ORDER IV. HEMI-PRISMATIC VITRIOL-SALT. 41 



HAUY and others. The shape which the small crystals as- 

 sume when forming in the fluid, seems rather to indicate 

 the pyramidal system, particularly if compared to the figure 

 given by Mr PHILLIPS, which represents the icositetrahe- 

 dron Ci, having only four of its unequiangular solid angles 

 replaced by additional faces, so that those faces by them- 

 selves would produce a rectangular four-sided prism. 



2. The octahedral Ammoniac-salt occurs in cracks and 

 fissures in the immediate vicinity of active volcanoes, and 

 is a product of sublimation. Thus it is also found near 

 burning coal-seams. It has been said to occur in slaty 

 clay along with prismatic Sulphur. 



3. Its best known localities are Mount Etna and Ve- 

 suvius, the Solfataras, the Lipari islands, England, par- 

 ticularly the neighbourhood of Newcastle, Scotland, Ice- 

 land, the neighbourhood of Liege, the Buchanan Tartary, 

 &c. It is often produced by immediate composition of its 

 constituent parts, or by various chemical processes. A 

 considerable quantity is produced in Egypt by the combus- 

 tion of the dung of camels. 



4. This salt, as it occurs in nature, will probably be of 

 very little use, on account of its scarcity. That obtained 

 by the assistance of art is employed in dyeing, in medicine, 

 and in several operations of metallurgy. 



GENUS VI. VITRIOL-SALT. 

 1. HEMI-PRISMATIC VITRIOL-SALT. 



Rhomboidal Vitriol or Green Vitriol. JAM. Syst. 

 Vol. III. p. 17. Hemi-prismatic Vitriol or Green 

 Vitriol. Man. p. 13. Sulphate of Iron. PHILL. p. 

 240. Natiirlicher Vitriol. WERN. Hoffm. H. B. Th. 

 III. 1. S. 235. Eisenvitriol. HAUSM. III. S. 1058. 

 Eisen- Vitriol. LEONH. S. 355. Fer sulfate. HAUY. 

 Trait^, T. IV. p. 122. Tabl. comp. p. 100. Traite', 

 2de Ed. T. IV. p. 140. 



Fundamental form. Scalene four-sided pyramid. 



