I reheated a mug of instant coffee in the microwave, but left it too long and it was boiling over when I took it out. I ran a little cold water into the mug to cool the coffee, and it boiled again. The tap water ran in gently, and large active bubbles appeared on top of the coffee. How could this happen?
John Davies, Lancaster, UK
This article appeared in print under the headline “Boil foils”
