1(Flame Fusion) A fine powder of the aluminum and chromium oxides is placed in a hopper at the top of the Verneuil apparatus. A hammer atop the apparatus strikes the hopper repeatedly; each stroke causes a small amount of powder to fall through the fine mesh that forms the hopper's floor. This discharged powder falls into a stream of oxygen that carries it down to a nozzle where it mixes with a stream of hydrogen and is ignited. The intense heat of this flame (around 3,600 F or 2,000 C) melts the nutrient, which falls onto a ceramic pedestal below the flame. Initially, the hammer taps at a rate of 80 beats per minute; after a suitable base for the crystal is formed, the rate is decreased to about 20 beats per minute.
After the base is built up to the desired diameter (about 0.8 in or 20 mm) and formation of the high-quality crystal proceeds, the pedestal is lowered at a rate that just keeps the top of the crystal in contact with the flame. After about five and a half hours, the crys