Melting Point Apparatus Carlton S. Graves University of Minnesota, St. Paul
The unique feature of the melting point devicc shown in the accompanying photograph is the cent,rifugal pump which circulates oil through the system. The Teflon-covered magnetic stirring bar rotates in the small cylindrical chamber. Centrifugal force impels the oil out the side port and up past the thermometer bulb (against which the melting point capillaries rest) and int,o the heated-oil expansion chamber. From there the oil returns past the Nichrome wire heating element down to the pump chamber. Dow Corning silicone fluid 550 is used because i t does not discolor or smoke a t high temperatures. The current to the heating coil is controlled by a variable transformer. A Teflon stopper holds the thermometer in place. In practice the apparatus is almost vibration free, the oil heats up and cools off quickly, a constant or slowly changing temperature is easily maintained, and the rapid circulation of oil assures quite uniform temperatures in the area of the thermometer bulb.
634 / Journal of Chemical Educofion
