How much Epsom salt should you put into a fire to make it white?

One-fourth cup of magnesium sulfate, or Epsom salt, is sufficient to turn a fire white. Education.com explains that this is the case if one-half cup of menthol is used as the solvent.

Alternatively, a cup of Epsom salt for every half gallon of water suffices if warm water is used as the solvent, according to HomeSchooling-Ideas. About.com states that magnesium sulfate, which is used in a variety of household tasks, can be obtained from many local drug stores. However, Epsom salts available in some drug stores may contain sodium impurities, which yield a yellow flame as opposed to a white flame.