Cleaning Mercury The situation often arises in the laboratory where one needs mercury that does not have to he extremely pure, hut the only mereuryavailable is very dirty. If one does not want todistill the mercuryorsend it off for purification, an acid wash procedure is usually employed. Common methods for cleaning off surface scum and removing base metals are: (1) t o pass the rdereury through a "pin holed" filter and a column of dilute nitric acid'; (2) t o filter the mercury through a glass frit followed bvwashine the mercurvin dilutenitrieacid for manv hours2? or (3)to draw air through mereurv while it is under procedures are time consuming a i d ineffective if dirt or similiar b a t e r i a l s i r e the contamidilute nitric acid."hese nates. An altcmatepnrcduredev~lc~ped in our hbornrory is to pretrrnt rhe mrrcur, by a tlotnt~mtechnique m d rhm 1usbwly p ~ thrr mercury thn,ughn elazsrulurnn ronrninlnr glass brad-and X A l nitric arid. Ihrr tr similiar material in rhe mercury is removed by placing the mercury in a side arm flask in a plastic tuhand flushing thesurface of themercury with running water. The mercury is then poured through a glass column which should not he filled more than two thirds full with glass beads and acid. Space must be left in the column for the solution to expand should any reaction occur. As the mercury strikes the glass heads, it disperses into small droplets which present a large surface area for reaction with the nitric acid. The mercury is then poured through a similiar column containing glass beads and distilled water. The acid-distilled water wash procedure is reoeated three times..chaneine the nitric acid and the distilled water after each cvcle. If the mercurv needs to be deereased prior to the acid distilled water cycle, a glass column containing g h s heads can he set up using an appropriate organic solvent, followed by a distilled water wash step. The wet mercurycan be dried by careful heatingin a porcelain dish on s hot plate at low heat (HOOD). If the temperature is too high, the mercury will first form an oxide film and then vaporize;' therefore, the hot plate must he just warm enough t o drive off moisture and not any warmer. Formation of surface scum a t this stage is an indication of residual contamination. As crude a s i t may seem, the appearance of the surface can often he used as a rough gauge of the purity of the mercury. The presence of base metals to a concentration of 1part in 10 million of mercury can be detected by the loss of the mirror-like appearance. Although the lower limit of base metal impurities which can he achieved by washing with nitric acid is uncertain, i t is thought t o be less than 1 ppm3 Noble metals will not he eliminated by the nitric acid wash procedure, and they must be removed by distillation if their presence is trouhlesome. The whole cleaning procedure should he performed in a hood (especiallythe acid wash and heating steps) with precautions taken against spills.5,fiThis procedure is not only fast and simple, but it also yields mercury that is reasonably clean. ~
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'Vogel, A. I. "Quantitative Inorganic Analyses," Longman Group Limited, London, 1961, p. 1056. ZCoetzee, J. F.. "Treatise on Analvtical Chemistrv," (Editors: Kolthoff, I. M., and Elvinp, P. J.) Part 11, Interscience Publishers, New kork, 1961, p. 234. 3Gordon. C. L.. and Wickers. E.. Ann.. NY. Acad. Sci.. (1957) . 65.369 . IRamy, H., '.Trpari\eon lnorcank. C'hrmistr)," Vol. 11. Elsevier Pth1i;hins Cornpony, New Pork. 1956, p 458. ',\ndrrson. D. H., Murphy, P.J.,and \I'h~te.W.\Y.,.l.CHEhl. ElJ1J~..53,ATI.(19781. 6Nrwmnn. 11. S.d. CHEM. EIXIC., 55. A X t197d1. University of New Orleans New Orleans, 70122
C. P. Monaghan E. J. O'Brien, Jr. Mary L. Good
734 1 Jouml of Chemical Education
