Of the four cauldrons here in the west, the one located at Felstone Field may be the easiest one in obtaining access to.  The Scourge have greener troops positioned here, though they should not be underestimated.$B$BGo to Felstone Field, northwest of Andorhal, and engage the cauldron lord there.  We think it has a key that will unlock access to the cauldron.  When unlocked, use this bottle to obtain a sample of the poisons inside the cauldron; we'll need it for study in developing a counter agent.