This is a vapor pressure experiment, the jar was sealed while the water was boiling on a hot plate, so the steam displaced all the air out of the jar. After sealing, the jar was quickly removed from the heat and let cool. now, there is only water and water vapor in the jar (give or take, there is some hair and dust in the water, and probably some remaining dissolved gases). The pressure inside is always equal to the vapor pressure of the water, which depends on temperature. At room temperature, it's almost a vacuum inside, and as the temperature increases, so does the pressure. At 100C, the pressure inside is one atmosphere, which is the same condition under which the jar was sealed. Whenever there is a heat transfer from the bulk water to the lid (condensing the vapor), the water boils, no matter the absolute temperature. In this case, the water was luke warm, and I could hold the jar while it boiled inside. Another interesting property is how easily the water cavitates. simply moving the jar around or tapping lightly on the top causes the water to separate from the walls of the jar, and it makes a clapping sound.
This is a jar full of only water (liquid and vapor). It boils at any temperature when you apply something cold enough to the top, like ice.
Do it! it is easy to do at home! Just wear some gloves and safety glasses, those jars can easily shatter during the heating process if you use too hot of a heat source. I recommend a glass top electric stove, or put some kind of metal plate between your jar and the burner to help spread out the heat. Once you seal the jar, take it off the heat right away, so it doesn’t build pressure. I boiled mine for a few minutes before sealing to try and get some of the devolved gasses out, and lightly set the lid on top to help the steam push out all the air.
Thank you for the answer. I’m tempted to try it, but I’m guessing this is not something you can easily do at home.
Do it! it is easy to do at home! Just wear some gloves and safety glasses, those jars can easily shatter during the heating process if you use too hot of a heat source. I recommend a glass top electric stove, or put some kind of metal plate between your jar and the burner to help spread out the heat. Once you seal the jar, take it off the heat right away, so it doesn’t build pressure. I boiled mine for a few minutes before sealing to try and get some of the devolved gasses out, and lightly set the lid on top to help the steam push out all the air.