cathodic peak potential of \(Ni\) is \((-0.6)\) V. The sensitivity of the proposed procedures is \((3 \div 8)\cdot 10^{-7}\%\); the coefficient of variation is \(8 \div 10\%\) \((n=5)\); the analysis time for one sample is 1.5–2.5 hours.

When determining \(Ni\) in salts and crystals of \(CH_2AsO_4\), 3 portions of 2 ml each of conc. \(HBr\) are added to the residue and the solution is evaporated to moist salts; the residue is dissolved in 0.5 ml of conc. \(HNO_3\) and again evaporated to moist salts.

Literature

1. Yu. A. Fedyashina, I. G. Yudelevich, T. T. Sorokina. Zh. analit. khimii, 21, 10, 1232–1235, 1966.
2. V. I. Kuleshov. “Zavodskaya laboratoriya,” 34, 950 (1967).
3. V. I. Kuleshov, N. V. Podkorytova, S. I. Nazarova. “Zavodskaya laboratoriya,” 39, No. 3, 284–285, 1974.

ON SOME FEATURES OF INTERACTION IN SYSTEMS WITH ELECTRON-TYPE COMPOUNDS WHEN STUDIED BY STRIPPING POLAROGRAPHY

A. A. Kaplin, I. P. Mamontova

The study of the mutual influence of elements in mercury and on solid electrodes is one of the principal physicochemical problems of stripping polarography. A comparatively large number of works are known on the study of the mutual influence of elements in mercury; the formation of intermetallic compounds (i.m.c.) has been noted, and the composition and solubility products of a number of i.m.c. in the solid and liquid phase have been determined. However, the theoretical and experimental studies previously developed for investigating the mutual influence of elements in the method of amalgam and film stripping polarography, based on the approximation of ideal solutions, did not make it possible to take into account interaction parameters or to correlate stripping-polarography data with thermodynamic quantities. The thermodynamic approach developed in [1,2], which takes into account changes in the activity of the components in the system, offers both the fundamental possibility of calculating certain thermodynamic parameters for metals and alloys and the use, in theoretical and experimental studies in the method of stripping polarography, of thermodynamic data obtained by other independent methods, in order to predict the nature of current–voltage curves in the presence of an interaction effect in the system.

Thus, in studying the literature data on binary systems of interest for the method of amalgam and film polarography with accumulation, we paid special attention to systems with electron compounds. These systems include \(Cu-Me\), \(Ag-Me\), \(Au-Me\), where \(Me = Bi, Sb, Sn, Zn, Mn\), etc. Thus, these compounds include the elements most often determined by the APN and PPN methods; moreover, silver and gold are used as substrates in the APN method and, consequently, are soluble to one degree or another in the mercury electrode. A feature of systems with electron compounds is a change in the sign of the enthalpy of mixing at a significant excess of the element with the higher valence. On this basis, and on the basis of a thermodynamic approach [1, 2], it was possible to assume a more complex character of concentration dependences in such systems in the method of polarography with accumulation when the ratio of the components is changed than was established in a number of works, for example, for the systems \(Cu-Zn\), \(Cu-Sn\).

We experimentally investigated, by the APN and PPN methods, a number of systems with electron compounds on mercury and solid electrodes. The procedure consisted in measuring the dependences \(I_n\), \(\delta\), and \(\varphi_n\) of each of the components while varying their ratio in solution and on the electrode over a wide range, from \(1:50\) to \(50:1\). The systems we studied include \(Cu-Sn\), \(Cu-Zn\), \(Ag-Bi\), \(Pb-Tl\), \(Zn-Mn\), \(Cd-Mn\).¹

In the systems studied, we for the first time observed a sharp increase and subsequent decrease in the anodic current of the element with the higher valence (\(Sn\), \(Mn\), \(Bi\)) at its constant concentration in solution and with a change in the content of the second component. The presence of a maximum is observed when the content of the second component in solution is considerably lower than that of the first. At ratios close to equivalent, a significant decrease in the anodic currents of both elements is recorded, associated with precipitation of a solid phase. In the region of the maximum one may assume the presence of a liquid phase of compounds of another composition and stratification of the solution. The character of the curves is preserved in going from a solid to a mercury film and then to a mercury spherical electrode, although “smearing” and a shift of the maximum toward higher concentrations of the element with the lower valence are observed. Similarly, when the content of both components in solution is decreased, “smearing” and a shift of the maximum are also observed.

The character of the curves is analogous to the change in concentration dependences—

…of the simplicity of excess thermodynamic functions in these systems and, thus, confirms the correctness of the thermodynamic approach to stripping polarography. The concentration dependences in the system [[unclear: system designation not visible]] are considerably more complex. From our experimental data, the dependence of the height of the anodic peak of lead, at its constant concentration in the solution and with a thallium concentration increasing stepwise, is an oscillating curve with a decaying amplitude, on which a monotonically decreasing component can be distinguished. It may be assumed that such a character of the dependence is associated with the oscillatory character of the interaction energy in this system, which may be represented as

\[ W \sim W_0 + A \frac{\cos aK}{aK}, \]

where \(K\) is the Fermi radius vector.

The experimental data obtained by us confirm the fundamental possibility of using literature data on the thermodynamic properties of binary and more complex systems. It is possible to distinguish the solution of such problems as predicting concentration and other dependences in the method of stripping polarography, using the mutual influence of elements to increase sensitivity and resolving power, and estimating errors introduced by a component, in particular at concentrations significantly lower than the detection limit under the experimental conditions in physicochemical and analytical studies. This indicates that the effect of the mutual influence of elements—of which the influence of the substrate in the SPE method is a special case—represents a promising means of increasing sensitivity and resolving power.

REFERENCES

1. A. A. Kaplin, in: Advances in Stripping Polarography, Tomsk Polytechnic Institute Press, Tomsk, 1973, p. 136.

2. A. A. Kaplin, T. F. Ryamontseva, in: Advances in Stripping Polarography, Tomsk Polytechnic Institute Press, Tomsk, 1973, p. 137.

EFFECT OF ADDITIVES ON THE CRYSTALLIZATION OF FORSTERITE IN OBTAINING IT FROM TALC

P. G. Usov, V. I. Vereshchagin, N. K. Glushkova

Forsterite, \(\mathrm{Mg_2SiO_4}\), is the principal crystalline phase of forsterite ceramics. Forsterite ceramics are among the most common high-frequency dielectrics at the present time. Forsterite materials are resistant to electrical…

1. The \(Ag-Bi\) system was studied by L. S. Anisimova and A. A. Kaplina. ↩