196 



DESCRIPTIVE MINERALOGY. 



ORDER II. SODA. 



1. Glauber's Salt. 



2. Natron. 



3. Common Salt. 



4. Hydriodate of Soda. 



GLAUBER'S SALT. 



[Named after its discoverer, I. R. Glauber, an alchemist of the 17th century.] 



Soudc Sulphate. Hauy. — Sulphate of Soda. Cleaveland and Pkillips. — Hydrous Sulphate of Soda. TTurm- 

 son. — Glauber Salt. Shepard and Daria. — Prismatic Glauber Salt. Jameson. — Prismatisches Glauber Salz. 

 Mohs. — Exanthalose. Seadant, 



Description. This mineral usually occurs in 

 the form of a white efflorescence. It has a bitter 

 taste, is soluble in water, and the solution gives, 

 on evaporation, crystals which have the form of 

 four or six-sided prisms, but the primary of which 

 is an oblique rhombic prism of 99° 36' and 80° 

 24:^ (Phillips), (Fig. 17). According to Haiiy and 

 others, it is an octahedron with a rhombic base 

 (Fig. 18). These crystals soon fall into powder 

 on exposure to the air. When heated, they un- 

 dergo watery fusion. Lustre vitreous on fresh 



fracture. Hardness from 1 .5 to 2.0. Specific gravity 1 .47. 



From common salt, it may be distinguished by the copious precipitate which is produced 



in its solution by chloride of barium. It is less bitter than sulphate of magnesia, and the 



latter salt yields a copious precipitate when it is treated with a pure or carbonated alkah. 



Sulphate of potash affords a yellow precipitate with chloride of platinum, which is not the 



case with Glauber's salt. 



Composition. A specimen from Vesuvius — Sulphuric acid 44.8, soda 35.0, water 20.2 

 (Beudant). This is in the ratio of one proportion of the salt to two proportions of water, 

 and the formula is NaO.S03-f-2Aq. 



Uses. This salt, which is extensively prepared by artificial means, is employed in glass- 

 making, and in the manufacture of the subcarbonate of soda. It is also used in medicine, 

 and promises to be an article of great value in agriculture. 



LOCALITIES. 



Glauber's salt seldom occurs in regular crystals, but is found, with various impurities, in 

 the form of efflorescences on soils and rocks of various descriptions. It sometimes also occurs 



