Mercury Reservoir Research Articles

A.C. polarography and faradaic impedance of strongly adsorbed electroactive species Part I. Theoretical and experimental study of a quasi-reversible reaction in the case of a Langmuir isotherm

The expression of the faradaic impedance is calculated in the case of a quasi-reversible system O+ ne R under the following conditions: (a) both the oxidized and the reduced forms are strongly adsorbed; (b) the adsorption rate is large, and does not control the kinetics of the system; (c) the adsorption of both O and R obeys a Langmuir isotherm. The results show that the tangent of the phase angle is proportional to κ s /ω (κ s =rate constant of the electrochemical reaction). When ω→o, the phase angle tends towards 90°: the faradaic impedance becomes purely capacitive. The equation of the a.c. polarogram has been derived; whatever κ s /ω, the peak height is proportional to the bulk concentration of the reactant, to τ 7/6 (τ=drop time), and to h −1/2 ( h =height of the mercury reservoir). When κ s /ω→∞, the shape of the a.c. wave is identical to that of a “diffusion-controlled” a.c. wave. The experimental results obtained by a.c. polarography for the three systems azo-hydrazobenzene, benzo(c)cinnoline-dihydrobenzo(c)cinnoline and phenazine-dihydrophenazine are in excellent agreement with the theoretical predictions.

A.C. polarography and faradaic impedance of strongly adsorbed electroactive species: Part I. Theoretical and experimental study of a quasi-reversible reaction in the case of a Langmuir isotherm

The expression of the faradaic impedance is calculated in the case of a quasi-reversible system O+ ne R under the following conditions: (a) both the oxidized and the reduced forms are strongly adsorbed; (b) the adsorption rate is large, and does not control the kinetics of the system; (c) the adsorption of both O and R obeys a Langmuir isotherm. The results show that the tangent of the phase angle is proportional to κ s/ω (κ s=rate constant of the electrochemical reaction). When ω→o, the phase angle tends towards 90°: the faradaic impedance becomes purely capacitive. The equation of the a.c. polarogram has been derived; whatever κ s/ω, the peak height is proportional to the bulk concentration of the reactant, to τ 7/6 (τ=drop time), and to h −1/2 ( h=height of the mercury reservoir). When κ s/ω→∞, the shape of the a.c. wave is identical to that of a “diffusion-controlled” a.c. wave. The experimental results obtained by a.c. polarography for the three systems azo-hydrazobenzene, benzo(c)cinnoline-dihydrobenzo(c)cinnoline and phenazine-dihydrophenazine are in excellent agreement with the theoretical predictions.

A Modified Mercury Tensiometer

AbstractThe present paper introduces a modified type of Hg tensiometer. The manometer in this tensiometer uses the usual principal as for other Hg manometers. However, the main difference is that the Hg manometer is contained within the tensiometer body itself. A relatively small volume of Hg is used and the small mercury reservoir can be filled or emptied rather easily. Once the reservoir is filled, the mercury can usually be safely left for the lifetime of the tensiometer. Tensiometers of the proposed design have been handled successfully for scheduling irrigation on shallow soils by unskilled farmers in Cyprus for the last 4 years.

Catalytic hydrogen prewave in the presence of selenocystine and nickel

Summary The polarographic study of seleno-cysteine, formed by seleno-cystine reduction, in nickel-containing acetate buffer, has shown that catalytic hydrogen prewaves occur at pH values of less than 7, at the same time as catalytic nickel prewaves. The effects of physicochemical parameters, such as: gelatin addition, mercury reservoir height, seleno-cystine and nickel ion concentration, pH and ionic strength have been studied. Catalytic hydrogen evolution in the presence of the metal ions shows that nickel complexes with seleno-cysteine are involved in this process. Among the several seleno-cysteine forms, corresponding to different degrees of protonation, the intermediate ones seem to be catalytically active for both hydrogen and nickel ions.

Polarographic behaviour of trans-oxymercurated allenes

The electroreduction of trans-oxymercurated allenes has been examined at the dme in 50% dioxane-water medium. These organomercurials give two well-defined and well-separated waves. The first one-electron reversible step is followed by a second one-electron irreversible step. Variation of the diffusion currents with temperature, height of the mercury reservoir and concentration indicate the diffusion-controlled nature of the waves. According to the suggested mechanism of the electroreduction, trans-2-chloromercury-3-methoxycyclotridecene captures an electron to generate an organomercury free radical in the first step. The organomercury free radical takes up another electron simultaneously with a proton to give the ether, resulting in the second wave. The effect of ring size and stereochemistry on the half-wave potentials is discussed.

