196 



DESCRIPTIVE MINERALOGY. 



tions to the Institute of Egypt. It was in consequence of the views of this celebrated 

 chemist, that the manufacture of carbonate of soda from common salt, now so extensively 

 carried on, was first established. 



COMMON SALT. 



Sonde Muriatfe. Haay, — Muriate of Soda. Cleaveland and PhiUips. — Hexahedral Rock-Salt. Jameson. — 

 Hexaedrisches Stcinsalz. Mohs. — Salmare. BeudarU. — Common Salt. SKepard and Dana. — Chloride of 

 Sodium, of Chemists. 



Description. Color usually grey or white ; sometimes also blue, red, yellow and green. 

 It occurs in granular, fibrous, radiated and prismatic concretions ; also massive, dentiform and 

 stalactitic. Lustre between vitreous and resinous. More or less transparent and translucent. 

 Hardness 2.0. Specific gravity from 2.12 to 2.30. 



Fig. 21. 



Fig. 22. 



Common salt is soluble in twice its weight 

 of water at 60° Fahr., and is but little more 

 soluble in hot water. From this solution, 

 regular cubes (Fig. 21) of a white colour 

 may be obtained by spontaneous evaporation ; 

 or if heat be applied to the solution, and then 

 withdravra, it forms hollow quadrangular pyra- 

 mids, resembling Fig. 22. These crystals are 

 but little changed by exposure to the atmosphere. When treated with sulphuric acid, muriatic 

 acid is disengaged, and there remain after evaporation crystals of Glauber's salt, which 

 effloresce on exposure to the atmosphere. The solution of this salt in water gives no preci- 

 pitate with chloride of barium or alkalies, but an abundant one with nitrate of silver. 



Composition. In its pure form, it contains chlorine 60.34, sodium 39.66; but whether 

 obtained in the form of rock salt, or by evaporation from brine springs or sea water, it is 

 usually mixed with the chlorides of calcium and magnesium, the sulphates of soda, magnesia 

 and lime, and frequently also with earthy matters. Its formula is NaCl. 



Geological Situation. It occurs in beds, imbedded masses and veins, associated with 

 saliniferous clay, gypsum, limestone, sandstone and anhydrite, in the salt formation ; also in 

 layers and crusts on soils of particular kinds, and deposited on the shores of salt lakes, and 

 in the vicinity of salt springs. 



Uses. The principal uses of common salt are well known. In addition to these, it is now 

 largely employed in the manufacture of sulphate and carbonate of soda, chloride of lime, etc. 



