582 REPORT— 1902. 



2. Tlie Colour of Iodine-containing Compoiinds. By Miss Ida Smedley. 



Professor H. E. Armstronf^ ^ has for some years contended that a generalisation 

 may be made as to the molecular structure of substances which are visibly coloured 

 in the conventional acceptance of the term, since almost all coloured organic sub- 

 stances may be represented by a ' quinonoid ' structure, if the term ' quinonoid ' be 

 regarded as including any compound which contains at least three centres having 

 some influence on the passage of light through the molecule. From this point of 

 view he regards iodoform as a quinonoid substance in which the three iodine 

 atoms act as centres co-operating to produce colour. 



Substances containing iodine may be divided into two classes — coloured and 

 colourless. Does any distinctive similarity of structure exist in the coloured iodine- 

 containing compounds ? 



Of the molecular condition of solid iodine nothing is known ; in solutions the 

 number of atoms in the molecule probably lies between two and four.- The violet 

 vapour up to 700° C. consists of di-atomic molecules ; but completely dissociated or 

 gaseous mon-atomic iodine is described as colourless. The iodine halogen com- 

 pounds are also coloured, the mono-chloride much more intensely than the tri- 

 chloride. When iodine acts as a trivalent element, combination with one chlorine 

 atom is insutficient to produce colour : thus di-phenyl iodonium chloride (IPh.,Cl) 

 is colourless, but phenyl iodide chloride (IPhCl.,) is yellow. 



Since the iodine atom itself is probably colourless, the colour of the compounds 

 must be attributed to the mutual effect of the halogen atoms. Further, a com- 

 parison of the iodine chlorides shows that the tendency to produce colour is greater 

 where the iodine atom is not fully saturated. 



Amongst the compounds of iodine with other elements, the readiness with 

 which double iodides are formed, the comparative insolubility of many of the 

 iodides, and the colour-changes they undergo on heating, .suggest that their mole- 

 cular structure is more complex than is usually represented. Nearly all the mono 

 and divalent elements give colourless iodides, and it is probable that the coloured 

 di-iodides are really polymerised. Mercuric iodide, for instance, which exists in 

 two coloured isomeric forms, gives a colourless vapour, the density of which 

 corresponds with the simple formula HgL. Among organic substances the excep- 

 tional case of di-iodoacetic acid and its salts,^ which are all described as yellow, 

 needs further investigation. 



In the case of tri-iodides and higher iodides generally, the appearance of colour 

 is determined, not only by the number of iodine atoms present, but also by the 

 condition of the iodine. Thus the nitrogen group of elements form deeply 

 coloured tri-iodides, while the tri-iodides of boron and aluminium are colourle.ss. 

 In hydrocarbon derivatives the three iodine atoms must be associated with the t^anie 

 carbon atom in order to produce colour, as in iodoform ; poly-iodo-derivatives in 

 which the iodine atoms are joined to different carbon atoms, as in tri-iodo-benzeno, 

 being colourless. 



3. On a Fourth Methylmorj)Mmethine.'^ By J. Hawthorne, B.A. 



Three isomeric methylmorphimethines have been up to the present described, 

 whilst the most recent formula suggested for these bodies indicate the existence 

 of a fourth. 



a-methylmorphimethine was first obtained by Hesse and Grimaux by the 

 action of caustic potash upon codeine methiodide; by the action of alcoholic 

 potash and other reagents it yields ^-methylmorphimethine. 



The third isomer was prepared by Schryver and Lees =^ by the action of 

 caustic potash upon isocodeine, and was named by them methylisomorphimethine ; 



' Proe. as., 1892. = Loeb., Trans. C.S., 1888, 



' Perkin and Duppa, Annalcn, 185. 



* The paper is published in full in the Bericlttc, xxsv. p. 3010, 

 " Trans. OS., vol. Ixxix. 1901. 



