• R S Subrahmanya

Articles written in Proceedings – Section A

• Effect of electric field on Tyndall scattering

The study of the action of an electric field on the scattering intensity of sols has thus led to interesting results. The study is useful in determining the shape of the particles. The present technique would be supplementary to the studies of double refraction, in that the latter cannot be conveniently investigated in a highly scattering system. With slightly conducting sols, large fields can be used so as to produce saturation effects. Under such conditions, the use of rotating fields would bring about a unique orientation of the discs. A superposition of two A.C. fields of different cycles at right angles to each other would have the same effect as the circular field. The use of elliptical fields would reveal any want of equality of the two axes in the plane of discs of flat particles. The technique itself is simpler than the flow technique. Since there is often a large difference in the dielectric constant between the particles and the medium, the orientation is marked even with small fields, and the electric field is thus more powerful than the magnetic field in bringing about orientation.

• The depolarisation of light scattered by sols

• The effect of wetting agents on the adsorption of crystal violet by glass

1. The effect of pH and of wetting agents on the adsorption of crystal violet at the surface of glass has been investigated.

2. At low pH values, a wetting agent at first increases the adsorption of the dye. But with an increase in the concentration of the wetting agent the adsorption falls off rapidly and drops almost to zero. At higher pH values the wetting agent diminishes increased adsorption of the dye. An explanation has been offered to account for these observations.

• Effect of salts on the determination of pH by the indicator method in presence of Igepon T

1. In presence of Igepon T, the pH of solutions, as measured colorimetrically with thymol blue and bromophenol blue as indicators, is found to be lower in value than that obtained with the glass electrode. The value of — Δ pH (pH by the glass electrode — pH by the colorimetric method) is found to be influenced by the presence of salts like sodium chloride, sodium sulphate and calcium chloride.

2. With thymol blue, an increase in salt concentration diminishes the value of — Δ pH, while with bromophenol blue the opposite effect is observed.

3. With calcium chloride, the effect of salt concentration on — Δ pH is far more pronounced than with sodium chloride.

4. The results are explained on the basis of the effect of the salts on zeta potential, in relation to the formation of complexes by the acidic and the basic forms of the indicator, with the wetting agent.

• A simple method for the study of variation of boundary tension with time

1. A new method for the determination of variation of interfacial and surface tensions with time, has been described. In this method, the advantages of the pendant drop method are combined with those of the drop weight method, thus simplifying the experimental technique.

2. Variation of interfacial and surface tenssions with time has been investigated for congorubin solutions. The rubin solution yields at the air-liquid interface a solid film and at the solution-benzene interface a gaseous type of film.

3. The effect of concentration of rubin on the variation of interfacial tension with time has been studied. At concentrations of rubin higher than 0·005% the fall in the interfacial tension will be large.

4. Salts like sodium chloride and potassium iodide lower considerably the interfacial tension between rubin solution and benzene. Lowering of pH also brings about a fall in interfacial tension.

5. The slow variation of interfacial tension has been accounted for, on the basis of changes in zeta-potential.

• Surface chemistry of congorubin solutions

• Polarographic behaviour of thionates

The polarographic behaviour of the thionates has been studied employing potassium iodide, potassium chloride, hydrochloric acid, and various buffers as electrolytes in the base solutions. The effect of incorporating 50% alcohol in the base solution has also been investigated.

The results indicate that the reduction process is essentially an irreversible process with tri- and tetrathionates while the opposite effect is noticed with pentathionate.

The tetrathionate shows the phenomenon of split wave which is practically absent in trithionate solutions.

A method has been suggested for the estimation of thionates in a mixture based on the use of 50% alcohol in the base solutions.

The mechanism of the reduction process has been discussed.

• Polarographic behaviour of metals in ethanolamines - Part I. Iron

Employing ethanolamines as the complexing agents a systematic study on the polarographic behaviour iron has been carried out at various pH values and in the presence of the following electrolytes: (a) sodium hydroxide, (b) sodium carbonate, (c) acetate, and (d) ammonium chloride-ammonium hydroxide.

