Decomposition of murexide in solutions of low pH (2–6) has been investigated spectrophotometrically. At pH<6, the characteristic absorption of of murexide at λ=530 mμ decreased irreversibly with time, following first order law; the corresponding rate constantk₁ had a value of 7·98×10⁻⁶ min.⁻¹ (25° C.) for an initial concentration of 0·125 mM of murexide at pH=2·2.

Reduction of murexide at the dropping mercury electrode was investigated. Data obtained at different concentrations in the range 0·5-2 mM showed that the half-wave potential of murexide was −0·38 voltvs. S.C.E. in 0·1 N KCl solution (neutral pH) and was not altered with concentration; with this last, the diffusion current increased linearly. Analysis of the plots log (i/i_d−i) vs. E indicated that the reduction was irreversible in nature.

Alternating and direct current polarograms of Cd⁺⁺ at different concentrations in the range 0·1 to 10 mM were recorded using 0·1 M potassium chloride solution as the supporting electrolyte. While the diffusion current i_d in dc polarography increased linearly with concentrations up to 10 mM, the summit current i_s at - 0·62 volts vs. S.C.E. (the half-wave potential of Cd⁺⁺) increased linearly up to 1 mM tending to saturate at larger concentrations. The potential width of the ac peaks was lower than the corresponding dc wave-spread indicating that analysis of a mixture of two components with their half-wave potentials close to each other, was possible in the ac polarography.

The decomposition of murexide in acidic solutions was studied spectro-photometrically employing different strong acids like HC1, HBr and HNO₃ and mixtures of these acids and neutral salts like KCl, KBr, KI and KNO₃. The velocity constant k appeared to be a linear function of the concentration C of the strong acid used, and obeyed a relationship:k/min^-1=2.56×10^-3C The slope of the line was unaffected by the change in the nature of the acid or added salt indicating that the anions had no effect on the velocity constant.

Alternating and direct current polarograms of cadmium were recorded at different pH values in the range 1–12. At pH < 11, cadmium was reduced reversibly at the dropping mercury electrode, giving well-defined waves on both ac. and dc. polarography. The wave-width of ac. polarograms was less than that of dc. polarograms in the entire range of pH studied.

Absorption spectra of 4-(p-nitrophenyl-azo)-8-hydroxy-quinoline (NQOH) in the visible region was studied at different pH values in the range 4–12. NQOH exhibited two absorption maxima, one at λ = 480 mμ in acid solution and the other at λ = 600 mμ in alkaline solution. The absorption at λ = 600 mμ was markedly variant with the pH of the solution; the data indicated two dissociation processes presumably due to the ampholytic character of NQOH with 7·3 and 8·1 for pK_b and pK_a referring in acidic and basic dissociation processes, respectively. The optical density values calculated from these constants agreed closely with the observed data.

The composition of cadmium ferrocyanide complex was investigated polarographically using KCl, KBr, KNO₃, (NH₄)₂SO₄, K₂SO₄ and NH₄Cl as the supporting electrolytes. Amperometric titrations indicated that the composition of precipitated complex was Cd₅K₆ [Fe (CN)₆]₄. The results showed the possibility of amperometric estimation of Cd⁺⁺ by Fe (CN)₆^-4 within an error 1 per cent.

Employing the absorption at λ=630 mμ of copper ammonium complex, a new method for determination of Cu⁺⁺ by sodium versenate was described. The experimental error involved in the method was less than 1%.

Dissociation of gallic acid at different temperatures in the range 300–380 Å was investigated using glass and calomel electrodes. Applying modified Debye-Huckel equation the thermodynamic dissociation constantK was calculated. The variation ofK with temperatureT appeared to follow:—$$ - lnK = \frac{A}{T} + B + CT$$ where the constantsA, B andC for gallic acid were 84·11, 5·59 and 14·29 ×10⁻³ respectively. From these, the thermodynamic functionsΔF,ΔH,ΔS andΔCp were computed. The effect of substitution of three hydroxyl groups in the nucleus of benzoic acid onpK andΔF was discussed. The radius of the anion of gallic acid was computed from the calculated values ofΔH; it corresponded to 0·78 Å.

Conductance measurements of murexide or ammonium purpurate solutions were made at 30° + 0.05°C. using a Serfass conductivity bridge. Ostwald’s dilution law was found to be inapplicable; equivalent conductance at infinite dilution and the classical and thermodynamic dissociation constants were computed by various methods applicable for systems involving ion association. The following physico-chemical constants of murexide were calculated :-