ALUM STONF- 129 



ivium. A^precipitate of alum falls which is afterwards wash- 

 ed and re-crystallized. The mother liquor left after the pre- 

 cipitation is also treated for more alum. This process is 

 carried on extensively in Germany, France, at Whitby in 

 Yorkshire, Hurlett and Campsie, near Glasgow, in Scot- 

 land. Cape Sable in Maryland, affords large quantities of 

 alum annually. The slates of coal beds are often used to 

 advantage in this manufacture, owing to the decomposing 

 pyrites present. At Whitby, 130 tons of calcined schisc 

 give one ton of alum. In France, ammoniacal salts are 

 used instead of potash, and an ammoniacal alum is formed. 

 Soda alum has been observed at the Solfataras in Italy, 

 near Mendoza in South America, on the island of Milo in 

 the Grecian Archipelago. Magnesia alum forms large fib- 

 rous masses, delicately silky, near Iquique, S. A. This is 

 the Pickeringite of Mr. A. A. Hayes. Ammonia alum oc- 

 curs at Tschermig in Bohemia. 



Alunite. — Alum Stone. ~t\°\. 



Rhombohedral, with a perfect cleavage parallel with a, 

 (fig. 62, p. 39.) R : R=89° 10'. Also massive. Color 

 white, grayish or reddish. Luster of crystals vitreous, or a 

 little pearly on a. Transparent to translucent. H=4. Gr= 

 2-58— 2-75. 



Composition : sulphuric acid 38-5, alumina 37*1, potash 

 11*4, water 13*0=100. Decrepitates in the blowpipe flame 

 and is infusible both alone and with soda. In powder, sol- 

 uble in sulphuric acid. 



Dif. Distinguished by its infusibility, in connection with 

 its complete solubility in sulphuric acid without forming a 



Obs. Found in rocks of volcanic origin at Tolfa, near 

 Rome, and also at Beregh and elsewhere in Hungary. 



Uses. At Tolfa, alum is obtained from it by repeatedly 

 roasting and lixiviating it and finally crystallizing by evapo- 

 ration. The variety found in Hungary is so hard as to ad- 

 mit of being used for millstones. 



Websterite. Another sulphate of alumina, in compact reniform 

 masses and tasteless. From Newhaven in Sussex, Epernay in France, 

 and Halle in Prussia. It is called also aluminite. V 



What is the color and appearance of alum stone? What its compo- 

 aition ? What its use, and where is it extensively employed? 



