 |
 |
In the laboratory, it is called 'superheating' and can happen with any solvent. Boiling chips are normally added to eliminate that problem in the lab. In the home, anything that will disturb the equilibrium like tapping or vibrating the wall of the container or throwing in salt for instance or a stirrer, the excess energy will be released suddenly. Michel "J. R. Bruman" wrote: > What usually happens then is the liquid is bumped or jarred, which is > just enough of a shock to cause the bubbles to rapidly form and expel > the hot liquid. The rapid formation of bubbles is also why a > carbonated beverage spews when opened after having been shaken." > > I have also had the experience of, after heating the water in the > microwave, and then adding the instant coffee, the liquid suddenly > bubbles up and overflows. This must be the same principle. > > If I had any spare time it might be fun to do some home experiments > in my microwave. One important factor is the container, which if not > a very good insulator may reach temperature different from the > contents- > But offhand I'd say the phenomenon reported is related to natural ones > on a larger scale, such as "old faithful" periodic geysers, and > certain types (I forget the name) of volcano such as Mt St Helens or > Vesuvius. Come to think of it, I own a little stove-heated espresso > maker named "Vesuviano". Cheers,