In triethanolamine solutions containing sodium hydroxide, sodium carbonate, and ammonium chloride-ammonium hydroxide, the polarograms consist of two waves corresponding to the reduction of ferric to ferrous and ferrous to iron. The ratio of the heights between the second and the first wave is less than two in the case of sodium hydroxide while in the other two cases it equal to two. The variation of half-wave potential with pH has indicated the formation of complexes involving triethanolammonium ion, triethanolamine, and hydroxyl group.

The suitability of using triethanolamine in base solutions for polarographic estimation of iron has been discussed.

Experiments conducted with mono- and diethanolamines show that the solubility of the complexes is very much lower in the base solutions which makes the study very difficult.

The formation of the following complexes have been indicated from the polarographic measurements: (1) [Fe (III) (Dien)2 (CO3)1]+ (2) [Fe(II) (Dien)2 (CO3)1] (3) [Fe(II) (Trien)1 (CO3)1] (4) [Fe(III) (Trien)2 (NH3)x]+++ (5) [Fe(II) (Trien)1 (NH3)y]++

• Polarographic behaviour of metals in ethanolamines - Part II. Cadmium

A systematic study of the polarographic behaviour of cadmium has been carried out employing mono-, di- and triethanolamines as the complexing agents at various pH values and in presence of (i) sodium hydroxide, (ii) sodium carbonate and (iii) ammonium chloride-ammonium hydroxide.

In base solutions containing triethanolamine, there is a marked tendency for the splitting up of the polarographic wave, while this phenomenon is almost absent when mono- and diethanolamines are used as complexing agents except when pH is below 11.

The polarographic reduction is reversible in solutions containing mono- and diethanolamines and mostly irreversible in triethanolamine solutions. An explanation has been suggested for the irreversibility of the process in triethanolamine solutions.

The formation of the following complexes is indicated from polarographic data:—$$\begin{array}{*{20}c}{[Cd(Moen)_2 (OH)_2 ] [Cd(Moen)_3 (OH)_2 ] [Cd(Moen)_2 (CO)_1 ]} \\{[Cd(Moen)_1 (NH_3 )_x ]^{ + + } [Cd(Dien)_2 (OH)_2 ] [Cd(Dien)_2 (CO_3 )_1 ]} \\{[Cd(Trien)_1 (OH)_4 ]^{ - - } [Cd(Trien)_1 (NH_3 )_y ]^{ + + } [Cd(Trien)_1 (CO_3 )_x ]^{2 - x} } \\\end{array}$$

Dissociation constant and the Δ F° value for the dissociation of the complex are calculated from polarographic measurements in the case of reversible reduction processes.

The use of mono- and diethanolamine in the base solutions is suitable for the polarographic estimation of cadmium.

• Polarographic behaviour of metals in ethanolamines - Part III. Nickel

• Polarographic behaviour of metals in ethanolamines - Part IV. Cobalt (II)

The polarographic behaviour of cobalt has been studied in ethanolamines employing the following electrolytes to alter the pH of the solutions: (i) Sodium acetate-acetic acid, (ii) Sodium carbonate, (iii) Sodium hydroxide, and (iv) Ammonium chloride-Ammonium hydroxide.

Studies of the effect of pH have indicated that in acidic solutions aquo-cobalt ion is reduced at the dropping mercury electrode. As the pH is increased to 9, the amine complex is formed, and when the pH is increased still further, hydroxyl group also enters into the complex.

The reduction of the ethanolamine complexes of cobalt at the dropping mercury electrode is essentially an irreversible process except in solutions containing sodium carbonate and monoethanolamine.

