1996 Mercury Sable leaking antifreeze

I was recently at a Pep Boys, that offers a solution to the start of your problem.
For about $12 you buy a tube of UV antifreeze goo, that comes in a colored tube, having a UV light and goggles helps too. But you add this stuff to your system, and run the car. Then after following the directions, and using the UV light and goggles (always wear them, for protection and enhances the results). You can spot the leak.

If your not having any running/smoking problems, then the most likely culprit is a leak around a gasket or where the hose meets the metal in the upper radiator hose.

If you are having smoking/running problems, then you have a leak in the head gasket in which case, you need far more help than I can give you.