POTASH. 203 



primary form ; or in some of its varieties, as Fig. 27 and 28. Lustre, when crystallized, 

 vitreous; if delicately fibrous, pearly. Transparent to translucent. Hardness from 2.0 to 

 2.5. Specific gravity 1.75. Taste sweetish and astringent. Very soluble in water, and 

 the solution gives a white precipitate with carbonate of potash. When exposed to heat, it 

 melts in its own water of crystallization, froths up in a remarkable manner, and is converted 

 into a spongiform mass of anhydrous alum. It gives a violet colour to the fiame of the blow- 

 pipe. 



Composition. Potash 10. 10, alumina 10.80, sulphuric acid 33.70, water 45.40 [Gmelin). 

 The formula of the artificial salt, according to Kane, is (KO.S034-Al303+3S03)+24Aq. 



Geological Situation. Alum is generally found incrusting various kinds of slates and 

 shales. 



Uses. It is extensively manufactured, being largely used in dyeing, lake-making, dressing 

 sheep skins, clarifying liquors, etc. 



LOCALITIES. 



This salt is found in efflorescences in various parts of the State. It is often met with on 

 the Hudson river slate, as in Albany, Columbia, Saratoga and Oneida counties. 



In Ulster County, on the Catskill mountain, in argillaceous sandstone, extending four 

 miles north of the Clove passage ; also in the same mountain, southwest from Cairo, where 

 it is stalactitical.* It also occurs in efflorescences in the Shawangunk mountains, and else- 

 where in the county. 



Chautauque County. Alum earth is found in the tovra of Sheridan, from which alum is 

 formed by the action of the atmosphere. It is not, however, thought to be abundant. 



* J. Pierce. American Journal of Sdtnce, VI. 86. 