The foregoing studies indicate the formation of the following complexes of cobalt:—$$\begin{gathered} (1) [Co (Moen)_1 (OH)_x ]^{2 - x} (2) Co (Moen)_2 (CO_3 )_1 \hfill \\ (3) Co (Dien)_2 (CO_3 )_1 (4) Co (Moen)_1 (NH_3 )_{y^{ + + } } \hfill \\ (5) Co (Dien)_1 (NH_3 )_{z^{ + + } } (6) Co (Trien)_1 (NH_3 )_{a^{ + + } .} \hfill \\ \end{gathered}$$

It has been indicated that the reduction waves of cobalt in mono- and diethanolamines can be used for the analytical estimation of the metal.

• Polarographic behaviour of metals in ethanolamines - Part V. Copper

The polarographic behaviour of copper-ethanolamine complexes has been studied at various pH values and also employing the following alkaline reagents, namely, sodium hydroxide, sodium carbonate and ammonium chloride-ammonium hydroxide.

It has been noticed that the reduction process is essentially reversible in presence of mono- and diethanolamines and irreversible with triethanolamine.

The phenomenon of split wave has been noticed only in solutions containing triethanolamine and non-ammoniacal alkaline reagents. In ammoniacal solutions the split waves are noticed with all the three amines. These observations have been suitably accounted for.

The formation of the following complexes is deduced from the polarographic data: Cu2(Moen)4(OH)3+ Cu(Moen)2++ Cu (Moen)3++ Cu (Dien)1 (OH)2 Cu (Dien)2 (OH)2 Cu (Dien)2++ Moen and Dien represent monoethanolamine and diethanolamine respectively.

It has been concluded that ethanolamine complexes of copper can be employed for analytical estimation of copper.

Thermodynamic constants have been calculated from polarographic data in systems giving rise to reversible reduction processes.

• Errata

• Polarographic behaviour of metals in ethanolamines - Part VI. Lead

The polarographic behaviour of lead has been studied at different pH values in presence of sodium hydroxide, sodium carbonate and ammonium chloride-ammonium hydroxide employing the ethanolamines as the com-plexing agents.

The results indicate that the process is substantially reversible in the case of mono- and diethanolamines. In the case of triethanolamine the reduction process shows varying degrees of irreversibility depending upon the concentration of triethanolamine.

The formation of the following complexes is indicated by the polarographic data:-Pb(Moen)1(OH)2 Pb (Moen)3 (NH3)a++ Pb (Moen)4 (NH3)x++ Pb(Dien)2(OH)2 Pb (Dien)1 (NH3)y++ Pb (Trien)1 (OH)2 Pb(T1ien)1 (NHg3)z++ Pb (Trien)2++ Moen, Dien and Trien represent monoethanolamine, diethanolamin and triethanolamine respectively.

The suitability of employing the reduction waves of lead in ethanol-amines for analytical purposes has been discussed.

Thermodynamic constants have been calculated from Polarographic data in reversible systems.

• Polarographic behaviour of metals in ethanolamines - Part VII. Zinc

The polarpgraphic behaviour of the ethanolamine complexes of zinc has been studied at various pH values and in the presence of sodium hydroxide, sodium carbonate and ammonium chloride-ammonium hydroxide.

The reduction process is essentially irreversible, the degree of irreversibility increasing with the number of ethanol groups in the amine.

It has not been possible to elucidate from Polarographic data the number of ethanolamine groups that enter the complex in solutions containing sodium hydroxide or ammonium chloride-ammonium hydroxide due to the closeness in the stability of the various complexes.

The following complexes have been indicated from the Polarographie data:-Zn (Moen)2 (CO3)1 Zn (Dien)2 (CO3)x2-2x Zn (Trien)2 (CO3)y2-2y Moen, Dien, and Trien represent monoethanolamine, diethanolamine and triethanolamine respectively.

The reduction waves of zinc-ethanolamine complexes can be used for the estimation of zinc in sodium carbonate solutions.

Thermodynamic constants are calculated from Polarographic data in the case of the reversible system.

Some important types of Polarographic wave forms obtained in the study of metallic complexes have been given.

The limitations regarding the use of irreversible wave equations to derive the formulæ of metallic complexes have been pointed out.

