More on experiment 2, and related phenomena

It seems quite clear that the maximum attainable temperature of vehement boiling is different in different types of vessels. I have easily observed differences of over 4°C in the temperature of boiling water in quite ordinary glass, metal and ceramic vessels. (Further details are available in Appendix 1 of a preliminary report on my experiments, 10 August 2004 .) It seems that a crucial factor is the smoothness of the surface, as predicted by the standard modern theory of bubble-nucleation (see further discussion of the theory). Overall, the results of my experiment are consistent with the glass-vs.-metal difference of 1.232°C reported by Gay-Lussac in the 1810s.

In the glass vessels I used (Pyrex), the temperature of prolonged vehement boiling was always over the standard boiling point, easily reaching 101°C. Even higher temperatures, up to 102.4°C, were observed in a beaker previously treated with high heat, and in a volumetric flask (with a long, thin neck). See Experiment 5 for trials with volumetric flasks.

In metallic vessels, the temperature of vehement boiling can be as low as 99°C. It is always lower than in glass vessels, whenever back-to-back trials are made. Among metallic vessels, great variation was observed depending on the quality of the inner surface: in a smooth-surfaced stainless pot, the temperature can be near that in glass beakers; the temperature is much lower in a rough-surfaced aluminium pot; the Teflon-coated pot produced the lowest boiling temperatures (see Experiment 4 for the action of Teflon chips in facilitating vapour-formation).

In a ceramic mug, the temperature is typically over 101°C. With water that has already been boiled for some time, it is possible to reach 103°C or above in ceramic. In one case (observed on 2 August) the temperature reached 106°C, and at that point the heating had to be terminated for fear of explosion, and a concern about disturbing the calibration of the Beckmann thermometer. Unfortunately I did not record that particular experiment, and have not been able to produce a similar result again. When boiling takes place in a ceramic container, the bubbles are clearly larger and less frequent than in other types of vessels, with some completely quiet periods.

The temperature variations do not seem to be a straightforward function of vessel size and shape, except as the shape affects the surface area of the water, as seen in Experiment 5.

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