Chemistry and Physics. 387 



gen ion in oxygen. The ions of sulphurous oxide gave the 

 slowest velocity, only one-tenth that of hydrogen. — Phil. Mag., 

 V, xliv, 422-440, November, 1897. G. f. b. 



3. On the Connection between Fluorescence and Chemical 

 Composition. — According to R. E. Meyer, the fluorescence of 

 organic compounds may be considered to be due to the presence 

 of certain atomic groups, which undergo no change in the several 

 fluorescent derivatives of a given substance. These groups the 

 author proposes to call fluophores or fluophoric groups. But in order 

 that there should be an actual fluorescence, the fluophore must be 

 placed between two massive atomic groups, usually benzene 

 nuclei. Thus in the derivatives of fluoran which embrace the 

 fluoresceins, naphthofluorans, rhodamines and the like, the fluo- 

 phore is the pyrone group which although not itself fluorescent 

 becomes so in the diphenyl derivatives. The same fluophore is 

 contained in the xanthones, while in the xanthens its reduction 

 product is present ; the effect of substitution being very marked. 

 It may be said that in general the entrance of heavy atoms or 

 groups into the benzene nuclei decreases the fluorescence, the 

 nature and position of the substituted body influencing the result 

 very largely. The presence of hydroxyl groups for example in 

 any position other than that ot the fluorescein hydroxyls may 

 greatly weaken or even destroy the fluorescence of the fluoran 

 and xanthone compounds. Only the direct derivatives of the 

 anthracene group and not anthraquinone are fluorescent. The 



fluophore in the acridine compounds is CH £ -^ N. In this 



case the effect of the position of the substituted body is very 

 marked, since benzoflavine, which has both its amido groups in 

 the "fluorescein position," is far more strongly fluorescent than 

 its isomer chrysaniline. If sulphur be substituted for oxygen in 

 the pyrene ring, the fluorphoric character is not destroyed, the 

 thiopyrene derivatives showing a weak fluorescence. Moreover 

 the azine, oxazine and thioazine rings act as fluophores in the 

 phenazines, phenazoxines and thiodiphenylamiue compounds, 

 which include many important fluorescent dyes, as mauveine, the 

 safranines and allied naphthalene compounds, the indulins, Lauth's 

 violet, and methylene blue; this latter showing a reddish-violet 

 fluorescence. The influence of the solvent is also important. — 

 Zeitschr. physikal. Chem., xxv, 468-508, December, 1 897. g. f. jb. 



4. On a new method of preparing pure Iodine.— Some months 

 ago Lean and Whatmough observed that no iodine was set free 

 when cuprous iodide was heated even to fusion in a current of 

 carbon dioxide, while it is well known that iodine is readily 

 evolved from this substance when it is heated in the air, even to a 

 moderate temperature. They have based on this fact a method 

 for preparing perfectly pure iodine. For the preparation of the 

 cuprous iodide, a solution of a mixture of copper sulphate and 

 ferrous sulphate was precipitated by a solution oi potassium iodide ; 

 a pure product ^eing obtained by proper dilution. This cuprous 



Am. Jour. Sci.— Fourth Series, Yol. V, No. 29.— May, 1898. 

 26 



