402 M. C. Lea on Optical Properties of Picrate of Manganese. 
Art. XXXIX.—On the Optical Properties of the Picrate of Man- 
ganese ; by M. Canny Lea, Philadelphia. 
[Read before the Am. Assoc. for the Ady. of Sci. at Newport, August, 1860. | 
BREWSTER and HAIDINGER have described a remarkable 
tion of principal prism, and _macrodiagonal, brachydiagonal and 
The optical properties of this salt are very interesting. It 
exhibits a beautiful dichroism. If the crystal be viewed by 
light transmitted in the direction of its principal axis, it appears 
rora-red in 
picrate, in which case both are pale straw color. ; 
But it also possesses in a high degree the property of reflecting 
be not pure white, but to have a purple shade. Hxamine 
with a rhombohedron or an achromatised prism of Iceland spar, 
having its principal axis in the plane of incidence and reflection, 
the ordinary image is white as usual, while the extraordinary 3S 
of a fine purple color, the phemenon having the greatest Cs: 
tinctness when the light is incident at the angle of maximum 
polarization. 
; * This Journal, Nov., 1858. 
