DEMONSTRATION OF ZONE-REFINING Submlrtcd by: Malrolm I). Hawkins, Chemisrry Department, hlnndrr ('hrrkrd by: William Uodd. Hiram Cdlrye, Hiram, Ohio 142.M
C'dleye, Urdford, England.
PREPARATION
Naphthalene, methylene blue; 12 V variable voltage transformer; Nichrome heating wire; thin twine; clock mechanism, electric motor or, alternatively, a wooden block and a large glass tank. Cut a piece of glass tubing approx. 15 cm long and 3-4 mm i.d. and seal one end. Using a dropping pipet, fill the tube to .within 2 cm of the top with a molten solution containing 0.1-0.4 g methylene blue in 100 g of melted naphthalene. Keep the tube in a vertical position until the molten mixture has solidified. Make a heating coil from a single turn of Nichrome wire.
DEMONSTRATION
Bring the top of the tube through the center of the coil and adjust the transformer output to give a molten zone approximately 0.4 cm wide. Attach the tube by a length of twine to the motor, or clock mechanism, or alternatively, (using a pulley) to a block of wood floating in the tank of water which can be slowly emptied to raise the tube through the heating coil. As the molten zone passes slowly (approx. 2 c m h r ) down through the impure naphthalene, the blue impurity is carried towards the bottom of the tube by the molten zone and pure, virtually colorless naphthalene crystallizes out. REFERENCE
Hawkins, M. D., Educ. in Chem., 9,95,1972.
A48 / Journal of Chemical Education
