate. * 



5. This salt, as produced by nature, requires first to be purified, in or- 

 der to be fitted for the purposes of the arts. Its artificial solution affords 

 it in regular crystals, having the form of the regular octahedron. A 

 great quantity of alum is obtained by the aid of chemical processes. Its 

 uses are various ; as for instance, in dyeing, in medicine, for the manu- 

 facture of leather and paper, and the prevention of putrefaction. 



ALUMINITE. (See Websterite.) 



ALUM-STONE. Rhombohedral Alum-Halo- 

 id e. MOHS. 



Primary form. Rhomboid. P on P 92 50' r. g. 



Secondary form. The primary form with one or more 

 of its lateral solid angles replaced by tangent planes. 



Cleavage parallel with the tangent secondary planes rath- 

 er perfect, that parallel with the primary faces indistinct. 

 The primary faces sometimes streaked parallel to the edges 

 of the secondary faces. 



Lustre vitreous, inclining to pearly upon the more dis- 

 tinct faces of cleavage. Color white, sometimes reddish 

 or greyish. Streak white. Transparent . . . translucent. 