• Polarographic behaviour of organic iodocompounds - Part I. Iodobenzene

The diffusion coefficients and the diffusion current constants of iodobenzene have been determined in aqueous mixtures of ethanol, dioxane and acetone containing 1 M lithium chloride. The diffusion current constant is found to be proportional to the square-root of the diffusion coefficient determined by the diaphragm cell technique and the number of electrons involved in the reduction process is found to be two. The diffusion coefficients determined by the viscosity and conductivity methods do not explain the anomalous variation of the diffusion current constant with solvent concentration noticed in the case of iodobenzene and they lead to erroneous conclusions regarding the reduction mechanism.

It has been found that half-wave potential shifts to more negative values with an increase in the concentration of the organic solvent. The values of E3/4-E1/4 have been found to be of the order of 0·09 V in all media indicating the irreversibility of the electrode process. It has been suggested that the polarographic method can be used for the estimation of iodobenzene.

• Polarographic behaviour of organic iodocompounds - Part II. Iodonaphthalene

The polarographic behaviour of 2-iodonaphthalene has been studied in aqueous mixtures of ethanol, dioxane and acetone containing 1 M lithium chloride. The diffusion current constant is practically unaltered with the solvent concentration. Employing the diffusion coefficients determined by the diaphragm cell method in the Ilkovic Equation the number of electrons involved in the reduction process has been calculated as two. The limitations in employing the diffusion coefficients obtained by equivalent conductivity and viscosity methods for arriving at the reduction mechanism have been pointed out.

The half-wave potential shifts to more negative values with an increase in the concentration of the organic solvent. The values of E3/2-E1/2 have been found to be of the order of 0·1 V. indicating the irreversibility of the electrode process.

• Polarographic behaviour of organic iodocompounds - Part III.o-iodobenzoic acid

• Studies on the polarographic behaviour of nitrophenols - Part I.o- andm-nitrophenols

• Spectrophotometric and potentiometric investigations of copper (II)-ethanolamine complexes - Part I. Monoethanolamine

Spectrophotometric and potentiometric investigations have been carried out on copper-monoethanolamine complexes. Job plots at 920, 760 and 620 mµ have indicated the formation of CuA++, CuA2/++ and CuA3++. The$$\bar n - pA$$ curves have been obtained by a slight modification of the method of corresponding solutions and by pH measurements. The$$\bar n$$vs. pA curves obtained at different metal concentrations coincide indicating the formation of mononuclear complexes. Experiments conducted with 0·1. 0·2, 0·5 and 1·0 M monoethanolammonium ion indicate the formation of mononuclear hydroxy complexes above pH 6. The nature of Emvs pA curves is closely analogous to that of$$\bar n$$vs. pA curves. Absorption spectra taken at pH 9·8 with different amounts of monoethanolamine has given evidence for the formation of (CuA3OH·A)+.$$\bar n - pA$$ curves have been analyzed and the values ofβ1, 1,β1, 2 andβ1, 3 have been obtained. Curves showing the distribution of complexes and the absorption curves of the individual complexes (CuA++, CuA2/++, and CuA3/++) have been calculated.

• Spectrophotometric and potentiometric investigations of copper (II)-ethanolamine complexes - Part II. Monoethanolamine (Analysis of mixed hydroxy complexes with polarographic evidence)

Potentiometric, spectrophotometric and polarographic evidence has been presented for the formation of mixed hydroxy complexes in coppermonoethanolamine system. A method has been developed for the analysis of Bjerrum formation curves taken in presence of 0·1, 0·2, 0·5 and 1·0 M monoethanolammonium ion with respect to hydroxy complexes. The formation of CuAOH+, CuA2OH+ and CuA3OH+ is shown and the corresponding stability constants are calculated at different concentrations of MEA ion. Curves showing the distribution of pure and hydroxy complexes at various pA values in solutions containing different concentrations of MEA ion have also been given.

