233 



In the same case with the glass models will be found tolerably perfect 

 crystals, belonging to the cubical system, of the following sub- 

 stances : 



657. COBB. Iron Pyrites. (Bisulphide of Iron.) 



Galena. 



Iodide of Potassium. 



Bromide of Potassium. 



658. OCTAHEDRON. 



Alum, small octahedra. 

 Ditto, a large octahedron. 

 Chrome alum, ditto. 



Chrome alum and common alum crystallized together in 

 one octahedron. 



Note. These remarkably fine octahedra were prepared and presented 

 by Mr. W. Copney. See P. J. [1], vol. x., p. 536. 



659. DODECAHEDRON. 



Iron Pyrites. 



660. HOLLOW PYRAMIDS. 



Chloride of Sodium. 



Models in wood of the following crystalline forms, also belonging to the 

 cubical system, will be found in the upper compartment of case 

 No. 9 : 



e. Octahedron. 



/. Rhombic dodecahedron. 



g. Trapezohedron. 



h. Tetrahedron. 



661. II. SQUARE PRISMATIC SYSTEM. (Pyramidal system, 2 and 1 



axed system.) 



a. Glass model (fig. 24), showing the following forms: 



White, short octahedron with square base. 



Yellow, long octahedron with square base. 



Black lines on the glass, square prism. 



Note. In this system the two horizontal axes, indicated by red wires, 

 are equal in length, while the vertical one is either longer or shorter than 

 the two horizontal axes ; all three axes being at right angles to one 

 another. 



b. Crystal of Ferrocyanide of Potassium. 



Note. This is a short octahedron with a square base ; the a.\ \ in 

 this specimen is truncated. 



c. Wooden model of Ferrocyanide of Potassium, 

 c. Wooden model of Mercurous Chloride. 



Note. For fig. of this model, see Phillip^ Trantl. of Pharm., p. 310. 



