WHERRY AND ADAMS: PINAVERDOL 403 



It is noteworthy that in every case the pseudo-faces which 

 have developed on pinaverdol crystals through contact with the 

 glass container show similar colors, corresponding to their posi- 

 tion. A most striking effect is obtained when a sheet, made up 

 of crystals lying in all sorts of positions, is removed from against 

 a glass surface and examined in reflected Hght, especially with the 

 aid of a low-power lens. Some of the grains are violet, some yel- 

 low, while the bulk of them are of different hues of green, the 

 whole effect being kaleidoscopic in character. 



When viewed through a nicol prism two components can be 

 recognized in the light reflected from each face. The brassy 

 prism zone faces yield for the two opposed directions of the 

 vibration plane of the nicol, a yellow (plane parallel to c) and a 

 violet (plane parallel to a) component; the green dome faces 

 green (parallel to c) and violet (a) ; terminal forms show violet, 

 which changes but sHghtly as the nicol is revolved. 



A similar pleochroism of reflected light has been observed in 

 but few substances. The best known case is magnesium platino- 

 cyanide, which has been described at length by Walter.^ A 

 dye known as diamond green or brilliant green, made by the 

 Badische works, was stated by the same author to show it also, 

 although no samples at our disposal do so. The mineral covel- 

 lite, CuS, gives a metallic blue reflection color on the base, and 

 Merwin^ states that the color varies noticeably in different 

 crystallographic directions. Goethite, FeOOH or Fe203.H20 

 yields nonmetalhc reflection from most of its faces, but one 

 pyramid is reported by Goldschmidt and Parsons'' as giving a 

 yellow colored signal. 



OPTICAL PROPERTIES 



Since pinaverdol is readily soluble in organic solvents, it is 

 necessary to use for its study by the immersion method under 

 the microscope aqueous liquids of known refractive indices, and 

 solutions of potassium-mercuric iodide and barium-mercuric 



* Walter, B. Die Oberfldclien oder Schiller farben. Braunschweig, 1895. 



5 Merwin, H. E. This Journal 5: 341. 1915. 



^ Goldschmidt, Victor, and Parsons, A. L. Amer. Journ. Sci. 29: 235. 1910. 



