44 PHYSIOGRAPHY. CLASS X. 



triol-salt, are used in dyeing, in making ink and Prussian 

 blue, and also for producing sulphuric acid. The residue 

 from the distillation, being red oxide of iron, is employed 

 as a colour, and for polishing steel. 



2. TETARTO-PRISMATIC VITRIOL-SALT. 



Prismatic Vitriol, or Blue Vitriol. JAM. Syst. Vol. III. 

 p. 19. Man. p. 14. Sulphate of Copper. PHILL. p. 313. 

 Natiirlicher Vitriol. WERN. Hoffm. H. B. Th. III. 1. 

 S. 235. Kupfervitriol. HAUSM. III. S. 1054. Kup- 

 fer- Vitriol. LEONH. S. 271. Cuivre sulfate'. HAUY. 

 Traite', T. III. p. 580. Tabl. comp. p. 92. Traite', 2de 

 Ed. T. III. p. 523, 



Fundamental form. Scalene four-sided pyramid 

 of unknown dimensions. Inclination of the axis 

 in the planes of both diagonals. Vol. I. Fig. 42. 



Simple forms, not determined. 



Char, of Comb. Tetarto-prismatic. 



Cleavage, very imperfect in the direction of the 

 faces T and M, Fig. 83., the latter rather more 

 distinct. Fracture conchoidal. Surface: the 

 faces n commonly deeply striated, parallel to their 

 edges of combination with M and T 9 which 

 faces are also sometimes striated, though not so 

 generally as n. 



Lustre vitreous. Colour, sky-blue, in different 

 shades, commonly deep. Streak white. Semi- 

 transparent ... translucent. 



Rather brittle. Hardness = 2-5. Sp. Gr. = 2-213. 

 Taste astringent and metallic. 



OBSERVATIONS. 



1. The theory of the forms in which the inch* nation of 

 the axis takes place at the same time in the planes of both 

 diagonals, has not as yet been perfectly developed. In 



