Experiment 2: Effect of different vessels

This clip shows five experiments, of water being boiled in different types of vessels. These experiments illustrate that boiling temperature is indeed lower in metal than in glass, as reported by Gay-Lussac 200 years ago. Note the difference not only in the temperatures, but in the shape, size and number of bubbles forming in the two different vessels. In an ordinary glass beaker, which we saw in Experiment 1, the temperature of full boiling goes over 100°C. (The second glass beaker has many fine scratches on the inside bottom surface, and this clearly helps the formation of bubbles from a low temperature. The temperature at full boiling is clearly lower than 100°C.) The trial with a ceramic mug showed high temperatures, with bubbles forming and detaching themselves with great difficulty; note the noise that the large bubbles make as they detach from the surface. With bubbles not forming at a high enough rate, the water cannot lose heat quickly enough, and ends up in a "superheated" state. In a stainless steel pot, the temperature is much lower, only around 99°C at full boiling. (Different viewers may differ on whether that constitutes boiling -- my colleague Dr. J. Gregory suggested an intuitive test: would you put the pasta in?) The variability of boiling behavior and temperature is illustrated most clearly in the case of the Teflon-coated pot: bubbles form very eagerly on this surface (from a very low water temperature, and the temperature of both the onset) and the peak of boiling is significantly lower compared to boiling in a glass beaker, reaching the maximum of only 99°C in the experiment shown here. (If you are a serious historian of science, you are probably starting to worry that what I made aren't really replications of the historical experiments at all. Click here and see if I can relieve you of the worry.)

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