Catalytic hydrogen discharge in the presence of cycloserine

In buffer solution on the dme, cycloserine forms a catalytic hydrogen wave of the pre-sodium type. With 10 −5 M Co 2+ the hydrogen wave produced by cobalt—cycloserine complex is well separated from the pre-sodium wave. Within the cobalt concentration range 10 −5–2·5 × 10 −5 M the pre-sodium wave is progressively displaced towards more positive potentials and over these concentrations only one wave can be found. This process, the superposition effect on catalytic hydrogen waves, explains the independence of wave height from the mercury reservoir height, because the composite wave contains a diffusion-controlled and a pre-sodium component. Owing to these phenomena a study of the influence of basic parameters on three kinds of catalytic waves was carried out, (1) diffusion-controlled, (2) pre-sodium and (3) composite wave. Interpretation of the results is by equations of the catalytic waves obtained on the hypothesis of both a zero-charge cobalt—cycloserine complex and a reducible complex with a pre-sodium component.

Polarographic behaviour of deoxyribonucleic acid

1. The polarographic properties of native and denatured calf thymus DNA have been studied. The dependence of the height of the polarographic wave on the concentrations of NH + 4 and of DNA, the height of the mercury reservoir and on the pH was demonstrated. 2. The electrolytic reaction has several stages: adsorption of DNA, protonation, and the attachment of electrons onto the molecule. The intensity of the current is limited by adsorption or by protonation, and depends upon the concentration of proton donors. 3. A double wave of partially denatured DNA was observed and a mechanism for its cause was proposed. The time-dependent decrease of the height of the wave characteristic for denatured DNA was ascribed to partial renaturation or/and aggregation of molecules. 4. The pre-melting observed polarographically mainly reflects changes of structure of DNA adsorbed on the surface of the mercury electrode.

A Modified Meyer-Wade Type Mercury U-tube Manometer

The mercury U-tube manometer reported by D. E. Meyer and W. H. Wade (Rev. sci. Instr. 33 (1962) 1283) has been modified in some respects. The “tip” i. e. the electrode N has been modified so as to prepare more easily. Instead of a spotlight, a tungsten wire heater is used. The gas is not air but nitrogen which is trapped in the spaces of both the mercury reservoir and the bulb in which the heater is inserted. These spaces are connected with a tube. The heater directly heats the trapped nitrogen gas in the bulb to raise the mercury level in the U-tube. As a consequence of the improvement of heater system, the modified U-tube manometer can measure the pressure even when the relatively rapid pressure change occurs in the system. The switching circuits devised here are presented in detail.

Experimental Study of Scattering from a Plasma Column

Experiments in microwave scattering from the positive column of a low-pressure (1.2 mTorr) discharge in mercury under steady-state conditions are described. A free-space environment is simulated with an anechoic chamber and a unique cw cancellation method. Both amplitude and phase of the scattered electric field for both polarizations in the 2.6- to 5.85-GHz frequency range are measured, so that diffraction characteristics, radar cross sections, frequency ratio, and phase shifts are determined. A calibration procedure using silver-plated cylinders provides a higher degree of accuracy than has been attainable heretofore. Diffraction measurements show that, for plane-wave incidence, the scattering is purely dipolar with a 95% confidence interval, except for overdense scattering where a significant monopole term characteristic of conductors is observed. Theoretical comparisons yield an estimate of the electron density distribution function and the damping of the Tonks-Dattner resonances, as well as providing a test of the various theories. The results of some auxiliary experiments to find the average electron density in the column and the effects of wall and mercury reservoir temperatures upon the observed results are also given.

1106. A greaseless valve for use in mercury reservoirs

1106. A greaseless valve for use in mercury reservoirs

Polarography of copper(II)-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetic acid

The polarographic behaviour of the Cu(II)-1,2-CyDTA system has been examined in acetate buffers. The effect of ligand concentration has been studied both in the presence and absence of excess metal. The effect of pH and mercury reservoir height has been investigated. Kinetic parameters of the irreversible reduction of the complex have been evaluated and a wave equation which explains the experimental results is given.

Polarography of copper(II)-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetic acid

The polarographic behaviour of the Cu(II)-1,2-CyDTA system has been examined in acetate buffers. The effect of ligand concentration has been studied both in the presence and absence of excess metal. The effect of pH and mercury reservoir height has been investigated. Kinetic parameters of the irreversible reduction of the complex have been evaluated and a wave equation which explains the experimental results is given.

