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XXXVIII. On an Apparatus for the Distillation of Mercury 

 in a Vacuum. By Wyndham R. Dunstan, M.A.,F.C.S., 

 Professor of Chemistry to the Pharmaceutical Society of 

 Great Britain, and T. S. Dymond, FJ.C, F.C.S.* 



["From the Research Laboratory of the Pharmaceutical Society.] 



DISTILLATION of impure mercury constitutes the best 

 method of removing foreign metals, and distillation in a 

 vacuum is the only feasible plan of conducting the operation 

 in the laboratory. It is doubtful whether mercury can be 

 completely freed from zinc by distillation, and it is therefore 

 safer to remove this metal, before distillation is resorted to, 

 by agitating the mercury with warm concentrated hydro- 

 chloric acid. 



Different forms of apparatus for distilling mercury in a 

 vacuum have been described by Weinhold, Weber, Wright, 

 and Clark. The action of these different pieces of apparatus 

 is primarily dependent on the same principle . but that de- 

 scribed by Clark (Phil. Mag. 1884, xvii. p. 24) is undoubtedly the 

 most convenient and is the form which is ordinarily used. It 

 possesses, however, several disadvantages. It is inconveniently 

 long, being at least 5 feet in length, and needs a special place 

 in the laboratory where it must be permanently fixed. More- 

 over the apparatus is only applicable when a comparatively 

 large quantity of mercury is available, since at the con- 

 clusion of the operation there remains in the apparatus 

 between one half and one quarter of a litre of undistilled 

 mercury, the amount being chiefly dependent on the diameter 

 of the distillation-tube. To this residue more mercury must 

 be added before distillation can be recommenced. 



The still we are about to describe does not entail these dis- 

 advantages. It is easy and inexpensive to construct, and 

 when once started is automatic in its action. It is rather 

 more than a metre long, and when required for use can 

 immediately be clamped on a retort-stand and may be as 

 readily dismounted again. The residue of undistilled mer- 

 cury which remains in the apparatus is less than 20 cubic 

 centimetres. 



The apparatus is constructed in the following manner: — 

 A bulb A is blown on one end of a piece of thick-walled soft 

 glass tubing B, and is made to assume somewhat the shape of 

 an oblate spheroid, so that nearly the whole of the mercury may 

 be distilled out of it. The other end of the tube has a small 



* Communicated by the Physical Society : read March 7, 1890. 



