A Convenient and Relatively Safe Mercury Still James R. Kuppers and R. H. Gibson University of North Carolina at Charlotte. Charlotte, NC 28223 Two recent communications~~2 in this Journal, referring to aspects of handling mercury, coincided with our need for the metal in an ultranure state and with our move into a new building with very efficient walk-in hoods. Our need for very Dure mercurv" orieinates in a com~rehensivestudy be. (iust . ginning) of electrical double-layer capacities in nonaqueous electrolvte media. Because organics and other surface-active materiais must be rigorously~excludedfrom the metal used in the study, i t was decided to purify the mercury by the ordinary chemical means and to build our own still for multiple distillations; the purity demands upon the metal made reliance unon commercial material riskv. We describe a still that provides for v k m m distillation a t low temneratures while maintainine intake and deliverv reservoirs at ambient pressure and temperature. To the bkst of our knowledee. the basic desim of the still should be ascribed to w."H. Reinmuth, ~ & m b i a University, now deceased. If we have omitted others who mav have contributed to the design, we sincerely apologize. w e believe that our modifications make the still safer and more convenient to use than earlier designs and that others who need very pure mercury might be interested. All parts of the still, including the vacuum pump, are isolated in a walk-in hood. Anangle-iron frame is attached to the back wall of the hood, and the still is supported on the frame a t point C in the diagram. A is the heating chamber (18 X 2.5 cm) and is enclosed in tube furnace B, a ceramic enclosed heating coil of about 1000-W capacity. Reservoir Dl is a thick-walled bottle (13 X 6.5 em), with a volume of about 250 mL; 0 2 is the collection bottle; Commercial laboratory jacks are at E. The air-cooled condenser F (32 X 1 cm) is augmented by a high-volume air blower. The condenser could, of course, be water-cooled and/or longer, and the air from the blower could be passed through coilsin a cold bath; these refinements, however, were not found to be necessary and add to the complexity of the still. We caution, however, that hood air-flow rates and ambient temperatures vary widelv at different locations so that additional cooling could be required under certain conditions. The small ballast bulb s hvdraulic bounce when mercurv is deliva t G h e l ~ orevent ered. ~ n t a k etube ~i and delivery tube H2 are 87 X 1 cm. Collection vessel J is 13 X 3 cm and is the same design as commercially available gas washing tubes. Reservoir D l rests in a large porcelain evaporating dish M. An importanr safety feature of the still is that a relatively small portion of the mercury in the system is ever above ambient temperature. In the event of sudden loss of vacuum, the heated mercury will drain back into the intake reservoir where it will rapidly be cooled on mixing with reservoir mercury, which is a t room temperature.
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Journal of Chemical Education
In operation, the mercury is delivered into J and periodically siphons into 0 2 ,thus avoiding constant delivery and thereby preventing spills. K is a simple tube trap, and L is the opening to the vacuum pump. With the dimensions of our vessel J, about 7.5 mL of mercury is delivered each 11 min, thus giving ample time to change collection bottles when necessary. The still can be operated continuously with periodic additions of predistilled mercury to Dl.The jack? permit easy and safe removal of full collection bottles and removal and cleanun of reservoir bottles (the still must he closed down for the latter operation). First-time operation requires the filline of tube J with flexible tuhine under vacuum. Obviouslv the better the pump, the lower tge operating temperature df the still. We use a rather modest DumD. and the mercurv distills at around 90 OC. The furnace itsdl'f must operate at considerably higher temperature because of rapid heat loss through the high air-flow rates used in the hood and from the blower. Very elaborate Teflon vacuum stopcock assemblies in supply line HI could be used to make the still truly continuous. We elected not to utilize this refinement.
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' Weber, J. J. Chem. Educ. 1986,63, A224.
Miozzo, G. F . J. Chem. Educ. 1986, 63, 826.
