PHYSIOGRAPHY. 



Tabular-Spar. 



221 



3. Sulphuric acid, or oil of vitriol, which is artificially produced from 

 the combustion of sulphur in contact with a little nitre, is of very exten- 

 sive use in chemistry, as well as in metallurgy, bleaching and some of 

 the processes for dyeing ; it is also employed in the formation of nume- 

 rous salts, as copperas, sulphate of magnesia, &c., and is administered in 

 medicine as a tonic and stimulant', and sometimes used externally as a 

 caustic. 



SYLVITE. 



Soluble with the taste of Common Salt, and crystallizable from solu- 

 tion in cubes, parallel to whose faces it cleaves. The aqueous solution 

 affords a yellow precipitate on the addition of muriate of platina. Treat- 

 ed with sulphuric acid, it leaves after evaporation aciculaa* crystals, 

 which do not effloresce in the air. It. is supposed to be muriate of pot- 

 ash ; and is found in small quantity, mingled with Common Salt, in the 

 mines of Hallein, and of Berchtesgaden. 



TABULAR-SPAR. Tetarto-pri srnatic Tabular- 

 Spa r. 



Primary form. Doubly oblique prism. PonT = 126i l 

 P on M = 93 40'. SI on T==95 15'. 



Secondary form. 



Fig. 430. 



M on i 

 T on i 

 P on a 

 P on e 



1 39 '48' PHILLIPS. 

 1 35 30 

 156 30 

 94 15 " 



Cleavage, in the direction of M and T easily obtained, but 

 one of them more perfect than the other ; parallel with P 

 indistinct. Fracture uneven. 

 19* 



