The main difficulty was the duration of a measurement, which normally exceeds 24 hours. This inevitably produces a slight change in the composition of the solution within the measuring volume, as will become clear from the plots in Chapter 5. A further difficulty was the evaluation of the measured resonances. Since the instrument was designed for water-like substances, automatic evaluation was not possible; every individual resonance had to be fitted manually.

5. Light-Scattering Apparatus and Refractometer

Because the measuring chamber of the light-scattering apparatus is made of glass, there were no material-compatibility problems and no modifications were necessary. The only difficulty was the requirement to measure as close to the critical point as possible, which was hard to achieve because the temperature control was not optimal.

6. Viscometer and Densitometer

The viscometer used was a falling-ball viscometer. Its resistance to nitromethane meant that it could be operated without major difficulties. The situation was different for the densitometer: obtaining a good measurement proved extremely difficult.

The problem arises from the sensitivity of the nitromethane–pentanol system. Despite careful filling, part of the solution remained outside the temperature-controlled region. Since the ambient room temperature was below the demixing temperature, the solution outside the apparatus separated into phases. The resulting concentration difference between the exterior and interior caused diffusion, which severely distorted the measurement results and could even induce phase separation inside the apparatus. This issue is treated in greater detail during the evaluation of the data. Here too, therefore, the required external temperature had to be maintained.

Original mathematical notation is preserved in the extracted image assets.