It crystallizes in glistening rhombohedra, melting at 70°-80° C., and boiling at Ioo° C. It is completely resolved into its components when warmed with dilute acids.
It forms colourless, transparent rhombohedra, like those of Iceland spar; the angles are nearly equal to right angles, being 73° 30', so that the crystals look like cubes: hence the name of "cubic saltpetre."
It crystallizes in rhombohedra belonging to the hexagonal system, having interfacial angles of 87° 40'.
Aluminium fluoride, AlF 3, obtained by dissolving the metal in hydrofluoric acid, and subliming the residue in a current of hydrogen, forms transparent, very obtuse rhombohedra, which are insoluble in water.
Wollaston in the angles of the rhombohedra of the carbonates isomorphous with calc-spar, he observed that the angle in the case of calc-spar varied with the temperature.
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