Here's a suggestion: Mix equal parts Isopropyl Alcohol and Epsom Salts by weight.
The by-products are mostly harmless, and it doesn't burn as hot as straight alcohol. Be sure to practice good fire safety, placing the cauldron well away from flammable materials, and on a fire-proof surface, and making sure to have fire dousing materials (such as a lid for smothering the cauldron, and a large box of baking soda for dousing anything unexpected) handy.
