VOLUME 33, NO. 12, DECEMBER. 1956
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APPARATUS FOR THE TRIPLE DISWLLATION OF MERCURY M. 1. JONCICH, C. A. ALLEY, and M. KOWAKA University of Tennessee, Knoxville, Tennessee
INTRODUCTION
In most laboratories there is a gradual accumulation of dirty mercury. The rising cost of mercury coupled with the extensive use of this element in vacuum work, polarography, etc., emphasizes the need for an efficient apparatus for purifying mercury. Since even minute amounts of impurities cause considerable changes in the physical properties of this element, it has been determined' that three distillations are required to purify this metal sufficiently for most purposes; hence, the commercial availability and extensive use of triple distilled mercury. It is desirable to have in the laboratory an apparatus to bring about this triple distillation. This apparatus should be easily constructed and inexpensive, and require a minimum of attention. A satisfactory still for single distillation has been described2 as well as an automatic, single-distillation mercury stilLs Distilling mercury three times through the same stiU is timeconsuming and can be effected more efficiently by carrying out the triple distillations simultaneously in the same apparatus. Such a still
has been described by Wheeler.4 Unfortunately, it is difficult t,o cdnstruct, except by a professional glass blower. This article describes a tripledistillation apparatus which requires a very small amount of attention and which can be constructed from materials readily available in the laboratory.
The apparatus shown in the figure consists of a leveling bulb (L) connected by means of tygon tubing (serving as a manometer) to a three-necked flask ( F I ) , which is in turn joined in series to two other threenecked flasks (li; and Fa). I n addition to these three flasks, there are four stopcocks (S1-Sa), and six condensers (CrC6). The three-necked flasks are commercially available, 500-ml. round-bottomed flasks, while the condensers were eight-inch, student-made condensers. The size of the glass tubing or stopcocks used is not critical. In this case, tubing of 8-10 mm. was used throughout, except for the manifold which was of larger size (20 mm.). Stopcocks S2,S3,and S 4 exit to the atmosphere a t one end, and lead to the bottom of H U L E G. ~ ,A,, Phys. Reu., 33,310 (1911). each flask a t the other end. They are connected to a JELINEK, H. N., C. F. HUBER, AND 31.J. ASTILE, J. CHEM. 19/38 standard-taper, ground-glass joint by means of a Eouc., 26, 597 (1949). WHEELER, CANNON, W. A..J. CHEM. EDUC., 28, 272 (1951). E. L., Anal. Chem., 24,751 (1952).
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distilled from flask F1 and simultaneously introduced through stopcock S , a t the same rate it was leaving F,. This was continued until flask F2 was approximately one-fourth full a t which time a Variac-coutrolled heating mantle under this flask was turned on. Mercury was then distilled from F, to Fz and from F2 to Fa until Fpwas one-fourth filled at which point a Variaccontrolled heating mantle was introduced under this flask. The system was then ready for operation. The mercury was introduced into the system through Sl a t ring seal. Stopcock grease was not used to lubricate the same rate at which it was being removed from these joints because this would contaminate the the system a t the outlet shown in the diagram. After mercury; rather, the joint was made vacuum tight by some initial experimentation this rate could he quite the application of sealing wax (Cenco Plicene Cement) easily controlled as well as the heating rate of the to the outside of the joint. By gentle heating, it is three flasks, F,, F2, and Fp. The purpose of the conpossible to diemantle this joint when desired. The densers is to restrict the mercury vapor to the system purpose of these entrances to the atmosphere in each and to keep it out of the manifold. The object of flask was to allow the entrance of air bubbles into each the three stop-cocks, S1, S3, and 8 4 , is to allow the inflask. To keep these bubbles small, the opening in the troduction of air into the three flasks. The air can be bottom of the flask was constricted. The opening to bubbled through one, two, or three of the flasks or can the atmosphere was made optional by the opening or be restricted from any or all of them. For most of the closing of the stopcocks. mercury purified, this air-oxidation treatment a t the A heating mantle was placed around each flask. It distillation temperature was sufficient to oxidize the was found that a separate Variac controlling each base metal impurities. The introduction of air also heating mantle was a more satisfactory arrangement eliminated any tendency for "bumping." than attempting to have all three heating mantles The still was operated at a pressure of approximately controlled by the same Variac. 20 mm. of mercury. Under normal conditions the The left end of the manifold was connected to a trap mercury was triple distilled a t the rate of approximaintained a t dry-ice temperature, which was, in turn, mately four pounds per hour. connected to the vacuum pump. The mercury still can be cleaned by carrying out a distillation of nitric acid through the system after the OPERATION removal of the mercury from the system. This It is necessary initially to fill each of the three-necked mercury can easily be removed by closing stopcock & flasks to approximately one-quarter of their volume and distilling the mercury from FI to F2 to F3 and finally capacity. This was done by introducing the mercury out of the system. The removal of nitric acid after to be distilled in the leveling bulb (L) and raising the the cleaning process was carried out the same way. leveling bulb, after the application of vacuum to the The system is essentially independent of changes in system, to a height sufficient to cause the mercury to go atmospheric pressure since the controlling factor for through stopcock S,. This stopcock was adjusted so the introduction of mercury into the system is stopcock the introduction of the mercury was a dropwise process S, which can be adjusted to the proper size opening. (approximately one drop per second under operating When in operation and after suitable adjustment of conditions). Initially, however, mercury was intro- stopcock S1 and the Variacs controlling FI, F2, and Fa, duced until flask Fl was one-fourth full. A Variac it was found that a check of the system and addition of controlled heating mantle was introduced around flask dirty mercury to the leveling bulb (L) every two hours F, and the temperature of the flask adjusted until was sufficient to keep the system operating satisdistillation of the mercury took place. Mercury was factorily.
