342 



Its iodo-sulphate is deep olive-green in its reflected tint, orange- 

 yellow by transmitted light, and possessing in an eminent degree 

 optically doubly absorbent powers, thin laminae being quite black, 

 but still thinner ones give a bistre-brown "body-colour" when pola- 

 rized perpendicular to axis. 



This alkaloid was also furnished me by the kindness of Mr. Howard, 

 but has not yet been sufficiently purified, or in the quantity necessary 

 to give certain results. 



It possesses one very peculiar property. When dissolved in chloro- 

 form and evaporated spontaneously on glass, the gummy and uncry- 

 stalline residue, mounted in Canada balsam, at once shows a deep 

 blue-green, epipolic, or fluorescent appearance. 



Pure cinchonidin does not possess epipolic dispersion and does not 

 become green by chlorine-water and ammonia ; and when it is dis- 

 solved in acetic acid or chloroform and the fluid is exposed on glass 

 plates to spontaneous evaporation, beautiful crystals in circular spots 

 or drusfe develope themselves, which under polarized light exhibit 

 black crosses and white or coloured sectors. 



These appearances are not exhibited by pure quinine or true qui- 

 nidin (/3-quinine), both of which give a gummy, uncrystalline, arid 

 perfectly transparent residue. 



Pure cinchonidin, thus optically and chemically distinguishable 

 from either quinine or quinidin, is still further remarkable for pro- 

 ducing with sulphuric acid and iodine an optical doubly absorbent 

 compound of intense power, even equal to the sulphate of iodo- 

 quinine compound ; these crystals are very similar in form to my 

 artificial tourmalines, and have long been mistaken by me for them ; 

 even at present I can only distinguish them by the tints in reflected 

 light and the complementary body-colour, viz. whilst sulphate of 

 iodo-quinine gives a cantharidin-green reflected tint, and a pink, 

 ruby-red, reddish-brown or black body-colour when polarized perpen- 

 dicular to the axis, according to the thickness of the plate examined, 

 the sulphate of iodo-cinchonidin is golden-green by reflected light, 

 and gives a sky or indigo-blue or black " body-colour" when polarized 

 perpendicular to the axis. I have not yet made sufficient chemical 

 analyses of this substance to enable me to decide on its formula, but 

 I have obtained 39'307 per cent, iodine and 8'864 per cent, sulphuric 

 acid, which sufficiently indicate a chemical difference in constitution 



