The final step in the production of alumina from clay in the pilot plant of the National Bureau of Standards is the conversion of hydrated aluminum chloride to alumina by calcination. The aluminum chloride crystals are fed into the hopper (fig. 6) at the top of the 20-foot Herreshoff furnace and are stirred constantly by rabble arms as they pass downward over the heated hearths. The alumina emerging from the bottom of the furnace (fig. 7) is removed by a vibrating conveyer so arranged that the lower end of the 6-inch glass outlet pipe is always filled with the oxide. Thus air is prevented from entering the furnace and diluting the hydrochloric acid gas issuing from the top, which is used again in the process.
National Institute of Standards and Technology
National Institute of Standards and Technology