tube outlet 14 contacting aluminum melt 30 the size of holes 24 is small to increase the surface area to volume ratio of the bubbles and to reduce the length of the diffusion path which chlorine gas in the center of each bubble must travel to reach the bubble surface thereby increasing the potential for reaction between the chlorine and the aluminum the reactor is placed in a furnace not shown that is heated by known means e g a resistance or inductive heater the reaction between aluminum melt 30 and the chlorine in bubbles 28 reaction 1 forms aluminum chloride al 2 cl 6 as a vapor because the melting temperature of aluminum metal is greater than the sublimation temperature of al 2 cl 6 additionally the higher vapor pressure chlorides of the impurities in melt 30 also are produced as vapors as bubbles 28 of vapors including the impurity chloride vapors pass upward through melt 30 the impurity chlorides react with the excess aluminum in melt 30 reducing the impurity chlorides to the lower vapor pressure metallic form and producing additional al 2 cl 6 vapor these reduced impurity metals redissolve in the aluminum melt 30 remaining there unless they are again exposed to fresh chlorine gas from bubbles 28 as the chlorine and impurity gases in bubbles 28 are depleted and more al 2 cl.