Journal of the Chemical Society Abstracts
Clark (A., 1916, ii, 44, 570), and examined by White (Scieizce, 42, 101)) determining in each case the PH range and the number of molecules of alkali required per molecule of indicator to raise the PH. value sufficiently to give the intense colour change characteristic of each indicator. The sulphonephthaleins, having no negative groups in the phenol residues, give yellow or orange solutions, their colours and conductivities showing that they exist largely in the quinoidal form. They are ('
... rm. They are (' self-indicators " requiring from 0.85-0.98 mol. of alkali before the intense colour change due t o the dibasic salt is observed. The monobasic sulphonic acid salt has practically the same colour as the almost completely ionised, free acid. The introduction of negative groups into the benzenesulphonic acid residue increases the affinity constant of this group, but does not appreciably alter that of the phenol group. All these facts and the experimental data support the quinone-phenolate theory of Acree (Zoc. cit.). The free sulphonephthaleins and their monobasic salts give absorption spectra containing a yellow band characteristic of the quinones. This disappears, and a deep red band appears when the dibasic salt is formed, indicating that the quinone group as such disappears, owing to the formation of a complex quinone-phenola t e group. By substituting bromo-, nitro-, methyl, isopropyl, amino-, and other groups in the benzenesulphonic acid group, and in the phenol residue, it is possible to change the ionisation constants of the sulphonic acid ?nd phenol groups, and hence prepare a series of indicators having a wide range of sensibility of hydrogen ions. W. G. Control of Water Supplies which have been Chlorinated. LE ROY (Ann. Falsif., 1916, 9, 339-345).-The iodide-starch reaction is the most sensitive of many reactions which have been proposed for the detection of active chlorine in water. The water to be tested should, however, be cooled t o loo or lower before the reagent is added; a t this temperature, 0*00006 gram of chlorine per litre of water will give a reaction, whilst a t 20°, 0.0001 gram of chlorine cannot be detected. A reagent, which will detect as little as 0*00002 gram of chlorine per litre may be prepared by dissolving 1 gram of hexamethyltri-paminotriphenylmethane in 10 C.C. of dilute hydrochloric acid (1 : l), diluting the mixture t o 100 c.c., adding animal charcoal, and filtering i t ; this reagent, which gives a violet coloration with chlorine, is more sensitive a t 20° than at! loo, and is less affected by nitrites than is the iodidestarch solhtion. It does not give a coloration with hydrogen peroxide. A description is given of a colorimeter for use in the estimation of chlorine by means of this reagent. w.. P. s. Reactions for Distinguishing between Perchlorates, Periodates, Percarbonates , Persulphates, and Perborates. A MONNIER (Aqzn. Chim. anal., 1916, 21, 237--240).-The wlution to be tested should be free from heavy metals,