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Previous communications have dealt with the antiseptic properties of compounds of the pyridine, quinoline, acridine and phenazine series, and also of the apocyanine, carbocyanine, and isocyanine groups, the object being to investigate relationships between chemical constitution and antiseptic properties. The following work comprises the preparation and examination of a large number of styryl and anil quinoline compounds, considerable variations in chemical structure being involved. The authors have previously drawn attention* to the possible influence of a particular chemical grouping consisting of a chain of alternate double linkages joining two nitrogen atoms, one being basic and trivalent, and the other the pentavalent nitrogen of a quaternary ammonium group. This arrangement is present in acriflavine (2.7 diamino acridine methochloride), and also in the cyanines, in all of which the antiseptic action is not diminished by the presence of serum. As shown by the graphic formulæ, the styryl compounds also include a similar system, whereas in the anils an additional nitrogen atom is interposed in the connecting chain in place of a —CH= group. This system will be subsequently described as the “ alternate linkage system.”

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A COMPARISON of the products obtained by chlorinating the isomeric chlorotoluenes, and by brominating the isomeric bromotoluenes, shows that the two halogens possess a different orienting effect. Cohen and Dakin (T., 1901, 79, 1111) found that o-chlorotoluene, on chlorination in presence of the aluminium-mercury couple, gives mainly 2:4together with some 2:3-and 2:6-dichlorotoluene; whilst Cohen and Dutt (T., 1914, 105, 501) found that on brornination o-bromotoluene gives mainly 2 : 5-, with a smaller quantity of 2:4-dibromotoluene. I n the case of the meta-and para-substituted toluenes the same products were obtained in both cases. It was thought that some further light might be thrown 6~2

the active esters submitted to optical examination included halogen, nitro-and nitro-halogen derivatives of benzoic acid. The results derived from the study of nine separate series of compounds clearIy indicated that, with the single exception of the ortho-isomeride of the iodobenzoic esters," the ortho-substituent had the greatest * We propose to study the effect of tcmperature on the rotation of the three isomeric iodobenzoic esters, View Article Online ISOMERISM TO OPTICAL ACTIVITY. PART v111.If, according to Winther (Zoc. cit.), change of rotation in a compound is conditioned by change in internal pressure, it seems probable that a temperature widely removed from the crystallising point, and therefore from the region in which molecular aggregates may be formed, will afford a more correct basis for comparison.It is for this reason that provisionally we are disposed to regard the values at looo as the more satisfactory for the purpose of comparison until more light has been thrown on this aspect of the * The rule laid down by Frankland and Wharton (Trans., 1836, 69, 1309, 1583), in which the para-isomeride is supposed to exert the greatest effect, is not only contradicted by some of their own and others observations, but seems quite incapable of proof where solvents are used, owing t o the indeterminate influence of the solvent.