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J. Perelman
"Entertaining physics". Book 2.
Chapter 7. Thermal phenomena


Take a small bottle (or jar or vial), pour water and place in standing on the fire a pot with clean water so that the bottle does not touch the bottom of your pan, you have, of course, hang the bubble on the wire loop. When the water in the pot to boil, it would seem, after that have to boil and the water in the bubble. You can, however, wait as you wish, you won't get it: the water in the bubble will be hot, very hot, but boiling it will not. Boiling water is hot enough to boil water.

The result is as though unexpected, meanwhile, it should have been foreseen. To bring water to the boil, enough to heat it to 100°C: I have to tell her considerable supply of heat to convert water into another state of aggregation, namely in pairs.

Pure water boils at 100°C; above this point its temperature under normal conditions does not rise, however much we it was heated. Hence, the source of the warmth with which we heated water in the bubble, has a temperature of 100°; it can bring the water in the bubble is also only up to 100°. When is the equality of temperatures, further heat transfer from the water pan to bubble will not.

So, heating the water in the bubble in this way, we can't give her that excess heat that is required to move water into steam (every gram of water, heated to 100°, requires more than 500 calories to go in pairs). That is why the water in the bubble though and heated, but not boiling.

The question may arise: what is the difference between the water in the bubble of water in the pan? Because the bubble is the same water, only separated from the rest mass of a glass partition; why the same does not happen with lei the same as with the rest of the water?

Because the wall prevents water bubble to participate in those currents that mix all the water in the pan. Each particle of water in the pan can be namelennogo bottom, the water bubble is in contact only with boiling water.

So, we have seen that pure boiling water, boil the water cannot. But standing in a pan pour a handful of salt, and it is changing. Salt water is not boiling at one hundred degrees, but a little higher and, therefore, can in turn bring to the boil clean water in a glass vial.

Entertaining physics J. Perelman


System Orphus


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