Re: Does water, vinegar, or milk boil down faster? Why?

     OK, first some initial conditions: 1) the fluids all start at the 
same temperature; 2) we're starting with an equal volume of each fluid; 3) 
the heat transfer to the fluid from the heat source is exactly the same in 
each case; 4) the fluids when boiling are vented exactly the same way; 5) 
we're starting with an appreciable volume of fluid; and 6) by "boil down" 
you mean drive off all the volatile matter in the fluid.
     The answer is milk. Why? The boiling point of water, 5% acetic acid 
solution (vinegar), and milk are all very close. So if you heat the same 
amount of each of them at the same rate, they'll all reach their boiling 
point at about the same time. The boiling point of water is 100 degrees 
Centigrade, or 212 degrees Farenheit; vinegar and milk are slightly 
higher, at least at first (the milk will actually start to boil at a lower 
boiling point after a certain amount of evaporation). So why does milk 
evaporate first? Simply because not all of the sample is volatile; that 
is, not everything in milk evaporates. So if the milk is, for example, 5% 
non-volatile, and you start the experiment with 1000 grams of each fluid, 
you need to make 1000 grams of the water and the vinegar evaporate, but 
only 950 grams of the milk.