• Studies in the polarography of metal-amino acid complexes - Part I. Cadmium

1. A detailed polarographic study of cadmium has been made employing glycine,α-alanine,β-alanine, valine, aspartic acid, glutamic acid and asparagine as complexing agents at various pH values. The effect of incorporating sodium hydroxide, sodium carbonate and ammonium nitrate + ammonium hydroxide, on the polarographic behaviour of amino acid complexes of cadmium has also been investigated.

2. The reduction process has been found to be reversible in all systems.

3. The small shifts in the half-wave potentials noticed due to increase in the concentration of sodium hydroxide and sodium carbonate in presence of amino acids have been explained on the basis of formation of mixtures of pure and mixed amino acid complexes of cadmium. Mixed complexes have also been noticed in presence of ammonium hydroxide and ammonium nitrate and amino acids.

4. Polarographic evidence has been obtained for the formation of over 30 pure and mixed complexes. The dissociation constant Kd, the Δ F° value for the dissociation, and standard potential value for the formation, of each complex have been computed.

5. It has been found that cadmium can be polarographically estimated in amino acid solutions.

• Studies in the polarography of metal-amino acid complexes - Part II. Lead

1. The polarographic behaviour of glycine,α-alanine,β-alanine, valine, aspartic acid, glutamic acid and asparagine complexes of lead has been studied at various pH values and in presence of (1) NaOH, (2) Na2CO3 and (3) NH4 NO3+NH4OH. All the polarographic waves have been found to be reversible.

2. Experiments conducted on the effect of variation of pH,i.e., 7&lt;pH&lt;9 (varying slightly in different cases), on half-wave potential keeping the total concentration of amino-acid have indicated the formation of Pb A and Pb A2. The data have been analysed employing the equations developed by DeFord and Hume as modified by McKenzie and Mellor.

3. Only pure complexes are produced below pH 11·2 in the case of aspartic acid, glutamic acid and glycine, while mono hydroxy complexes are produced inα-alanine, valine and asparagine systems.

4. It has been found that no mixed hydroxy and mixed ammonia complexes are produced in presence of sodium hydroxide and ammonia-ammonium nitrate, respectively. However evidence is obtained for the formation of mixed carbonate complexes in glycine and aspartic acid systems in presence of sodium carbonate.

5. Thermodynamic data have been calculated from polarographic measurements for 18 complexes.

6. The suitability of incorporating amino acids in base solutions for the polarographic estimation of lead has been tested.

• Studies on the polarogrphic behaviour of nitrophenols - Part II.p-Nitrophenol

• Studies in the hydrolysis of metal ions - Part I. Copper

The hydrolysis of cupric ion has been studied at various ionic strengths (0·01, 0·05, 0·1 and 0·5 M). The results are analyzed employing ‘core + links’ theory, log-log plot, normalization plot, and extrapolation method for obtaining the pure mononuclear curve. The stability constants of Cu2(OH)2++, Cu3(OH)4++, Cu(OH)+ and Cu(OH)2 have been reported.

• Spectrophotometric and potentiometric investigations of copper (II)-Ethanolamine complexes - Part III. diethanolamine (Gaussian analysis of electronic spectra in mono and diethanolamine systems)

Spectrophotometric and potentiometric investigations have been carried out on copper-diethanolamine system. Job plots at 900, 900 and 580 mμ have indicated the formation of CuD++, CuD2++ and CuD3++. Then- pA curves obtained indicate the formation of CuD++, CuD2++, CuD3++, CuDOH+, CuD2OH+ and CuD3OH+. Then- pA curves have been analyzed to obtain the stability constants of these complexes. Absorption curves of pure complexes have been computed by a graphical method. Gaussian analysis of the absorption curves of pure and hydroxy complexes show the presence of a second band, indicating that the structure is that of a distorted octahedron.

• Studies on the hydrolysis of metal ions - Part II—Nickel

A detailed investigation of the hydrolysis of nickel in the lower concentration range has been made. The results have been analysed on the basis of ‘Core + links’ theory and on the assumption of the formation of one predominant complex. Evidence is obtained for the formation of Ni2 (OH)62− and its stability constant is calculated to be 1038.78

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