I went online and found out a lot of information about boiling water. If you cover the tin and allow the water and air to cool down, the air will cool and contract, lowering the pressure in the tin. If it lowers enough, the partial vacuum will collapse the walls of the can! The boiling point definitely reduces with air pressure. There is a famous demonstration where boiling water or coffee is drunk, the trick …showed first 75 words of 346 total…

…showed last 75 words of 346 total…the container close to the heat source may be hot enough to cause some boiling in that area which produces some local bubbles. To be sure that all of the water is "at the boiling point," you should wait until there is a large amount of bubbles rising to the surface. The bubbles in boiling water are made of, air and/or water vapor, depending on how much air has been dissolved in the water.