Gin Clears up a Foggy Glass

Last night my father was served 2 beverages at the same time: a glass of ice water and a gin & tonic with ice. They were in identical glasses, and both glasses were coated with condensation. The condensation on the gin & tonic was transparent, however, where the condensation on the ice water was foggy. Why would they be different?
- John Coppersmith (age 56)
Homosassa, FL, USA

Great question! I'm not sure of the answer, but here's a guess. Alcohol and other solutes lower the melting point of ice. (That part is for sure, not a guess.) So the gin and tonic would get colder than the ice water before its ice stopped melting. (Both will then slowly melt further, as heat leaks in from outside.) The colder glass should cause more water condensation from the outside air. If enough water condenses, it will form a continuous layer, easy to see through. A smaller amount of condenstation will leave many tiny beads of condensed water on the galss. Their uneveness scatters light, making the sort of foggy look that you usually see on a window as it starts to cloud up.

It might be fun to repeat the experiment, just to make sure it's reproducible, and not just due to some accidental difference say in the amount of detergent left on the glasses. 

Mike W.

(published on 12/05/2018)