404 WHERRY AND ADAMS: PINAVERDOL 



iodide in diluted glycerol were found to be satisfactory. Crystals 

 greater than 0.02 mm. in diameter are practically opaque for 

 ordinary white light, but by dissolving a little of the substance 

 in hot methyl alcohol and allowing the liquid to cool rapidly, 

 minute needles of satisfactory transparency can be obtained. 

 For red light, which may be obtained by the use of a Wratten 

 E-red No. 23 ray-filter, the transmission of light is much better. 

 The following optical properties could be observed: 



In ordinary light: Crystals, rods with oblique or square termi- 

 nations, breaking into irregular fragments. Color very intense, 

 with pleochroism from violet-brown to brown to deep greenish 

 brown; or, in very thin crystals violet to brown to yellow-brown. 

 By the use of a monochromatic illuminator, the crystals showing 

 violet-brown color were found to transmit the red end of the 

 spectrum from the limit of visibility to the orange of wave length 

 about 600; on decreasing the wave length, marked absorption 

 was exhibited, the crystals being highly opaque for the yellow, 

 green, and part of the blue; but on reaching the middle blue at 

 about wave-length 470 transmission was again noted, and con- 

 tinued to the end of the visible violet. The directions in the 

 crystals giving brown or greenish brown behaved differently, 

 however, the red end of the spectrum being absorbed, while a 

 slight though distinct transmission appeared in the yellow and 

 green, with absorption in the blue and violet. 



Refractive indices: There is such a tendency to yield metallic 

 reflections on the part of the pinaverdol crystals that refractive 

 index determinations do not yield very satisfactory results. 

 The lowest index a, which is shown lengthwise of the crystals of 

 the usual prismatic habit, is about 1.58, for light of wave length 

 625; this is the direction in which the transmission is usually 

 greatest, and the color violet. The other two indices are much 

 greater than 1.75, which is that of the highest liquid which it 

 has been found possible to prepare. They probably reach a value 

 of at least 2.00. The greenish brown and yellowish brown colors 

 correspond to these, the absorption being great in both of them. 



In parallel polarized light, nicols crossed: The extinction is 



