Can someone tell me the name and make of the chemical that is used to age and rust metal tracks such as fruil tracks.

There are several on the market now. MOst of the big model paint manufactures offer their version of it. Originally it was called Blacken-it. Sold in model railroad stores. I'm fairly sure AK, AMMO, Wilder to name a few sell it. I know that's not much information but perhaps it'll get you started.

You also have the option of just painting them, which is what i've done with my last few sets.

I usualy mix equal amounts of copper sulphate(bluestone) and sodium chloride(salt), add water, stirr and immerse the tracks in the solution.Some shaking helps bubbles in escaping.
Depending on solution strength 5 to 10 minutes are enough for beautifull rust.
Once happy with the colour, I rinse the tracks and let them dry overnight.