Features of Measuring the Electrical Conductivity of Distilled Water in Contact with Air

The paper describes the results of experiments on measuring the electrical conductivity (specific conductance) of distilled water during prolonged contact with air. To carry out the experiments, a hardware-software complex was developed and manufactured that made it possible to measure the electrical conductivity of water with a relative error of the order of ±0.1% with a change in its temperature within 2–50°C, and a temperature error of ±0.06°C. It is shown that the time of diffusion and dissolution of carbon dioxide in water significantly affects the time dependence of the specific conductance of water when its temperature changes. The peculiarity of measuring the electrical conductivity of distilled water for open and closed systems is shown in the results of experiments with partially and completely filled conductometric cells. Thus, in a filled cell in the absence of gas exchange between water and air, the temperature coefficient of electrical conductivity of water is close to the known table value. In this case, in an empty cell, the gas exchange process significantly reduces the value of this coefficient, and the degree of decrease is proportional to the exposure time between the temperature setting and the moment of conductivity measurement. The experimental results are supplemented by theoretical dependences of the specific conductance of water on temperature for various gas exchange conditions between water and air. It is also shown that when measuring the temperature coefficient of electrical conductivity of distilled water in contact with air, it is necessary to take into account not only the time of dissolution of carbon dioxide in it, but also the design features of the electrolytic cell.