202 



DESCRIPTIVE MINERALOGY. 



MURIATE OF POTASH. 



Chloride of Potassium, of Chemists. 



Description. This salt occurs in cubic crystals, which liave a saline and bitter taste, and 

 are destitute of water. It is soluble in three parts of water at 60° Fahr., producing so much 

 cold as to be employed as a freezing mixture. 



Composition. Potassium 52.60, chlorine 47.40; the formula being KCl. 



Chloride of potassium exists in the water of many brine springs, in sea water, and in the 

 ashes of plants. Its principal use is in the manufacture of alum. 



HYDROBROMATE OF POTASSA. 



Bromide of Potassium, of Chemists. 



Description. This salt, which has been detected in very minute quantities in the Sara- 

 toga waters, crystallizes in cubes or in rectangular prisms. The crystals being destitute of 

 water, decrepitate when heated, and enter into fusion without suffering any change. It is 

 very soluble in water, and slightly so in alcohol. It may be recognized, by giving, with oil 

 of vitriol, orange red fumes of bromine. 



Composition. Potassium 33.42, and bromine 66.58. Formula KBr. 



ALUM. 



[From its containing alumina.] 



Alumine Sulfatee Alkaline. Haiiy, — Sulphate of Alumine and Potash. Ckaveland. — Alum. Phillips and 

 Shcpard. — Native Alum. Dana. — Potash Alum. Thmison. — Octahedral Alum. Jameson. — Octaedrisches 

 Alaun-Salz. Mohs. 



Fig. 26. 



Fig. 27. 



Fis. 28. 



Description. Colour white or greyish. It occurs in crystals ; but more frequently in 

 farinaceous effloresences on argillaceous minerals, or in concretions, stalactites, and fibrous 

 masses. When artificially prepared, it crystallizes in the octahedron, Fig. 26, which is its 



