investigated in its Optical Relations. 



289 



If the colours of the two quinine combinations are compared, 

 the following result is obtained : — 



Substance-colour, polar 

 ized in the direction 

 of axis .... 



Ditto, polarized perpen- 

 dicularly to axis . 



Surface-colour, polarized 

 perpendicularly to the \- Pinchbeck-brown. 



Hydroehinon. Herapathite. 



Obscure violet-blue. Greenish -white. 



Very dark violet-blue. Very dark red. 

 Grass-green. 



axis 



Now the substance-colour of pure iodine is yellow in different 

 tints, the surface- colour blue. I examined the substance-colour 

 lately for the purpose of comparison with some small crystals, 

 which Dr. Ragsky had obtained by evaporation from a solution 

 in bisulphuret of carbon. The long six-sided plates of about 

 128°, and four angles of 116°, were opake in the thickest parts, 

 at the edges changing through reddish-brown, dark honey-yellow 

 into paler tints. There was, besides, evidently a difference in 

 the intensity ; the colour in the direction of the small diagonal 

 of the rhomb of 128° polarizes paler, the colour in the direction 

 of the long diagonal polarizes darker. 



But during the observation through the microscope with a 

 magnifying power of 90 diameters, I saw the volatilization was 

 even progressing, and in a remarkable manner the crystal plates 

 became thinner and thinner towards the centre of the hexagon, 

 and of a lighter honey-yellow ; then appeared a hole that grew 

 larger and larger, while small particles were again deposited like 

 a beard, especially on the edge parallel to the small diagonal of 

 the rhomb of 128°. 



It requires certainly no very violent supposition to detect the 

 colour of the hydroehinon and of the iodine in the Herapathite. 

 The less dark violet-blue is neutralized by the less deep yellow 

 into the almost colourless weak greenish tint of the substance 

 colour when polarized in the direction of the axis. The very 

 dark violet, with the somewhat stronger yellow, leaves red behind ; 

 the metallic yellow with the blue gives metallic green. Certainly 

 a comparison of this kind deserves still further attention, although 

 for the present occasion it is only approximately ventured as a 

 first attempt. 



Phil. Mag. S. 4. Vol. 6. No. 39. Oct. 1853. 



U 



