ORDER IV. HEMI-PR1SMATIC NATRON-SALT. 27 



Compound Varieties. Reniform, botryoidal, sta- 

 lactitic ; thin crusts : particles of composition, if 

 columnar, and very thin, commonly of a pearly lustre. 

 Massive. Pulverulent. 



OBSERVATIONS. 



1. The octahedral Arsenic-acid consists of 



Arsenic 75*82. 



Oxygen 24-18. BERZELIUS. 



If exposed to a high degree of temperature, it is entirely 

 volatilised ; upon ignited charcoal it emits a strong garlick 

 smelL Its white smoke condenses itself again upon cold 

 bodies. It is soluble in water. The poisonous qualities of 

 this substance are well known. 



2. The repositories of the octahedral Arsenic-acid are 

 the mineral veins, where it probably owes its existence to 

 the decomposition of other minerals. It is chiefly accom- 

 panied by native Arsenic, hemi-prismatic Sulphur, rhom- 

 bohedral Ruby-blende, hexahedral Lead-glance, &c., and 

 has been found at Audreasberg in the Hartz, at Joachims* 

 thai in Bohemia, at Bieber in the principality of Hanau, &c. 



ORDER IV. SALT. 



GENUS I. NATRON-SALT. 



1. HEMI-PRISMATIC NATRON-SALT. 



Prismatic Natron. JAM. Syst. Vol. III. p. 39. Man. 

 p. 5. Natron. Carbonate of Soda. PHILLIPS, p. 190. 

 Natiirlich Mineral- Alkali. WERNER. Hoffmann, Hand- 

 buch. Th. III. 1. Abth. S. 212. Soda. Trona. HAUSM. 

 III. S. 832. 833. Kohlensaures Natron. LEONH. -S. 614. 

 Soude carbonate. HAUY. Traite', T. II. p. 373. TabL 

 comp. p. 21. Traite', 2de. Ed. T. II. p. 207- 



Fundamental form. Scalene four-sided pyramid. 

 P- {77! 14'}, 154 3V, 115 28'. Inclina- 



