198 
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 Muriatee. Hauy. — Muriate of Soda. Cleaveland and Phillips. — Hexahedral Rock-Salt. Jameson. — 
Hcxacdrisches Steinsalz. Mohs. — Salmare. Beudant. — Common Salt. Shepard 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. 
Common salt is soluble in twice its weight 
of water at 60° Falir., 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 
withdrawn, it forms hollow quadrangular pyra¬ 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. 
Fig. 21. Fig. 22. 
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 
salimferous 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. 
