The Cleaning of Mercury 133 



V. THE CLEANING OF MERCURY. 



The method adopted to this end will largely depend upon 

 the history of the mercury. It may at once be stated that any 

 mercury which has been used for amalgamating zinc battery 

 plates had either better be kept solely for that purpose in 

 future, or if by accident a quantity of such mercury becomes 

 mixed with a large stock, practically the only satisfactory 

 method of cleaning will be that of distillation. It is said 

 that mercury contaminated with zinc can be cleaned by 

 shaking with sulphuric acid, but experience points in the 

 contrary direction. 



Mercury which has become dusty through much use in 

 glass tubes may be cleaned by means of a separating funnel, 

 or, what will serve the purpose equally well, a dry filter paper 

 in an ordinary funnel, filled with the mercury, and having a tiny 

 hole pierced with a needle at the bottom of the filter cone. It 

 is astonishing what improvement the liquid will exhibit after so 

 simple a process, and also what a quantity of dirt this process 

 will remove. The mercury must never be forced through the 

 filter paper nor even tapped to make it run more freely ; such 

 action will carry dirty mercury through. 



The filter cone may be refilled until all the mercury is 

 dealt with. 



Should the liquid still leave a " tail " when run over a sheet 

 of paper, it should be shaken with concentrated sulphuric acid 

 in a strong well-stoppered bottle, when it will become granular, 

 exposing a great surface to the action of the acid. The con- 

 tents of the bottle should, after several such shakings, be poured 

 into a large quantity of water, and the mercury collected in a 

 porcelain dish, dried with blotting or filter paper, and again 

 tested. If not yet satisfactory repeat with dilute sulphuric 

 acid, or place it in a funnel drawn out to a very fine point, and 

 dipping into a long jar filled with dilute nitric acid. The jar 

 or wide glass tube should be at least 3' long, and the 

 mercury should come through only in the smallest of beads. 

 A jar is conveniently made of a length of i" diameter glass 

 tubing. After several passages down such a tube, the mercury 



