56 PHYSIOGRAPHY. CLASS i. 



= 2-807, of a solitary crystal. Taste saline 

 and astringent, feeble. 



OBSERVATIONS. 



1. According to measurements with the reflective gonio- 

 meter by Mr PHILLIPS, the angle of P given above as 

 = 120 12' is equal to 116 20', that of P + equal to 

 83 20', and the incidence of P 05 upon P + co = 104 15'. 



2. The prismatic Brithyne-salt consists, according to 

 BRONGNIART, of 



Sulphate of Lime 49-0. 



Sulphate of Soda 51-0. 



Its chemical composition is expressed by Na S 3 + Ca S 9 , 

 and it consists accordingly of 22-35 Soda, 20-35 Lime, and 

 57'39 Sulphuric acid ; that is to say, of one atom of anhy- 

 drous sulphate of lime, and one atom of anhydrous sulphate 

 of soda. The forms of both these substances are prismatic, 

 those of the prismatic Brithyne-salt are hemi-prismatic. 

 Hence it is not one of those cases, in which one of the sub- 

 stances contained in the mixture impresses its form upon 

 the whole, as is the case in hemi-prismatic Vitriol-salt, 

 which may contain sulphate of copper without change of 

 form. Also the determined proportions in the constituent 

 parts of the Brithyne-salt agree with this observation. If 

 immersed in water, it loses its transparency, and is partly 

 dissolved. The same happens if exposed to a moist atmo- 

 sphere. Before the blowpipe it decrepitates and melts into 

 a white enamel. 



3. It occurs in imbedded crystals in hexahedral Rock- 

 gait, at Villarubia near Ocana in New Castile. Another 

 locality is Aussee in Upper Austria. The combinations 

 described above have been observed in the Spanish variety. 



