319 



fore a- and /3-prisms crystallizing together from the same strong alco- 

 holic solution. 



The more frequent form in which this salt shows itself, however, is 

 as the a-prism, from solutions in which the alcohol is vastly predomi- 

 nant over the water ; whereas with quinine, /3-prisms always develope 

 themselves under similar circumstances (vide ' Proceedings/ vol. vi.). 

 This new quinidin salt has a very great similarity in its optical pro- 

 perty to the quinine salt. Its reflected tint is a metallic blue-green, 

 when in liquid or in contact with glass ; but after filtering, and when 

 exposed on paper, it has a brownish-olive colour, and loses all appear- 

 ance of metallic reflexion to the naked eye. Its transmitted tint is, 

 when polarized parallel to its axis, a brownish-yellow green, even in 

 thin plates, but verging to brown in thicker. Its "indicative body" 

 colour is brownish red. 



One great peculiarity attends upon this salt ; if it be permitted to 

 remain in the acid mother- liquid, it disintegrates by gradual solution, 

 and disappears, whilst, upon the side of the bottle, solid and 

 large crystals slowly form, of a rhombohedric form, or having 

 some of its modifications, the more frequent of which is that with 

 replacement upon the short axis of the rhombohedron by triangular 

 planes. These crystals have a deep sienna-brown colour by trans- 

 mission, and a dark steel-blue by reflexion, verging on purple ; 

 they strongly polarize light, and differ materially from the garnet-red 

 iodo-sulphate previously described, by the greater intensity of their 

 optical properties. 



When we attempt to purify the optical thin prisms by recrystalli- 

 zation from alcohol, the same modification appears to be produced ; 

 but the crystals are acicular rhombic prisms ; the optical charac- 

 ters are the same, however, as those of the rhombohedral form. 



The characters, therefore, by which this salt is known from qui- 

 nine are many. 



1st. Its crystallizing as a-prisms, or as a- and /3-prisms from strong 

 spirituous solutions. 



2nd. Its brownish- olive reflected tint as seen by the naked eye. 



3rd. Its deeper yellow and brownish- green transmitted tint. 



4th. The probable difference in the primary form of the laminated 

 variety, being a very acute prism of a rhombic form, having 30 as 

 the acute, and 1 50 as the obtuse angles. 



VOL. ix. z 



