220 Royal Society .— 



fore a- and /B-pvisms crystallizing together from the same strong alco- 

 holic solution. 



The move 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, j3-prisms always develope 

 themselves under similar circumstances. 



This new quinidine 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 metaUic 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 ; 

 hut 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 diff'erence 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. 



5th. The modification which it undergoes by resolution or recry- 

 stallization, and the formation of a salt more resembling the garnet- 

 red iodo-sulphate, but having strongly marked differential characters 

 from this beautiful salt, viz. its strong tourmaline powers of absorp- 

 tion and its deeper colour, being nearly a brown-purple, and by its 

 disposition to assume the I'hombohedric form. 



The author has not yet analysed this salt, but hopes ere long to 

 accomplish this matter and communicate his results to the Royal 

 Society ; but he ventures to hope that it will be found to contain 

 2 atoms sulj)huric acid and 3 atoms iodine, like the analogous quinine 

 and cinchonidine salts. 



The author has also assured himself that there is an analogous 



