If you melt ice by dissolving salt in it, it's melting point lowers, it absorbs heat as it changes states, and therefore makes whatever it's in contact with colder. If you've ever felt an aerosol can get colder as you spray it, it's basically the same thing, except that it's going from liquid to gas instead of solid to liquid.
Not quite, although I won't pick too far because if you consider NaCl(soln) to be a different state than NaCl(s), then your original comment is not too much in error.
Another benefit of liquifying the ice is that it now has more surface contact with whatever you're trying to cool, so it cools faster. That's the way old-time ice cream makers work.
That doesn't answer my question. You aren't making ice-cream, which requires cooling the solution below its freezing point, you are chilling a beverage that you DON'T want to freeze.
The others have explained above that the lower temperature salt/ice water makes heat transfer faster, which I can buy, but the conclusions are based on the presumption that you want to chill to 38 degrees (which I don't think you want to do, myself), and that you know when to stop it.
In terms of my question, adding salt (which was what I asked about) does nothing to changes the contact of the surface area compared to non-salted icewater.
Personally, I think regular ice water is more than sufficient for this job, because you don't have to worry about leaving it in too long, and even if you take it out early, it is still in a more appropriate temperature range to drink.
I use regular ice water for my Mountain Dew all the time.
