I almost hate to say it but...taste them after tasting knowns.  You probably
won't die.

With the lights on, put a piece of scrap B&W film in each. The one in
the one that turns black is in the developer, and the one in the
PermaWash will stay pretty much the same.

Kelly -

Another replier has suggested putting a scrap of film into each of the
mystery chemicals, and the developer will be the one that causes the film
to turn black.  But there are three other things that you might also try.

First, developers tend to have a pronounced odor, while PermaWash is
odorless.  So take a sniff.

Second, some developers have a faint color (typically brown), while
PermaWash may have a slight blue cast.  So pour a little of each into
glass containers, and then compare them.

Third, developers are what chemists refer to as "bases".  Another replier
suggested using a pH meter - that will work, but another way to identify
bases is to stick a couple of fingers into the liquid, and then rub the
fingers together.  Bases will cause your fingers to feel "soapy". In the
old days, soap was made by combining animal fat with lye, a strong base.  
In a similar fashion, developers will cause a soap-like substance to be
created from the oils in your skin.  By the way, unless you have
allergies, this is perfectly harmless.  And if you are allergic to photo
chemicals, the time to learn this is now so that you can take appropriate
protective steps.