A greaseless valve for use in mercury reservoirs

A greaseless valve suitable for controlling mercury from a reservoir to a high vacuum system is described. The valve has positive absolute shut-off and is capable of fine control. The construction is simple and adaptable for use with manometers, McLeod gauges, Toepler pumps and cut-offs.

A mercury reservoir for cut-offs or McLeod gauges: F S Baker and J Pritchard,J Sci Instrum, 44 (8), Aug 1967, 652–653

A mercury reservoir for cut-offs or McLeod gauges: F S Baker and J Pritchard,J Sci Instrum, 44 (8), Aug 1967, 652–653

A mercury reservoir for cut-offs or McLeod gauges

A compact and reliable mercury reservoir suitable for use with ultra-high vacuum systems, and requiring no auxiliary vacuum for operation, utilizes flexible stainless-steel tubing for the control of mercury levels.

THE MEASUREMENT OF SOIL WATER TENSION IN THE FIELD

SummaryThe water in soil under growing plants is not in equilibrium and knowledge of the soil water tension must be based on direct measurements from several tensiometers. A cheap, reliable and easily maintained tensiometer for field use is described. The instruments are constructed mainly from nylon, with mercury manometers, and have been assembled in sets of six with a single support and mercury reservoir for the manometers. The nature and extent of the variation of the water tension from point to point in the soil have been measured at a number of sites in the Oxford district. On arithmetic scales frequency distributions are very skew but may be normalized by logarithmic transformation (to pF). The degree of variation is in general moderate: coefficients of variation range from 4 % to 25 % depending on kind of soil and time of year. Since the cost of the tensiometers described is low there is no reason why comparative studies on soil water tension should not be carried out with adequate replication.

Electrochemical behaviour of cadmium in the H 2O-D 2O system-I. Polarographic study

The diffusion current of Cd 2+ in a H 2O-D 2O system with a supporting electrolyte of 0.1 M KCl + 0.01 M HCl has been studied as a function of parameters such as time, height of the mercury reservoir and electrolyte temperature. The characteristics of the process are those of a reversible diffusion-controlled process. In the H 2O-D 2O system, the values of the diffusion current were smaller than the corresponding ones in H 2O, at 25°C. The decrease was proportional to D 2O concentration when this was greater than 35 per cent. This fact may be used as an analytical means of determining D 2O in H 2O mixtures.

Polarographic Determination of Dehydroacetic Acid (DHA)

The purpose of this investigation is to determine a small amount of DHA in foods by DC-, and AC-polarographies. And the results obtained are as follows:DC-Polarography: DHA undergoes one electron reduction with the half-wave reduction potential of -1.510V (vs SCE) at pH 6.0, in a electlytic solution of 0.1M Me4NBr and 40% EtOH.The limiting currents of DHA are proportional to square roots of the heights of mercury reservoir and the temperature coefficient from 15°C through 35°C is 2.0% per degree. These facts lead to the conclusion that the limiting current of DHA is the diffusion current.DC-, and AC-Polarographies: The heights of each waves are proportional to the concentration of DHA in the range of 10-4M to 6×10-3M and can be used for quantitative analysis.This method is applied to some honey extract, contained the interfering substances for other analytical methods such as colorimetry and ultraviolet spectrophotometry, and good results are obtained.

Automatic Toepler Pump with Built-In Gas Quantity Meter

A description is given of an automatic Toepler pump for collection and measurement of gas quantities. The pump, the construction of which is simple and inexpensive, has proven to be reliable and easy to manipulate, while the measuring sensitivity relative to other systems is increased. For collecting and measuring of the gas only one mercury reservoir is required; many difficulties inherent to other types are thus avoided. The simultaneous measurement of volume and pressure, as well as the calculation of the amount of gas, is given.

Apparatus Drawings Project. Report Number 31. A Versatile Mercury Reservoir for Demonstrating Properties of Gases and Vapors

This article describes a simple apparatus for demonstrations of properties of gases and vapors requiring a mercury-filled tube. Its key features are a glass tube with a vacuum-tight valve on the top and a reservoir deep enough so the entire tube can be immersed in the mercury to expel the air. With the valve closed the tube can be used as a barometer. If some air is left in the tube, Boyle's law can be demonstrated. A simple modification of the valve allows the vapor pressure of volatile liquids to be measured.