Ancillary equipment for polarography

Mercury. Double distilled mercury is usually recommended for polarographic work. The re-distilled mercury of commerce is generally satisfactory for most determinations it should be filtered through a filter-paper cone with a small pin-hole in the tip (or through a sintered-glass funnel) before use in order to remove any surface oxides or dust. 

Used mercury should be washed with water, thoroughly agitated for about 12 hours in contact with 10 per cent nitric acid (a filter flask, arranged to admit air through the bottom of the mercury and connected to a water pump, is satisfactory), then thoroughly washed with distilled water, dried with filter paper, and re-distilled under reduced pressure. 

CAUTION. Mercury vapour is a cumulative poison. All vessels containing mercury should be stoppered. Any spilled mercury should be immediately collected and placed in a flask containing water, and the bench (floor) dusted with powdered sulphur. Employ a tray under all vessels containing mercury and for all operations involving the transfer of mercury. 

With careful treatment, a capillary should remain serviceable for many months. It is absolutely essential that no solid matter of any kind should be allowed to reach the inside of the capillary. The electrode must never be allowed to stand in a solution when the mercury is not flowing. 

The following procedure is recommended. The sample solution is de-aerated, then, with the tip of the capillary in the air, the mercury pressure is raised at least 10 cm above the previously found equilibrium height, the capillary is inserted into the cell, and the mercury level is finally adjusted to the desired value. After completion of the measurements the capillary is withdrawn from the cell and washed thoroughly with a stream of water from a wash bottle while the mercury is still issuing from the tip and is being collected in a microbeaker. 

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